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Lord of Combustion
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Discussion Starter #1 (Edited)
this will be a project considerable time... so if you guys would so good as to not get on any huge derails or debates until i can get it done, that would be appreciated...

i have wanted to chronicle all for the interested do it yourselfer on the 2 different TRX 450 head styles:

the EARLY 94mm bore 04-05TRX's

and the later 06 and up 96mm bore TRX's

... but WOW is picture compiling and cataloging...plus darn slow/ dead stop being my 2 typing speeds making this a BIG undertaking for me....

at least i will be able to say i have all the pics now, and have at least begun the writing...

Porting ... Theory....Tools....Technique
this is a HUGE topic...and it's going to be hard to explain everthing i detail on the first go around... especially since i am a 2- finger typer...
i have to assume that the majority of you do not do engine develpoment for a living...and i also know that there are many quite versed in engine dynamics, but have yet to add porting to your engine building/tuning skills...... so i will explain a lot of stuff that some of you already know, to put a little background theory in for those just starting their engine addiction...

i want to be able to do a beginning draft and then come back in and fill in all the blanks and tangents that would be too time consuming to finish on the first go around... or even the third go around....

first i have to say that in engine dynamics...everything has an effect on everything...

so i guess i just have to start somewhere and talk my way in widening and meandering circles....

OK ... you need to think of an engine as a complete unit, rather than a collection of parts... if all the parts are trying to do the same thing, then it's like all the members of a tug of war pulling simultaneously...if not, all parts may be stallar, but not working together at the right time in the powerband...

simplified, our engines are an air pump... except that between the getting in and the pushing out... we have a bit of gas mixed with our air so we can burn it an make a powerstroke in between...

the collection of the parts... intake.. carb ... cams ...exhausts ..etc.. all are trying to add their part of efficiency to an engine.... and no matter what part you put on or in, they all need to make use of the engines flowparts/ ports /porting in the cylinder head... those flowpaths are sort of a hinge piece in the puzzle, since they infulence the connection and efficiency of all the other parts....

beyond the mechanical, there is another dynamic force that affects engine performance:

Pressure waves... intake tract resonance / waves that can be timed to have an extra , above atmospheric, pressure right behind the intake valves as they open over a desired rpm band...the waves can be positive OR negative.. good or bad... sometimes they are tuned to advantage...sometimes the engineers come up with clever ways to dampen or negate them altogether ... less of the good to also make for less of the bad...

there are also waves the work in the exhaust system.... propery managed they add efficiency to exhaust evacuation... and can also be used to work past the open exhaust valves and pull fresh intake charge into the cylinder before the piston can even start making vacuum....

timing those waves to work together during the short time when the cam has both the intake and exhaust valves open during overlap (piston near top during exhaust stroke + intake valves slighty open before intake downstroke begins) you can have resonances in the intake pressurising the intake charge above atmospheric AND the exhaust pulses creating sub atmospheric pressure in the combustion chamber.... that's where the engine sort of thinks it's supercharged... because it is... only by pulses rather than a mechanical supercharger....

still, all of it works through the ports in the cylinder head....
i really hope to go back and fill in and expand on all this...it's a lot of ground to cover if you dont already have a good technical base in engine dynamics...

from my experience and viewpoint, i also consider valve and valve seat geometry part of the "porting"... they are right smack in the middle of the flowpath..and their shapes influence airflow quite a bit when the valves are in the low to mid portions ot their lift... which happes twice per intake valve event... during opening and during closing....

on the same line of low to mid lift flow... the combustion chamber itself is part of the flowpath... when the valves are open at lower lifts, combustion chamber walls can also either block flow or promote flow , depending on the geometry / proximity to the valve

lets cover "valve unshrouding" first... for no other reason than i typically start there first.. . at lower valve lifts the flow is referred to as "curtain dominant flow" what that means is that the valves are lifted below a point where the overall limit to flow is at a point in the port itself... the amount of available flow area is still limited by what can get past the valve seat, the valve, and the crowded / shrouded parts of the combustion chamber...
once the valve is open a certain amount, the port itself will become the "limiter of flow"... cams and ports cam be changed to bias an engine to make use of one type of flow more than the other... big topic to cover later for sure...

back to unshrouding.... combustion chamber walls that are close to the perifery of the valve are a limiter of low to mid lift flow.... the very best combustion chambers as far as the design not shrouding any low lift flow potential, is found in the yamaha 5-valve heads and the Suzuki LT-R450 heads... more valves means more area available for low lift flow, when compared to just one bigger valve... one of several reason multi valved heads were developed in the first place...

