many many many times in the past i have had questions regarding the the power value of BIG BORE kits......

and it is always a less than effective\ accurate evaluation to just tell someone 2~3 more peak HP and 2~3 more peak torque....... the throttle response and added pull is from idle to the rev limit...and more power no matter what rpm you are at.....hard to put into an explanation what adding power across the entire band really feels like.....

so here's a graphic representation of what it looks like on a dyno.... no changes other than going from 439cc 95mm bore to 470cc (468 really) at 98mm bore..... both setups are @ 12.25:1 pump gas compression...

first graph shows that the power with the 470 is greater from idle to rev limiter......and that the power is just starting to "roll over" near the rev limiter... the stock bore ws still on its way up @ the rev limiter before, and the big bore setup had hit its peak a few hundred rpm before....andnthe gains were at there greatest in the 7000 to 9000 RPM band.... which is a VERY nice place to have the best boost occuring....

before, the stock bore broke the 50HP mark @ 8200 rpm.... now the BIG BORE breaks it at about 7400 rpm.... just putting a piece of paper across the horizontal axis is an interesting study in how much sooner the power hits a certain rpm.... if you look at the 56hp mark, the big bore hits it about 1200 rpm sooner..... and in riding, it feels every bit as dramatic as it looks.....

blue = stock machine
black = modded stock bore
red = modded BIG BORE

we've finally hit the "30 more hp than stock @ the rev limiter point".. :)

Click to view attachment

and now the torque graph....

the BIG BORE is making more torque by 4200 RPM than the stocker ever made @ its peak... even with higher rpm biased cams....

and then check out the 7000 rpm mark...... 35 is a FULL 40% more torque than 25...... and it only has an even bigger spread from then on up.....nice...

Click to view attachment

and now some more \ different graphs for everyone's entertainment.....

i will start a thread on this topic on its own.... but this is a Air\fuel Ratio (A\FR) graph of these setups....

they aren't perfectly flat , but they are AMAZINGLY straight!! even when printed on a full size chart.....

i have not really seen anything this good on a carb'd machine before ... flat\ straight to the point that lots of fuel injectd afr lines aren't this good....

this is a stock FCR carb done for me by Sredrum\ Chris (work of art , BTW)..... taperbored from 39mm to a 42.25mm venturi.... with a Venom R.A.T. stack epoxied on it....and with a modded & shortened ESR intake.... it didn't look this flat until after the shortening of the intake.....but boy o boy did this setup ever like the shortening!!

for anyone interested, the current jetting is...all per Chris's suggestions:

2.5 turns on idle fuel screw
45 pilot
06 Honda HRC kit needle, middle clip (yes, a honda needle in a yfz)
and a 200 main jet

Click to view attachment

this is just for fun ONLY..... NOT 1 to 1 comparisons since the dyno runs were NOT started\stopped at the same point in time or speed.....

what you can deduce accurately though.... is the steeper the line, the quicker the acceleration

Click to view attachment

Click to view attachment

next step in the EVILution is 501cc's with a 98mm bore + Stroker WR crank setup......

then i'm totally done...

for a while....

cant say much other than that is an amazing build, mixxer. 30hp more than stock!!!!!!! all i can say is that is very impressive. it has to be that HONDA needle in the carb. that is the only explanation. lol

that's exactly what i thought!...lol...

sredrum's plan is to sneak in all the hidden honda parts he can...!

lol

to bad you don't have a 14.25.1 98 mm piston to throw in there.. it would be nice to see what the gain from the upped comp. wolud do.. do you have the +1 valves in this build ? i sure like the looks of this !!

I'd be lying if I said I didn't want a YFZ. I've always like the looks better...

+1's will be going in when it comes apart to make it into the 501......!!

i did have a 14.25:1 to begin with...! had to cut it down to make it a 1:1 big bore comparison...and to see if i would be interested in making pump gas big bore kits for the YFZ's...and i probably will.... especially with the advent of the Hot Rods stroker cranks adding compression to whatever build they are paired with....

race gas compression (12 vs 14) will add another 1~2 hp to the setup......

ever since tress PUSHED me into doing more pump gas setups on the Honda's, i've been on sort of a pump gas data quest..... lol...

bite your tongue!

they DO look cool.... different, not better!!

hot blonde Vs hot brunette thing..... which is really better??

one of each is the best solution!!

lol

i'm waiting for the Hot Cams\ Cylinder Works Big Bore cylinders to become available.... i know the Yamaha ones are in 98mm bore...perfect.....

but...

if the crank is done before the cylinders are available.... then i will probably try it out with the 98mm punched out oem cylinder i am running as a 470 right now..... the pressure of the 501 setup might break it....but it might let me get through dyno tuning and testing just fine.....

wow nice job u can see how the big bore would just stomp the stock bore

an again that's a huge increase over stock

very nice

johnny boy you shoulda ran the piston at 14.25 before you cut the top off it!

wow. I dont like to admit it but thats pretty darn good for a yamaha.

chit...it aint over yet!

