Last week I participated in a full day coached session at our local Portland International Raceway. It was my first experience on the track and my main takeaway is I have a lot to lean in terms of driving skill. My 928 S4 5spd performed flawlessly and I was impressed at how well the brakes worked (street pads), how predictable and neutral the car handled the corners and awesome the engine sounded as we raced down the straightaways against the walls.

I did have several problems downshifting from 3rd to 4th. I would often not be able to find the gate and resort to shifting back to 4th. My front and rear pivots are new. However, my shifting is still notchy and the GTS short shifter makes life more notchy. I know my transmission is missing the centering spring, unfortunately, I was unaware of Collin’s replacement when I had the tranny out of the car. I am wondering if I should change the tranny gear oil to something that would be more helpful. IIRC Greg Brown has some recommendations.

My second question is regarding oil consumption. I think I went through ½ -3/4 quarts of oil (Mobile 1 15/50) during that session. Is that normal for a track day? Under normal driving, my car does not use much oil at all, maybe ¼ quart over 3000 miles. Where is the oil going? Blow by? Is the oil vapor getting sucked into the combustion?

All in all it was a positive experience and there were no less than 3 928’s on the track that day, my car, my instructors, and this stripped down monster. The owner told me its and 82 body with an 85 euro 5L motor in it. He claims to have it producing 400HP at the wheels. I looked at the motor and it was all stock looking under the hood. Stock injectors and stock ECU program. He claimed it has hot cams. Is that possible? Seems like a lot of hp.

Here are some picks

 

That guy should have used some chalk lines when drilling those holes in the center of the front bumper, or better yet, drilled them to read 928.

 

Very cool. I've got a track day at Limerock in a few weeks and you bring up an important issues I forgot to include in my prep list. Oil control. Most likely the oil issue is from sustained RPM causing crank case pressure. Then it blows some oil vapors out of the breather and in to the intake.

As for the shifter issue, You may want to make sure your clutch is fully releasing or perhaps adjust it for max release for track days. Also check the indexing of the rear linkage and your mounts becasue if you were trying to shift when the chassis was stressed or weight shifting the movement of the drive-line relative to the chassis have put the detent where you were not expecting or allowed the shifter to contact the frame under the boot and limited it's movement. When a car is heated and stressed from racing lots of issues can present that had not presented before.

 

Excellent point. The crankshaft lobe for #2 cylinder is also directly below the crankcase venting assembly that's part of the oil filler assembly. At sustained high RPMs, oil is slung from that lobe into the breather, then the pressure forces it out.

I have available one of Hans' Oil Control Baffle Plates. It allows the pressure / vapor to pass through it (slowing it down), but blocks the oil and allows it to drain back. It's a beautiful piece made of billet aluminum and anodized black. I had it installed for a short time and just cleaned it up this weekend in my ultrasonic parts washer. Comes with the sealing o-ring for the bottom side and the top uses the OEM gasket (not included) that normally seals the oil tank assembly. The grey areas in the photos are remnants from some sealant I had it installed with.

Roger sells these for $95 plus shipping. I'll do this one for $70 shipped USPS Priority Mail.

 

The answer to the gear oil question is long and very involved. (Actuallly, all of the answers to your questions are long and involved.

Short story to gear oil.

I've used 75/90LS Mobil one, for years. Protected the gears well, worked great for the limited slip. The synchros were "crunchy"...even on transmissions with brand new synchros. However, since all of the transmissions, with this style synchro, that I had ever driven were "crunchy", I just assumed that this was normal.
And then, I had a client bring back 4 of his 928's from Germany. Both GT's shifted like butter. Absolutely no "crunch"! I tried very hard to identify what gear oil was in them, to no avail....however, this sent me on a quest to find a better gear oil and I began trying everything I could get my hands on. The current "best of anything" is Sta Lube 75/90 Hypoid/Limited Slip dyno oil (SL-2463). Tough to find. Napa sometimes can get it. Sometimes can be found on the Internet.

Oil consumption:

All 928's used on the track will have this problem. Most will have this problem when driven aggressively, on the street. The oil, at higher rpms, begins filling the cylinder heads (lots of space in the heads below the valve cover.) Once the oil "covers" the oil return passages (in the heads) to the crankcase, the problem gets worse, in a big hurry. Now the crankcase isn't able to communicate with the heads and crankcase pressure builds. This increased pressure pushes back on the oil in the heads, which increases the resistance for the oil to return to the crankcase. More oil fills the heads, and the excess oil is pushed into the intake system. (If you remove your air fliter and the MAF, have someone hold open the throttle, you will be able to "see" the "lake of oil" sitting in the very bottom of your intake manifold.) The oil getting into the intake system reduces the effective octane of the fuel, "knock events" increase, and the "super soft" stock rod bearings will pound and fail very quickly. (you can ruin a set of rod bearing in one day....cut open your oil filter and inspect it for metal, ASAP.)

Eventually, given enough time and rpms, there will be 4-5 quarts of oil "stuck" in the cylinder heads....not leaving enough oil in the crankcase for the pick-up. The oil pump sucks air and the rod bearings fail....almost immediately...spewing connecting rods out of the side of the engine.

