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Which Would You Buy?
E34 BMW 525i Turbo vs. E34 BMW M5

November 14, 2012 by Matt

BMW E34 M5 Gray Grey M-Pars M-Parallel Wheels Rims

Pedigree versus performance. “Character” against raw power. The factory-sanctioned package or the DIY approach.

Let’s wade into a bit of an intramural debate here, but one whose principles hold true for many different car types and families. The subject is the ’89-’95 BMW 5-Series, known by its internal model code E34. The two flavors of the E34 pitted against each other are the range-topping ’89-’93 US-spec M5 and the entry-level ’91-’95 525i. The M5 is powered by a flame-spitting 311-hp 3.6l straight-6, whereas the 525 leaves the factory with a more sedate, miserly 189-hp 2.5l engine. The basic chassis is identical between the two cars, the M5’s driveline and suspension beefed up accordingly to handle the extra power, but nothing that can’t be bolted onto its lesser relative. An E34 M5 in a good state of tune will run you a bit north of $10K, and a clean 5-speed 525 is a comparative bargain at $2-3 grand.

So no contest, right? Does the M5 win the “desirability war” hands-down? Well, frankly, yes—unless you equip the 525’s engine with an equalizer: A turbocharger.

BMW E34 Turbo Engine Motor 525i M50 Jon Kensy Purple

It does take some effort, as no ready-made bolt-on kit exists to fit a turbo to BMW’s M50 engine in the E34 chassis. Other than the hurdle of having to DIY most of the project, it’s almost like the 525 was designed from the outset to accommodate forced induction. The M50 engine’s cylinder head, completely stock, flows well enough to support over 700 hp, and the bottom end is sufficiently stout to handle 400+ without internal mods. The ’91-’92 525’s ZF 5-speed transmission is bulletproof, as is the rest of the driveline, and the engine bay is more than spacious enough for the extra bits and bobs required. Total cost, not counting the initial purchase price? Easily over $5K to do it correctly, but still well below the “floor” asking price of an unmolested M5.

BMW E34 M5 Engine Motor S38 S38B36

Can the M5 match the speed of a properly turbo’d 525? In a word, no. When fitted to the M5, BMW’s S38 engine was nearing the end of its life, and its development potential is limited, not to say ridiculously expensive given the engine’s rarity and finicky nature. Just to rebuild the engine will cost very near the purchase price of the car, whereas a 525’s M50 engine can be found all day every day for $500 in a junkyard, a boon if your DIY turbo efforts accidentally grenade one.

So if not speed, what does the M5 offer above and beyond the 525? Character. Pedigree. Its big, rip-snorting naturally-aspirated inline-6 is essentially a mildly detuned race engine, and loves to be spun hard and wound out (making a lovely noise as it does so). Not only that, but the engine’s integration with the chassis from the factory is nothing short of perfect—BMW made sure every component from the steering to the shifter to the suspension and throttle response worked harmoniously together to create an impression of a total car more than the sum of its parts. Those enthusiasts who’ve driven an M5 say it’s an irreplaceable experience.

Which to choose, then? The project or the factory package? More power with less personality, or fewer ponies and more character? A truly tough decision.

Editor’s note: This post is part of an ongoing series wherein I stack up the pros and cons of two broadly similar cars from an ownership perspective. Read the other installments here:

Filed under: BMW, Which Would You Buy?

14 Comments

  1. The factory package, but then again, that’s nearly always the case with me. Others’ mileage may vary.

  2. Jack says:

    oh goodness, really poking the bear with this one sir. That said, I’ll take one of each please and thank you

    • Matt says:

      Heh

      I reserve the right to shake the hornet’s nest every now and then. :)

      Besides, it’s really the principle that I’m after… I tried to bookend the post with more general statements to underscore that.

  3. John D says:

    Man oh man. Tough choice. I love everything about a high output turbo charged engine…except working on it. Actually it’s not so much the ‘working on it’ that I mind, it’s the diagnosis that can drive me insane…though I may just be wounded from my FD experience with it’s 85 vacuum lines. At this point in my life I would probably take the one that is most reliable. They both sound like tons of fun and I’d like to think that I could appreciate the attributes of both. But if push come to shove, I’d lean toward the turbo-charged engine with MORE POWER (especially if it’s not going to be an ongoing project to own/operate).

  4. joobles says:

    hands down 525i turbo with suspension mods for anyone doing any form of motorsports……of course any one doing motorsports woud have said e30 or e36 > e34 in the first place.

  5. amir says:

    Definately the turbo 525. you couldnt be any more correct when you stated that the car seems as if its designed to accomodate forced induction. i have one and man that engine is sharp and bulletproof. looks like it has the potential to double its hp easily. i did have a question however regarding the transmission. you said that the 5 speed is bulletproof. well how about the 4 speed auto? i know that transmission is very durable and will handle alot of torque but im not sure if i should actually do it?

    • Matt says:

      The ZF 5-speed in the ’91-’92 525 is bulletproof, the earlier and later Getrag boxes, not so much—though they are strong. Not sure about the auto. I guess I’ve always been of the mindset that if you’re going to shell out several thousand to add a turbo to your 525, why not spend an extra $500 and do a 5-speed swap? It’s not difficult.

      • amir says:

        wow is a 5 speed swap really only 500 to do?

        • Matt says:

          You’d have to get a used clutch at that price, but if you’re diligent and scour local junkyards you could probably find everything you need for around that much. Or just find a dead, clapped-out 525 5-speed for $500 and swap everything over. They’re not exactly rare.

  6. Dan says:

    Turbo! Turbo! Turbo! Turbo! Turbo! Turbo! Turbo! and, if you really want to go nuts, make it a Miller Cycle w/custom camshaft. I did that on a fairly new Audi 200 I had way back when… just be ready to hold on for dear life.

  7. ghettotube says:

    Under the guidance of chief designer Claus Luthe, BMW based much of the design on the E32 7 Series. Following Spada’s departure from BMW and styling approval in 1983, J Mays finalized the design for production in mid-1985. In December 1987, the E34 sedan was unveiled to global press.

  8. Les says:

    Question. The 525i in the photo listed above. Where did they buy the turbo kit? (piping, intercooler, turbo, exhaust manifold, waste gate, etc) What stage turbo is used? how many bars?

    Thanks.

    • Matt says:

      Hi Les! That’s Jon Kensy’s E34. Not sure the specs on everything but you can look it up. Almost all of it is custom-made. I do know his cylinder is bone-stock non-VANOS M50, and the bottom end is built and 2.8l. Made 685 rwhp on 93 octane and 50/50 water/methanol injection.

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