Who would one calculate/determine actual compression ratio based on static compression of the motor, displacement size, and psi of boost? TIA :)

Keith

 

http://www.rosspistons.com/calculator.php

Try this out.
3.898 bore
3.622 stroke
.054 Crushed Head Gasket Thickness
.010 deck height
LS1 Head Volume 67cc
LS6 Head Volume 62cc or maybe its 64cc..I can't remember everything.

Have fun.

 

Actaully I was looking for something like this:

static compression of motor: 8.9:1
displacement of motor: 408
psi of boost: 12

I am guessing that the actual compression ratio would be about 11:1ish based on the motor and amount of boost, but I would like to know for sure. The reason that I am asking is to determine what level of octane I would have to use.

Keith

 

You should have been more specific about your request.
Your welcome anyway.

Being that I am a helpful type of person as well as an butt to people who deserve it...I will direct you to Jim Halls website. He used to have a Calculator where you could calculate boost compression ratios this will require you to fill in the data...looks like you have some of it. I could guess but last time I guessed I was only 99% correct...so good luck.


Looks like Jim took it off. So after you figure out the CR numbers that you want. There are a couple of different ways to get to 8.9:1 CR. Example,
-8cc Dish Piston, 72cc Head Volume, .054 head gasket thickness (crushed), .010 deck for a 346cid. You will need a 4" stroke and I think a 4.060 Bore to get your 409cid, you may have to change the dish or chamber volume of the head to get to the desired CR of 8.9:1....You should just go with 9:1 or 9.3:1.

A couple of examples of CR and required octane level. Andy's new F1R Prochared 409 is at 9.5:1 CR and he used 91 ocatane and a can of Torqo. My CR is 9.67:1 and I used 104 Sunoco for 16lbs of boost...that is why my Torque is over 700+ft/lbs at the rear wheels.

We will be redynoing my car at Andy's this weekend to see if my clutch is broke in enough to hold my power...last time it slipped after peak power and still made 593/709 rwhp/rwtq. My CR is a little high for A turbo motor..about 1/2 a compression point if you compare it to a recent LPE 427TT (9.3:1). But the truth of the matter is I can't even use that power on the street so I don't even turn the boost controller on...and just use the 11lbs base boost setting.

After you figure out your specs for your motor...try this calculator. http://www.rbracing-rsr.com/compression.htm

or
http://www.turbofast.com.au/TFcompB.html

[Modified by Shinobi'sZ, 8:12 AM 1/13/2004]


[Modified by Shinobi'sZ, 8:26 AM 1/13/2004]

 

I thought I was, but I guess I was wrong. The two calculators are exactly what I was looking for. Thanks a lot :)

Keith

 

Cool..........now all we need to know is what our VE is and we will be set. :cheers:

 

I think that this is a good basic link that shows some very helpful information.
http://www.bulletproofperformance.co...atiotable.html

 

There used to be a couple of pages of formulas in the back of the Edelbrock catalog. One of the formulas allowed for the calculation of CRs taking into effect boost and altitude. I have not looked at an Edelbrock catalog for a long time so I don't know if it is still there.

 

I would not put too much value in these calculators.

They might give you some general indication, but there are so many things missing from the calculation.

The cam and the resultant valve timing are going to have a huge impact on cylinder pressure. You might find a calculator that takes this into account.

 

I did have a link to a calculator that ask for Rod Length and Valve Opening ABTDC (0-90 degrees). I will have to find it. It was only a little different than with the end result than the ones listed above...not really enough to matter. I don't consider 18.5 Boost Compression and 19.2 that different...I need race gas for that much boost regardless.