Dozens and dozens of these engines have failed on both the track and on the Autobaun, from these problems.

The "cure" is complex, because the problem involves multiple "sources" of potential problems. However, at the "beginner to mid level" driving ability, keeping the oil out of the intake becomes your first priority. Install one of my baffles under the filler neck. Remove your valve covers and install my valve cover breathers in all four places (add two more 90 degree elbows on the driver's valve cover.) Do a simple re-route of the hoses (I can tell you what to do and provide the pieces.) (I originally made a complete different breather system to control this problem, but I found that my valve cover breathers, some small changes to the design, and my crankcase breather cures 95% of the oil ingestion problems.) (Jorj uses my pieces on his 219mph open road racecar and completely eliminated oil consumption problems over that 90 mile, high rpm all the time, course.

Last thing, for you:

15/50 Mobil One is adequate for use on the street. Not adequate for use on the track. You need to run some other higher quality oil! Lubri-Moly 10-60 would be my first choice.

400rwhp from 5 liter Euro engine:

I'm not going to say he's wrong or exaggerating, but that would be absolutely, incredibly, amazing. (Although dynos that are extremely "optimistic" do exist and I know of several where one can "obtain" results like that.)

He should be thrilled if it makes 400 flywheel horsepower, on an accurate dyno.

 

Everyone thank you so much for the very thoughtful and useful responses.

I did instal an oil filler baffle when I did my intake refresh back in March of this year. I used the Hans Baffle referenced above but still saw fairly high oil consumption. I was definitively running high RMP's on the track.


@icsamerica interesting suggestions on the heat/flex issues impacting shifting. That definitively makes sense I will definitively inspect the rear mounts (front mounts are new). Although, I would say my notchy shifting wasn't worse on the track than for normal street driving. It's pretty notchy on the street but it's made worse when driving really fast, jamming on the brakes, downshifting, and turning all in a very compress window,

@GregB Extra thank you for the time to give extended explanations. Very useful and and you have successfully scared the crap out of me! Would these "knock events" be audible? I will cut open the oil filter and inspect for engine parts ASAP and look for the "oil lake" in the plenum. Hopefully I didn't damage anything. (I wish I had all this information when I did my intake refresh this past Spring). I am interested in your crank crankcase breather solution. Please send some information over either in this thread or direct message me. I had so much fun in my last intake refresh, I cant wait to do it again!

I'll take your advice on both the engine oil and gear lube recommendations.

thanks again everyone!

PS, I am with you @GregBBRD on those dubious 928 race HP claims. I would not expect those stock injectors to provide enough fuel flow for that kind of HP even if they ran full duty (always open). And, given that the owner did not do his own work and claimed his 18" Cup 2 wheels were OEM was a good indication he wasn't too keen on the facts, also note the restrictive single exhaust... Kudos for the lightweight though!

 

This /\ /\ /\ /\

I personally don't like 15W50 mobil 1 as I have seen some lifter wear with its use. But all street oils should really not be considered for track use.
There are some great track oils with good protections in them. But most street oils have lots of cleaners in them. This is desperately needed on the street. But those cleaners are not wanted on the track.
You are best to drain the oil the day before the track, fill with race oil, drive to the track, beat the **** out of the car for the weekend, drive home, drain and put the street oil back in.

 

To put things in perspective, a local 928 race car has a 4.7 liter EuroS engine, 10.4:1 measure compression ratio. 5psi of boost from a Murf928 supercharger system, headers, free flowing exhaust...... This engine is making just under 400hp at the wheels (I don't recall the exact number).

I can only speculate who sold him the camshafts sold him on the power levels. Even 400 at the crank is far-fetched for this setup.

Stock injectors are 24lb and could make 400rwhp with the right tuning / fuel pressure though.

Are you recommending this for all 928 manuals or just the later ones?

 

I've not tested this oil on the early transmissions, but I see no reason for it to not work on those transmissions, also.
However, since it seems so difficult to find, it may not be worth the effort, for those transmissions. Just getting enough for my own use, in the shop, is difficult. We can't get Napa to order more than a couple of gallons at a time. Right now, I'm getting two gallons every 2-3 weeks....and the effort required to do that is....insane.

 

Those power numbers are not going to happen with an AFM. I assume the stock injection system to be the one originally intended for your '82, not the MAF '85 Euro injection system. The L-jet 5L Euro engine can make pretty close to 300rwhp, though.

 

Good to know, thanks!

My 80 needs a trans fluid change and I'm pretty good at finding stuff like that. It was rebuilt less than a couple thousand miles ago by Zimbrick Porsche (10 years ago). Shifts like butter and I'd like to keep it that way.

 

Why don't you just order it from Amazon?

 

We certainly could.

Mary tries to buy things at less than retail +30% and pay sales tax twice....

Tends to make our clients happier.

Silly woman....I know.

 

I do not agree with this at all.

For tracking their cars, Chevrolet does not specify C7 Z06 owners to do this, neither does Porsche for their GT3's, GT4's, etc.

Doing so would be a colossal waste of money for no good reason at all.

 

JL dyno'd at 375 rwhp, almost exactly 100 rwhp more than he did NA.

20 rwhp per pound of boost, centrifugal, which is what all our cars have done.