Where to start? GPX mod

S

Snojet Steve

New member
Joined
Apr 4, 2006
Messages
125
Age
45
Location
Moncton, NB, Canada
I have begun tearing down what will be my more modified GPX engine.
It will run 38 VM's that came from a Polaris TXL so no powerjets.
The pipes are 77' SRX, cylinders are ported and polished to match those.
I'll be running Wiseco forged flat ring pistons and not be raising the compression any.

Top Q is I want to know if you guys agree with my starting point of using
a 78' SRX settings and then richening up on the mains somewhat. They run (in the maritimes which is close to sea level) 280-310 mains so I was thinking of starting off at 350-360 with the 77' pipes. The pilots would be #30 and everything else would be the same as SRX (cutaway and nozzle tubes)

Any thoughts on this?
 
Oh yes. 93 Octane with 35:1 Amsoil to start, is that good enough? I'm not shaving any heads but the cyls are ported and smoothed out. It doesn't have a really drastic port job but it matches the carbs and is supposed to work with the pipes which hit sweet at over 9000! So that means running a Comet clutch or later SRX style. I have a 102C or 108 C which should do the trick to keep the bottom end solid.
 
TWO THINGS, RUN THE COMET 102c AND YOU MIGHT BE ALITTLE LITE WITH JUST 93 OCTANE. YOU SAY YOUR NOT SHAVEING HEADS BUT I BELIEVE YA MIGHT NEED TO BE ALITTLE HIGHER. CAN YOU GET RACE GAS WHERE YOUR AT ? 35:1 AMSOIL IS FINE. 3:16 (tony)
 
I have everything tore down now. I found a nice motor surprise too. The seals that looked fairly new were cracked! The outside PTO bearing also sheared it's locator pin but didn't do any damage. That damn thing would have worn it's own groove in the case then BOOM! Actually, the inner bearing would have kept everything in line but still... not tollerable. The locator pin is a friggin roll pin! At least it broke clean. I'm going to put a new bearing in just to be safe and use a solid pin. Now for another major point. Have there been any major problems with the window type drivers that the GPX's use? Especially when they have to drive over 140 studs! I have spares for cogs from the ole 75 GP so it's not all that bad. Some people have told me though that the drivers break right on the shaft. Thats not a happy thought to have when winding a 350 lb monster down a strip.
 
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