Compression Ratio for Pump Gas

I have a 437 former race motor sitting in my garage, wishing that it could be under my firebirds hood. The problem is that the motor was previously running Alcohol so the compression ratio is somewhere between 12:1 and 14.5:1. I'd like to know exactly but the motor has been modified alot. It was a 455, that has been destroked and bored over .30, the block was then decked to gain the compression back. It's also running different pistions. I'd like to run premium gas or at worst 110 lowlead avgas. What compression ratio should I run with either of these, and could I get away with avgas as the motor stands now?

What octane is premium gas is your area?

And also does the engine have aluminum or cast iron heads?

Premium gas is 91 unleaded, and/or 93 leaded, but I'm at around 6,000ft elevation, and my motor has cast iron heads. Anything else I forgot?

I would say 9.5-9.7:1 compression. If you had aluminum heads it would be 10.5 compression.

Well the stock 69 motor ran 10.75 on leaded, with iron heads. So I assumed that would be fine. Why could I run more with aluminum heads? Do they dissipate heat faster? Oh, and what do you think for avgas?

Originally posted by Blue02R6
Well the stock 69 motor ran 10.75 on leaded, with iron heads. So I assumed that would be fine.

NO! 10.75 is too much for pump gas. Back in the 60's and early 70's they had like 97 or better octane. Now with only 93, you are limited to about 10:1. But since you said you are at 6000 ft elevation, I put in a little compensation.
Yes aluminum heads dissipate heat better.

Ok. Thanks, I think I'll just run the Av gas

How much is AV gas per gallon?

At the airport $2.80/gal. The worst part is that the bird never got much better than 9mi per gal. Oh well, I just drive it on fridays.

u cant run a car motor on straight av gas,u will burn it up.av gas is a dry,non lubercate gas.if u use it,u will need 2 mix it with race gas or 93 pump gas.if u decide 2 use aluminum heads,u can run 10.5:1 to 11:1 compression on 93 pump gas.

I didn't know that. What kind of ratio should one mix the AV gas/93 octane or AV gas/race gas?

If you are only running 10.75 a 50/50 mix should be plenty fine. You could probably get away with 70/30 PUMP/AV combo if you back the timing off a little, but that just takes power away so I would go with a 50/50 mix. Plus a 50/50 is easier to mix.

Thank you much.

I would not recommend running AV gas, although AV gas has a very high octane rating it is also a very slow burning fuel, it is designed to run in low compression engines at a constant rpm, the reason for the higher octane is the altitude. Running AV gas is a car engine will result in a very slow burn or flame front, power will be low, and overheating will often result from the delayed ignition.

As a better alternative you should use toluene as an octane booster. Toluene is a pure aromatic hydrocarbon that is used by oil companies to raise octane levels in automotive fuels, it is also used extensivly in octane boosters and high performance cars, like the 1500HP 1.5 liter turbo Honda F1 engines.

Toluene will also not damage any emmision control or computer device and it is dirt cheap. As an octane booster the following results are possible;
Mixtures with 92 Octane Premium
10%...94.2 Octane
20%...96.4 Octane
30%...98.6 Octane

Volvord:

I have visited your website in the past(which is very nice by the way) because I have always been interested in engine swaps. I have an LT-1 clone which I've had for years collecting dust and rust and finally decided to rebuild it and stick it into something. Last year, a neighbor was having a moving sale and I bought his(mine now) 1962 Pontiac StratoChief(similar to a Catalina/Bonneville, but it is a Canadian version, Eh!). It will be the LT-1's new home in the near future. My question is if one adds toluene to 93 octane fuel to get up to 98 octane as you mention, what would then be the maximum safe compression ratio using either iron or aluminum heads?

Marty

Your swap sound like a nice one, and in a very cool car eh (I am Canadian).
Also thanks for your comments on my website.

To answer your question there is no black and while answer. Let me explain, octane rating actually reduces the flashpoint of the fuel so preignition does not take place, but items other than static compression ratio have an infuence on detonation, these being dynamic compression ratio, combustion chamber design, quench area, air/fuel ratio, etc.