the Honda TRX heads have more room to benefit from valve unshrouding... and especially the 94mm bore size of the 04-05 TRX heads.... everything about the first TRX was based on the CRF , just not the bore size...it was dropped from 96mm to 94mm.... meaning even more shrouding by combustion chamber walls with the smaller bore size


first a bit on the tools... what they are and where to get them... then the unshrouding / combustion chamber pics...Good Place to Get tools and info from:



CC Specialty.... family owned and i have been a customer of these fine folks since 1974... sure there are lots of places to get stuff from, but these are very good people to deal with for all things porting... even info !

good lord, i wish they would change the cartoon drawings they have though... still the same catalog cover as the one i had in 1974

Tool Types next.... i use hand held die grinders and a variety if cable driven tools ... mostly all of that helps me with work flow since i dont have to change tools in a handpiece all the time... i just swap to a pre-loaded handpiece... if i had to pick one tool setup though, i could get it all done with the stronger / square shaft drive cable tool, and just swap,tool pieces in the handpiece...




then the carbide cutters for fast material removal... these are my 2 most used styles of carbides.... "egg shaped" and "rounded tree shape"



then Stones , for cutting down valve guides...and Cartridge Rolls (aka tootsie rolls) which are for smooting, blending, polishing... depending on the grit you choose.... i would from 60 grit coarse for quick blending /shaping , to 180 grit with jewelers rouge for polishing...and 100grit and 120 grit for in-between those levels







and another essential tool for porting is the shop stereo system... lol... if you dont play at least one Alice In Chains tune during the job, i'm sorry, it just isn't porting...




so... first off we will start with "unshrouding the valves" which means we will blend combustion chamber walls that are close to the valve and would inhibit flow while the valves are at "low lift" ... which happens twice per valve event...while starting to open, and then again during closing....

first I will show you a head that doesn't need much in the way of unshrouding work... the Yamaha 5 valve head on the yfz450.... im just cleaning up the edges because I cant resist.... but you will notice that in order to take advantage of the peripheral flow of a multi valve arrangement, Yamaha engineers have left lots of open flow area around the outside edges of the valve seat






Next ....a honda trx head... this will show you a better pic to illustrate how a valve can have low /mid lift flow blocked by tight chamber walls

walls are very tight to the valves and you have some room for improvement here



and then this is the type of unshrouding I like to do using one of the 1/4" egg shaped carbides....






next up is the exhaust port....

port volume affects the port's velocity... naturally.... same gas volumes moving through tighter spaces would need to go at a higher velocity....

in ports, what you are looking for is to have an "efficient port" not necessarily just a "big port".... if volume itself were the only trick needed for efficient flow, then bigger and bigger would always be better and better.... but it definately isn't.... if you look into the hot rod muscle car era of the 60's and early 70's.... and then check out engines now... the engines they make now make more power over a wider band, as well as just plain more overall power... in the 60's the "bigger is better" rule was the word of the day for port sizes...now, the more powerful engines are making all that extra power with smaller ports.... big ports are lazy and slow flowing, and slow responding... efficient ports use the energy you get from velocity to make good things happen...

later, we will look at how both yamaha and honda made more power over a wider range when both of their 06 models ...and both of them made more power and throttle response everywhere by using higher velocity / reduced volume ports compared to the 04-05 models

the key is that VELOCITY is a huge factor in EFFICIENCY.... and an efficient port just plain flows more by making other things work ....

now...

in porting, the biggest influence is the shape of the infamous SHORT SIDE RADIUS.... hereafter referred to as SSR since i am typing with 2 fingers...and now i know i need to include a port diagram drawing with labels of what everything is at some point....if someone can find some good existing drawings to add, that would be great...and save me some work...

so SSR... the area directly behind the closed valve is known as the BOWL or THROAT where the bowl takes a turn towards the port RUNNER, the tight bottom turn is the Short Side Radius... the more relaxed turn at the roof is the Long side Radius....

the big airflow enhancing trick is to get airflow , moving at high speed, to stick to that SSR and make that turn to feed the back side of the valve.... high speed air ...like anything with mass at a high speed...doesn't like to make sharp turns... if the airflow separates from the SSR a couple of bad things happen... no flow to the back of the valve AND the port sort of chokes itself to a smaller volume with that overshot airflow making a restriction of its own....

so to get airflow to make a good SSR turn, you need to have a wider port floor (wider parts of a river slow the flow rate) and you need to make a smooth / gentle radius that the airflow can track...early on, ports with a wider SSR floor were called "D" ports because the wider floor looks more like a capital D laying on its back...and the making of the gentler SSR radius is called "laying it back", because yo take some liberty with moving the radius back a bit right where the turn is made....

