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Discussion Starter #1
this guy mixxer has got me thinking... and that's dangerous. i have decided to start shopping for a 12:1 or 13:1 piston kit and a cam. i want to do the swapping myself but have many questions of course. so here goes...
1. what cam and compression combo will give best low-mid hit?
2. what octane rating (race gas) will i need?
3. how dificult is swapping these parts, especially the piston? should i try this myself or just pay the man?
4. will the cylinder need honing? will the head need any machine work to accommodate higher compression? if so, i will have to send it out. :(

i have looked in the service manual for some direction. it seems straight forward as far as tear down and reassembly of the head and cylinder. just wondering if there are any trade secrets that might be left out of the manual and are important for retaining some of the motors reliability. go ahead and answer as if i have no clue... because on some of these issues i really don't.


if it's as simple as picking the right combo and "swapping internals" then i think i can manage with the service manual as a guide. i have seen schmitty's pics of the cam swap and it looks pretty simple. i am mainly concerned about the piston and any changes that may need to be made on the head as a result of higher compression. when i do this, i will be taking lots of pics and documenting this project as i go. i just want to find a low budget method to creating a MONSTER and then share the info so we all have a chance to kick the competitions @ss!

btw... Happy 4th everybody!
 

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Discussion Starter #2
here's what i am thinking after a little bit of research...

JE 12:1 piston... so i can still run 93 octane. could i still run 93 octane at 12:1?

hotcams stage 1... so i don't loose any bottom end by getting too aggressive.

does anyone think i would loose bottom end by going to a stage 2 and staying at 12:1? where does the sparks aggressive cam fall? closer to stage 1 or 2? any other options are more than welcome and appreciated. like i said before... i want a good bottom to mid hit.

thanks :)
 

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Lord of Combustion
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RedDogg, JE pistons are the best quality pistons going , bar none. Wiseco, JE, and Carillo rods are owned by the same parent company. The rings supplied with kits ordered directly from JE are the same ones used for thier Wiseco counterparts. Customized piston kits can be ordered in any form from JE but for customs you have to order a minimum of 4 pistons. The best place to get your pistons from is Curtis Sparks. Curtis is very sharp and realizes that a few small gains add up to a bigger gain in the end. Curtis orders his customized piston kits from JE specd for OEM Honda rings which are thinner than Wiseco spec rings. OEM Honda rings have less friction and are less prone to ring flutter than the general purpose Wiseco rings. On the crf version Honda relieved the sides of the cylinder base somewhat like a 2-stroke to allow for easy access to compress the rings on installation. Why this feature was omitted from the trx cylinder is a mystery to me. For whatever reason, in my 30 years of engine building (back in my day there weren't any dirt bikes, just dirt), I have never had such a fight with getting rings into a cylinder. I actually ended up cutting a steeper, and wider, ring feed ramp into the cylinder base to ease the process. It could just be me. My suggestion would be to use a Hot Cams stage 2 cam with a 13:1 piston. The stage one doesn't have quite enough intake duration to fight back the BlueTide. Don't be scared to budget for race fuel: with the price of pump premium the diff is usually +$1.00 to jump to 110 octane \ the stability of race fuel is CHEAP insurance against a host of tuning variables \ the lead in it extends the life of your valve seats and guides \ and even if you use 100 gallons a year, what's that compared to what you get in return for your 100 bucks, hardly anything costs that little in our sport. You won't need any head mods to accomodate the piston. Gear it 13/40 and wait for Magnum to get Hi-Rev CDIs in stock..........Mixxer
 

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Lord of Combustion
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I forgt, the sparks cam is the 108-x2 grind from www.megacyclecams.com. Again don't be scared of octane and compression, 4-strokes LOVE lots of both!...mixxer
 

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Thanks mixxer :D I know a few guys that have run the megacycle cams and love them, they make some good stuff.
 

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Discussion Starter #6
thanks mixxer... thats the kind of info i was looking for. i hope that lots of people can benefit from this thread. i was trying to save money by purchasing a JE piston on ebay or from a local speed shop, but if i'm not going to get the same quality (rings, etc.), then i will just call sparks for their 13:1 kit. the hotcam stage 2 is where i will try to save and i will definitely be ordering the shim kit.

thanks again,
jason
 

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Discussion Starter #7
mixxer, i am looking at the pdf file from megacycle cams and can only find the crf cams. are these the cams you are talking about? i don't see a section for the trx. the 108-x2 grind for the crf has .412" of lift on the intake and .385" on the exhaust (pg. 28).

http://www.megacyclecams.com/catalog/catalog.pdf

Hot Cams Satge 2...
intake .398" lift
exhaust .343" lift
 

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Discussion Starter #9
KGB, do you know what the specs are on the HRC cam?
 