I want to add to this compare-o here. I built a stock bore 14.1 '06 stock stroke +1 Venom yfz engine and took my "spare" (haha) WR 480cc lower end "just in case" to the dunes in Okie one trip. It ran strong as hell and rev fast! Well after a day and a half of riding the base gasket started to leak and then I knew the head gasket would soon lose it's torque and so I use Mike garage (old dyno shop) and changed out my lower ends. I did the work with the help of 2 friends and we had the lower ends switched out and into the frame and head installed and fired up in a hair under 2 hours! Went back out to the dunes for some back to back sand drag testing. All I can say is the 480cc hands down is faster, better, and I have no interest to go back to a stock bore (unless it is stroked). The 480cc rev just as fast, hit the same rpm as the stock bore, but pulled so much Stronger every where in the rpm band. It was amazing. I did not notice a change it peak HP but the 480cc ran so much stronger I don't think I'll ever run a stock bore stock stroke setup ever again. Night and Day difference doesn't even begin to tell the story of the way the two motors felt in the sand.

I might have to order a HRC needle

absolutely couldnt agree more eric...i know its possible to make good power out of a stockbore...but people OFTEN overlook the complete powerband...i wouldnt trade my 480 back for a stockbore ever...and hell im getting ready to add another 23 cc's...i dont even know why im making my yellow bike faster...guess its a disease LOL...

eric...you wanna run the 750 in KOTH in dumont in february? just a thought...but if i could get it ready in time im down for a road trip if you are!

Sorry. Man that would be awesome to take your 750cc yfz to KOTH, but I go a few other racing commitments to do between now and April. I am sponsoring a mx friend of mine and we are going to a few races, looks to be 3-4 total between feb 9th and April 15th. I'll be wrenching on his two yfz's and prepping them for the races. Then traveling with and tuning them up for the race events. Seems I have more wrenching time these days on others then riding on my own.

dammit...guess ill have to either nitrous it up hard and pilot it myself semi truck style.......OR......get one of the girls to get their pilot status in order....

....okay so maybe ill have to hit up KBR for some nitrous LOL

well, i had an extra 14.25:1 98mm on the shelf...... then millertime\corey asked me to hang onto it for his new yfz build.... i told him i would...and then like a fool i didn't tag it for him....then during the next day tress sold it.....so neither one of us got it...

all apologies to corey... i should have done what i said i would do......

on order... 6 weeks to the next batch :(

but.... somewhere between 1~2 more hp would be the answer...and sharper throttle response @ low\mid rpm too......

i don't think you are allowed to run a Honda part in a Yamaha unless you also own a Honda... or at least have a honda tattoo....lol....

thanks for same day ride comparo!..... i don't think i've ever dune ridden a stock bore and same setup big bore in the the same day for comparison.....

the big bore or stroker displacement boost is a bottom to top bump in power...there isn't any place in the band you would hit the throttle and not notice the difference.....

Great job John! The BB is more power everywhere I feel. I don't ever plan on going SB again! And buster don't lie,just look at lines on the chart.

And good to hear the 06 TRX HRC needle works great in that YFZ FCR. I really like how it has that extra taper on the tip. You have more control in the mid range. With a needle that does'nt have enough taper you have to raise the needle so it does'nt block off the nozzle/main jet.

But by raising your needle to much to make up for the main jet you go rich in the mid. And thats why I like the HRC needle. The tip tapers down even more than the Q needle we use in the YFZ FCR's.

Oh and BTW,can't wait till I get my Venom 501 Yamaha pistons

the extra "step\taper" on the end is also good in that it makes all of the 3/4 & up throttle position solely controlled by the main jet...just as it should be....

step-tapering the needle end is something i always do for alcohol carb use.....with alcohol jetting it's pretty easy to have a main so big that the needle becomes the full throttle restriction instead of the main jet....the needle isn't supposed to influence 3/4 to full throttle...so step-tapering the last 1-1.5 cm is a perfect solution...

going by the graphs, that's not 30 hp increase, was that a typo?
anyway good job, for a yammi!

thanks for the yammie props...


the 30 horse statement refers to the rev limiter HP....at this point in the build process, the 470 is making over 30hp more than the stocker did at the rev limiter...

I see........I stayed up to late last night