The electromotive system includes a knock sensor. Its more likely that something was very very wrong, ie very overheated, incorrect ring end gaps to begin with, or retard not working, to much boost, and or bad gas. Again with everything RIGHT a couple of degrees one way or the other, AT THE NUMBERS CITED, ie 30 or 32 should make no difference.

Gas is so unreliable that the knock sensor is almost mandatory. If you turn everything down so that it can't possibly knock with bad gas, it will loose all the power you wanted to begin with in other words why bother with the turbo? The electromotive system has the additional advantage of one coil per cylinder. Along with all the electronics you can do the latest and greatest of everything and for not hardly any difference in price.

Snowman,

Has the Electromotive knock sensor proven to be effective on 911's? OEM's spend literally millions on developing these things, and I have a tough time accepting that a universal device will work well enough. However, I will say the J&S seems to be pretty well engineered and is better than the systems employed by most aftermarket EFI systems.

Are you suggesting 30 to 32 degrees should be OK for this engine at 1 bar of boost?

Incorrect ring gaps will leave tops of pistons in the bores so I doubt that was the problem.

use the stock setting, maybe +2° if it doesn't ping. turbos don't sound the same as NA cars when they ping under boost. the exhaust sound goes from a roar to a raspy hiss. a distinct change of tone, and a power dropoff. 35° would be asking for broken rings, and/or burned pistons. snowbob is thinking of NA cars.

I think electromotive is ahead of the whole pack, except GMs. THat said, GM never implements what it knows, or if it does it is already 10 years behind.

On the broken rings, what does it mean to "leave the top of the pistons in the bores"? The typical problem is when the ring gets bigger than the bore, either because the engine is to hot or the ring dosen't have sufficient end gap to begin with. Once this happens, the ends of the rings butt togather, and next the ring shatters.

If there is detonation, usually there will be additional signs and or other damage. The very first sign will be damaged spark plug insulators. Next most likely will be broken piston ring lands and next the ring that goes with the broken land. An alternative sign, depending on the piston design and strength is holes burned in the pistons, broken pistons in the major sections.

In the case of the turbo I would suspect insufficient ring gap due to excessive heat. I would want to see 0.0045" per inch of piston diameter MININUM THat would be about 0.016" mininum and a couple of thou more for an older engine without good spark control.

Like I said before, and I will repeat because somepeople seem to forget what I said, UNLESS IT KNOCKS. It cannot ever knock.

This car has never over-heated. Has the wastegate stuck? Not that I know of. Has the retard failed? It is working now. Have I increased boost with stock IC? Yes, 1 bar. Have I got some loads of bad gas? I'm sure that has happened before.

Matt,
Piezo sensor run well at about 1000-3500 RPM but are too sensitive at higher revs. There is so much noise in the engine that the sensor 'invents' ping.
This is why knock sensor are effective before 4000 RPM only.

This is problematic for performance on tuned engines:
With actual ECU strategy at high revs, spark advance is reduced corresponding to any ping detection at lower RPMs. DSP are often used to filter the knock sensor signal and reduce its sensitivity about a certain RPM.
That means that an engine which has been tuned (viewed on 964 engines) cannot have an optimal ignition at high RPM because of this strategy...

"I run my 912 race engine at 38 degrees, with 12 to one compression and 115 octane race gas. no problems. I run one of my 912 street engines, 9 to one compression at 30 degrees, pump gas (91 octane) no problems. My 911 engine, 8.6 to one compression, 87 octane, 35 degrees, no problem"

Snowman, I think you mean well, but a 930 engine at full boost has an effective compression ratio that laughs at all of the above probably around 14/1 or so and we do it on 93 octane not 115.

As another side note and I could be VERY wrong on this but this is my understanding. Your 912 probably has a fairly aggressive cam. Our 930's from what I am told have fairly mild cams. An agressive cam will leave the Intake valve open for some degrees while the piston is beginning its upstroke to compession. This lowers the effective compression. Our 930 cams have the intake valve closing much sooner I believe. Now I do understand that at high RPMs the open intake valve on your motor is fine because the velocity of the intake charge is so fast that it will fill the chamber with light pressure somewhat overcoming the loss of the first few degrees of the compression stroke. Either way these are very different beasts. Not to mention that our intake charge is warmer due to compression of the intake charge and only contributes more to potential knock. I don't mind being corrected if I wrong:)

You all did notice I suggested 32 degrees max, not the higher number I am running on the 912? Also at high RPMs the agressive cam dosen't give up ANY compression, it only does so at low RPMs. Bye the way the 912 s effective pressure is about 110% of atmospheric due to ram charging. Also with agressive timing, and knock sensors you all are looking at numbers somewhat higher than 32 degrees, see others posts on this.

There is no point in running effective compression ratios of 14 to one if one cannot extract the power from them. In other words people who are into something for nothing will be sorely dissapointed.

With everything said so far EXACTLY what do you all think the max timing should be for his engine? With the additional constraints that I haven't mentioned that it can NEVER KNOCK. If you set the timing at say 25 degrees max vs 32 how many little horses have gone bye bye? Considering this, why are you running 1 bar boost??? Dosen't make much sense if you ask me.

If you're having issues with timing and getting the right equipment - then I agree with the previous posts - an Electromotive HPX system would be a good solution. You can custom-map your timing then...

-Wayne

Snowman,

You seem to provide a lot of advice with much confidence, but no necessarily with the experience to back it up. Running 32 degrees of advance on this engine under full boost will most definitely wreck it. Turbo engines just can't run the same boost as NA engines. Just because they have to run less ignition timing doesn't mean it's not worth while running boost.

And I did some digging on Electromotive's use of knock sensors. I'm not quite sure why you think there stuff is so hot. On my quick look, some issues I found were:
-one knock sensor for all engines (they are not universal)
-they recommend disabling it over 4500 RPM
-no mention of per cylinder retard, so I assume all get dialed back at the same time
-no ability to set the knock threshold versus RPM

Knock frequencies are tied to bore size, so the fact they only sell one sensor and don't even tell you that you may need a different one is a pretty good indication their system is not very well developed.

Finally, when one calculates "effective" compression ratio by looking at boost, you'll end up with "effective" compression ratios that seem rather high. This isn't a real good way to determine how much boost or octance a vehicle requires when comparing turbos to NA.

Heh, what a "can-o-worms" this post turned out to be. I have a car with what appears to be a California distributer, bbut most of the other federalization was stripped off prior to my purchase some 12 years ago. I never maintained the car myself until this rebuild, so this was never an issue before now. The broken rings have me wondering what happened....

Thanx everyone for the spirited discussion. The knock sensor Mr. Beau is talking about looks very interesting and the price is very reasonable.

Why would anyone increase the boost on a Turbo? That question was made by a man who has never owned one ;-)

Les
'85 930

It ain't really a can o worms. With the information provided, contact the manufacturers yourself, talk to them, ask them the questions brought up on this forum and then with their answers, you should be able to make an informed decision.