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Lord of Combustion
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RedDogg, Sorry for not clarifying, I was referring to the CRF450 cam in the Megacycle catalog. The X1 and X3 profiles won't work in the TRX unless the intake valve guides are sunk deeper for clearance. The X2 cam pushes the clearance but will be ok.
I don't know the specs on the HRC cam but I would appreciate getting some.
I assumed the HRC cam would be a fairly mild increase in timing since Honda did not offer the kit with a higher compression piston to compensate for low end loss.....Mixxer
 

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Code:
450R cam specs:

                                  Stock       HRC
                    Intake Lift:  .337        .390
                   Exhaust Lift:  .290        .350
  Intake Timing  Opens @ 1.16mm:  10° BTDC    20° BTDC
  Intake Timing Closes @ 1.16mm:  40° ABDC    60° ABDC
Exhaust Timing  Opens @ 1.16mm:  40° BBDC    55° BBDC
Exhaust Timing Closes @ 1.16mm:  10° ATDC    25° ATDC
 

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Lord of Combustion
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Thanks 86atc250r! The HRC cam is a little bit more serious than I thought. Do you have a Honda part # for it? Can it be ordered separate from the kit? By the way I've had good luck dealing with Service Honda, good prices / good service. By the way did you check for Lazaras' dyno post on the Pulse Charger yet?.......mixxer
 

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I don't think the HRC cam can be ordered separate.

Anyone have the specs for an '02 CRF 450R cam? I was told it was very close to the HRC cam, but would like to see for sure.

I installed a '02 CRF cam and a JE 11.5:1 piston. Was not happy with the performance, and then it blew up.

I am leaning towards a Sparks cam.

Where can I get a cam shim kit?

Jon
 

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Originally posted by mixxer@Jul 5 2004, 02:20 PM
For whatever reason, in my 30 years of engine building (back in my day there weren't any dirt bikes, just dirt), I have never had such a fight with getting rings into a cylinder.  I actually ended up cutting a steeper, and wider, ring feed ramp into the cylinder base to ease the process. It could just be me...........Mixxer
It is not just you. We had the same problem. Checked and rechecked the oil ring 5 times just to make sure we didn't have an overlap.

And we thought it was just us. :wacko:
 

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Lord of Combustion
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CrowleyOffroad, the shim kits are sold by anyone who sells HotCams and you get 3 each of about 50 sizes, in 2 excellent storage packs. Hallelujah Brother!!!
Honda has their shims in .0005" increments for about 300 total sizes, the HotCams kit makes the jumps in .001" . Good enough!......mixxer
 

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Discussion Starter #16

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Thanks RedDogg!

2002 CRF 450R cam
Intake Lift: .380" 249° 106.5°
Exhaust Lift: .356" 272° 107°
Intake open: 29 atc
Intake close: 63 bbc
Exhaust open: 51 abc
Exhaust close 18 btc
TDC lift in .098" ex = .116"
Running Clearance: Intake:.005"-.0075", Exhaust: .010"-.012"


The CRF and HRC cams don't look "almost identical" to me.....

HRC
Intake Lift: .390
Exhaust Lift: .350
Intake Timing Opens @ 1.16mm: 20° BTDC
Intake Timing Closes @ 1.16mm: 60° ABDC
Exhaust Timing Opens @ 1.16mm: 55° BBDC
Exhaust Timing Closes @ 1.16mm: 25° ATDC
 

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Lord of Combustion
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The Sparks cam and the HRC cam are VERY close in specs. Thanks to 86atc250r these comparisons can be made.

.....................HRC..........Sparks
int lift:______.390 _____.412
lobe cntr:____110 _____108
ehx lift:_____.350_____.350
lobe cntr:____105_____108
LSA:________107.5 ___108
int dur:______260_____260
exh dur:_____260_____268
overlap:_____ 45 _____ 48

These are both more radical profiles than any of the CRF cams.
From the HRc specs I would guess that there would be significant low end loss without a fairly high compression piston (13:1+) installed also. Does anyone have firsthand experience?....................mixxer
 

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I have HRC cam. I have not been unhappy with low end performance, however I never rode it stock, so I have no comparison. I do not have a 13 tooth sprocket either, I run a 14/39. I ride dunes, weigh 230 and have no problems with low end, espicially after the installation of the FCR40 carb. Bottom end is super strong now. I run a 7 paddle hauler 20". I run no air box, a DS650 intake plennum, and a DS650 K&N (2 times the size of stock 450 filter), and a LRD full system. I am going to go into the engine soon, and want to pick up some top end performance.
I played with the graph. The difference column is the difference from Sparks cam to HRC cam.
 
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