JBL930

What do I do then, I certainly don't want my pistons to look like poor DonE's, if the best we can get in the uk is equivalent to 93 then I’m on a time bomb????

senna21

No. 93-US (or US equivalent) should be fine. Just don't push up the boost above 1bar. Also if you are running a lot of boost switch to a step colder plug.

I'm just letting you know that you guys have got about the same stuff as we do here. I've said it before and I'll say it again. Boost doesn't kill engines. Knock kills engines. But, as you increase your boost (or compression) you increase the chance of getting predetonation.

JBL930

so at 1 bar with standard P@C's and 27 degrees BTDC 93 octane SHOULD be safe

WERK-I

DonE,
I forgot your previous post regarding your engine details. I seem to recall you are using the Electromotive EFI, yes? Did you twin-plug the engine?

DonE

Yep and yep.

Timing from 100 kPa starts at 24 and ends up at 15 (208kPa). Timing at 2300 rpm is 34, then comes down to 30 at 3500 then 28 from there.

Since there is not sign of detonation anywhere else in the engine (examine plugs, pistons), I am considering this is an injector problem. You guys know that I try to be scientific about what I am doing and I try to do it with quality equipment. Well, with 2 blown engines in less than 5000 miles, that method is out the f***ing door. Right now, it looks like I will order 6 new pistons since the min order is 4. Now I have to decide which CR, as well as have the injectors tested. Obviously, this has been a nightmare.

I hope this helps you guys with your cars.

WERK-I

.....OR an errant/erratic fuel pressure problem. Fuel pumps or pressure regulator?

My87Targa

wouldnt that cause it to dumb fule unevenly across the board then and not in just one cyl. then he would notice knock most likely as well as the other pistons being scared up too. or am i wrong??

m42racer

Does the Tec 3 show the Timing at the crank? Are your Timing numbers inclusive of the machanical base timing?

Take comfort that these engines when built and mapped correctly do last. Something is amiss, so before buying anything, find out what the cause was. Talk to someone that knows these engines and does this all the time. Call the guy I PM'ed you. He will tell you very quickly what is going on, and what to look for.
When a Piston melts like yours has, and on the Intake side, this always points towards a lean condition.

JBL930

What I meant to say was, is a modified 930 with standard pistons and cylinders putting out 490bhp at 1bar of boost (along with other mods obviously) safe with 93 octane fuel, forgive me for being dumb I don't do any work on my car I leave that to the specialists, I’d like to be fore warned

sewell94

Don,
Sorry to see this happen. It looks like a tuning issue to me, knowing that Essa tuned the first engine means it was gonna happen on that one. I know quite a few people whose cars have blown up from his tuning, I can't believe he is still in business.
It looks like the car was running really lean on cruise. u can do that on a water pumper but not on our air cooled engines. maybe it is an injector but what cylinder went on the engine before, unless its the same one i would doubt it, but inj are cheap in comparison to building an engine over and over.

A930Rocket

How and where do you install a knock sensor on a 80's 911 Turbo? I thought there was too much rattling going on with the timing chains and all for one to do any good? I understand the later model 911 Turbos have one though because the engine is quieter.

m42racer

Knock sensors can are fitted to 930 engines. Most systems have the ability to dial out the engine noise, or set a threshold that above this point, you will consider any noise, Knock. The sensors are fitted under the Throttle mount between it and the case. The damage caused to the above Piston would certainly rattle the case, as does most knock. Anything to give an indication of detenation is worth the trouble our friend now faces.

DonE

I use the stock stuff which seems to work very well. I don't think this is a problem since the O2 sensor (datalogs) does not show erratic performance - on the street or dyno.

Win Rice

Don,

After the first engine problem, were the pistons Zygloed? Any microscopic cracks will cause a heat concentration and speed the erosion of the material under high heat loads. A crack could have originated at the base of the valve pocket, where the piston head is the thinnest.

Was this piston out of one of the previous split cylinders? Once a high strength aluminum alloy is over heated, it becomes annealed and looses significant strength.

After the injectors and ECU wiring are checked, it would be interesting to have JE or someone else thouroughly check that piston, and maybe a couple of the others. Zyglo and hardness. The original detonation problem could have had something to do with this.

Food for thought.

Win

DonE

I use the TEC3 crank sensor system for timing. I double check with a timing light to make sure its on, and it has always been spot on.

One of the problems I am still facing is all the opinions on how to tune this thing. And the opinions are far apart - one has very aggressive timing, another states nothing above 30 degrees. One states 11.5 AFR on boost, another says nothing below 12.5. I set cruise AFR at 14, others say I could have gone higher.

The only two tuners I have used have only set WOT timing and AFR's. That's not tuning to me.

Another issue is CR. Should I stay at 8.0:1, tune better and keep the boost under 1 bar or should I go down to 7.0:1, tune better and run boost at 1 bar?

Yet another issue: deck height. Currently, I'm at .069. The reason for this is that my heads have been shaved by the previous owner to bump compression. I ordered special 8.0:1 CR pistons and had my machine shop measure everything to give me proper deck height. He told me 069 rather than 039 because that's how the math works out to get proper squish and CR. No one agrees with him on this issue except me because he has my parts and he is a reputable machine shop/builder/NA tuner.

WTF....