Opinions on a M30 B35 Engine Swap & 5-Speed Conversion

T

Tate

Active Member
Messages
48
Reaction score
17
Location
Seattle, Wa
Assuming the work is all done properly - Would appreciate thoughts & opinions on E9s with M30 B35 Engines & 5-Speed Conversions.

I asked the same question, on a For Sale thread, regarding a current listing on BaT. My interests are in general, & not specific to that vehicle.
 
The easiest and least expensive way to upgrade to FI (fuel injection)

The 5 speed is a great way to keep 4 speed performance with a loafing on the freeway gear
 
I just did the conversion last year and do not regret it. More power and it opens the door for realistic highway cruising with the extra gear.

Never seems to hurt value either, at least for non concourse cars.
 
It really depends on the full combination of engine, trans, differential, and your desired driving experience.

Years ago a small group of us on RoadFly were discussing this, so I made up the Excel table below, and we drove our cars to see how accurate it was. The cars were:
  • 1988 635 with an M30B35 Motronic engine, a Getrag 265/6, and 3.45 diff (Scott's 88)
  • 1980 635 Euro with M90 L-Jet engine, 265/6 trans and 3.07 diff (Scott's Euro)
  • 1980 635 Euro with M90 L-Jet engine, 262 CR trans and 3.07 diff. (John Calvin's Alpina Euro)

SpeedsInGears.jpg


These tests were a bit hard to do because it is hard to drive, and watch the tach and the speedo, and maintain a constant engine speed all at the same time. Tire sizes also cause some errors. However, the results show the significantly different character of these powertrain combinations.

All three engines make about the same power, the M90's are 218, and the M30B35 is 208, IIRC. The M90 torque is broader and higher than the M30B35, and, being Motronic, is buttery smooth. The 3.07 diff really brings out the character of the 265 overdrive, but I suspect that would be lost in an M3B35 car, because it doesn't have the torque bandwidth to pull those high ratios.

I was not able to drive John's car, but he reported that one data point. I would imagine with its higher torque engine and lower gear ratios, that car would be a blast to drive in the twisties, but a bit of a slog on the highway. The 265/5 3.07 combo on the other Euro makes for a good mix of slower speed acceleration and high speed cruising.
 
Last edited:
I've driven a couple of cars with this swap, and the simple answer to your question is this combination is straightforward and provides really good low end torque, which you will feel and use every time you drive the car. And because BMW made so many of these engines, it has the added benefit of being serviceable by any BMW mechanic.
 
This is what I have found in my travels with several e9 coupes: All US 2.8L coupes had a 3.45 diff and the 3.0 had a 3.64. With a 3.64 the 265/6 OD trans is highly recommended as it drops rpms by 750 or so but keeps things around 3,000 rpm at freeway speeds allowing the torque to be utilized easily. The 3.45 diff also benefits from the 265/6 but as it is 5% taller the difference is a little less. In my 2800 I did not install an OD trans as I wanted to keep the original ZF four speed and I have gotten used to it this way. If I had not valued originality I would have gone with the 265/6. Earlier this year I drove a CSL roughly 450 miles to NorCal and since the CSi motor combined with the 3.25 diff I did not miss the OD at all. 200hp vs 170 in a carbed coupe makes a big difference! I can not even imagine installing a 3.07 unless there was 265/5 CR box.

My last coupe had the b35 with a cam, Motronic 1.3 and stock headers and the torque as stated was really nice to have. I could climb the Cuesta Grade on the 101 leaving San Luis Obispo in OD and still be able to accelerate. So why didn’t I install a b35 in Chamonix coupe? As the last coupe I will ever own I wanted to go back to what the driving experience was back when it was new. Oh, and I for sure don’t drive as fast as I did when I was younger but I can still enjoy spirited drives. And most of you know I have that desire for originality.

If I had a chance to start over with just one coupe it would be an injected CSL with the stock motor, trans and 3.25 diff. Every iteration will provide an enjoyable driving experience. If you want the torque go with the b35 or m90 but I just don’t see the need for an s38 or s54 motor.
 
