Re: 745i Copper Head Gaskets? (archive)

Hi John,
Thanks for your input, it certainly has relevance to my situation but here's the rub, the car in question is an '82 745i with a twin turbo setup designed by Corky Bell. I recently bought this car, it was in Seattle, with the intention of driving it home (Boston). Made it into Montana where I decided to step into it for the first time. Had it matted at top end for less than a mile then backed off a bit. Looked down and my eyes were greeted by a temp guage about to peg. Roadside diagnosis: head gasket. U-Hauled it the rest of the way home. Did compression & leakdown tests yesterday and they confirmed head gasket failure. The car was running WAY fat as evidenced by the plugs and the fact that range was just about 200 miles on a full tank. Boost was set at 10 psi, car is equipped with a J&S knock control system, Greddy Profec boost controller, etc. I don't know what the compression ratio is, but I think it may be a bit high, which is something I'd want to address now. I don't have much background on the mechanicals of the car at this point, but I may be going through and kind of reengineering the thing anyway. I just have to decide how nuts I want to go with it, and more importantly how much cash I feel like blowing ;) Dunno if I'll fly with a copper headgasket or not, just considering my options at this point.
Best,
Keith Way

Anyone know of a source for these? Tuoma used to have them, right? Maybe there are some still kicking around... I've heard that one of the tradeoffs of a copper head gasket is that external oil leaks become a concern. Any thoughts on that?
Best,
Keith

The question is why you think you need one.

If it is because you are running elevated boost pressures? Above 1 bar ? (about 16 psi at sea level) Above 1.8 bar (about 28 psi)

What follows is my own opinion and experience.... So take it for what it is worth....

I am (regularly) running bursts up to 1.2 bar on a 230 000 mile engine on 93 BP pump gas with no special additives .... and .... have been doing so for about 2 years.....

IMHO, you don't need copper head gaskets in a street engine.

What kills headgaskes on boosted engine.... ? knock ... predetonation ..... what ever you want to call it.

The secret (and it really is not a secret, just a law of physics and thermodynamics...) is to keep the mixture rich .... rich .... rich... Yes, you can you go overboard kepping it a bit too rich and not get the absolute power possible by leaning it out to the ideal mixture based upon the boost pressure....

But what is the risk.... a blown head gasket or worse, a blown piston or worse yet a hole in a piston and bent con rods caused by a lean fuel condition generating predetonation...

Yes, the mid 83 and later 745s have knock sensors, but even the best, properly functioning sensor/computer set-up may not be fast enough...

Like I have said many times, keep it rich enough and it wont knock... regardless of boost pressure
Do you need larger injectors to keep it rich enough...? IMHO .... no. I have yet to find a need. Nowq if you need more than 400+ hp.... consider larger injectors... but be willing to accept the associated headachs of screwing up the factory fuel map even more than it already is... (particularly if you need to pass an emissions test...)

Now if you want to spend thousands for new aftermarket fully programable ECU.... go for it...

So the short answer to the original quesion, No, IMHO you don't need a copper head gasket.

I have yet to find a need for them upto 1.8 bar. The secret is sufficient fuel to avoid head damage and knock which (ever so slightly) lifts the head, breaking the seal and allowing water to seep in which over time further weakens things.... you get the picture....

Regards

John Stein

Follow Ups:

Keith, I came very close to buying that car myself Bob745 01:21 4/15/2002 (0)

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