NOTE: you can't.. or make that shouldn't have a radius that goes all the way to the valve seat... once the flow makes the turn it needs a good 1cm of straight bowl wall to let it adhere and straighten out before it needs to circumvent the valve....

looking into the TRX exhaust port from the combustion chamber:




and then in from where the exhaust header bolts up




then you can use the stones to take the steel valve guide down to the level of the aluminum at the guide boss.... and start with a carbide to blend everything into an aerodynamic shape.... you don't want to take a ton of material out because the big volume left over would make for slower exhaust port speeds and worse throttle response from mid or lower rpm...







next you would concentrate on the SSR of the port floor.... wide / smooth / gentle radius is the rule of the day here.... carbide or coarse sanding roll to begin this work...



then you can go back and sequentially blend all your work here together with sanding rolls of finer and finer grades of grit...and then add in some jewelers rouge compound on the finest roll to get a shine....
the polish doesn't help flow.... it helps for cleanup from carbon deposits... a rougher surface is better for flow ... so no prob with polishing exhaust port...it will have a carbon surface on it within the first half hour of running











better pic of wide/ smooth port floor




and its tough to get short side radius pics .... but here you want a smooth blended radius


 

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Lord of Combustion
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Discussion Starter #2 (Edited)
ok... here we go with the 800 pound gorilla of port flow power makers.... the Intake Port...

huge topic... but lets cover a decent amount of ground and make way for further thought and discussion...

the combustion chamber and exhaust ports can be polished (and no, they don't have to be) in order to reduce surface area and heat sinking that comes with it.... in theory it slows heat absorption by the head and keeps it where it will work for us...in the combustion chamber and exhaust... but mostly it makes for an easier time when cleaning the exhaust port during the next freshening up session...

the polishing is really just part of the smooting and blending, only taken a bit further....and it all gets covered up by carbon after only a short run time anyways.... so maybe the reduced surface area helps a tiny bit in heat build up resistance... the combustion chamber looks awesome when polished after valve unshrouding...but I prefer a carbide cut surface finish in the event that it could help preserve some of the turbulent movement of the intake charge swirl and tumble... all minor points and preferences there...

now... on to the port that DEFINATELY shouldn't have a polished finish : the INTAKE PORT...

airflow behaves as fluid flow...same dynamics apply...and airflow moves faster...with less surface tension/friction...if there is a rough texture to the surface...i dont mean potholes and waviness in the port...that's bad for airflow... i mean the surface texturing should be rough where you don't want air to "stick" to it....

same reason golf balls aren't smooth...they fly farther with the dimples breaking the air tension on the surface...

same reason race boats and fish have a scaly texture to their surface.... bird feathers too.....

so, i do all my port re-shaping with carbides...then rough sanding rolls...then go a bit more towards polish with finer rolls because that helps me see fine areas of imperfections that need a bit more blending work...and after its all the way it should be, i rough things back up with 60 grit sanding rolls or lightly texturing with a carbibe cutter....

intake port inlet should be same size as cab outlet... then neck down to the ALL IMPORTANT HIGH SPEED CHOKE AREA before the bend towards the bowl.... motoman has lots of stuff written on the topic...and this neck down region is the main reason that todays ports make more power than early muscle car era sewer pipe ports....it acts as sort of a "flywheel' to the intake charge...it provides speed and inertia to the intake flow...and that is what supercharges the cylinder while the cam still has valves open after the piston has reached the bottom of its stroke and would want to push the charge back into the intake port.... todays performance cams will hold the intake valves open some 60 to 70 degrees after the piston reaches the bottom and starts up on the compression stroke.... they can do this because flow SPEED and from a well designed intake port will have enough INERTIA in the intake charge to keep packing more charge into the cylinder even though the volume is decreasing with the piston on its way up the bore....

people will all have their own ideas on percentage of choke area vs valve seat area (both big topics) , but my own development and testing has shown that a choke area of 83~87% of the intake valve head diameter makes for the widest and best overall power... early torque peak combined with good peak power to the rev limiter....

