• 1981 B7 turbo

Getting it running right and hoping it will last....

Updated: Oct 12, 2019

Recall the B7 spent months and months in Sacramento, where it was tuned so it could pass smog and then was tuned so that it was running great (according to the guys up there). Then on a spirited test-drive after it seemed to be all dialed-in, the diaphragm on the control pressure regulator blew. They rebuilt the regulator and got it running decently, but didn’t get it right. And they had to squeeze their tuning of it around other cars as they have a maintenance and repair shop to run, with regular customers, and only so much time for exotic projects like mine. Since I wanted to take the B7 to Monterey for the Legions of the Autobahn this past August, I ended up taking it running just ok.

Also recall that it ran ok but was frustrating on not only the trip home from Sacramento but even after some roadside fuel injection tweaking on the trip to Monterey and back. Yeah, after the tweaking it was running better than before. But it was not running close to right. By the time I got home, I was determined to find a shop that had the necessary resources, skill and time to getting it running right. Who, I wondered, might have a clue about the old, weird, unique Pierburg fuel injection that Alpina used?

The Pierburg system is mechanical fuel injection, not electronic. Electronic fuel injection is easy to tune, of course. But mechanical requires a little old-school know-how. And this injection is very unusual and finding parts – or even someone who has seen one before – can be very difficult. One of the things that makes it so weird is that it has flap for an airflow sensor, much like Bosch K-Jet injection, but only upside down.

The B7 motor with original Pierburg injection

I pondered whether there was a turbo-charged car that used a similar injection system and thought: early Porsche 930 turbo with Bosch K! I asked around about who might be expert on those who also had a dyno? I came up with nothing. Then I started looking just for someone familiar with turbos with a dyno. I asked a friend about a particular shop that had drawn my attention and he offered that they were also a repair and maintenance shop, like the one in Sacramento, and probably couldn’t dedicate the time. But he suggested Hoover at Turbo Hoses in Livermore. Hoover, he said, tuned the ex-David Hobbs e21 BMW 320i turbo racecar for BMW of SF. That, certainly, was impressive.

In the meantime, I complained – I mean explained – on FaceBook that I was having troubles with the fuel injection and another B7 owner offered this: his would go through this cycle where he’d get it running right, enjoy driving it, and then it would deteriorate – the control pressure regulator would start acting up again and require rebuilding. Rinse and repeat. His solution? He took out the Pierburg and installed a modern electronic injection, concluding: “It’s made a massive difference to how the car runs; as soon as I started it I could tell the difference. I’ve done about a thousand miles now and it’s been great I wish I had done it years ago.”

I wondered if I would have the same experience but decided to try to get it running right with the Pierburg first. Granted, almost every B7 owner I’ve talked with has told me they have problems with the fuel injection and at Legends in Monterey there was a green 6-series B7 that had an electronic fuel injection conversion that looked well thought-out. If I could get something that did not alter the body or Alpina-specific bits and didn’t look too out of place, that might be acceptable – if it really improved how the car ran.

B7 modified to EFI

But, wanting to see if he could get the Pierburg working while still open to a possible EFI conversion, I contacted Turbo Hoses. A couple of phone calls and a drive over to Livermore later and the car was in Hoover’s hands. I told him my history with the car and we discussed the goal to getting it running right with the Pierburg, but also the possibility of an EFI conversion that looked stock.

After Hoover had the car a few days he gave me a ring. First he checked everything about the ignition, making sure spark was good before moving to the injection. It wasn’t. The plugs were gapped incorrectly and inconsistently. And they were oily, meaning the engine may need to be rebuilt but for now we’d see if we can get the car running right as is. He changed the plugs, gapped them correctly and squared the ignition away.

With the ignition sorted, it was on to the fuel. With the car on the dyno, Hoover was able to get it running damn close to perfect. On full throttle and boost, for the last 1,500 of RPM, the pump doesn’t deliver enough fuel for maximum performance but otherwise he got it running strong. We decided that the instances of full throttle and boost are rare enough that it wasn’t worth addressing the fuel shortage – for now, at least. In the future I may be looking at a higher-flow fuel pump.

Getting it running right took time, of course. It was running very rich and was only putting out 180bhp. There are a couple adjustments on the fuel injection and as he changed one to improve running on boost, idle would deteriorate, requiring adjustment. Tweak one screw, run it on the dyno and tweak another. Rise and repeat. This took awhile but it got there, finally.

On the dyno....

The final power numbers were a little lower than when new from Alpina. The B7 originally, depending on the amount of boost, put out between 250 and 300bhp. According to the dyno chart, Hoover got it to put out around 210 at the rear wheels for about 240bhp at flywheel (Hoover said there was a 15% reduction). But he turned down the boost while dyno’ing the car. Turn up the boost and presumably the power will go up, too.

The dyno chart

Curious whether the air-fuel mixture was going to stay constant, I also had Hoover install an air-fuel ratio gauge. He found one that fit in the auxiliary Alpina gauge pod. Originally, the three-gauge pod had a boost gauge and two oil temp gauges – one for the motor and one for the differential. The air-fuel ratio meter replaced the latter temp gauge.

One of these gauges is not like the others...

So, how’s run? Pretty damn good; not perfect, but pretty damn good. I picked it up a few weeks ago, drove it home and have gone on a couple of short drives in it since. It starts easily. The idle is strong (unlike before) and the fuel injection smooth and constant throughout the warmup process. It runs strong when on boost, sounds like a jet plane but pulls like a train – lots of torque and power! Intoxicating and demanding you get it in boost! We’ll see if it lasts…..

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