dynamic compression

[chris_r]

What do you all think my DCR 7.87:1 with iron head in a 78 ford f-250 4x4 am i good for pump gas?

[My427stang]

Depends on how you calculated it and how well it's tuned.

However, If everything is measured carefully, and PKelley's calculator, that's completely fine for almost anything that will come out of a pump, assuming you aren't lean, over advanced, or too hot

[chris_r]

I used the Wallace i cant get the Pat Kelley to load on my apple

[My427stang]

I have a large number of builds using the PKelley calculator, but zero with the Wallace.  If you put your information up on the build I will run it through, but results can be very different, so I can't comment on your combo.

For instance, Pipemax calls DCR on my 489 9.52:1 and hits cranking compression ratio spot on, same with my 445 but puts DCR at 9.19.  Its a respected calculator and, and both engines run on pump gas. PKElley's calls the 489 8.33:1 and the 445 8.10:1.  The engine doesn't know what the calculator assigns, but repeated use of one tool can give info when comparing one output to others.  If I compare numbers from different calculators, it's not applicable, or at least it may not be

For laughs, I just went through and ran my 445 and 489 numbers on Wallace and my 10:1 445 came up at 7.86:1, 3% lower, my 489 came up at 7.98, 4% lower. So you aren't far off, even at 4% you'd be at 8.18:1, right at the edge of a heavy vehicle, if tuned well, but that's a big sloppy WAG

[plovett]

I got the same result with both the Wallace Racing DCR calculator and the Pat Kelly one.  I used 0 boost and 0 feet altitude in the Wallace calculator.   I'm guessing the minute difference is just different rounding or truncating somewhere in the calculations.

Wallace Racing:  8.38:1

Pat Kelly:  8.36768:1

For whatever that is worth.

paulie

[chris_r]

Ross thank you for the calculator. bore 4.36, stroke 3.85, rod 6.605, static c/r 9.8:1, intake ABDC 61, LSA112, Adv. intake duration 262 if you need more just let me know thanks again

[plovett]

Sorry, not trying to butt in.  Just waiting for a kids birthday party to start and trying to think about something else.   Neither my dad or my stepdad hosted birthday parties for me when I was a kid.  Now I have to hang out and chat with all the moms.  Welcome to 2016.  It's not my forte'.  But I digress.   

I put your combo in the Pat Kelly DCR calculator and got a DCR of 8.03:1.    Maybe Ross can confirm that.

It turns out your intake centerline is at 110 degrees based on your intake closing point? 

I'm thinking high octane pump gas (91 or 92) with a good tune might work okay.  Is your truck geared pretty low?  Good radiator and good ignition curve?

paulie

[chris_r]

thank you Paulie

[My427stang]

I got 8.03, assuming 460 with a 6.605 rod, and the same cam numbers Paulie came up with.

So, yes I think it's likely fine, but keep in mind is a much bigger bore and chamber than an FE, which work against you.  I'd expect it to be fine though.

It's a pretty mild cam for a 460 though, especially with the wide lobe sep.  Ever consider more cam on an earlier centerline?

[chris_r]

Thanks for your input Ross and Paulie

[plovett]

de nada, enchilada!

paulie

[63.5xl]

I used the Wallace i cant get the Pat Kelley to load on my apple

Found this app for the Apple iphone  today. Engine Toolbox App. Does ACR and DCR. Don't know how accurate. I have been away from home and computer all weekend to compare with the Pat Kelley one. It does ask for your intake closing point where The Pat Kelly one will put that in for you.