NZ4age wrote:Hey everyone,

Would anyone know what the compression ratio would be if using smallport 10.3:1 pistons, .5mm skim off head and .8mm TRD headgasket?


Any help would be much appreciated,

Cheers Grant

yoshimitsuspeed wrote:http://www.csgnetwork.com/compcalc.html

Bore 81
Stroke 77
Headgasket bore 82mm for stock
Compressed HG thickness stock should be 1.2mm
Combustion chamber volume is about 36
Deck should be very close to 0

It would be best if you can get piston dome measured directly off the piston because the numbers I have seen just don't quite add up.
Since we don't know that we can leave it as our variable right now and solve for 10.3:1. -.4 cc gets us to 10.28:1.

Now you can just play with changing the HG thickness. .5 skim and .8mm hg would get you to about 11.4:1.

How much compression you can run on an ECU depends on too many variables to easily answer.
I do have a customer running 11:1 pistons with poncams and he is getting a little detonation in the mid RPMs. I don't think it's enough to be worried about but it is noticeable. One thing though is he isn't running his EGR. This may be contributing to the knock. I would say though that on stock cams at that compression level you will NEED to monitor for knock and you may have some trouble controlling it. If you have your EGR then that might be enough.
That said you would be smart to run some cams anyway. It will open up the top end a ton and due to the compression bump you should still gain a little in the low to mid RPM but up top it should feel much faster.

This is by far my most popular selling cam. http://matrixgarage.com/store/tomei-1

These are the pistons I designed for the aforementioned customer build. They should be 11:1. He wanted to keep it non interference with the poncams so the reliefs are a little deeper than normal. If you wanted to go with an interference motor the reliefs could be smaller and the top much smoother. These were custom Wiseco's and the price is pretty impressive and in my opinion well worth being able to tailor a piston specifically to your build. It will also be stronger and hold up better to the occasional detonation or tuning error.
If you went with an 18mm rod supertech has a pretty nice 11:1 piston. I am working with them on a design based very closely off the custom Wiseco's above. For these a piston and ring set will be pretty close to OEM pistons and rings.

oldeskewltoy wrote:
.8mm gasket will add about 4/10 of a point, so from 10.3 to about 10.7. A half millimeter skim on the head will drop volume of chamber to about 34.75cc. That should bump compression a further 4/10s, so to about 11.1 to 1


Concerning porting.... having glanced @ the link you posted... a few of the pics are mine... but there are a few inaccuracies.... the biggest one is the exhaust side NEEDS rather extensive porting... it requires changing the taper the two exhaust streams merge at inside each port. Only polishing the exhaust port only really helps the port shed carbon build up, it doesn't improve flow to any significant amount

NZ4age wrote:
Thanks for your reply, would you think just changing the headgasket thickness would be the better way to go without running into too much trouble? The tomei poncams you sell, are they compatible with the oem valve springs?

NZ4age wrote:Thanks for your reply, do you have any detailed info/photo's or webpage links regarding the exhaust side porting?

oldeskewltoy wrote:
notice the amount of material removal between the top panel and the middle panel.... the bottom panel is once the taper has been changed, blended and mostly finished

apsogosGTi wrote:Hello and good morning!have you relocate the battery?and where exactly?thanx

apsogosGTi wrote:awesome sauce mates!perfect a clean like mine!+ 20bhp from me!