for my own knowledge, for those of you with higher compression, what octane do you run?

(yes, I know other variables are important, you can list your timing too)

-dave

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what part of "illegal" is so confusing???

anybody?

it can't be that closely guarded of a secret


-dave

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what part of "illegal" is so confusing???

Variables make the question so broadband that it's almost ridiculous...

Some guy might be running a tight cam and performance timing with 'mild compression' and have to run only super...but he might be able to run it with less timing and get less power and mileage and run regular....

Others might run a long-rod and be able to run on pump regular due to detonation resistance, and run super when they make 'drag runs' to get all the mech timing it can take...

For the most part, if you go to 9:1 compression with a mild cam you will be able to run on regular if you fine tune the timing and carb, but your power might 'suffer' a bit depending on lots of 'variables'....you could get your power back and keep or lose some mileage running more octane (plus or super...)...



Where are you getting at with the question anyway (do you have a build in mind, are you wanting to 'bump' your compression for a bit more power)



???

-D.Idiot

You are asking a VERY vague question here as camshaft, ignition timing, carbs - all influence octane needed. Also, this information exists many times over on this site if you search.

In a nutshell, I consider pump premium to be fine for up to about 10.5:1 comp, low octane good to about 9.5:1. This assumed timing curve and camshaft are matched properly to your comp ratio.

Lou

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Home of Slant6-powered fun machines since 1988

I run about 9.2:1 with a compcams 252 and 2x1bbl carbs and run 87 octane no problem

9.25 CR, Comp 264, Highway driving only , 5 speed , 3000lbs, 3.23 gears, 24" tires, Super6 BBD, 87 octane.....shift down outta ping!

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Yeah....Im the one who destroyed this rare, vintage automobile.....

My compression is going to be close to 11 to 1 (not finalized yet, depends on what the block gets decked). holley 390, clifford manifold and headers. cam is a .5 lift clifford, 280/290 duration with over sized valves in the head, full port and polish

ignition hasn't been decided on yet. I have read most of the threads on here and am decideing between the msd 6 or the GM hei conversion.

what timing do you suggest for this set up?

weekend "fun" car useage, not a daily driver

looks like lou may have answered it for me, since around here premium is considered to be 92/93 octane, soo it looks like I will need a bit better than that.

I have also read on this site that nobody seems to like the octane boosters either. maybe I'll aim a bit lower so I can still use the 92

any comments on any of this?

-dave

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what part of "illegal" is so confusing???

If you really are going to have 11:1, then get a bigger cam and you can run pump premium. Shoot for 245-260 @0.05" duration.

Initial timing 15 deg, total mechanical advance 28 deg.

Lou

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Home of Slant6-powered fun machines since 1988

Thank you very much lou-

a bigger cam than 280/290 duration and .5 lift though? It has a duration of 246 in./256 ex. at .050 right now.....I think this is close what you reccomended unless I am misreading you

thanks again to everybody

-dave

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what part of "illegal" is so confusing???

OK, that is probably enough duration. Give 'er a go.

Lou

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Home of Slant6-powered fun machines since 1988