PCA Southeast Michigan Region

From the Blog

My Porsche Story – Erik Ohrnberger (part 2 or 2)

  • Broken engine & rebuild

The following year, in the middle of the summer, the engine started to develop some interesting characteristics. When first started cold, it would idle really roughly, like it was running on 3 cylinders, but once warm, it ran just fine.  Good and strong.  During an oil change, a small fragment of what looked like a valve spring was found.  Hmm.  But the darn car ran just fine.  Hmm.  A month or so later, that valve spring gave up completely.

Pulling the head in order to replace the valve springs, and  figuring other ones were about to let go as well as well as replacing the valve guides and seals, and perhaps getting a fancy value grind, we saw scratches in the cylinder bores.  Well that can’t be any good.  I was wondering where the motor oil was going.  Now I knew.  It was sneaking past the rings in the bore scratches, and I was losing performance as well.

Oh boy.  This was going to be a big job.  Different people repair the scratched bores in different ways.  Some people over bore the block and put steel sleeves in.  Others refinish the bores and put oversized rings in.  Lastly, there are some folks who Nikasil plate the bores.

Knowing that steel and aluminum have different rates of heat expansion, I really didn’t like that idea very much.  What if a sleeve slipped in the block?

I wasn’t in favor of refinishing the bores, just to have that happen again, and I didn’t know whom to trust with this type of job in the area. It seemed rather exotic when compared to fixing Detroit iron.  So Nikasil plating was the solution decided on.

At the time I made the decision, I didn’t know that this would also require the replacement of all the pistons, but now that I think about it, it makes perfect sense.  The OEM pistons were made of aluminum that was designed to ride on the polished silicone surface in the bore.  Now that this surface was going to be replaced with a much harder plated Nikasil, the pistons would have to be made of a much harder material as well.

The Porsche pistons for the 911 are the same dimensions as the 944 pistons, and they are designed to run on Nikasil plating, as this is how all the 911 engines are constructed.  Porsche wanted Porsche prices for their pistons, so that was quite expensive.  J&E wanted a few hundred dollars less, but still expensive.  I found Diamond Racing, which would fabricate custom pistons to my specifications.  They do this for all the Detroit area drag racers and their engines, so I went with that.

Once the pistons were delivered, the pistons and the bare, stripped block were shipped to US Chrome in Wisconsin, which would do the Nikasil plating and the honing of those bores to the pistons.

When that was completed and shipped back, I took the crank, the pistons and the rods to Crankshaft Craftsmen for balancing and weight matching.

There were some slight balance adjustments to the crank, and these guys did a fabulous job at weight matching.  3 of the 4 rotating assemblies are exactly the same weight, and the 4th is a mere 0.1 gram lighter.  In addition, the pistons were on average, 47 grams lighter than the OEM ones.  Great!  This is going to be one super engine.

Now that all the parts were back from the various shops, it was time to assemble.  Vaughan and I built the bottom end,- crank bearings, and block skirt.  Big Mike from Munk’s Motors helped a lot in the rest of the engine assembly with included all new bearings, all new gaskets and all new seals.  If it was worn, or likely to need replacing, it was replaced.  This was going to be an engine build that should last at least 200K miles.  I was more than happy to be Big Mike’s helper.  Big Mike was getting on in years, and my running back and forth getting and handing over tools was the least that I could do to help him out.

Finally, it was time to drop the engine back into the car and time the cams.  I knew that I wasn’t capable of doing this work, but I had well placed my trust in Big Mike.  He was great.

Yeah, there was a thing or two that we missed.  Once of the balance shafts was 180 degrees out of phase, but other than that, it went really well.

  • Suspension upgrade #2

Having come this far, and developing driver skills, it was a toss up as to what maintenance items and upgrades needed to be performed next.

Inspection revealed that the ball joints were worn out and loose.  So I got the RennBay track rated ball joint kit to repair that.

