DARISC

That's exactly right! I never heard a thing like a ping as my turbo'd, carburetted, futilely water injected 280Z block did its silent internal meltdown as I poked at the gas pedal, cussing myself for letting my gas tank run dry (though it read 3/4 FULL!).

4 out of 6 pistons with holes in their heads, buncha burned valves, Oh, the humanity!

That's what I had in mind by "you better know what you're doing!".

LA964RS

By the way...as a turbo guy w/engine upgrades I mix the trick w/regular...don't need to use the 91 w/the trick gas...I go 1/2 n 1/2 and it works great. Allows me to do 1.2 bar w/no issues except stupid look on my face.

Steve Weiner-Rennsport Systems

Be sure and look closely at your spark plugs from time-to-time,...

Amber Gramps

Steve, I read the link and my head is spinning. 90% was way over my head. I have a sweat, stock, rather tame, but quick 3.2. I'm thinking that it is totally unrequired for my little sunday cab. I'm gonna stick with the 91.

thank you so much for putting it all out there.

Ian Ledger

From here in Europe my 1987 3.2 requres 98 octane. I seems sensible without a knock sensor to follow this recommendation from Porsche. Higher octane would not give an advantage, but lower would be silly.

84_Carrera

Steve -
Dumb question, and I may have asked this before, but is there a simple way to add a knock sensor to the case, with an idiot light at the dash (not tied into the DME on early 3.2L cars), - looking at doing something simple like alumalloy'ing / tig-ing a threaded block to the case somewhere? & tripping a warning light with a pre-set threshold at a certain voltage coming from the knock?

Or, is it just safer / better all around to look into a dual-plug setup assuming this totally removes the problem? Is converting to a 3.6L harness & DME an option to incorporate a knock sensor?

What about PENDING fuels 5-10 years down the road? If MTBE could go & we end up with Ethanol issues, what's next? 20% Ethanol being mandated? (shudder)

I know you've discussed dual-plugs with me on the phone before, but I don't recall the costs to convert a 3.2L to it. Assume we're looking at during a complete rebuild only, cost-effectiveness-wise?

DARISC

I've always wondered about knock sensors - do they sense an impending knock, then do their thing before a knock knocks? Or do they sense a knock knocking before they do their thing?

If the latter, even if the engine only knocks once per warning/shutdown, aren't the destructive affects of detonation cumulative?

Edgy01

I ran something like that in my 911SC-Turbo which had a relatively high CR for a turbo, while running a conservative boost (and no intercooler). It WAS needed, no mistake about it. Otherwise count on an engine exploding on you.

For my current car I would like to mix some of that in,--it knocks at times with the 91 we generally find in California. The Variocam helps detune the car to the fuel it finds in it.

Mike Murphy

I don't think the stock 3.2 would benefit from 100 octane. Maybe the 997 would in California, because those guys are hearing knock on their engines.

I have a motorcycle that requires 86 octane gas. I've tried 91 and 93, but it's just a waste.

Steve Weiner-Rennsport Systems

Hi Fred:

No such thing as a "dumb" question. Those are what we call the ones that are never asked,...

Porsche did a LOT of R&D to find the right place to mount the knock-sensors on these inherently noisy air-cooled engines. They found that the bases of the cylinders were the best places to detect vibration without interference from combustion and valve train/cam drive noises.

These cylinders are manufactured with cast-in mounting bosses for the knock-sensor bridges and its not feasible to weld such things onto other 911 cylinders without permanent distortion of the bores.

IMHO, its FAR more practical to deal with this proactively by employing measures to prevent detonation in the first place. One of the most effective is using twin-ignition to "raise the bar" and help prevent the engine from knocking (pinking). The 3.2 Motronic engines are the easiest to do this as it only requires a 3.6 dual distributor with harness, a Motronic splitter, an additional coil, and different software. Of course, the heads and lower valve covers must be machined for the lower plugs.

With regard to fuels, MTBE use is already discontinued as mandated by the EPA and now the main oxgenate is Ethanol added at 10%. I too, hope Ethanol use is not expanded as the fuel systems on these cars is not compatible with that stuff. In fact, its not the greatest choice for a motor fuel due to lack of miscibillity with gasoline, its affinity for water, and latent heat of evaporation that makes it tougher to start and run in cold weather.


DARISC:

Porsche's knock sensors work by detecting the tiny vibrations from detonation and retarding the timing in 2 degree increments until its gone. The Motronic system then waits 720 degrees of crank rotation before adding the timing back in. This is all done on an individual cylinder-by-cylinder basis, too.

This design maximizes performance as these systems adapt to every grade of fuel thats used.

Mike Murphy

Thank god computers don't get worn out for thinking too hard. This sounds like a whole lot of calculation and adjustment back and forth, even though 20 gallons of gas can take quite a while to burn. I guess it's also for the temperature changes throughout the hour...

Amber Gramps

Holly octaine batman..ontario airport to john wayne in 12.3 mili-moments. and I got pictures too. let's just say it was the best $42.00 i've spent in a while....I was unable to use my 20/20 I was bouncin' off 7,000 without hittin the rev limiter.. how do I get the dumb look of my face. and it's 110 out and the temp gauge is horizontal...

JonH

are you drinking the race gas now?

Amber Gramps

smooth idle, quick run up in RPM's, revs past rev limiter before it can kick in, makes second gear an even bigger thrill ride, zero to 110 on an even shorter onramp, ....who made this stuff legal....of course it could just be that I'm not draggin' my wife around with me!!!!!!! I did 8 gallons of 100 octane on top of about a 1/4 tank of 91. lets call it a modest 95/96 octane blend. and yes John, I'm drinkin' it too.

JonH

^ that's actually a pretty funny shot, I think the pump is smiling at you!