i also broaden the top "shoulders" of the long side radius around the guide boss, but the port floor has to be the widest part to ensure slower flow speed at the floor to get the flow to make the tight bend of the SSR without separating..... laid back / smooth radius / and wider at the SSR floor is the way to get it to work....

the 04-05 TRX heads have a lot more open volume in the intake port compared to the 06 and up style.... something to keep in mind on port velocity is that the bigger an engine gets with bore kits and stroker cranks...the smaller and faster the port flow will be through the same size port.... which makes sense because if a bigger engine is trying to pull more volume through the same size port...the velocity has to go up....

the early model TRX port was larger... and it was the same for the 04-05 YFZ intake ports... in 06 both companies made changes to the intake port shape and reduced volume to get sharper response and an earlier/ wider torque curve.... those earlier ports lend themselves well to big bore and/or stroker engines... the bigger displacement adds speed to the intake charge...

on to some pics for illustration

stock pics first;

a look from combustion chamber into the 04-05 style intake:





and then from the carb's eye view....



so... now...same thing for the guide and boss area .... stones to take the guide down to the boss... and then carbides to begin the shaping into an aerodynamic structure...

do NOT get over aggressive in the area of the smaller bump at the base of the guide boss... there isn't a lot of material here... and nobody wants to see the camshaft from the intake port ... ;)












stock port floor has a rounded/circular shape to it.... not what you want to slow flow to get it to stick to the floor to make the turn to the backside of the intake valve.... if the flow separates / overshoots the radius.... then the flow itself will narrow itself top to bottom of the floor...and it cant use the entire periphery of the valve for flow at the low to mid lifts ... it effectively makes the valve flow area smaller by making the part close to the SSR useless







so what we want to do to get the flow to actually stick the turn is widen it a bit to slow velocity along the floor...and start to provide a long gentle radius for it to make the turn with....















now... VERY important!!! you want a nice radius...but you DONT want that radius to keep on turning right until it hits the valve seat..... you need a straight / cylindrical section from port floor to valve seat so the flow can straighten itself out and travel along the walls before it has to navigate around the valve!! 1 cm works well.... a little more would be better....





notice the transition / SSR area is wide and has a gentle radius to help the air adhere to the turn...







that port arrangement works VERY VERY well on a wide range of 04-05 TRX setups.... even up to big bore strokers.......

if you wanted to cut down port volume a bit and speed up flow for motocross with a stock bore stock stroke machine , you can easily add jb weld epoxy to the port roof and take all the guide boss transition out.... this port is one I did for pro flattracker #25 Chuckie Creech .... it actually has epoxy top and bottom... this head is was great for shorter tracks and hard runs out of corners.... he said he could setup a pass on the way into the turn...and this head made the pass stick immediately on the exit....


 

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Lord of Combustion
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Discussion Starter #3 (Edited)
"Drag Port" really has no meaning at all in the 4-stroke world... some people like to say drag port.... some people like to charge for drag port.... but the term itself is silly for a 4 stroke engine....


in 2-strokes, which i have ported since my very first dirt bike as a teenager, it is the equivalent of port flow and camshaft when you work the ports....all open and closed port timing as well as mass flow is done by the port layout....so, porting a 2 stroke controls the same thing as porting + valve sizing + camshaft in a 4-stroke... so Drag Port actually has meaning in the 2-stroke world


in the 4-stroke , the ports have to match EVERYTHING ELSE.... from camshaft to valve size to carb size.... you can't just do what you want, you have to know what to do to maximize efficiency of the other factors already present in the engine.... if your porting doesn't match the rest of the components and engine size.... if it works at all, it will work only over a very narrow range

i have to tell you that port dynamics are not dependant so much on what riding you intend to do...

a LOT of it is fixed based on what size carb and valves you run... the valve size itself sets all the ratios for bowl and choke point size in an engine....

you can lift valves with big bucket and high lift cams...and then it would change what you did with the port to change its bias from flow around the valve , to flow over the open window, shooting across the valve.... which is how 2 valve per cylinder setups of the NHRA drag race world work....

what you do with porting is actually sort of fixed most by valve size, you need to keep velocities up to levels that promote swirl, charge the cylinder after BDC with inertia... and a big / low velocity setup has terrible atomization and terrible vacuum signal delivered to the carb... the port volume being too large end up acting like a capacitor... not good

next up... you are fixed on port volumes based on carb size... big carb feeding a small port is not ideal... nor is a small carb feeding a sewer pipe of a port....

camshaft being used and engine displacement is another set of factors that determine flow around or flow over valve...and engine size being fed has a big effect on velocity in the port... you can HVP with port volume... or you can HVP by upping the size being fed....

