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Discussion Starter #1
with the new rendition of my sbc 350 i am pretty sure i will have to start running higher octane gas because of my compression ratio. My question is, with the price of gas it may be cheaper to just run fuel additives that are an octane booster instead of buying premium 93 octane gas. Is there a difference between fuel additives and actual higher octane gas or is either one ok to run and not have any problem with detonation or anything else.

I know to avoid problem i can just run my timing down but what would be the fun in that ;)
 

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I have just under 12-1 and drive on 91 octane. I did the Power Tour with 14.5-1 and tried a number of additives that did...NOTHING.
 

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Depends on your setup but the "too high" compression ratio is now the street compression ratio with the better heads, fueling and ignition systems.

I would NOT want an engine that needs race fuel or additives if its a street car.

Not sure about 12:1 on pump fuel but if its said it might be so.

With the best flowing aluminum heads and a great EFI the most I have seen is 10.5:1 If you can use higher compression ratios with pump fuel then I like it.

Solly AJC. Back to yer Q. Id pump the fuel and NOT buy bottles of octane additives... JR
 

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With the best flowing aluminum heads and a great EFI the most I have seen is 10.5:1
Seen the new Mazdas with 13+ and run on 87 octane?

I did the entire Power Tour with my iron head 406" that was 14.5-1, and in some states the best premium was 90 octane. I'm not saying there wasn't some rattling going on, but I put a lot of miles on that engine without any more than pump gas.
I've raced my current combo on straight Arco 91--it's not happy at high RPM, but ran 6.60/101---with good fuel it runs 6.40's/105
 

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Depends on your setup but the "too high" compression ratio is now the street compression ratio with the better heads, fueling and ignition systems.

I would NOT want an engine that needs race fuel or additives if its a street car.

Not sure about 12:1 on pump fuel but if its said it might be so.

With the best flowing aluminum heads and a great EFI the most I have seen is 10.5:1 If you can use higher compression ratios with pump fuel then I like it.

Solly AJC. Back to yer Q. Id pump the fuel and NOT buy bottles of octane additives... JR
JR,

For what it's worth, my LT1 used to run pump reg on 10.25:1 (before tuning for more power) and many GEN-II guys run 12.5:1 on pump premium due to the reverse flow cooling.

To the OP:

Just run premium. I think some of the octane boosters have been known to foul or leave residue on plug electrodes.
 

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Why build a 10-12 to 1 compression engine then try to skimp on the fuel?

I would just run 91-93 octane with 0 ethanol and leave the 5-10 dollar bottle of no octane booster on the shelf.
 

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I haven't run an octane booster in years, but my understanding in the "raises octane 8-10 points = .8-1 octane number. Also that year, I put the car away with the octane booster in it, and maybe completley unrelated but I had to replace the tank, clean the carb and all the lines out when the gas turned to varnish. With the right cam, I have run 10.7-1 on 93 with steel heads.
 

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one thing i've stumbled on in our ethanol world , is find non ethanol gas , a fuel distributor usually keeps it , if they supply a marina , golf course , anywhere small engines needs non eth fuel

a good chamber helps , a big chamber sux , sharp edges in the chamber or across the piston ,,, i think a trough type valve relief would be better than individual valve reliefs on the pistons , it loses some compression , but it looks like to me , it would allow more even heating of the piston , and more even cooling , and more even combustion , it would reduce the chance for hot spots to occur in the arc of the valve reliefs and the pointed edge between them , also have better combustion across the piston

i've never tried to buy aviation gas , but i've talked to people that have and liked it ,

for a street strip car, most people like to ride the ragged edge , i'd say the best would be to mix a couple gallon of race gas on race day
 

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You don't mention in your post how your new engine is set up. What is your compression, and what are your heads made of?

My 355 with aluminum heads has 10.25:1 compression (not really all that high) and I had a lot of trouble with detonation at 30* total timing on 91 octane, even though my quench area is right about 0.041. Then I installed an MSD Digital 6 and my problems went away. I think the more complete combustion eliminated a lot of residual hot exhaust gas in the chamber that was causing the pinging. Now I'm running 35* total timing without any clatter at all on 91 pump gas. I'd run 93 if I could find it, but the next step up from 91 in my area is 95 octane, and they get over $6/gal for that; not cost effective.

As far as octane boosters, every one that I've tried was a complete waste of money.
 

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Discussion Starter #10
My new heads are 305 fulie heads that are opened up to 2.02 intake and the combustion chambers are apened up to 62cc's. Thety are iron heads. I should be around 10:1 compression.

Ok i figured octane booster was a waste but i figured i would just get people opinions. I will just go with using sonoco 93 octane.
 
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