@ScottAndrews Whatever happened to John Calvin? He used to travel to Monterey from Utah with one of his e24 coupes and the last I had heard he had sold all but one off and that one had some racing provenance. He was such a gentle spirit and kind man.
 
in the FAQ, @HB Chris has a thread on speedo / diff ratios. in post 2 of that thread i have the different speeds / rpm for the 3.64 / 3.45 + 3.25
HB Chris

Thread 'Speedometer and Differential Ratios'

The e9 coupes came with three differential ratios and could be found both open or unlocked and locked or LSD. The speedometers were matched to the car based on which differential was fitted.

Differentials

The differential ratio is expressed as a fraction and is stamped on the right lower side of the differential on a flat boss. The presence of a stamped or painted S indicates locked or LSD.

3.25 = 39/12
3.45 = 38/11
3.64 = 40/11

These differentials were typically found on these models:

3.25 Open - CSi
3.25 LSD 25% locking - CSi and CSil
3.45 Open - Euro 3.0CS/CSA
3.45 LSD 25%...
  • Like
 
HB Chris said:
@ScottAndrews Whatever happened to John Calvin? He used to travel to Monterey from Utah with one of his e24 coupes and the last I had heard he had sold all but one off and that one had some racing provenance. He was such a gentle spirit and kind man.
Click to expand...
Not sure. His Henna Alpina 635 was beautiful!. Last time I saw him was about 15 years ago. We had a shark fest in Las Vegas. He drove down from SLC.
 
Tate said:
Assuming the work is all done properly - Would appreciate thoughts & opinions on E9s with M30 B35 Engines & 5-Speed Conversions.

I asked the same question, on a For Sale thread, regarding a current listing on BaT. My interests are in general, & not specific to that vehicle.
Click to expand...
The folks who uphold originality above all else might say otherwise, but I test-drove coupes before buying mine that were stock motor and 4 speed and I am happy for the extra horses and ability to cruise. That being said, if I had found the right completely stock, 'perfect' car and everything ran well, I don't know that i'd bother to change it. But having the 3.5 and 5 spd, and it being setup with the webers... It's visceral in a way that you should experience if you can. I love the idea of efficiency inherent in FI, but for me, it's the carbs and big displacement that wins the day. It's nice to be rolling along in 5th, at 70mph and only just begin to tickle 3000 rpm. Its better to drop down to 4th, step on it and hear the engine literally roar to life while you push past 80, 85...

And the nice thing about the 3.5 upgrade is that it doesn't destroy the value of the car like other 'non matching' mods might. Same with the 5 spd.
 
rsporsche said:
in the FAQ, @HB Chris has a thread on speedo / diff ratios. in post 2 of that thread i have the different speeds / rpm for the 3.64 / 3.45 + 3.25
HB Chris

Thread 'Speedometer and Differential Ratios'

The e9 coupes came with three differential ratios and could be found both open or unlocked and locked or LSD. The speedometers were matched to the car based on which differential was fitted.

Differentials

The differential ratio is expressed as a fraction and is stamped on the right lower side of the differential on a flat boss. The presence of a stamped or painted S indicates locked or LSD.

3.25 = 39/12
3.45 = 38/11
3.64 = 40/11

These differentials were typically found on these models:

3.25 Open - CSi
3.25 LSD 25% locking - CSi and CSil
3.45 Open - Euro 3.0CS/CSA
3.45 LSD 25%...
  • Like
Click to expand...
I mis-spoke. The two 635s I discuss in my post above had 265/6 OD trans. With the 3.07 diff the Euro is a blast to drive
 
My coupe has a M90/B34 from a Euro 635 paired with a Getrag 265/6 and a 3.64;1 diff. It a great combo. I only use 5th gear on the highway, otherwise its a really a 4sp with an OD, as others have said. My engine is a torque monster, pulls great from down low in any gear. Very happy with this set up for what its worth.
 
Last edited:
I can offer a different but not necessarily contradictory perspective - I have a Euro CSi, so that has a bit more power (than the CS) but also the 3.25 final drive. For the road conditions here, I don't find myself looking for a fifth gear - largely because the distances to be covered are relatively small and with our road conditions, it's not often you can sustain 70 (ish) mph cruising for any distance, let alone open the thing up! If there was the opportunity to cover larger distances at greater speeds, then a 5 speed might be worth a look, i.e. probably nice to have but not essential
 
You must log in or register to reply here.
Back
Top