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[quote i don't have much faith in a lot of the internet hype about using high compression numbers with pump gas. my experience says 9.5:1 is the practical limit with iron heads.

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From my experience, (not internet hype) a person can go much higher than 9.5 with 91....See above....IMO, with any cam at all, and a decent combo, 89 should handle 9.5. To add to the above...I had 2 SBC 355 dirt motors at around 10 to 1. They never saw a drop of anything but pump 91. 35 nights or so on those motors, never an issue. They might have had .055ish quench, maybe not that tight. Buddy had numerous SBC dirt motors, all at 10ish, never an issue with detonation...If you are not familiar with dirt racing, usually on gas, you are running in the neighborhood of 220-230 plus on water temp....which sure doesnt help....

FWIW, I am building a SBC 383 for my sister in laws pickup. GM makes a crate 383 (HT383) (which I am basically copying) with an advertised comp of 9 to 1, that is advertised as being able to run on 87. In reality this motor has to be closer to 9.25 or so...Ive only been able to find one fellow had problems with detonation...This fellow had too fast of curve in his dist. Fixed that and no more issues..Keep in mind this was in a K5 Blazer, tall tires, etc. Further there is very little possiblity that these motors have a tight quench. From the rough data Ive come up with they use .051 gasket, and the pistons are .025 or more in the hole...Yes, the Vortec chamber is a nice design, but still.....Further the crate HT motors come with a baby of a cam..something around 198/205 @.050. With a mild street cam Im not seeing detonation being an issue....

Every 5.0 Fox Body Stand for quite a few years were advertised as 9.0....A few buddies had them and they ran fine on 87...Yes, I know, fuel injection, but still.....

Thats what im building, a sbc 406, just was wondering if any mopar SB's were running high compression on pump gas.

Von, what cam are you running,I'm between a rock & hard place on this build, i stated out with just going a stock freshining, then was advised to run FTs, then stayed with the small Lunati cam, then came acrossed a set of Iron Eagles 200cc that were CNC ported, they are sharp, 500.00 bucks guideplates & all, but there 64cc instead of 72cc like i was hoping, so i'm back to the drawing board, thought of MLS gaskets, but there 160.00, with a .070" it'll drop compression to 10.2, maybe that'll be ok with this small cam,1 thing thats a total plus is the little bit i have into it