anyways.... bottom line is there are lots of factors that determine what you can do , given valve size being the biggest factor....

you can bias a bit one way or the other, but valve sizes are the factor that you need to work with to make the port as efficient as possible....






ok... now to show the difference in the port size on the 06 and up models..... much less port volume compared to the 04-05 models....


but the same principles apply.... minimize the profile of the guide boss and guide area.... widen the shoulders around the the lead in to the guide a bit....and make the floor wider and flatter with a gentle slope to the generous smooth radius of the short side radius














in the pic below...notice how the manifold connection face of the port has less material on one side now (it would actually be the top of the inlet to the port if the pic wasn't upside down) this port was being setup for use with a carb that was bored from stock 40mm to 42.5mm.... the bottom of the FCR carb where the center ring attaches does NOT get machined... all the added size goes offset tot he top of the carb mouth.... like balancing a penny on its side and then rolling a nickel up behind it...same bottom, taller top...




























it is too bad that its IMPOSSIBLE to give a good 3D representation in a 2D picture.... but what can you do but live with it?!? this is supposed to show a longer / more gentle / more radiused SSR as the port "pours" over into the back side of the seat/valve.... i can see it somewhat, but then i did it in 3D my head sort of knows what the 3D image would be...lol

 

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Lord of Combustion
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Discussion Starter #4 (Edited)
hope the above illustrations and explanations give you some insight into what porting is and how it does what it does....

you can easily pick up 10% hp across the entire rpm band with good port work.... some places it will be more than 10% , but if you have more effiecient ports it helps at every point in the rpm band...

you buy carbs / cams / intakes / pistons and pipes.....

but guess what they all have to breathe through?? lol.... the ports.... make them work and it makes every single mod you have work better/ more efficiently....

my own focus in 35+ years of doing this is for track based racers ... endurance racing engines..... and I am a lifelong offroader , mx, hare scrables, and woods rider myself... with a focus on wide/ early power... with lots of throttle response to control the machine with..... once the band shifts and narrows and moves towards top end only power... I lose interest quickly.... some of the highest output machines I have ever dialed in on my dyno... have been complete unresponsive / sluggish midrange pigs on tracks and woods courses.... it doesn't take long on a track to see if your improvement on paper is a help to you out of tight corners or on a rhythm section.....lol

more torque and wider band will let you gear up and shift less...accelerate more... less clutch feathering... more traction... and less fatigue .... all advantage with no negative for track based competition...

so , info from me is biased to gains everywhere and no trade off bottom to top end.....

hope this is a help to anyone that was wanting to start learning for themselves... lots more to cover...but you gotta start somewhere....

for an excellent overall view into the world of 4 stroke performance you could hardly find anything more worthwhile than the Kevin Cameron book Sportbike Performance Tuning Handbook...

and a good source for more pics and info (no such thing as too much knowledge) is the motoman web pages.....

I will go back and fill in some more info with the pictures as I get some time... but I wanted to start this tutorial forever... glad it's at least started... whew

and if anyone would like to see what the 5 valve world of the YFZ450 port arrangement looks like.... here's a link:

http://www.yfzcentral.com/forum/32-yfz-powertrain/115722-porting-theory-tools-techniques.html
 

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Huge thanks for taking the time to write this, the only question that comes to mind, is where is exactly the choke point in the port ? I would guess by the valve guide boss or right before the turn.
Also the are the 87 % figures the total valve surface including the seat or the effective port aera above the valve ?
 

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Lord of Combustion
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Discussion Starter #6
Huge thanks for taking the time to write this, the only question that comes to mind, is where is exactly the choke point in the port ? I would guess by the valve guide boss or right before the turn.
Also the are the 87 % figures the total valve surface including the seat or the effective port aera above the valve ?

excellent question.... you are right about the location of the choke area of the port .... the port itself is like a long version of a velocity stack and the necked down area that speeds the charge up and adds inertia is just upstream of the guide/ guide boss area...

the 87% is from the total area on the outside of the valve face....

very welcome for the writing.... if it helps out with someone that has been wanting to get into port configuration...then its worth the time spent :):
 

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Nice pics and details for someone to start doing there own porting. Glad you took the time.

HVP? Where did this term come from? Is it even a real term or some buzz word introduced by Motoman made popular by his article on epoxy porting?

What would be nice for readers to know is how big to make the ports and how the figure is derived and measured.

Thoughts?
 

