SEW QUIK

I am hoping you guys can help me with this issue regarding a potential 1978 930 purchase. I currently drive a 87 Carrera and am looking to upgrade to a 930. The car will be driven on the street in the Bay Area (91 octane gas) and needs to be reliable. I looked at a 1978 930 which was rebuilt (~25K miles ago) by Imagine Auto ("BIg Bad") to about 440 fwhp with SC cams, K27, full GLH, etc. Boost is stock (0.8 bar), as is intercooler. Compression was raised to 7.5:1 by fly-cutting the heads. I spoke with two prior owners who highly recommended the car.

The car looked and drove well and I had a PPI done in San Jose by an shop experienced with turbos. There were minor issues (expected), a bunch of oil leaks (including front and rear seals) and leakdown was 8% on #3 and <5% on all others. The mechanic detected detonation on boost, however, and told me that that this would eventually cause substantial engine damage. The car has not been dyno'd recently and AFR's have not been done. His advice was to have the owner deal with the detonation issue prior to further discussion of purchase. He listed options including adjusting spark advance, etc. but stated that this detonation might not be fixable given the engine mods. Running higher octane will obviously help, but is not always feasable with a near-daily driver.

My question is whether this can be fixed with Lee Rice fuel enrichment, Andial fuel enrichment, "Brent-CO" rebuild of WUR, etc. The mechanic seemed to think that adding a larger intercooler or EBC (which I had planned) would not help detonation. Perhaps this is not the car for regular use for me? Any suggestions would be appreciated.

thanks,

SEW QUIK
'87 Carrera

Steve Weiner-Rennsport Systems

Hi:

You've asked some good legitimate questions.

It sounds like your mechanic is giving you some good advice and I'd simply add a few comments.

930's, due to having forced induction and being air-cooled, are quite octane sensitive. Under the right circumstances of high outside air temperatures and borderline fuel, I can get a bone-stock Turbo to detonate (ping).

I'm pleased to hear that this car is still at .8bar as thats a big part of staying together for a long time and helping to deal with marginal fuels. Detonation prevention is based on several variables that must be controlled:

1) Boost pressure

2) Charge-air temperature

3) Oil temperature

4) Octane availabilities

5) Air/fuel ratios

If you read the owner's manual on these cars, you'll see that 92 octane is the recommended minimum by Porsche. To enable a Turbo to run on 91 octane without detonation involves controlling oil temps with a big cooler, a larger intercooler, and making sure that the A/F ratios are in the 11.2-12.2 range, on-boost. With higher static compression, you might need to add some 100 octane unleaded in warm weather.

When we modify 930's such as this one is, we always add twin-ignition to prevent detonation on pump gasolines and limit boost pressures to 1.0 bar or less. Although this is not inexpensive, it may be your best option for running with 91 octane premium fuels. Its certainly cheaper than buying new P/C's,....................

Remember, you cannot detect detonation in a turbocharged, air-cooled motor until the damage is done so my best advice is to deal with this proactively.

Kevin

I can't fathom anyone that would have all these mods and not upgrade the stock intercooler.. Detonation will happen on crap gas and if the charge air temps are to high.. Throwing more fuel at it is not the only issues.

I would stick this car on a dyno with at least 92 octane, better yet throw some 100 in and see how the AFR's are..

Since Imagine built the engine, I would have the fuel head redone IF you need more fuel, but until the car is run on a dyno, you are only guessing..

Earlierapex

Sew Quick,
I used to own this car and sold it about 5 years ago. Fantastic machine. I never had any problems at all but always ran on at least 93 octane.

Since the car is running only 0.8bar (same as when I had it) and it has C/R bumped a little (to 7.5 if I recall???), it shouldn't be detonating unless it is a really hot day and you are using crap fuel. Sounds like the latter is your problem.

How did the mechanic "detect" detonation? Just listening for it? That's pretty tough to do with a 911 engine. I'd put it on a dyno and run the AFRs to see what's up.

You probably shouldn't be running any 930 on 91 gas, even stock. That's just begging for a flogging.

-dc

PorschePhD

Put an intercooler on it and it will be fine. You also should consider a modified fuel head. The other enrichment systems do not work as well nor in the needed spots. You can detect detonation by looking at the plugs. If they look like they have little ***** on them that is detonation. Any audible detonation is not good and is causing damage.

special tool

For whom it may concern...

I am looking for a 3.3 test car in New England to install Vitesse 3.2 motronic (fully tuneable), wideband datalogger and a modern Garret turbo on. Installation will be free.
Parts/dyno budget will be under $6000. Dyno will be mustang load-type.
We will be conservative and aim for only 550 RWHP (687 HP) and widest powerband.
Pm if interested. Thank you.

PorschePhD

You might want to add you are looking for someone with rods or rod bolts. Those numbers will yield a result that is less than desirable.

special tool

Thanks kido - I had that covered.

PorschePhD

Wow I haven't been called that in 20 years. Thanks. Maybe the trend will keep going and someone will card me