# 1991 525i ProCharger or Turbo?



## DLS_91_525i (May 15, 2011)

So I got my hands on a M50B25 out of a 1992 525i with just a little over 160,000 on it.
I'm going to get it bored to clean up the cylinders, new piston rings, rod bearings, crank bearings, etc. All new gaskets, new timing chains. Plus all the little nick-nacks to get everything back up to specs.
Getting head studs and thicker gaskets as well.

The BIG question is. Should I go with a ProCharger or a Turbo on the motor?

So what do you guys think and why?

Feel free to ask any questions if you need any more Info about the build.

DARRiN


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## ICS (Jun 12, 2011)

DLS_91_525i said:


> So I got my hands on a M50B25 out of a 1992 525i with just a little over 160,000 on it.
> I'm going to get it bored to clean up the cylinders, new piston rings, rod bearings, crank bearings, etc. All new gaskets, new timing chains. Plus all the little nick-nacks to get everything back up to specs.
> Getting head studs and thicker gaskets as well.
> 
> ...


Please keep in mind the early 92 M50B25 does NOT have knock sensors. Get yourself a 3281 -5281 engine 1996-1999 Years, convert it over to OBD 1 93-85 Harness (325 or M3) ECU completed set up.

I would def do a turbo kit hands down.

Hope this helps, best of luck.


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## DLS_91_525i (May 15, 2011)

ICS said:


> Please keep in mind the early 92 M50B25 does NOT have knock sensors. Get yourself a 3281 -5281 engine 1996-1999 Years, convert it over to OBD 1 93-85 Harness (325 or M3) ECU completed set up.
> 
> I would def do a turbo kit hands down.
> 
> Hope this helps, best of luck.


Why is it a problem that it does not have a Knock sensor?

and why would you choose a turbo?

Thanks


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## GG///M3 (May 14, 2011)

Turbo you will have more choices down the line. I would suggest getting in contact with Trm as they have tuned ur setup with no knock sensors in the past I believe. What kind of power are you looking to make. Going with a super charger is cheaper, but I wouldn't go that route being that it is a e34 and it will feel under powered for the weight of the car.


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## snailinduced (Sep 30, 2011)

The semantics of knock, pre-ignition, or detonation can be argued among automotive engineers, however it is basically an uncontrolled ignition of the air fuel mixture. The uncontrolled part means that it doesn***8217;t occur at the desired time in the combustion cycle. Normally the timing of the ignition is designed to maximize pressure in the cylinder so that it will push the piston down with the most force. Knock can cause high cylinder pressures at times when it actually counteracts the force and also cause shockwaves within the cylinder. It is the shockwave that emits the characteristic "tinkling" sound you often hear when the engine is knocking. In reality by the time you hear knock the chances are that the engine has been knocking for a while. Car manufacturers are continuously researching better ways of detecting knock and in the future we may see more direct methods such as pressure sensors and ionized current measuring however the majority of cars still use an indirect method of detecting knock by listening to the ringing sound of the cylinder using a piezoelectric knock sensor. 

Turbo or supercharger? Well, they are two different beasts. Turbochargers generally allow for much higher bhp numbers as boost can be cranked up depending on your engine setup. Chargers are more reliable but generally have lower hp numbers. What are you looking for?


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## DLS_91_525i (May 15, 2011)

snailinduced said:


> The semantics of knock, pre-ignition, or detonation can be argued among automotive engineers, however it is basically an uncontrolled ignition of the air fuel mixture. The uncontrolled part means that it doesn't occur at the desired time in the combustion cycle. Normally the timing of the ignition is designed to maximize pressure in the cylinder so that it will push the piston down with the most force. Knock can cause high cylinder pressures at times when it actually counteracts the force and also cause shockwaves within the cylinder. It is the shockwave that emits the characteristic "tinkling" sound you often hear when the engine is knocking. In reality by the time you hear knock the chances are that the engine has been knocking for a while. Car manufacturers are continuously researching better ways of detecting knock and in the future we may see more direct methods such as pressure sensors and ionized current measuring however the majority of cars still use an indirect method of detecting knock by listening to the ringing sound of the cylinder using a piezoelectric knock sensor.
> 
> Turbo or supercharger? Well, they are two different beasts. Turbochargers generally allow for much higher bhp numbers as boost can be cranked up depending on your engine setup. Chargers are more reliable but generally have lower hp numbers. What are you looking for?


I'm wanting horsepower gain, but I would also like the uniqueness of a supercharger on a E34 and I love that signature whine of a supercharger!  oh! and Reliability is key!


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## snailinduced (Sep 30, 2011)

Then go supercharger.


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## DLS_91_525i (May 15, 2011)

snailinduced said:


> Then go supercharger.


I so want to, but I've never seen a E34 with a supercharger.
Do they even make them??? :dunno:


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## Gravik (Nov 14, 2010)

DLS_91_525i said:


> I so want to, but I've never seen a E34 with a supercharger.
> Do they even make them??? :dunno:


Someone on bimmerforums has a supercharged E34 535i and if I'm not mistaken a couple guys SC'ed their 540i. Haven't seen a S/C'ed or turbo'ed 525i yet though :/

Supercharger whine sounds great  But so does the sound of the turbo spool and BOV.


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## DLS_91_525i (May 15, 2011)

Gravik said:


> Someone on bimmerforums has a supercharged E34 535i and if I'm not mistaken a couple guys SC'ed their 540i. Haven't seen a S/C'ed or turbo'ed 525i yet though :/
> 
> Supercharger whine sounds great  But so does the sound of the turbo spool and BOV.


Agreed! It's such a hard choice! 

DARRiN

Sent from Samsung Gem using Bimmer App


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## ghart (Oct 9, 2011)

It would be a novelty if you could supercharg it as well as turbo charged it. I know Lancia tried that.


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## WDRAcing (Apr 22, 2012)

Just a couple things to add. Preignition is what takes place before the spark event, detonation takes place after the spark event. Preignition almost always ends with a part of the rotating assembly failing, usually a hole in the top of the piston. Preignition is mostly caused by the wrong heat range spark plug and or hot spots that form in the combustion chamber. Using the correct heat range plug and making sure the engine doesn't run hot will keep preignition at bay.

Detonation is what happens when you reach the octane limits of your fuel. The higher the octane of the fuel, the more boost you can run for any given compression.

The "knock" sound you hear is actually the rotating assembly absorbing the shock load of the detonation occurring. A motor can run for years with light knock. However, you don't want ANY knock if you're going the FI route.

The best way to avoid detonation is with alcohol/water injection.

Turbo's own superchargers in almost every category. You'll make more useable power with a turbocharger since they'll produce full boost far earlier in the rpm band then a centrifugal supercharger will. The centrifugal type supercharger, imho, represents the ultimate form of lag. Full boost comes as you max out your desired rpm.

Lets use 8 psi as a max boost #. The turbo will be at full song by 3000 rpm give or take, the supercharger will likely only be at 3-4 psi and slowly increasing until it peaks at 8 psi as you're about to shift.

Another benefit of the turbo is your ability to control the amount of boost with a simple controller. No swapping pulleys around and messing with belt tension. Just turn a knob. Very handy because you can run 2 different levels of boost real easily. Use a low boost setting for daily driving and use a high boost setting while you're at the track, or feel the need for a little irresponsible hwy driving.

Here's a video that highlights how beautiful a turbo sounds.

WD


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