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Nice pics and details for someone to start doing there own porting. Glad you took the time.

HVP? Where did this term come from? Is it even a real term or some buzz word introduced by Motoman made popular by his article on epoxy porting?

What would be nice for readers to know is how big to make the ports and how the figure is derived and measured.

Thoughts?

I can't speak for Mixxer, or anyone for that matter, but in my opinion, motoman was a little misguided, but he was on somewhat of the right track. Keep in mind that his info is getting pretty far in the past now days.

In my opinion, it's not so much about taking the velocity higher unless it needs to be higher. It's more about getting it correct for the engine and usage, which is complicated. I use pipemax from maxracesoftware, but even with that, it's still complex.

Where Motoman was right in my opinion, is that there are many ports out there, even today, that are bigger than they need to be, and it was done on purpose. Take the 04-05 TRX for example. That's a head that benefits greatly from using epoxy, at least in most situations. Maybe it's me, but I have ended up putting epoxy in every 04-05 head I've done. Even one for a 501 XC build.

06+ among the other changes, they got revised porting (smaller) and those have more throttle response, and are easier to get more power from. You needed a reason to trade off your old one, so they gave you one. Honda knew how to make it better before the 04-05 even came out. I mean take an honest look at a stock 04-05 port and try to tell me that that was their best effort. :rolleyes:

Long story shorter, Engines like the TRX are a very oversquare design. With so much more bore than stroke, it allows for quite large valves. It's easy to fill the cylinder very rapidly with so much valve area per cc, so if you make the port efficient, you can move the minimum cross sectional area (MCSA motoman referred to as a choke point) up the port, on the other side of the valve guide. This is the design that I would consider high velocity porting, and it doesn't always require epoxy. It's incorporated in the design of some heads now days.

On a side note, motoman's diagram is pretty horrible on MCSA placement if I remember correctly. I know following his work threw me off the first time I tried it. My first attempt, using clay on the flow bench failed miserably. A while later, I tried it again, and played with it till it worked, and I found that I was able to increase flow, and reduce the MCSA boosting this velocity we hear so much about. ;)

The old way, or low velocity porting if you will, followed suit with 2 valve per cylinder stuff where the MCSA was the valve seat. That is what motoman was working with.

That type still be found today, in other designs where there's not enough valve area to fully satisfy the demand of the engine, aka the block outruns the head. High velocity portwork is not useful in those.


That's my opinion/ramble


By the way, thanks for posting this Mixxer! Things like this help more people than you may realize.:cool:
 

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Lord of Combustion
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Discussion Starter #9 (Edited)
Nice pics and details for someone to start doing there own porting. Glad you took the time.

HVP? Where did this term come from? Is it even a real term or some buzz word introduced by Motoman made popular by his article on epoxy porting?

What would be nice for readers to know is how big to make the ports and how the figure is derived and measured.

Thoughts?

i have been using epoxy to alter ports even as long as in the 70's on 2 strokes....

ever since i started using epoxy in the ports of the 04-05 450 yamaha's and the 04-05 hondas... in 04 and 05 mind you:):.... i came up with the name then myself... HVP... just as a way to tell people part of what i was foing was to increase the velocity of the intake port.... it was easier to say HVP than to write a big explanation every time

and...oddly enough... both honda and yamaha reduced the volumes in factory supplied HVP on both 450's in 06.... better response and more power over a wider band was the result in both instances

ever since then there have been lots of people using the term HVP to describe similar processes

lots of times i a using it to raise the port to get a better down draught style of approach to the SSR.... like in KTM heads and in the FI yfz heads.... so while i may go for a velocity increase, i am also changing the angle of the port itself....

so in lots of cases i am doing both the volume reduction and port angle changing... both to a benefit...

but for me it's just easy to attach my HVP moniker to the process rather than a big explanation.... i have quite a few pics of HVP work on the ne fuel injected yfz450's over on the yamaha forum
 

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Lord of Combustion
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Discussion Starter #10
I can't speak for Mixxer, or anyone for that matter, but in my opinion, motoman was a little misguided, but he was on somewhat of the right track. Keep in mind that his info is getting pretty far in the past now days.

In my opinion, it's not so much about taking the velocity higher unless it needs to be higher. It's more about getting it correct for the engine and usage, which is complicated. I use pipemax from maxracesoftware, but even with that, it's still complex.

