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I'm not using any... I think you'll find that adding enough of anything to actually make a difference is going to be horribly expensive. Tell us more about your engine/situation?

Bear
 

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You should be able to get by with a gallon of 108-112 racing gas per 10 gal of 93 octane. 2 gal would be better. Since your cam has that much advertised duration, it should keep your dynamic compression fairly low, as compared to one of the popular steep ramp cams. So, if you keep the timing advance down a little, and don't hammer on it, you might be able to get by on a good grade of 93.

In my 455 bracket engine, with #215 heads, I ran 2 gal of 108 with 3 gal of 93. It ran 7.30's in the 1/8 mile--no problems.

But racing gas is about $10 per gal. :( And most octane boosters don't add enuff octane to make a difference.
 

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I've used Octane Supreme 130 in my '65 and it works as good as blending race gas. The stuff is tetraethyl lead and is not street legal in my state, though. It does indeed work. None of the other octane boosters work...the 104 stuff, etc. The TEL130 Octane Supreme is expensive, though. Really no cheaper than mixing race gas. It is way more convenient.
 

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I just began using Octane Booster. Wild Bill answers all emails, if you have questions. This also has lead in it.

I had been using Lucas Ethanol Treatment for treating my gas (auto). Too soon to tell if any gains but according to my combustion ratio Bill confirmed I should be at 98 oct. I use 93 Sunoco. 1.8 2 oz per 5 gallons. I want to give it a while and see how the engine performs. This will eliminate the need to use Lucas and add the lead back into the system.

Octane Supreme Specs

 

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I use non-ethanol premium 91 octane from the pump mixed with five gallons of 110 octane leaded race fuel. No ethanol worries, and plenty of octane for the 10.75:1 compression ratios.
 

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So if you just do a factory rebuild of a 350hp or 360/400 can you run on the the standard premium or are their ping issues? I assumed that when doing the heads, all the places replace the valves to work on unleaded.
 

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So if you just do a factory rebuild of a 350hp or 360/400 can you run on the the standard premium or are their ping issues? I assumed that when doing the heads, all the places replace the valves to work on unleaded.
Not a safe assumption, and it's not the valves that are the problem anyway. It's the valve seats in the heads themselves. The exhaust valve seats get extremely hot (duh :D) and what the lead (being a soft metal) in the fuel used to accomplish was to provide a cushioning effect of that (also extremely hot) exhaust valve slamming shut onto the valve seat. When the lead went away, auto manufacturers had to adopt a special process to provide extra hardening in the area of the exhaust valve seats. Without that, what could happen was that under heavy load conditions (like, say, pulling a trailer up a long hill) the effect of the hot parts slamming together could actually hammer the valve seat deeper into the cylinder head. Not good for engine longevity :nonod:

Today, there are (at least) two schools of thought on this topic. One holds that if you're going to run early cast iron heads from the leaded fuel era that don't have hardened seats, then you MUST have the seats replaced (a machining operation that involves cutting out the old seats and replacing them with specially hardened inserts). The other school of thought is that unless you spend a lot of time in heavy load conditions (pulling a trailer, lots of racing) that you'll generally be ok with factory heads without having to go through all that. When I was running cast iron heads on my engine, I chose door number 2 for myself. However, that's a personal decision and I would not ask anyone to agree or disagree with me just on my say so. Do your own research, make your own decision.

As for the 'stock rebuild' question. The number you want to look at is static compression ratio. I don't mean 'advertised', I mean calculated yourself after measuring everything yourself: combustion chamber volume (again, actual - on your engine - not 'advertised' or 'factory spec'), actual cylinder bore size, stroke, head gasket compressed thickness, piston deck clearance, and volume present in the valve reliefs in the piston tops. For a street engine, the -general- rule of thumb is that this number needs to be the same as the octane fuel you'll be using. I.E. 9.3:1 on 93 octane fuel. Etc. Do people get away with more? Yes they do - sometimes - a lot depends on other dynamics at work in your engine and on other variables (fuel system, cooling system, etc, cam timing, etc).

However, consider these two ideas:
1) Even in a relatively strong engine (I'm running a stroked 461 with a solid roller cam, other various goodies such that it makes somewhere close to 550 hp at the flywheel) the difference between 9.5:1 and 10.0:1 is only going to make a difference of a measly 5 to 8 HP - everything else being the same.
2) If you push the envelope on compression and then find out that you pushed it too far (pinging, detonation) then you'll have to resort to some fairly radical means (super expensive and not available everywhere fuel, taking out so much ignition timing that it runs like a dog in quicksand, starting over and rebuilding the engine completely) in order to keep the motor from destroying itself.

Definitely one of those, "Well? Do ya feel lucky?" situations.

Bear
 

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To simplify, doing a stock rebuild of a '60's era GTO engine will necessitate high octane fuel to avoid detonation. Lead has nothing to do with it, other than the fact that TEL will increase the octane when added to unleaded fuel. If you can get 95-100 octane unleaded, you will be fine. If I were to overhaul a GTO engine in this day and age, I would either use dished pistons to lower the CR, or more probably, add aluminum cylinder heads. The days of being able to run a high compression engine on pump gas are over, at least in CA where it's 91 octane.
 

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WHen I freshened my engine I put pistons in to get 9:5 to 1 compression. Runs great on pump gas. I have also used low octane in one situation to get it home and it didnt ping. 32 degrees total timing.
 
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