As a rough guide take a look at http://www.dunegoon.org/compression.html this is an interesting calculator although I really don't know how accurate it is.
Another intersting article http://www.faqs.org/faqs/autos/gasoline-faq/part3/section-1.html

Hope this helps

Volvord,

Thanks for the quick reply! I guess I was incomplete in my first message: although one could not get a 350 in a 1962 Stratochief, one could get one with a SBC, a 283, so this is not really a true "swap". Thus my next point: I also have a 283 SBC(which was in the Stratochief) that I want to swap into one of the following vehicles:
Chev S-10, probably the easiest of the three;
Volvo 240 or 740;
and this last one seems interesting BMW318 or 325, preferably the 325 since it must have beefier springs for the 6 inline.
I also thought of a 300ZX but don't have enough $$$$ for a decent Z.

I actually prefer Ford over GM then Mopar in third. My third project will be to swap in a 351 Clevor(Windsor block with 2V Cleveland heads) into a Ranger. I beleive the hardest parts to buy for this one will be headers.

Any Comments?

So, MRL, is the StratoChief a Canadian Pontiac? Those were the only ones of the era that came with Chevy engines. Seems like an awfully lot of car for such a small engine. I don't believe I've ever seen a StratoChief. Interesting concept. Any pics available?

This 437. You said it was a 455, but destroked. Does that mean it's Pontiac 455 with a 421/428 crank in it? Which cylinder heads do you have? (casting number is on the center exhaust ports)

For a lot of great information on the Injun Engine (traditional Pontiac V8), get Jim Hand's book "How to Build Max-performance Pontiac V8s". It's only been out a few months, and is loaded with CURRENT information on building street Pontiacs. You can get it at Performance Years or Ames Performance, as well as many book stores. SA Designs is the publisher.

For a Pontiac with iron heads, 9.5 is the limit for 93 octane.

Yes, aluminum heads can run higher compression on the same octane. As others have said, it's due to the heat "sinking" capability of aluminum. But, what hasn't been said, is that all other factors being equal, an engine with aluminum heads MUST run higher compression, to make the same power. This is also due to the heat sinking. Extracting the heat from the combustion makes the process less efficient.

The comments on AV gas are right on the money, as well. While it does raise the ocatne level a bit, it's not well suited for automotive applications. Between constant/low RPM operation, and high altitude, it's better for the aircraft. The popular method of raising octane, that actually works, is to blend 93 with racing fuel. 3 parts 110, 7 parts 93, will roughly equal olden times 100.

A Stratochief is basically a Catalina/Bonneville but it's the base model. I believe the closest U.S. counterpart was called a Starchief, according to the owners manual I got from ebay. Yes, in my opinion also, it's a big car for a 283, but what's worse is that you could actually buy them with a 6 inline! That's why I am sticking in a 350 LT-1 clone. I think the 283 will do well in an S-10, since the vehicle is alot lighter(I figure about 500 lbs. min). Unfortunately, I don't have any good photos right now since my car is stripped down(I have to redo the body). As for the rest of your message re. the Pontiac engine, I think you have me confused for someone else.

Thanks for the info.

Nope. I was addressing the original question from blue... I got sidetracked when I heard a Pontiac thing I hadn't heard of before (always interested in new Pontiac stuff, even if it's old).
MRL, might I suggest, rather than a run-of-the-mill small block, a 383. The stroked small block will make near "big block" torque numbers, something seriously needed in such a large car.

That's a really good idea. I actually thought of going with a big block but did not feel like changing the front springs and stuff. Plus I already have the small block.
What would be required to do that, a 400 crank? Do I have to change my pistons and rods? By the way, my block is bored .040 over. The 400 crank has bigger dia. main and rod journals, no? What effect will that have on compression ratio, I can go upto 93 octane in my area.

MRL, if this car is a pleasure cruiser, and not intended for competition, I would suggest the Eagle "street/strip" rotating assembly. It comes with crank, rods, pistons, rod and main bearings, and rings. The competition versions are a LOT more money. You have a choice of pistons to arrive at the desired compression ratio.
There's some significant clearancing needed in the crankcase, to allow for the increased stroke and resulting rod interference. Most competent automotive machinists have been through the process.
You can e-mail me direct for more specific information. I can point you to the right stuff.

cvms@cstone.net

where do you buy that from?

I got a 383 kit from www.northernautoparts.com they are great to deal with.

so whats really the safest way to raise octane. Out here in cali the premium is 91 octane.

thanx

so whats really the safest way to raise octane. Out here in cali the premium is 91 octane.

thanx

Torco Race Fuels makes an octane booster. 6 quarts for 75 bucks to your door. One quart
Raises 92 octane 20 gallons to 97
Raises 92 octane 10 gallons to 104
Raises 92 octane 5 gallons to 107
They make a unleaded and a leaded formula