Where Motoman was right in my opinion, is that there are many ports out there, even today, that are bigger than they need to be, and it was done on purpose. Take the 04-05 TRX for example. That's a head that benefits greatly from using epoxy, at least in most situations. Maybe it's me, but I have ended up putting epoxy in every 04-05 head I've done. Even one for a 501 XC build.

06+ among the other changes, they got revised porting (smaller) and those have more throttle response, and are easier to get more power from. You needed a reason to trade off your old one, so they gave you one. Honda knew how to make it better before the 04-05 even came out. I mean take an honest look at a stock 04-05 port and try to tell me that that was their best effort. :rolleyes:

Long story shorter, Engines like the TRX are a very oversquare design. With so much more bore than stroke, it allows for quite large valves. It's easy to fill the cylinder very rapidly with so much valve area per cc, so if you make the port efficient, you can move the minimum cross sectional area (MCSA motoman referred to as a choke point) up the port, on the other side of the valve guide. This is the design that I would consider high velocity porting, and it doesn't always require epoxy. It's incorporated in the design of some heads now days.

On a side note, motoman's diagram is pretty horrible on MCSA placement if I remember correctly. I know following his work threw me off the first time I tried it. My first attempt, using clay on the flow bench failed miserably. A while later, I tried it again, and played with it till it worked, and I found that I was able to increase flow, and reduce the MCSA boosting this velocity we hear so much about. ;)

The old way, or low velocity porting if you will, followed suit with 2 valve per cylinder stuff where the MCSA was the valve seat. That is what motoman was working with.

That type still be found today, in other designs where there's not enough valve area to fully satisfy the demand of the engine, aka the block outruns the head. High velocity portwork is not useful in those.


That's my opinion/ramble


By the way, thanks for posting this Mixxer! Things like this help more people than you may realize.:cool:


VERY well said... and i agree with all of what you point out...!

my pleasure to share anything that helps people... just paying a bit back for all the info i was so glad to have access to over the years....


i have to give motoman credit for all the expalations he illustrated ...and all the engine theory he took the time to explain...

and his pictorial is great for showing how to do all the prep for epoxy work...

i have just found that a lesser degree of choke/MCSA and a sooner beginning to the SSR works best in my testing....
 

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VERY well said... and i agree with all of what you point out...!

my pleasure to share anything that helps people... just paying a bit back for all the info i was so glad to have access to over the years....


i have to give motoman credit for all the expalations he illustrated ...and all the engine theory he took the time to explain...

and his pictorial is great for showing how to do all the prep for epoxy work...

i have just found that a lesser degree of choke/MCSA and a sooner beginning to the SSR works best in my testing....

Spot on, I sure didn't mean to sound discrediting to Motoman in any way. His page is still one of the best sources out there for some good tech. I still go back and flip through it from time to time.

I have found the same with the SSR and MCSA. It felt so wrong the first time I laid the SSR back as far as they need to go in that TRX head. It's surprising just how angled the port can be when it meets the seat before it becomes a problem.

Do you still use JB Weld for your ports? Ever had any separation issues? I use Z-spar, and I had one develop a crack (my own thankfully). The others have all been fine.
 

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Lord of Combustion
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Discussion Starter #12
been jb weld forever.... a type of devcon too, way back ...worked good... never used z spar but was going to try it some time
 

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No such thing as HVP! :eek:oh4: - at least the way I see it.

Efficiency of the engine (VE) occurs at X port speed. Not below, not above. Port speed is a function of the size of the port in relation to the piston diameter, stroke and curtain area.

To me it is like adjusting camber or caster in a suspension. If I move caster one way it will give and take one thing from another.

Port diameter does the same thing. The larger it is the less port speed for the same RPM and thus less power until it reaches optimum velocity.

On a drag motor the idea is to get as high in RPM as possible and keep it there. So the port speed is designed around the optimum port speed for high RPM usage. On a trail bike porting should be higher velocity at lower RPM where it is needed.

Hence the question of the optimum port size...

HVP? Sheesh...
 

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Mixxer, I was wondering about porting for turbocharged engines, do you know if the ports are any bigger to keep speed down, the air weight twice, the pressure differencial doubles, I hardly imagine the air following the SSR without separating and become turbulent. I would think that the port need a bigger % choke aera/Valve surface too. Those with good NA breathing characteristics, usually see more HP per manifold PSI, turbo work less so less backpressure and allow the use of more overlap
 

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Lord of Combustion
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Discussion Starter #16 (Edited)
No such thing as HVP! :eek:oh4: - at least the way I see it.

