Compression question

[Touring23]

Does this article apply to our 302's?
Thanks.

 

[Touring23]

All righty then....

How does everyone feel about 170psi?

 

[Touring23]

 

[NIKwoaC]

I just skimmed through it, but to answer your question, basic engine fundamentals apply to ANY gas fuel piston driven engine. While individual tuning parameters may vary between designs, constants like calculating static compression ratio, cranking compression, etc. can be used to determine needed octane for any engine. So yes, you can apply the concepts outlined in that article to our 302s.

 

[Touring23]

Thanks.

 

[Brian@PAR]

As NickowaC says yes this does apply. Cranking compression should be looked at but sadly without software it is difficult to calulate. I use EA for this and I've never seen an online calculator.

185 is a good target cranking pressure for a pump gas motor. The thing is that you can't just adjust the cam timing to get you where you need. This can through off the other events so much that it is detrimental.

A good place to start in picking a cam is to calculate Dynamic Compression ratio Shoot for 7.5-8.0 to get you in range for pump gas.

Here is a Dynamic CR calculator

http://cochise.uia.net/pkelley2/dcrvb6.zip

 

[Touring23]

Thanks for the info and the DCR file, and Happy New Year everyone!

Random thoughts:
*I'm following the other thread (Black1987mustang's) about 11.5 on pump gas.

*Thanks Brian; here are two sites on topic, the second will calculate cranking pressure:
understanding DCR (dynamic compression ) - The Forums at Chevy Talk
Wallace Racing: Dynamic Compression Ratio Calculator

*I'm currently at 7.5 DCR, 155psi cranking, with aluminum heads and 92 octane.
*edit* Not that anyone cares, but it's interesting that my dual-plug turboranger is at 8.44 DCR and 168psi cranking.

*This is an interesting graph from that link above. Vizard?

 

[Brian@PAR]

Let me just clarify something. When I'm talking cranking comression and dynamic CR it's at the .050 spec. Seat timing is hard to determine and I've found .050 spec more closely relates to real world.

 

[Touring23]

Copy that. I notice both conventions are being used: The Wallace calculator uses .050" timing but the Kelley DCR calculator uses advertised. Seems those that are using .050" figures add 15* to the intake closing point, but that doesn't always fit. My Steeda cam would need to add 30* (280-220)/2. Seems to be a case of caveat emptor.

Thanks for posting, I'm enjoying this more technical discussion and also following the 11.5 thread.

 

[Touring23]

Found this article by David Vizard while continuing my research.
Cheers.