I wanted to know if I can use a lower grade gas than 93. I never asked this, I was just looking at the world sportsman II heads. I know that I don't have 64cc heads, because my compression would be at least 200 psi, on a compression test, or that's what i've read. I'm guessing I have 72 cc heads, it seems like an educated guess. By the way my compression psi was 160 cold. I was reading, I should have almost 9:1 ratio, with my flat top pistons, and i'm using their reccomended head gasket, Fel pro 1003. Is this correct, and if so, can I run a lower grade gas. I haven't checked it hot yet. I will today if all goes well. Next I will probably switch the carb if my gas mileage is that bad, back to vacuum secondaries.

 

Cranking compression depends on your cam as much as on the mechanical compression ratio. That being said, 160 sounds about right for a 9:1 motor with a stock or mild cam. But even with a 64cc head, stock bore, thick .040" head gasket and stock deck height of .025" your compression would still be only about 9.5:1- not outside the realm of possibility for a 160 PSI cranking compression.

Somewhere on those heads the comubstion chamber size should be stamped or cast into it. Or maybe there's just a serial number stamped into them and you could call Dart and trace it back from there.

 

I lost the cam card, but I think the lift was .500/.510, it was a comp. I will check when I have the valve covers off, there was a number. So do I need high octane gas? I'm also running have a dart kool can intake, and a 700 dp. thanks

 

Just try it and see. Put in a half tank of the cheap stuff (running the current gas level down as low as you dare before filling up). See how it runs and if there's any detonation. If there is, try knocking the spark advance back about 4*. If that doesn't get rid of the detonation then put the ignition timing back up and keep using premium. If you need to retard the spark more than about 4* between premium and cheap-o then you're better off continuing to run premium. Severely retarding the spark advance to compensate for detonation will cost you as much in gas mileage as the difference in price between the two grades of gas will save you- and, of course, it'll make a lot less power with the spark advance pulled way back.

 

Honestly I don't know what a ping would sound like. I've been around cars for a while, and I worked in the field for about 2 years, and I never heard pinging. I will find out what it sounds like I guess. I'm running 14 degrees advance base timing. thanks

 

Throw an armload of pop bottles in your hatch area, and drive over some rough roads - that's what detonation sounds like.
you'll know it when you hear it (unless you're running open headers, then hearing yourself think is even out of the question... unless you think very loudly).
Try damons test, lug it around a bit. Not like 5th gear from a stop sorta thing, but normal driving - but you'll hear ping at low-moderate speed, with a high load. Like accelerating up a mild hill in 3rd gear after driving through a school zone (err, slowly that is). That's a super easy-to reproduce test near my house so that's what I think of.

 

Thanks, I will try it when I get the car on the road. I appreciate it, guys.

 

http://www.wallaceracing.com/dynamic-cr.php
Dynamic compression ratio is lower than static.