I am looking for a few ideas on a pretty mild cam. 400sbc with Vortec heads and Vortec lower TPI intake. Compression is going to be around 13.1. Not looking to turn past 5500rpm or so.

 

13:1 compression? on what gas?

 

slightly better than pump, if need be. But, I do believe I can make it run properly on 93, which is what I will be attempting to do.

 

Now I have never run a CR that high but from what I understand anything over 11.1 will require more than a 92 octane, and 13.1 is a whole different ballgame, like racegas 110 octane requirement. But I could be wrong, as I said I've never run something like that. But if I were you I'd definetly check it out.

 

Common knowledge says you are correct about the 13.1. I am trying to do something different, which I dont know if it will work or not, but I am willing to try. Its how progress is made...LOL

 

Heck there was a guy at the engine masters challenge year before last that had 16.1 on pump gas on a small block , mind you that it only had to make 3 pulls..........LOL. But with correct tuning I have seen several guys run 12.5-13.25 cmp. but it takes a very large duration cam and aluminum heads....and you have to have your timing spot on... good luck with your project and hope you get it worked out but if I had to drive it on the street I would opt for a more reasonable ratio, but if your going to use it as a pump gas event drag car go for it...GOOD LUCK.

 

OMG... I sweeting 9.3 to 1 on my 383.. With Aluminum heads you can get 1 more comp ratio but 13:1 you will need alcohal..

 

13:1 isn't enough for alcohol unless you're going blown... we run 14.5-16:1 ish on methanol n/a. - The reason you have to run so much duration w/ that much compression is that a high duration cams will bleed off more compression. You have to run a higher static compression to make up for the loss in dynamic compression(running compression). There's an article in Hot Rod a couple months back about compression theories and pump gas. Really good article. If you go to Keith Black's website they have alll the compression calculators for you to plug in all your engine info(cam, piston height, head cc, etc...) to give you your dynamic compression. Thats the number that actually matters...

On that note, the highest I've ever got by w/ on pump gas for a car that gets driven is my current combo. It's running around 11:1 static and something like 9.89 dynamic. It's very tempermental about timing and the like...

 

Thanks, looks like good reading