Efficiency of the engine (VE) occurs at X port speed. Not below, not above. Port speed is a function of the size of the port in relation to the piston diameter, stroke and curtain area.

To me it is like adjusting camber or caster in a suspension. If I move caster one way it will give and take one thing from another.

Port diameter does the same thing. The larger it is the less port speed for the same RPM and thus less power until it reaches optimum velocity.

On a drag motor the idea is to get as high in RPM as possible and keep it there. So the port speed is designed around the optimum port speed for high RPM usage. On a trail bike porting should be higher velocity at lower RPM where it is needed.

Hence the question of the optimum port size...

HVP? Sheesh...

well if it bothers you that much, you can think of it as High-er Velocity Porting:):.... since any port I am lowering the volume on will definitely have higher velocity on it than one that I don't....

ford isn't eco boosting anything either... lol... when their turbos are in boost mode, they are boosting anything "green".... just another name for turbocharger

I am not now...nor have ever been...or will ever be interested in drag motors... its not what I like ... and engine building , for me, is all about my own area of interest... which is why I got tired of driving to dynos and bought my own in 2005... lots to test on a dyno and then on a track...

you would be flat out floored at how many dyno queen setups don't work in and fashion on a real track based event... again why the dyno faces the track out the back window.... the dyno helps you data log and see what the changes you have made have done... then the track tells you if was worth anything...or if it was actually a detriment...

there is so much to the response of an engine setup that the track testing will prove or disprove.... sort of like the old tried and true saying of :
"horsepower sells engines and torque curves win races"... In 35 years of doing this, I have never known a truer statement than that one right there...

all depends on what river you swim in.... my own is for track and woods... theory is a great guide ... track is the acid test

I have notebooks of everything from 35 years of dyno runs and track tests and race results.... and I meant to give people an insight into what porting entails here... not hand over everything I have ever worked for with a bow on top...lol

sorry you don't like my HVP naming for smaller ports that use epoxy fill and generate higher velocity than the original port....
 

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Mixxer, I was wondering about porting for turbocharged engines, do you know if the ports are any bigger to keep speed down, the air weight twice, the pressure differencial doubles, I hardly imagine the air following the SSR without separating and become turbulent. I would think that the port need a bigger % choke aera/Valve surface too. Those with good NA breathing characteristics, usually see more HP per manifold PSI, turbo work less so less backpressure and allow the use of more overlap

all sounds like solid logic for the above atmospheric crowd.... I wish I could help here... but I have never tested anything turbocharged...
 

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I can throw my experience in about forced induction but by no means do I have concrete data that captures the changes enough to make a valid analysis. There are just too many variables.

Overall, the design of the port is relative to what the engine is designed for, as stated several times within this thread. Up to a certain point, the increase in power in a forced induction system coming from a re-design of the ports is proportional to the gains seen in N/A form. I've heard people mention that power can increase exponentially under boost -- not the case. Is there an optimum port for working under boost? There could be gains seen (depending on the baseline combo) if that's the only change but there are so many other variables at play that can make the entire system more efficient such as cam profiles, turbine sizes, compressor ratios and efficiencies, engine dynamics, etc... Another event that comes about is the change in boost pressure when the VE of the head changes. On this scale, I would expect this to be minimal (maybe a 1-2psi difference at most in a controlled type environment). I can attest that boost fluctuates by that amount just from intake temp variance. The point at which a port becomes less efficient for a turbo application would be along the same guidelines for an N/A engine. I have tried a couple different heads on my build and from my findings, the power curves were nearly identical at the same amount of boost with all else equal.

I would love to be a guinea pig for some data collection on different combinations to see how it effects power but that goes along with anyone else wanting to know how a different cam or pipe or head will work on their combo. Time and money.
 

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Thoughts?


There is no real simple way for this unless you do a percentage of valve size and call it close enough. I suppose for a simplified method, I would say figure the throat area. Measure the diameter at the tightest point of the throat, and convert it to area. Make your MCSA area 70-80% of the throat area, and hope that you get the convergence and divergence right. In the 450R I usually place the MCSA just before the valve guide, just after the divider.

A simple, quick test for measuring MCSA area is to roll some clay in grindings (to keep it from sticking in the port), push it through the MCSA, and compress it to fill all the available space. Push it back out and measure the circumference with a string. You can figure area from the circumference, for a simple, quick test that doesn't require a port mold.

The truth is, it's much more complicated than that, but it would get them in the ball park if they guessed right. It would almost certainly have more torque than a stock head, or one without some method of filling space.
 
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