I am building a D all motor I have the P29 pistons and I will be punching it .5mm oversize. Problem is according to the compreassion calculators I will be over 13,7-1!!!

How do I lower the compression ~1.2 points?

I have an idea of milling a pocket in the center slightly offset toward the sparkplug to lower the ratio and concentrate the charge near the plug. I think I only need to remove a small amount of material, but does anyone have any suggestions or other ideas?

 

umm how about a thicker headgasket instead of ruining your head....and what comp calc are you using(by the way...dont trust them!)

 

i would not suggest custom designing your own piston. They are designed the way they are by engineres for a reason. You may do more damage than what you acctually hope to accomplish. I would suggest going to a lower compression pistion.

 

ahem u checked that out on knology compression calculator.... u din actually entered the piston to deck height+ compression height plays a major role... that varies with the p29s.... i have done a same setup on the Z6 as urs and the compression according to the calculator was 12.6 with a 2 layer HG.....so it wouldn't be a problem for you......

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by awadkhan &raquo;</TD></TR><TR><TD CLASS="quote">ahem u checked that out on knology compression calculator.... u din actually entered the piston to deck height+ compression height plays a major role... that varies with the p29s.... i have done a same setup on the Z6 as urs and the compression according to the calculator was 12.6 with a 2 layer HG.....so it wouldn't be a problem for you......</TD></TR></TABLE>

Good answer

I think I will wait till I assemble the engine a little more and actually cc the cylinders and head before I do anything.

Also the headgasket thing will work, doesn't cometic or some make a .060 HG?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Super Chicken &raquo;</TD></TR><TR><TD CLASS="quote">

Good answer

I think I will wait till I assemble the engine a little more and actually cc the cylinders and head before I do anything.

Also the headgasket thing will work, doesn't cometic or some make a .060 HG?</TD></TR></TABLE>

BY far not the cheapest place on the internet however they do sell cometic HG and you can find all the sizes there

also unless i am dreaming i do believe that cometic makes custom thickness HG to

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Richard... &raquo;</TD></TR><TR><TD CLASS="quote">

BY far not the cheapest place on the internet however they do sell cometic HG and you can find all the sizes there

also unless i am dreaming i do believe that cometic makes custom thickness HG to

</TD></TR></TABLE>

they do make custom gaskets but the thicker the headgasket the less longevity ull get out of it. if ur comp is gonna be 12.6:1 all u need as a 3 layer and ull be fine to run on 93 octane.

 

so, basically run a D16Y8 HG and you'll be fine. DONT MESS WITH YOUR COMBUSTION CHAMBERS!!!! If anything, use a wire wheel to knock off the carbon build-up and thats all. Anything else and it will seriously affect the way air gets into the cylinder...may even cause detonation.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mightyjoecivic &raquo;</TD></TR><TR><TD CLASS="quote">so, basically run a D16Y8 HG and you'll be fine. DONT MESS WITH YOUR COMBUSTION CHAMBERS!!!! If anything, use a wire wheel to knock off the carbon build-up and thats all. Anything else and it will seriously affect the way air gets into the cylinder...may even cause detonation. </TD></TR></TABLE>

^^^^ this is true. when u screw around with a combustion chamber and you dont know what ur doing it changes the flame pattern around. if you dont know what your doing dont do it.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mightyjoecivic &raquo;</TD></TR><TR><TD CLASS="quote">so, basically run a D16Y8 HG and you'll be fine. DONT MESS WITH YOUR COMBUSTION CHAMBERS!!!! If anything, use a wire wheel to knock off the carbon build-up and thats all. Anything else and it will seriously affect the way air gets into the cylinder...may even cause detonation. </TD></TR></TABLE>

I won't be changing the combustion chambers at all only the piston crown...if needed. I have seen it done on motorcycle piston before where they used a stock piston welded up on the sides and milled down in the center to concentrate the charge near the plug. The p29's have a little material that can be fly cut near the center to remove 1.5-2cc maybe? Like I said I need to cc the engine to be sure

I need a cam and springs keep an eye out for me if you see any bargains out there

 

Those calculators are BS, most of them add the higher CC's of the P29's but dont take into acount the 40k lower wristpin height on the P-29's. I ran I set of P-29's on a motor with the head milled 80k, one layer head gasket, and still ran on 93 pump. The calculators said I was above 14:1 lol

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by BIGTUNA &raquo;</TD></TR><TR><TD CLASS="quote">Those calculators are BS, most of them add the higher CC's of the P29's but dont take into acount the 40k lower wristpin height on the P-29's. I ran I set of P-29's on a motor with the head milled 80k, one layer head gasket, and still ran on 93 pump. The calculators said I was above 14:1 lol </TD></TR></TABLE>


SICK!!! you're crazy! Did you figure out what your compression actually was?

 

Not nearly as high as my new motor with Bisimoto custom spec pistons

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by BIGTUNA &raquo;</TD></TR><TR><TD CLASS="quote">Those calculators are BS, most of them add the higher CC's of the P29's but dont take into acount the 40k lower wristpin height on the P-29's. I ran I set of P-29's on a motor with the head milled 80k, one layer head gasket, and still ran on 93 pump. The calculators said I was above 14:1 lol </TD></TR></TABLE>

I forgot about the different wrist pin height. Good to know

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by BIGTUNA &raquo;</TD></TR><TR><TD CLASS="quote">Not nearly as high as my new motor with Bisimoto custom spec pistons
</TD></TR></TABLE>


OMG!!!