Well, first, does anyone even use the skunk2 "high compression" valves out there? The ones that don't have concave valve heads...

these


I'm trying to figure out exactly how much more it will bump compression but I don't know exactly how to do it..

I'm assuming you subtract off the combustion chamber volume...

But I don't know what difference in volume is for the concaveness in stock valves VS. the flat valves from skunk2

say im using stock ITR valves...


[Modified by Toda Party, 11:08 PM 9/8/2002]

 

probably a very small amount.

 

Since "probably not that much" wont really help you, lemme school you on CR.

First of all without knowing what the engine, block, head, or pistons are i cant really help you, but i can tell you how you are going to calculate the CR.

If you are calculating cylinder volume (CV) im pretty sure that the equation is:
Cylinder Volume = x (1/2 bore) x-squared stroke
So to find this, you need to find what the bore is of your engine. Say that your running an Ls engine, the bore is 8.1 and has an 8.9 stroke, a total of 458.6cc

If you need head gasket volume the equation is:
CV = x(1/2 bore) x-squared gasket thickness
Now still using the Ls example, 8.1 bore and a 0.06cm thick gasket the head gasket is going to be about 3.1cc

If you need the Ring Land Volume the equ. is:
RLV = x bore x piston-to-wall clearance
Say your still using stock pistons, the clearance is 0.0038 and a ring-land that is .05cc

But to find the rest such as the cylinder head volume, Deck Height and Piston Dish Volume you are going to need to do is use the water technique. If you dont know how to do that just reply back.

And to finally find out the Compression Ratio your going to need to get all the numbers for all the different volumes and heights and add them together.

i.e. 497.65cc ---> 39.05cc @ TDC. Do the division and you some up with 12.7:1

Now that you know how to do it, research, hit the books, down some asprin and hope you dont **** up the calculations and make the rod slam into the head. Yikes!

-TS04

 

Or to make your life alot easier, goto http://www.superstreetonline.com
HOME SCREEN
-Car Tech Located on left side of screen
-Calculations Located at the bottom of Car Tech
-Compression Calculator All the calculators are on the screen under
-MPH/RPM Calculator the calculations section
-Gear Calculator

 

hehe thanks for the lecture, i basically knew all that already

i was just asking to difference in displacement between a stock valve with a "bowl", and the skunk2 valves w/o the "bowl" and just a flat surface.

i was assuming that the combustion cylinder volume would be decreased slightlywhen working out the equation, but i didnt know exactly how much


[Modified by Toda Party, 12:40 AM 9/10/2002]

 

I heard that the stock concave valve volume is .8cc's. I havent bother verifying it though. Get a piece of lexan. Make a small hole, apply a thin (thin as possible because every bit is measureable) layer of vaseline to the outer surface of the valve. With a buret or graduated syringe fill the hole with alcohol, thats how many cc's.

 

I purchased a set of endyn flat valves and the calculation was in the .3-.5 range for a B18C I had only the exhaust valves, ITR intake valves and a mugen gasket and .0010" mill on my P72 head with a stock C1 bottom end making 205, 212, 210 and 218 in the row so go figure. thats about 10.5-10.6:1 I would imagine. I know the ITR makes 205-225 in the row at 10.6:1. I bought them from Mike K and he said to expect .4cr roughly with the ITR intakes as they have more compression area than the GSR intake valve also


[Modified by MikeSarr_GSR, 9:28 AM 9/10/2002]

 

There is some good info on the new issue of SCC about CR.

 

to find out the volume of the combustion chambers with these valves you need to get the head CC'd.

I dont know which engine you're referring to but i know the stock B16 head
and type-R heads have stock volume of 42.7cc per chamber.