schwank

Finally got things situated with the race car and managed to get a couple races in at the track last weekend. The engine is a freshly rebuilt 86, with steel cylinder liners, all new bearings, etc.

It was reasonably warm and I was running 20-50 Brad Penn once I flushed out the break in oil. What I am seeing is lower oil pressure than I would like. The car runs fine, but I am about 1 bar off of where I should be. Last year even on my 157K motor, I would get 5 bar under full load and about 2 bar at hot idle, fresh off the track.

You can see my first (shortened) race and watch the oil pressure gauge here: http://www.vimeo.com/5211536

This weekend I got perhaps 4 bar at full load and maybe only 1 bar at idle. When I came off track from my final race if the engine went to idle it would trigger the warning light. At cold idle I get maybe 2.5-3 bar which is too low based on past experience.There are zero leaks and the dipstick shows the car is FULL. So I need to figure out where this pressure drop is coming from. Obviously I am looking at all external factors before contemplating looking back inside the new motor.

The oil pump is out of my old 87 and rebuilt by me to clean out 22 years of gunk. I have tried both a 1 piece and a 3 piece OPRV... both install just fine and produce the same results. I am using the exact same oil pressure sensor that I used last year, and it is only 2 years old. Previously I used the standard NA oil cooler but now have switched to a 86 951 unit with custom AN lines plumbed to a 19 row Mocal cooler. The cooler is mounted in front of the radiator on the drivers side. The inbound hose runs to the top of the cooler and the return line from the bottom runs back to the filter housing. I will post some pics once I get home.

Any chance the Mocal could be responsible for the pressure drop?

I don't have spare hose but I guess if I did I could fab up a simple loop between the two ports on the filter housing. If I have good pressure I would at least know the culprit. But it seems these are used by enough other people that they must be good.

Anyway, thanks for your thoughts and input....

Jeremy Himsel

Did you actually check bearing clearances or did you just install new ones?

KuHL 951

How was oil pressure using the break-in oil? I assume you used used straight 30W for that? It's hard to imagine the extra cooler causing a pressure drop.

schwank

The only part of the motor I did not assemble was the crank, rods, and pistons. I basically received the bottom end preassembled, and then started from there, adding the pickup and pan, head studs, head, balance shafts etc. Cam housing and lifters were pulled directly from the old motor and installed in to the new one.

The engine shop is not a dedicated Porsche shop but has been around for 60 years and has done 944 motors recently that have run quite well through several endurance races without issue. This includes setting the crank as in my motor. I agree Jeremy that the bearing clearances could be the issue but as I said I am trying to clear external causes first before digging back into the internals. I just checked the receipt and the clearances are not listed... will call them tomorrow and see if I can pry out any info.

Break in pressure was also a bit low, and the oil was Joe Gibbs break-in oil. The break in oil was only run at idle and for one session to set rings, then swapped to the Brad Penn. It came up a bit with 20-50 but... not enough for my liking.

tjbreen

I run a 22x9x2 Setrab in front of my radiator (biggest I could fit) in place of the standard turbo oil cooler and have no problems with oil pressure. I run 20W50 Royal Purple and get 5 bars when cold and at speed. Idling after a hot run session will leave me at about 2.5 bar but never much lower than that.

I noticed no difference in the behavior of the pressure gauge after changing to the new cooler.

KuHL 951

I would call the builder and see if he actually used Plasigage or not and if he still has the records. It would seem mandatory to me from a good shop so I would assume it was done. Did they do any crank work or just a micro polish for a standard set of bearings? The low break-in oil pressure is not an encouraging sign either.

schwank

Tell me about it... Crank was magnafluxed, drilled, and polished, and the motor was balanced.

I am not enthused about it but would be even less enthusiastic if I threw a rod in this fresh (and expensive) motor. I do have to assume he knows what he is doing as the other 44 motors he built have run just fine. But... one never knows.

Honestly, if the motor has to come out, or even bearings need to be checked, I am throwing Wipeout's 60K factory motor in for the rest of the year, and will figure the new motor out and install it over the winter. No time to do all that extra diagnosis... 3 races scheduled in August!

KuHL 951

Not to go back to your past oil pressure issues but you said it was a good shop that did the lower end. Lining up that girdle on the block is critical and they nevr line up without persuasion of some sort. When you switched to the late oil pump last week did you get a chance to see how well the girdle was flushed up with the block before sealing it up? I know Ski had to go back in and stone the mating surfaces after a nagging oil pressure issue ( plus a tiny leak) and he was only off a few 1000's.

schwank

No I only lowered the pan a little bit and did the oil pump with the engine in the car.

Interesting to hear about the super tight girdle tolerances. I will definitely be following that line of questioning next.

Wipeout

...heh, look for a "how do I run an early motor in a late car" in a month?