Dennis Wilson

Considering it was Porsches first computer and analog to boot, it obviously doesn't compare to the LH/EZK but it is programmed for a boosted engine and was used in the 300+ HP 924GT that won its class at LeMans.

Concerning the dieseling, I was referring to a diesel engine that ignites fuel with high compression and no ignition spark not the runon called dieseling that results from hot carbon in the combustion chamber.

Dennis

hacker-pschorr

We are talking about the same thing. When something other than the spark plug sets off the air / fuel mixture it's pre-ignition. Reason why boosted cars should be running a colder spark plugs since this reduces the chance of the spark plug turning into a glow plug causing pre-ignition.

Dennis Wilson

Yep, and it can be caused by a high CR engine running too much boost. Not sure how much boost would do it though. IIRC diesels run around 20 to 1 compression ratios unless they are boosted. A crude calculation would indicate a 9 to 1 CR would cause dieseling at about 32.2 psi. Any math wizards out there are welcome to correct my figures.

Dennis

89 928 turbo

Very good discussion.!!!....and generally spot on. It is a balance of boost, CR, intake temps, colder plugs, managing the knocks, measuring everything....it ultimately goes to reliable forced induction (SC or Turbo) over time (or mileage if you choose).

We haven't seen any real issues under 7-8 pounds and the engine (in reasonable shape) can cope. 5#'s boost and is easy and doesn't seem to really stretch any of the stock engine setups. But we know that.... In original setup/testing, we failed a head gasket, upon removal the engine (109,000miles) and subsequent inspection of it, the gasket was cleary already in very poor condition. I think I 've seen some other discussion threads regarding HG's and condition.

I'd be careful consistently running 15lbs of boost and anticipate that the ongoing maintenance cost is going to be incrementally high unless the engine has really been gone through or an engine history with detailed files is available. Ultimately, I would build some safety into an engine to cope....mostly an upper end review and head studs. I like my cometics.....no problems running this car hard in 12,000 miles....touch wood.

Methanol at these levels of boost help a lot from what we can see so far and the install is pretty easy. We have it set up so that it doesn't even engage until 5lbs and a much larger reservoir (1.5gal) mounted in the boot. It adds to the fuel mixture a bit,but if the injectors need upsizing, they need upsizing...the ST lines this out clearly in the data logging and when it starts going south.

Shark tuning is critical to get your best shot at surviveability and tying all of the other elements (good gas/bad gas, colder plugs, etc), and its best to do it on a car by car basis.

......but there are a bunch of SC cars running around with good records.....and (I think) bolt on's and not much tuning.....please correct me if this perception is incorrect.

JT

Mongo

So 5 psi would be a safe bet JT on a stock motor just looking for a minor gain?

I would like to do a setup like this not to break 400 HP, but to get more of a kick in the seat. The fact the car would sound like an F-14 at Zone-5 is just a fun accessory and benefit to it!

Dennis Wilson

Actually, 7 lbs is very safe for a converted NA engine. General motors proved this in 79 when they took the 3.8 V-6 and bolted on a turbo mated with a 4 barrel quadrajet. This was a very hardy engine. The weakest point was the turbo bearings due to the lower quality oils they had at that time. No IC or water/methanol injection was required until the ante was raised with the Grand National engines. BTW If anyone is interested, I have a complete set up for the early version, less the quadrajet.

Dennis

89 928 turbo

Sure, as with any set-up there is a certain amount of engine prep to do with vacum lines, and a little re-plumbing for any developing crank pressure but with a solid base, it is very do-able. The psi range of any basic turbo sizing also allows a bit of a range up to 7psi by a simple change of spring in the waistgate.....a $25.00 upgrade that can likely pull 30-40 hp.....on top of getting 390+/- at the rear wheels with 5lbs

Mongo

What plumbing would be necessary to cope with the pressure increase you mention. This is crankcase pressures correct?

Dennis Wilson

The easiest way to gain boost is by fooling the wastegate. This is done by putting a variable restricting valve on the boost line feeding the wastegate. I've seen these setups with $10 valves bought at the local hardware or more expensive valves that are electrically controlled by a dial in the instrument panel. I wouldn't use either of them without a good boost gauge to prevent overboost.

Dennis

Mongo

Some of the guys with 930s I knew a while back did the same thing and had a dial in the cockpit to turn the boost. It's as tempting as it is catastrophic if you're careless.

Dennis Wilson

Yep, it is scary. I have the 930 1 bar wastegate in my 931 and even that is not safe if any connections are loose or blow off. It's happened once to me. The rush is great until it hits the rev limiter. From there it's all downhill. BTW I have a boost gauge but it happened too quick to catch.

Dennis

89 928 turbo

Yes, you have to pay attention, low end plastic boost dialers and low end gauges are not the best cost savings now that you have invested all this and are putting an $5-8,000 (or more?) potential engine rebuild on the table.

We tried the little dial up plastic deal, but moved quickly away from it....its important to have a boost gauge with good range to see what's going on, but things do happen quickly.

We have never had an issue with tubing blowing/knocking off the various pieces parts, but we single and double zip tie everything.....you still have to check them out once in a while.

Mongo

Ehh, I don't think I'd ever turn the boost up if I went turbo on this car. Even at 10:1, sometimes I feel that compression is too high to turbocharge or supercharge, regardless of how durable the engine is.

89 928 turbo

We just go off a day tuning at the dyno with Chuck's car with good results.

Boost: 5.5lbs

Dyno was a DynoDynamics:

380.1 RWHP/406 Ft/lb

AFR's mostly in the mid to high 11's, timing next.....

30# injectors, RR-FPR @ 58psi, 96,000 miles all else Stock.

We will post the dyno sheets and AFR's as soon as we can figure out how to make them small enough to upload off the scanner.....I'd take some advise on this...

jt

89 928 turbo

Oh, and his car dyno'd stock at 265-270hp......