PDA

View Full Version : Lbs. of compression on a 2004 trx450r


reptikes
08-09-2007, 05:26 PM
Im wondering what a stock 2004 trx450r has as far as lbs. of compression? And what would the compression lbs. be with a full exhaust and HRC kit ?
Thanks,
Mike
TRX450RACER174
08-09-2007, 05:41 PM
Compression does not change with a exhaust and cam, you need to change the piston or deck the head to see a change in compression.
patrickj75
08-09-2007, 05:50 PM
stock should be around 108psi. mine checked out close to 120psi.
reptikes
08-09-2007, 06:51 PM
So what is compression for? Because my boy i ride with has a 250r that has 200 lbs. of compression, but yet i can beat him out of the hole and beat him threw all the gears. And its not the rider! He's been riding for 10 years ive been riding since the begining of the year. So what is all the compression good for?


Mike
TRX450RACER174
08-09-2007, 07:11 PM
Your ? is throwing me off, you are stating 200lbs, thats cyl compression it has nothing to do with piston volume, all your stating is that your compression test measure 200lbs, thats good but a higher compression piston gives you more power, the higher the compression ratio the greater power the motor will make, your test just means your rings are good and is holding pressure.
GPracer2500
08-09-2007, 09:29 PM
Cams specs do change cranking compression. The longer the intake valves stay open the lower the dynamic compression.

On the TRX450R the cranking compression is set according to how the auto-decompression device is adjusted. Without somehow disabling the auto-decompression device there is no way to actually measure a 450r's non-decompressed compression. That's why the PSI spec seems so low. It would be much higher without the auto-decompress bleeding off a bunch of compression (which happens automatically as soon as the engine fires and reaches a certain RPM).
pro-rider46
08-09-2007, 10:07 PM
gpracer i took my quad to get fixed at the stealership and we took our other 450r in to swap parts to keep cost down. they did a comp. test on the good one and it built 125psi and mine built only 75psi, can that be because of my new cam. and i think they disabled the decomp. too. does those numbers sound correct without the decomp. disabled. oh they are both on stock 10.5:1 pistons.