Need help with engine choices

[peerless]

Ok, help me out here please. New to the M50/S50 engines. I have a customer who is wanting to possible purchase a used S50. But we also have a complete M52, M50 iron short block, S50/52 M3 cams, and a 3.0L crank?

Sorry if this seems kinda newbish, but if you can help set me straight with the best combo for the money.

Here is a quick quote from the customer,

m52 w/m3 cams would only be a 2.8, so I don't know how much difference in displcaement/power it would be between a 3.0 and a 2.8. Do you know if m50 and s50 rods are the same length? I'm going to need to find out how much bigger we could bore an m50 (iron) block. It would mean custom pistons, but with a 86MM crank(s50/3.0) I am curious how large a piston we could use in the iron block to increase displacement.

Can you help me answer some questions? Thanks,

[PiercedE30]

Ok, with an M50; take the s50 crank (85.8mm stroke), use the s50 (or m50 nonvanos) rods (135mm), and you get a 2.9L with a CR of like 12.5:1 or about there. If you use a .098" thick head gasket (MLS) then you will lower the CR to about 11.4:1 compression ratio.
That, and a set of M3 cams (assuming the use of a Vanos M50), some injectors, and PROPER ecu tuning, then you can easily make 250 whp.
Hope that helps

[Brew]

Best bet is to go with a complete engine. Rebuilds can get mighty expensive with motorsport parts.

[peerless]

Ok, with an M50; take the s50 crank (85.8mm stroke), use the s50 (or m50 nonvanos) rods (135mm), and you get a 2.9L with a CR of like 12.5:1 or about there. If you use a .098" thick head gasket (MLS) then you will lower the CR to about 11.4:1 compression ratio.
That, and a set of M3 cams (assuming the use of a Vanos M50), some injectors, and PROPER ecu tuning, then you can easily make 250 whp.
Hope that helps

Thank you for taking a little time out to help. Regarding pistons, how big can I go on a overbore on the M50? Custom pistons would be purchased for this project.

Also regarding the ECU, what would be the best ecu for this application. We do not want to go standalone, so we where thinking maybe the M3 Bosch 3.3.1 OBD1 ECU?

Thanks again,

[FredK]

Don't bore. Just buy a good condition S50 block. that way you can use all S50US running gear (crank, rods, pistons).

A good overbore to 86.00 mm will cost around $250 - 300, which is probably more than the same cost of a good S50 block.

Just use the M3/325i 413 or 506 Bosch DME, and use S50 software. Or, get a custom burned chip.

[peerless]

Ok, What is the essential difference between the M50 block and the S50 block?

I already have access to a good M50 block.

Also for the sake of this thread, cost is not a major issue. Its about building a solid and powerful street/track motor. We want the best power/cost ratio, but not at the expense of our goals.

Thanks again for the help and comments.

Robert,

[FredK]

There should be no difference between the castings. HOWEVER, I've heard from Stu Mc that only the non Vanos blocks can be bored, but this is secondhand information.

Maybe the water jackets are cast thinner on M50TUs or something. I have no idea.

There was this guy on Bimmerforums who was going to lay that myth to rest by boring a M50B25 TU to 86mm, but he ended up scuttling his project.

Stu Mc is running a 3.0L that was made from overboring a non Vanos block.

The S52 is becoming a dime a dozen. I'd just get a complete S52, install OBD-I stuff on it (DME, wiring harness, temp sender, CPS, vanos extension cable, etc) and call it a day. The stock engine is very durable and reliable, and has many known power-adders.

[PiercedE30]

For ecu choices, Turner Motor Sports has a ecu burn specifically for this setup, only problem is they are one of the few that has one ready made and it will run you, just for the chip, about 800 bucks. I would contact Mark D'Sylvia (i believe that is his name) about this set up and talk with him about getting him to burn a chip for you.
Either that or there is a company (can't remember who it is) based out of CA that has a plug-n-play TEC3 system for about 2500. It has had the plug on the ecu modified to accept a engine wiring harness from an e36. I believe it comes with a base map on it as well.
That 2500 also includes tuning I believe.