ThePabst

Hi all. I need to drop the compression on my L82. It simply will not run properly on the girl scout water with corn squeezins' they sell in Upstate New York. Oh, and its well over $4.00 per gallon, no thanks.

(On vacation in Denver this year I saw 84 octane sticker on a pump!! WHAT! Is this the future? I bet it would be easier to light a lump of granite with a birthday candle... I had no problem filling that POS Chrysler SUV rental to the rafters with it tho, THAT felt good.)

Anyway, I am about to freshen the engine in my Silver Anniversary. I don't think the motor has never had any real work done on it. Purists, please, don't kill me... its a 'nice' car but not a gem, no one is gonna miss her.

I have found the usual conflicting information on the net. So far, this appears to be what I need: Going from 10 to 1 down to 8.5 to 1 will require about .060 more head gasket width... Correct?

Any tips would be appreciated.

resdoggie

Why would your gas be a whole lot different than lower state NY or other neighbouring states causing the engine to run poorly? Anyway, a thicker head gasket will do the trick but I doubt that's your problem with your car's poor performance. Most in here will increase compression for better preformance and other tweaks such as timing curves, change cams, heads. Have you confirmed that your distributor and advance mechanisms are up to par and the car is properly timed?

7t9l82

L-82's only came with 9-1 compression. timing adjustments should allow you to run crap gas. if your doing work on the engine anyway a set of aluminum heads with the same size chamber would keep detonation at bay. I'm not sure i would do anything until you see if things will stay as bad as you seem to think they will get.then again it is new york and any goofy thing could happen.

ThePabst

All basic stuff is good. Distributer etc. I can't run her at past 4 deg. advance with out knocking. Yes, a cam swap will be part of the refresh. I'm sure its in 'used' condition a 95,000 on the clock.

Detonation is always an issue in these motors, it was then it is now.

I want to spend a little upfront so I can get away from Premium fuel. I don't need to go fast at my age and this is not a trailer queen, I drive it every day, I'm being practical.

Revi

Not sure where the problem is, but compression isn't it. It could be many things (timing/vacuum leak/carb issue, etc.). An L-82 should run fine on pump gas. My 70 L-46 (10.4 cr) runs fine on 93 oct.

Have you tried buying gas from different stations or is it always from the same place. My car never detonates, but once after a fill-up from a Krogers, detonation all the way home. Obviously bad gas or lower octane than advertised.

resdoggie

As others will tell you, do a compression/leak down test first. If that's OK, then you can move on to cam/head/intake selection depending on your budget. I'm thinking you have other issues like worn engine components if, as you say, the engine is basically original without any major work being done on it ever with 95K on the clock. It may be very hard "to spend a little up front" with that mileage. Maybe plan on a little bit more up front and consider a crate engine replacement?

63mako

Your actual compression if it is stock is about 9 to 1 actual. The cam in an L82 is the same cam used in the 1969-1970 L46 with 10.4 to 1 actual (they run on pump fuel also). Compression is not your problem. Could be slipped balancer, excessive carbon buildup, lean carb adjustment, vacuum leak, improper advance curve. cooling issues, high underhood temps, cam has been changed out or a variety of other issues but to high of compression is not one of them. A thicker head gasket and wider quench will actually increase detonation sensitivity.

davidchristopher

You shouldn't be knocking on regular gas- something else is up here. Since you're refreshing anyway, opportunity knocks so the motor wont - but I doubt your 9:1 compression ratio is the problem.

gbvette62

The factory settings for the 78 L-82 were 12 deg. at 700 RPM with an automatic, and 12 deg. at 900 RPM with the 4 speed. Even with today's 10% ethanol fuels, you should still be able to run the car at the factory settings.

Detonation was never a problem "then", with a properly tuned engine, and shouldn't be now.

The L-82 was designed to run on unleaded regular, not premium. I'm not even sure premium unleaded was offered in 1978. If it was, it was just beginning to become available.

As 7t9l82 and others have said, your 78 L-82 came with 9.0:1 compression, not 10.0:1. The base L-48 used 8.5:1 pistons. Changing from 9.0:1 to 8.5's, is going to have little to no effect, on how your car runs on today's gas.

Personally, I think you need to determine why your car "will not run properly", before getting into an engine rebuild and lowering the compression.

ThePabst

Maybe I don't have a stock configuration after all! I decided to 'freshen' the motor instead of a complete rebuild because I did indeed do a compression test, I was reading in excess of 210 psi. and it does have an after market hi torque starter.

I have no real history on this car so it may have had some engine work done at some point... looks like I'm gonna have pop the top and have a look around.

wcsinx

As others have mentioned, your engine's compression is already low enough that you should be fine with a proper tune. You likely have an issue elsewhere be it a vacuum leak, timing, excessive carbon, etc.

Lower octane fuel actually burns more easily (and violently) than higher octane. Thus the reason an intake charge of low octane fuel cannot be compressed as much as one using higher octane fuel. Lower octane fuel actually also has more chemical energy bound up in it than higher contrary to popular belief. Hence you're not doing an engine tuned for 87 any favors by feeding it 93.

Mike Ward

Higher altitude lessens the potential of detonation due to the thin air, which lowers the octane requirements. Denver and other similar places have always had gas that's 2-3 points lower than sea level locations.

AirBusPilot

Agreed.

My bone stock 79 L82/4spd would easily ping on 93 octane.

After some investigation, I found the valve guides to be totally worn and that was dumping oil into the combustion chamber (oil in the mix will cause all kinds of combustion issues).

Does you engine "use" oil? I know the L82's were all mostly oil burners due to the loose tolerances on the forged pistons, but mine was really burning oil bad.

Based on my experience, I'd start by pulling the intake manifold and taking a look at the intake valve stems. If there coated with burnt oil, you probably have pistons with excessive carbon build up.

This also assumes your engine is stock.

ThePabst

Like I said, she is going under the knife, looks like I have some digging to do...

REELAV8R

Looks like you may have a higher CR than stock. 210 PSI would be more like 10:1 or there about, and maybe a different cam giving you higher than stock cylinder pressures.
My 9.9:1 engine has an average of 209 PSI with 108 LSA cam.

AirBusPilot

Take pictures!

ddawson

Don't forget DSR vs CSR.

http://cochise.uia.net/pkelley2/DynamicCR.html

scottyp99

Yeah, a stock L82 should come in at somewhere in the neighborhood of 160 or so. 210 means you have more compression than stock. Perhaps a PO installed 64cc combustion chamber heads at some point? Or maybe even domed high compression pistons. (Probably not as likely, though, that would require a complete engine tear-down, which would leave signs.) Can you remove a valve cover and give us some casting numbers?

Scott

ThePabst

I'm going to tear into it next weekend. I'll know more then.

ThePabst

I calculated it at 10:1 using that compression test. I assumed that 10:1 was a standard set up for a motor of that era.