Stroking an s50 to 3.2L

[erik325i]

What would be needed in order to stroke an s50 to 3.2L?

I have access to an s52 crank. Besides the crank, would I need anything else like pistons/rods?

How much more power do you think I would see after stroking the motor? I also plan to run schrick cams, 3.5" HFM, 24lb injectors, turner chip...

All that will go into my '89 m3.

-Erik

[FredK]

I believe in the absence of headwork an S52 with Schricks is at around 250whp.

You'll need S52 pistons. The s52 crank is 3.8mm longer in throw so the pistons have to compensate somehow. So, the piston geometry is different. However, the S52 and S50 both have the same length rods at 135mm.

[Vedubin01]

What would be needed in order to stroke an s50 to 3.2L?

I have access to an s52 crank. Besides the crank, would I need anything else like pistons/rods?

How much more power do you think I would see after stroking the motor? I also plan to run schrick cams, 3.5" HFM, 24lb injectors, turner chip...

All that will go into my '89 m3.

-Erik

I do not have your answers but I am in need of a S50 crank. If you want to sell let me know. Id even take the rods and pistons.

But I think you need the crank rods and pistons from the S52 to stroke it up. You would also have to bore it out a bit. But that is my guess and do not hold me to that!

[FredK]

Yes, you need to bore slightly to 86.4mm.

[Vedubin01]

I thought that but are the rods the same?

[FredK]

Yes the rods are the same length, but the S52 rods are supposedly lighter, according to Addissimo.

[Stu]

You can put the 3.2 crank in a 3.0 block, use the 135 rods, 3.0 86mm pistons--machine them to get ~11:1 cr.
My brothers M50 was setup this way, and made exactly 250whp with stock cams.
Or like Fred said, you can bore and use 3.2 pistons to have stock cr

[erik325i]

I do not have your answers but I am in need of a S50 crank.

Sorry, but the reason I am able to get the s52 crank is because my friend wants to trade it to me for my s50 crank...

You can put the 3.2 crank in a 3.0 block, use the 135 rods, 3.0 86mm pistons--machine them to get ~11:1 cr.
My brothers M50 was setup this way, and made exactly 250whp with stock cams.
Or like Fred said, you can bore and use 3.2 pistons to have stock cr

What is the stock compression ratio? Which setup would create more power? Why did your friend decide to do this instead of boring and using s52 pistons?

-Erik

[Stu]

Sorry, but the reason I am able to get the s52 crank is because my friend wants to trade it to me for my s50 crank...


What is the stock compression ratio? Which setup would create more power? Why did your friend decide to do this instead of boring and using s52 pistons?

-Erik

Stock C/R on all US M/S50's is 10.5:1, with the exception of the Non-VANOS 2.5 which is 10:1.

Both Alex and I had out motors built (Thanks Dad!) from '91 525i blocks, and 3.0 M3 pistons which were at our availability. Alex sprung for the 3.2 crank, so decided to go with a .040 overbore on the 525 block to fit the 3.0 pistons and 3.2 crank. As you can picture, the 3.0 pistons need to be machined down due to the stroke difference, but 86x89.6 was achieved with high-compression. It's a pretty straight-forward recipe for a lot of torque and HP--though not quite the CC's of a standard 3.2 bottomend (I believe they use 86.4 on the pistons, marginal difference).

The only 24v E30's I've driven have been mine and his, my dads 2.9, and a friends 2.5. I can tell you that the 3.2 crank makes a MASSIVE difference in the 2000-4000 range. While my 86x86 3.0 pulls well and makes plenty of torque, it doesn't really start to haul ass until 4000revs.

Any nicely setup M/S50 will pull well at high revs, but that is only used when you're racing somebody, or are on-track. If you plan to use your car for a lot of around-town driving, a 3.2 crank is a really good way to go. (PM Jason89i for more insight)

I can't say whether an 86.4x89.6 will make more power than a high c/r 86x89.6, but either setup with the right bolt-ons will make more power/tq than our brakes need!