Pistons/CR/Squish/Deck Height/Gaskets...

[Quadzilla]

OK boys and gals,

Real simple question here (I hope). I don't want to turn this into a 15 page thread.

Need to know what brands of pistons to use with what gaskets to acheive proper CR (compression ratio) deck, etc. I'm after (as I'm sure many are) the path of least resistance. In other words, to try to do this without decking of cylinder or milling of the piston, etc. Just piston, gaskets and be done with it if possible.

Can somebody (prb will be mutiple people) provide the proper "formula" of brand of piston and gaskets for the following:

Assume all are 10.8:1 or 11:1 roughly to run pump gas

416 Piston (brand)
gaskets (brand and thickness)

425 Piston (brand)
gaskets (brand and thickness)

440 Piston (brand)
gaskets (brand and thickness)

I know that Wisco is notorious telling you that you are buying an 11:1 piston and what you get after using stock thickness gaskets is more like a 9.75:1. I'm still unclear as to how close JE and Ross are on their specs. It would be great to know the real combinations of manufactures to use (piston and gaskets) to acheive the proper CR, etc without milling and decking if possible. All here on the thread building a motor would benefit.

Another thing to consider is if most rate too high on the CR than actual, could I (we) just buy say a 12.5:1 and use stock thickness gaskets and then it would roughly equal out to 11:1 (I know that I over-simplifid this question somehow) or would that cause other issues? At lleast this would probably fix the issue of peoples cam timing being retarded from using thinner gaskets. Thanks!!!!!!

[Colby@C&DRacing]

That is pretty easy to figur the JE and Ross pistons with the stock gaskets are pretty much right on the money:)

[y2k400ex]

and if I remember correctly if you use the XR 400 gasket it will bump the compression up 0.2 of a point.......

[Colby@C&DRacing]

I use the cometic steel flex gaskets

[Quadzilla]

Just got off the phone with "Honda" Jim from Ross (formally from JE as well). He said that the Ross 400EX piston and the XR400 piston are literally the same piston with different part numbers. Well this is prob not new news to anyone, but remember one thing. The 400EX stock gastkets are thicker than the XR400, thus lowering the compression. So if you buy a Ross 11:1 and use stock thickness gastkets in a 400EX, it won't be 11:1, it will be less (not sure by how much). So you must use XR gaskets to acheive proper compression, thus retarding the cam timing by a bit (anyone know if this really has any significant negative effect?). He was not sure what JE is currently doing, but when he left there 4 yrs ago, it was the same as Ross is doing now.

[PHIL_B54]

Originally posted by Quadzilla
I don't want to turn this into a 15 page thread.

i take it you gave up on reading have you decked the cylinder
http://www.exriders.com/vbb/showthread.php?s=&threadid=48435
some of the info you seek is in there, i printed it out so it would be easier to read.....warning dont print the sigs it will be like 90+pgs long


Originally posted by y2k400ex
and if I remember correctly if you use the XR 400 gasket it will bump the compression up 0.2 of a point.......

if thats true, that would put the Ross and JE off .2 on a 400ex and that would be close enough for me

[Colby@C&DRacing]

The difference between a stock 400ex and xr400 gasket is 8 thousands of an inch. making a very minor diff in comp. but to fix any differnce in comp I use a thinner base gasket and head gasket to change the squish and raise the comp. So yes there is some difference in comp but it is marginal when compared to the wiseco pistons