BeaverGuy

My '57 currently has a really good running 327 with 11.25 compression pistons, 300 hp heads, a 7017360 '62 FI and a '70 LT1 solid lifter cam. The obvious problem is too much compression for today's 91-93 octane gasoline. I have heard that 9.5 to 1 is the highest compression ratio that should be used with today's 91-93 octane although aluminum heads might allow a 1.0 ratio more. Anyone have any advice on this dilemma short of totally rebuilding this engine?

MikeM

Yes, I would suggest you leave it alone unless you have solid evidence to support your compression is too high or you have other problems like timing is screwed up.

Why do you think the problem is "obvious"?

BeaverGuy

I said "obvious" because I assume the the CR is pretty close to what it was built to be - 11.25:1. The engine builder used the same forged pistons that were in the '62 327/360 engine. There is probably some test equipment that would tell me the true CR. I'm dropping this engine in the restored frame before dropping the restored/painted body over it so I don't want to guess that the engine is OK.

Mike Ward

Lots of guys are running 11:1 with straight pump gas without issue. Why can't you?

66since71

I've got three examples. Those pistons, those heads, similar (2) or same (1) cam, 36* total centrifugal advance....runs fine on todays pump premium.

Harry

Allcoupedup

The engine builder should provide you with the calculated CR based on bore, head gasket, piston/deck clearance, head combustion chamber volume, stroke, piston dome.

That's just static compression ratio. Other factors affect how CR and detonation are related like iron/alum heads (like you mentioned) and camshaft selection.

Your best bet is to get all of those measurements from the builder and post them here for some opinions. Or better yet, use this calculator
http://www.csgnetwork.com/compcalc.html
Brian

BeaverGuy

Thanks for the help. Brian. Unfortunately that engine was built many years ago by a very good engine builder who is no longer around and did not provide any of the data that you mention. All I know is that it is a standard stroke 327 with a .30 overbore and stock '66 300 hp heads . I really appreciate everyone chiming in on this problem. Reference the comment about running the CR as is, it was a Shell Oil engineer who told me that 9.5 CR on pump gas is the max that should be run on today's 91-93 octane gas.

Boyan

You can easily run 10.5 or more like said above on pump gas. Take a feeler gauge and put it where the head meets the block. See how thick your headgasket is and then roughly calculate your CR. The advertised CR was with a steel shim headgasket that was thin. Yours was probably assembled with a thicker gasket. I doubt you are at 11 to 1.

Mike Ward

Oil company engineers are not typical the best source of info for engine config.

Crunch527

I am running 11:1 in my 383 w/ Dart Iron Heads and it runs fine on premium pump gas...

65 fi

I remember having pre-detonation issues in 1971 with a 70 Z/28 I had. It was due to cheap gas (Gemco I think). The dealership mechanic suggested I try a higher grade gas with a higher Octane. It worked.
Today's computer assisted engines can run with higher compression without issues but an old-tech engine does not usually have the advantage of current technology to overcome the inherent flaws of crummy gas. I had my L84 built to 10.5 and the engine seemed to have no issues on the dyno. The h.p. was close to factory and with some work on the heads exceeded the factory numbers.

Zoomin

It would be a good idea to concentrate on ethanol related issues.

robert miller

I am with you here mike, on the timing or something worse in the motor build. To the OP here was this motor really put together with #1 at top dead center. Plus how are you are whom ever really checking and doing the timing of the motor.
I don't mean that someone don't know what he is doing here. Just saying if you are letting someone else do this, are they saying they have done this work and really not checking and doing it. Just to get more money out of you down the road. As me how I know this one. But if it is set up correct with 11:5:1 this motor will run good with 93 in here. May have to pull a little timing out on the top end. Robert

BeaverGuy

Thanks for the advice. I checked the engine TDC before putting on the heads.

MikeM

Hey Beaver!

I run a very similar engine combo to yours. I could say it's built to stock specs but I'd be lying. It has been bored .040, block decked to .019 piston clearance and it has the .039? Felpro head gaskets on it. That's about .020 thicker than the OEM shim gasket. So, I'd guess the things that affect compression in my engine are very similar, bottom line to OEM results. Whatever that is. I also run the same 097 camshaft. I run stock timing curve and advance. My engine runs really well on 89 E10 with only a little rattle on initial throttle tip in.

If you engine has similar specs close to OEM, I wouldn't worry about it as I posted above and so did a few others.

robert miller

Have you had the dist check out in the car. I didn't mean nothing on any one here at all. Just back in the past took my car to a shop to get something fixed. Came back and they had me build for almost 700.00 more and said all this other stuff was wrong.

BeaverGuy

Thanks Mike! Good to hear from someone who is running pretty much the same setup. I'd be interested to know the induction setup you are using.

I just talked to a local engine machine shop that has an excellent reputation. He will remove the heads and see where we need to go from there. He has access to a dyno so we can install the FI and make sure the engine runs well before we put it into the restored frame and drop the body on.

Ironcross

I run a GM 1970 LT-1 crate engine and was told years ago it would not work with my FI.....The only drawback is sometimes it`s hard starting when hot which I attribute to todays gas....I surmised this because when new and in Miami it never reacted that way nor did it in Michigan before the government fuked the gas up and when 100 octane was available everywhere....

In all fairness to todays fuel there is a NOS solenoid in the spider to preventing the cylinders from getting into a expensive hydraulic drain back situation and thus breaking expensive parts..Has to crank up fuel. .Otherwise the engine has had zero issues with 93 when it became the only so called high octane fuel....

I have used aviation gas when near an airport and additives don't work, it merely makes that 93 pump junk more expensive when added together

the above won't change any minds....but Whatever

ohiovet

My 62 Corvette 340 HP 11.25 to 1 CR runs fine on Shell 93 octane with ethanol.
My 57 250 HP low compression (9.0 to 1??) also runs fine on the same fuel. No percolation, vapor lock, starting or any other problems.
A anti siphon solenoid is essential on all Rochester FI units.

BeaverGuy

Thanks for the input. When I was in Redmond Oregon last weekend I noticed that the local Shell service station was selling "no ethanol" premium. That looks like a good choice if I could find it here in Tacoma. My FI unit has been totally restored and has an anti siphon solenoid. It's stored in the closet awaiting this engine in the the completion of the '57 restoration.