[schatzy]

Hi, I was just wondering what would be a target dynamic compression ratio to shoot for with both cast iron and aluminum heads for 87 and 92 octane. If anyone has any suggestions I would appreciate it. Thanks,Don

[Old Yeller 1970]

Chevy Hi Performance had something on this a few years back. They were building an angine with 8.7:1 compression and Vortec heads with a 268 Comp Cam. It made good hp on the dyno but after they got it in the car it was a slug coming off the line. They diagnosed the problem as being to low on the dynamic compression. I think they said it was around 120 PSI. I believe they said not to go over 180 and 160 was about optimal. But I'm only going from memory and that was at least 4 years ago.

I've never been able to find any more on it since. It seems to me that knowing the dynamic compression is a great way to build an engine because it takes the guess work out of trying to figure the right camshaft vs Static Compresion Ratio. But most people just figure a certain amount of increase in the staice comp. ratio based on how large the cam is and what size engine it's going into.

[schatzy]

Thanks for the reply. I heard that around 8 to 8.25 to 1 is what the dynamic compression should be, but I don't know if that is for cast iron heads or aluminum.

[Old Yeller 1970]

OK, what I was talking about was dynamic cranking pressure. I'm not sure what the dynamic compression ratio is supposed to be but I found a website with a calculator that might be able to help. However, it requires a subscription to their website.
http://www.smokemup.com/auto_math/dy...sion_ratio.php

[Brian S]

KB Pistons has a dynamic compression calculator website that doesn't require a membership.
http://kb-silvolite.com/calc.php
There is no set number for DC on pump gas. Way too many variables.