Vaughan mentioned that the rear end bushings were probably due for replacement, and would improve the feel of the car.  So we tackled replacing the spring plate bushings with poly-graphite, the trailing arm and the banana arm bushings with Delrin. The OEM spring plate bushing is a large rubber bushing that isolates the torsion bar from the rear suspension blade onto which the rear trailing arm is bolted.  It’s the place where the ride height is adjusted. Knowing that harder bushings cause odd suspension noises, popping, groaning, grinding, I figured that it would be better to be able to get some grease in there, but how?  It’s buried way in there as it’s the heart of the rear suspension.

The bushing fits into the mounting arm, which is bolted to the body of the car.

Trailing Arm Bushings

On the inside of the bushing on a machinist’ lathe at Chris’ machine shop, we cut a helical kerf on the inside diameter of the spring plate bushing.  Then we cut a circular kerf on the outside diameter of the bushing.  We connected the two kerfs with a through hole, and on the mounting arm opposite of the through hole we drilled another hole into which we screwed a zerk fitting.

Here’s the idea: Squirt some grease through the zerk fitting into the through hole drilled into the bushing.  As the torsion bar twists during normal driving, the helical kerf on the inside diameter distributes the grease across the entire face of the bushing.  If the bushing’s through hole wanders away from the zerk fitting, the grease can travel around the circular kerf until it fins the bushing through hole, and again the helical kerf will distribute the grease across the entire face of the bushing.  Neat idea, eh?

So with all the tightening up of the suspension, it was time to corner balance the car. So Vaughan and I spent a weekend in his garage, drinking beer and fiddling with suspension adjustments until we hit 52% front and 48% rear weight distribution with excellent cross weights.  I’m sure glad that he’s got a set of scales specifically made for the task.

Within 2 turns on my way home, it was like “Holy Cow!”  “What a difference!”.  It felt so planted, so even, so confidence building.  Amazing!  And as you’d expect, Porsche designed the ability for this adjustment right into the suspension from the get go.  Yup.  So that’s why you buy a Porsche.  For these little, but oh so important, race bred features and abilities.

  • Period correct Porsche sports seats, now in black

As driving skill increases, speed improves, and along with that, cornering forces are greater.  With the stock seats, with the smaller, nearly nonexistent seat and back bolsters, it was a continuous fight to keep my butt in the seat.  The car was always threatening to throw me out of the seat in corners, and the only choice was to keep that left foot firmly planted on the dead pedal, and nearly locking my knee, bracing myself into the seat, all the while driving the car.  That’s very tiring.   I needed to do something to reduce the workload on the driver, as a tired or overstressed driver never performs at his best.

I managed to find a pair of period correct Porsche sport seats that came out of a tan tracked 944.  The previous owner decide to go for aftermarket full street / track seats  I could have made that choice as well, but I wanted to maintain a less audacious look of the car.

The Porsche sport seats have tall bolsters which keep my butt and back in the seat, and thereby lower the driver workload.  The added bonus is that they are very comfortable for long distance driving as well.  Perfect dual use seats.

  • Full Crew Chief now for Chris & #55 DSR Gen 1 Stohr

By about this same time, I was the ‘Crew Chief in Training’ for Vaughan’s wife Merritt, as she tackled her first few years on the track.  Vaughan was the race engineer, and it was here that I learned the majority of my race craft.  Again, something that I have to continue to thank him for.

I had progressed nicely from newbie to experienced hand, to about as far as I could get without bumping the current crew chief off his spot.

As it turned out, Chris Marsh had upgraded from a caged 924 racer to a D-Sport Racer and needed a crew chief, as his existing 924 crew chief was bowing out.

Now this is a very different beast.  A Japanese 1 liter, 4 cylinder 16 valve engine that revs all the way up to 12,000 or 13,000 RPM before redline.  It’s still got the bike 6 speed wet clutch trans, but it’s built around a tube chassis that could almost be an open wheeler, but has carbon fiber or fiber glass body work which provides the down force.  Yup, this was quite a different beast.

Crewing for Chris we’ve raced a bunch over at Waterford, and a few times down at the Mid-Ohio race track.  I knew that I wanted to do DE’s at other tracks beside our home track of Waterford.

