Camshaft, Rod Length, Boost and Altitude Correction to Compression

Your engine summary is as follows: Bore 4 inches, stroke 3.48 inches, rod c-c length 5.7 inches, with a static compression ratio of 8.832 :1. Your camshaft specifications call for an inlet valve closing of 42 degrees ABDC (after bottom dead center).

Your chamber volume is 91.50 cc's. With this camshaft your dynamic, or effective stroke is 3.15 inches. Your dynamic compression ratio is 8.08 :1 corrected for cam timing, altitude, and rod length. Your dynamic cranking pressure, corrected for cam timing, rod length and altitude is 161.04 PSI. Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and 10 PSI is 13.58 :1.

Altitude is ~9 meters here in Jax.

 

anyone?

 

damn, nobody has anything to say?

 

thats over my head

 

I don't think that there is any standard definition or way to interpret "dynamic boost compression ratio". I sure don't know what it means. I know that it can't have the same implications as dynamic compression ratio for purposes of estimating octane requirements or detonation potential. I mean, there are plenty of cars running pump fuel with a combo like yours. And there is no way that could happen with a 13.6:1 CR. So, like I said, just what does it mean?

Rich

 

That 13.6, I think is factoring in what the compression would be with 10psi. The calculator I used required that I put in a boost pressure. Just to make things simple I entered 10psi. I think the actual dynamic compression was mentioned earlier on in the results at 8.08:1.

I searched for several dynamic compression calculators, and this one was the only one that looked worth a damn. I know 13.6:1 is way too much for pump gas, much less pump gas with 10psi.

Does that help or make sense?

 

That's my point, what does it mean? And even if we knew, how should it be interpreted? IOW, it's meaningless.

Rich

 

Ok, I'll try this again.

I plan on putting a T70 on an LT1 with a static compression of 8.8:1. I used the cam's specs and a dynamic compression of 8.08:1 with the intake valve closing at 42* ABDC. I simply wanted to know that given the numbers I mentioned earlier, do the numbers given by the calculator look correct?

I've seen posts where people ask "Is this compression good for boost?" and the usually give a static compression number. The more knowledgable people usually say something to the extent of dynamic compression is the determing factor. I used a calculator available online, and thought I'd be a little more prepared to make a post.

That any better? LOL