My son recently had his 350 engine rebuilt in a 69 Camaro Coupe and has 12.5 compression to one piston ratio if I am saying it correctly.

He was told by the mechanic we use that it can only run on racing fuel or an additive and not pump gas. Recently they added CAM II while getting the car ready for the road so it would not ping or during the timing set.

My engineering buddy told me that there should be no reason why Amoco or Sunoco 94 octane cannot be used for street use. He also said that CAM II can do damage if not handled properly and of course is very expensive. He told me that during street operations there should be no problems with 94 octane. The only problem would be predetonation under acceleration and suggested my son retard the timing and run the mixture rich, which will effect street performance somewhat, shorten the spark plug life but keep the car from damaging itself. ALso go with cooler plugs like N9Y.

The mechanic disagrees with the above and since I am not mechanical I cannot guide my son and dont want them do something that will harm the engine after my son paid $2,200 to have it rebuilt.

What is your experience with this compression and the fuel requirements?

Thanking you in advance.

Ken Miele

Ken, you have a very good question/s, both of the guys are right. I just wouldn't play around with de-tuning and chancing detonation. I would side with the mechanic (even thought the engineer is also right except, how will race fuel hurt the engine?) I disagree with that. Is this a race car or a street car? If it is a street car you will be money ahead to just lower the compression (the race fuel will add up fast) also detonation doesn't take long to ruin an engine. If it's a race car, then just buy the good gas and don't get to far from home. Pump gas and high compression just don't mix well. Personally I wouldn't run anything other than race fuel with that much compression. I'm sure people will tell you they do it all the time (and they might), but I have seen first hand what detonation will do to an engine (it's not pretty and gets expensive). One other point, You do not always hear detonation so be careful.

Royce

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70 Camaro 383ci
69 Camaro 385ci
91 Camaro RS V8 (305 TBI)
Link to my 70

http://profiles.yahoo.com/camaroman7d

Thank you. I should have noted this car is for street use and once in a while do the quarter time at the track.

<BLOCKQUOTE>quote:</font><HR>Originally posted by camaroman7d:
Ken, you have a very good question/s, both of the guys are right. I just wouldn't play around with de-tuning and chancing detonation. I would side with the mechanic (even thought the engineer is also right except, how will race fuel hurt the engine?) I disagree with that. Is this a race car or a street car? If it is a street car you will be money ahead to just lower the compression (the race fuel will add up fast) also detonation doesn't take long to ruin an engine. If it's a race car, then just buy the good gas and don't get to far from home. Pump gas and high compression just don't mix well. Personally I wouldn't run anything other than race fuel with that much compression. I'm sure people will tell you they do it all the time (and they might), but I have seen first hand what detonation will do to an engine (it's not pretty and gets expensive). One other point, You do not always hear detonation so be careful.

Royce

<HR></BLOCKQUOTE>

To be able to run full advance and tuning you need 98-100 octane in most cases with 12.5-1 compression. Aluminum heads and EFI will allow more compression than carbs and iron heads. If this isn't an EFI or catalytic converter-equipped car, I'd mix race gas with the 94 to end up with 98-100 octane. In other words, 1/3 tank (say 5 gallons) of 110 octane race gas plus 2/3 tank (10 gallons) of 94 would give you 99-100 octane and would save a BUNCH versus running straight 100 octane unleaded (94+94+110=298; 298 divided by 3 (each number represents the octane of 1/3 of the gas in the tank) = 99.33 which is the octane of the entire tank when mixed).

Hopefully I'm not confusing you but mixing will save you money.

Jody

Is it a real 12.5 to 1 or just have the pistons in it? If the deck is not min. or the heads milled to CC specs it will be no where near 12.5 to 1. You need to run a lot of cam 260deg+ at .050 preferably a roller that will kill more cylinder pressure than a reg. flat tappet. When it is using 92 oct. run no more than 28deg. total advance. If you put race gas in it at the track the timing can be kicked up to where it should be. I have a friend that uses this approach
and it works quite well and actually runs alright with the timing retarted on the street. Almost forgot it does have alum. heads.


[This message has been edited by oger (edited 08-18-2001).]

It is a real 12.5 to 1 milled to spec and running an 850 carb.

I have to disagree - 12.5:1 is hopeless for a street engine, unless you have a nearby source of race fuel at $4.50/gallon. There are several ways to "trick" it into running on pump gas, all of which SEVERELY compromise both performance and driveability. I've been building small-block Chevys for nearly 40 years, in all manner of both street and race configurations, and 12.5:1 is for a trailered race car, not a car that sees primarily street usage. It's your car and your decision, but whomever advised your son to have a street engine built at 12.5:1 either didn't know what he was talking about or gave him BAD advice, most likely both. On today's 92/93 octane premium pump fuels, 9.5:1 is the practical limit with iron heads, and 10.5:1 for aluminum heads - for an everyday street engine.

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JohnZ
'69 Z28 Fathom Green

Well John said what I was trying to say, but he was a little more direct and to the point. I tried not to step on anyones toes. I agree with him, you would be money ahead to just lower the compression. Max out the lower compression engines performance instead of de-tuning the high compression engine (what good is the engine if you are going to strangle it?) With both engines tuned to run on pump gas the lower compression engine will more than likely out perform the de-tuned engine and will definetly last longer.

Royce

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70 Camaro 383ci
69 Camaro 385ci
91 Camaro RS V8 (305 TBI)
Link to my 70

http://profiles.yahoo.com/camaroman7d

What do you have to do to lower the compression? My feeling is my son made a car that is not useable or he has to spend $50.00 per tank by mixing the CAM II. Please dont worry about stepping on toes. I want to get my sons head in the right direction so he can drive the car every day.

I was not saying it was practical I just answered his question. You are right about some one giving him some real bad advice. I don't know what heads you have but going to a 76cc head if you have a 64cc is the easiest. The best is to mill off the domes if they aren't hollow.

<BLOCKQUOTE>quote:</font><HR>Originally posted by oger:
The best is to mill off the domes if they aren't hollow.

<HR></BLOCKQUOTE>
Remember you would have to have the engine rebalanced when milling large dome pistons