  • AC & cruise control fixed for summer (distance driving is now enjoyable)

If you are going to do DE’s at tracks you have to drive a few hours to get to, during the racing season, which is summer, you are going to want 3 things on your car:

  1. Air conditioning
  2. Cruise control
  3. A good stereo with a wide selection of music

So these had to be made functional in the Porsche, as this was the car that I was going to be driving to these far away DE’s.

  • Data Logger & Video

Part of improving the driver’s skills is to be able to set a baseline, and see where you excel, and where you fall short and work on the parts where you fall short.  Seeing what you did on the track (the video) and measuring what you did on track (the data logger).  Between the two, you have a nearly perfect record of what and how you did when on the track, can compare laps and lap times, sectors and sector times, and make notes on what you need to do next time to improve.

  • Now track rubber!  DOT-Rs for grip

With greater driving skills comes the competitive drive; the will and desire to go faster yet.  The weakest link the system from track to car are the tires.  Additional grip from the tires directly translates into a larger performance envelope that the car can deliver in both braking and cornering.  With the DOT-R tires, I have seen decels (braking) at 1G peak recorded, and I’ve seen 1G lateral being recorded, although not both at the same time, talk about exceeding your friction circle!  Now the challenge for the driver is to consistently hit those marks.  Yeah, it ends up being a lot like golf, just a lot more exciting.

  • 2013 – Tire trailer – Off to the DEs! (distance tracks)

With the hatch back design of the 944, when you flop the back seats down, you do have a significant cargo space.  Well, significant in comparison the to rest of the car.  It’s a pretty small car.  I have figured out exactly what I need to load where and in which order to get everything I needed to the track, including 4 wheels.  The bad part is that there is really no room for anything more, and once at the track there’s nothing to store it in, so it’s laying all over the ground.  If you do over night trips to far away tracks, well, then, you’ll need camping gear, food, drinks and beer, and  a cooler.  There was just no way to pack all that into the back of the hatch back.  No room.

Others that I’ve seen at the race tracks have solved this problem with a small tire trailer. just large enough to carry 4 tires strapped flat down on the tire bed.  I stepped this up one level, in that I had a tire rack constructed out of 2 pieces of plate aluminum bolted to the trailer rails, with a crossbar running though the center holes of the wheels.  This uses ½ of the trailer’s bed space, and this allowed me to strap down a large, waterproof tool box on the back ½ of the trailer’s bed.  I have to thank my driver for the aluminum plates and other tire rack materials, as I couldn’t have done this part without his help.

The Porsche manual for the 944 said that it has a cargo weight of 1,000 LBS, and a tongue weight of 100 LBS.  Although I’ve never weighed the trailer, I can easily lift the tongue, so it must be less than 100 LBS, and adding up all trailer cargo, I know I’m well below 1000 LBS, so all is well.

The car pulls the trailer almost like it’s not there.  The trailer tracks straight and true, and on the expressway, the cruise control holds speed with the trailer hooked up, so everything is working great.  Best of all, I can get up in the morning, hook the trailer to the car, and be off to the track for a DE with 10 minutes.  Also very cool, it only takes about 15 minutes to load up the trailer, so lots of time is being saved, and a lot of convenience is gained.

  • The future

So what does the future hold?  Well, immediately, as in this winter during the off season, I need to maintain a few things that have cropped up during this season

  • Steering rack rebuild
  • Fix or bypass air bag module
  • Front sway bar bushings a bit soft
  • In the coming years
    • Trans rebuilt / refresh – rattling lag shaft, LSD & cooling loop are options

There is a nasty low speed, not while under load, rattle coming from the transmission.  I’ve been told by Rennlisters that it is the 5th gear lag shaft, and I’ve been reassured by friends who know these cars exceedingly well that it’s normal and not something to be concerned about, but I just can’t stand that rattle while I’m putting along through the neighborhood.  I want to cure it and make the transmission nice and quite again.

  • Paint and interior work
  • More DEs and adding to the track decals