450r building questions - Honda TRX Forums: Honda TRX 450R Forum
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post #1 of 6 (permalink) Old 10-02-2019, 07:07 PM Thread Starter
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450r building questions

Hey guys I have a 2005 trx450r that I built here at the beginning of the summer. Stage 2 hotcam, 480 kit, jetted, white brothers exhaust, +3mm stroker crank. I have a 10:5:1 compression piston in it now and it’s time to change it after the 20 hours 😒. I’m wondering what is the biggest compression piston I can run that wine make contact with the spark plug. I’m not sure and I want to don’t out before I go with the trial and error method. I’m not worried about the cost of race fuel because I’m already jetted for it and I’m already running it. Any help would be appreciated. Thanks 👍🏼
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post #2 of 6 (permalink) Old 10-03-2019, 02:45 AM
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You wanna change it after 20 hours?I assume you want more power or.... you for some reason thinking it needs a top end rebuild already?

Also if you go higher compression you will need to actually go down a little on jetting too, it's hard to just claim you're jetted to run race fuel because yes you may be jetted close enough for 10:5.1 Compression, but will run totally different with 13:1, honestly would probably be to rich if you ran a 13:1 piston with the same jetting because the 13:1 pulls less air volume in on the intake stroke then what the 10:1 does.

As for Pistons:
You can get a 13:1 Piston that is a 97mm Bore through CP, I do know that is not going to have any clearance issues with any of the Hot Cams and or piston hitting the spark plug. I my self have a 97mm CP Piston That is 13:1, my head is decked at .030" thousandths and Stage 3 Hot Cam and I have no clearance issues at all. I believe my Compression ratio is around 13:75.1 (every 10" thousandths you remove from a head is .25 Compression ratio bump I believe) CP also Makes a 13:5.1 Compression Piston in 94mm (which is stock bore).

If you know how to.... I would suggest to use Clay to check your Valve to Piston Clearance, that is what I did on my build.

I'm sure guys with more experience then me will come in and help point you in the right direction as well. So don't only take my advice and run just yet.

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post #3 of 6 (permalink) Old 10-03-2019, 11:51 AM
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First off, welcome to the ORG!

As far as piston replacement after 20 hours that is totally unnecessary. That was Honda’s original service limit for the stock Cast piston, but even then it was unnecessary. These aftermarket forged pistons are very durable and the Nikasil cylinder coatings hold up well together for many hours.

No shelf piston will make contact with your valves using that cam, and it especially won’t hit your spark plug. As mentioned, it’s always good to check your clearances by claying your motor, but your combination is pretty safe. I personally really like the CP M2055 13:1 piston like Ryan is running. That piston with your stroker will give you about 13.4:1 compression.
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post #4 of 6 (permalink) Old 10-03-2019, 09:49 PM Thread Starter
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Thanks guys for the reply’s. The 20 hours is what the recommendation was when I bought it that’s what I was going off of but that makes it a little easier on the wallet because I figured it up to be about every three races and it was starting to make me not want to race 😂.
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post #5 of 6 (permalink) Old 10-03-2019, 10:47 PM
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Let sput it this way: unless your drag racing and beating the ever loving poo out of it-20 hours is way to low a number.



I beat the poo out of my quad and wont rebuild till 100 hours or it smokes or fails. I currently have 80 hours on my 450 since rebuild and no issues

-2004 450R. Far From Stock.. Sold, crank was going
-2006 450R. New WHIP..
-Do it right the first time, and you wont have a problem later. Being cheap or taking the easy way out only makes matters worse later.
-Your Backyard Mechanic Extraordinaire: Responsible for bringing you redneck, ingenious and often interesting ways how to fix things.
-You can watch things happen, you can make things happen, or you can wonder what the H*ll happened. Captain Phil Harris
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post #6 of 6 (permalink) Old Today, 09:21 AM
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I have beaten the crap out of my two engines, summer hairscrambles (12) races, practices, winter snow racing, studded ice racing, hauling the kids on our camp site, 2 years and not showing a hint of fatigue. I have everything stacked up for replacement but it just won't give !! 20 hours for me is just broken in.
That stands for 3 rings pistons, but if you happen to have a 2 ring piston, they are good for 20 hours, they are easy to spot, the engine puke oil trough all the seals lol

2008 TRX 450ER XC racing
FMSQ # 281
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