milling heads on nt

[verserv]

I have been trying to find out how many millimeters need to come off the heads in my car to increase compression from 9:1 to 10.4:1(i have an nt of course). Is there a way I can mathematically calculate this? (No one say why bother go buy a turbo, because this work is done absolutly free, and I have a gsx project car also) The shop just needs to know the amount to take off since they do not normally work on 4 bangers of any type(its a strict race shop).

[destrux]

It's easy... if you like math.

First off, use mm for all measurements, it's alot easier.

right now the volume of the combustion area at bottom dead center is 9 times the size of the combustion area at top dead center.... right? right...
so..
at BDC you want it to be 10.4 times the size of it at TDC..
and in order to do this you want to make the TDC volume smaller...
so..
first you need to find out the stock volume (cc's) of one of the combustion chambers on the head, then take this amount and add it to the volume of the cylinder at BDC
(pi x radius of cylinder x radius of cylinder x distance from piston at bdc to top of cylinder wall) to find the total combustion chamber volume.

Then take this number and divide it by 9 to find the "compressed" combustion chamber volume.

Take this number and subtract the volume of the combustion chamber in the head.

Now... take this number and SAVE it, you'll need it later.

OK... now that you have the critical numbers, you can find the amount of mm's that need to be shaved off to increase the compression.

Take the TOTAL combustion chamber volume you found before and divide it by 10.4.

Take this number and subtract the number that I told you to save from before.

This is the new cylinder head combustion chamber volume (in cubic millimeters) you need for 10.4:1 compression.

I'm not sure how to convert this to an accurate amount to shave off without using a computerized contour of the head chamber to subtract volume.
If you can get them to "cc" the head after they shave a little off untill it's right you can do it that way.

That's how I figured out the new compression ratio on my motorcycle after the head was shaved. It seems very accurate..

Maybe there's a computer program that does this stuff too?..

[Rdy2race]

OUCH MY HEAD!!!

heheh J/K


Info packed got to love posts like that!!


yes I know that some of the motor dyno CUP programs can do this, What one?? That slips me at the moment. I don't own one, =-)

BM

[verserv]

well its 1997cc engine of course. so how can i work it? Maybe list it more mathematically and less linguisticlly. might help my state college educated ass

[destrux]

I would try to make up a formula so you could just plug in the numbers, but i had a hard time getting it right to begin with.
I forgot two things in my directions.... the space between the upper ring lands, and the top of the piston... and the contour of the top of the piston....
for my formula to work the piston would have to be perfectly flat on top and the ring land would have to be at the exact top of the piston (impossible)..
I hate to say it, but maybe if you contact a decent honda engine builder they might beable to help you with the math, hondas are more known for "all motor" engines than dsm's are.
btw..
If this is a serious race shop then why dont they know how to figure it out?
The math works the same no matter the number of cylinders(8 or 4 or 1 or 16)...since you are only working with one cylinder to calculate the compression ratio.

[verserv]

its a serious shop but the guy i am giving it to doesnt know dsm's. the work on big ass race cars. im sure they can figure it out, but if i can get it set before hand life will be easier.

[destrux]

Yeah i understand what you mean.
Most serious shops like that in my area wont even touch a part unless it's from a V8 or something of american design (even though DSM's were partly chrysler). I was going to have my head milled on my eclipse, but the only place that would do it wants me to sell my kidneys as payment..