detonation?

1980 911 sc · 01-26-2004, 11:43 AM

Hellos!

I would first like to say this board is the greatest!, the only problem with it is it gives me all these crazy ideas!

Ok down to my questions....

I have a 80 SC targa, I love it! it is a euro. One thing I noticed is it doesnt have an O2 sensor on the exhaust or the light on the dash. also the destributor # match a 79, per the porsche 911 performance handbook, and it also has the air pump. According to the Vin # it was the 3999 one built so it wasnt liek early in 80....are euros supposed to come this way in 80?

Next question.....

If I put my foot on it hard, I could hear a noise I think is detonation. I used a sears timing light to check the timing and at idle the thing is right at the mark on the crank. It does advance as RPM goes up, but i really dont know how much....based on the mark being 5 degrees I would say like 20 or 25 degrees...do you all think that is close to correct?

Also....

would an incorrect mixture be a cause of this detonation? I have read a few posts on detination and everyone seems to agree that advancing timing can lead to detonation.....what are the general relationships between AF mixture and detonation?

And finally some questinos I have been dreaming of...

I see some very cool posts about turbos added onto SC's. In general I see them adding an extra injector controlled by a pressure switch located in the pressurized intake manifold. OK at this point I must admit I am seriously considering adding an Eaton M90 SuperCharger to my SC( that IS what SC means anyway right?) How in the heck do they know what thier AF mixture is? I mean wouldnt it be better to control it with an O2 sensor? for that matter, especially in the case of a supercharger, would it be better( as in more controled) to modify the CIS fuel distributor to add more fuel? I am seriously considering building a megasquirt EFI system, but if the CIS can handle a turbo before the O2 sensor, why not a supercharger? I guess what I am saying is what exactly is the difference between a factory turbo CIS, my NA euro CIS, and well an aftermarket EFI system liek megasquirt or maybe TEC3?

WOW that was quite a ramble...LOL

Thanks in advance for reading that whole thing and clarifying this stuff >=P

Jadams1 · Jadams1's Garage

I have a 1980 Euro myself, #707 to be exact. Mine is set up the same as yours. It's set up like a 1979 US model but it has a euro pre-muffler instead of the CAT, lower compression than the US model and a slightly different CIS setup with larger diameter intake runners.

Have you checked for broken head studs? I run 87 octane in mine and no pinging.

Bill Verburg · Bill Verburg's Garage

The pinging in those engine is often inaudible. Way back when my C3 ran fine on leaded 87 but would audibly ping on unleaded 87 when ambients were high and usage was pushed. I suspect that it may have neen inaudibly pinging w/ the leaded. Hi test(93) cured the problem. At least till the head studs began to snap.

masraum · 01-26-2004, 01:38 PM

Maybe you've got some slop in the drivetrain, and what you are hearing is something moving around. Could be engine/tranny mounts, bushings, or something in the tranny/differential.

1980 911 sc · 01-26-2004, 02:48 PM

hmm,

Sounds liek I am hearing i prolly have broken head studs.... I am gonna have to do a oil change/valve adjustment/head stud inspection....

If that comes up clean I will pull the chain covers off and check the upgraded tensioners and ramps as well....

so back to my one question does a lean or rich mixture result in pinging?

masraum · 01-26-2004, 03:15 PM

lean

Gordo2 · Gordo2's Garage

When I first got my SC it had noticable detonation. Not only could you hear it, you could feel it when you jumped on the gas!

I held off on driving it until I figured it out, detonation is hard on an engine, let alone one with 170k miles on it.

Digging into it I found my timing was off and my plug wires were arching (nice light show in the dark coming from the braids). I timed it the same time I replaced my wires (w/8mm Magnacores) so I'm not sure which was the major culprit. May want to take a look at your wires in the dark to see if you are getting any spark jumping around.

Once I had it tuned it still had a nasty tick that I thought might still be detonation, but I wasn't sure how. Sounded more like valves ticking. Good look at the underside turned up a crack on the cat converter (where it's welded to the collector flang). Gooped it up with exhaust sealer (plan to replace the exhaust sometime) and it sounded and ran smooth.

Good luck,

Gordo