m102 vs. M30

[Velocewest]

OK, I drink my TCD kool-aid daily and I know an M30 is a completely satisfactory base for a turbo project. But if I can get a good deal, is there any real reason NOT to use the M102? And when I say good, I really mean great, and when I say M102, I really mean a complete 745i with some hi-po goodies.

[T_C_D]

OK, I drink my TCD kool-aid daily and I know an M30 is a completely satisfactory base for a turbo project. But if I can get a good deal, is there any real reason NOT to use the M102? And when I say good, I really mean great, and when I say M102, I really mean a complete 745i with some hi-po goodies.

A m30b35 is the best choice. A m30b34 is the second best choice. A m106 is the third and the m102 is the worst! I would rather have a used motor that has never seen boost than a motor that has seen boost it's entire life.

Todd

[Duke]

A m106 is the third and the m102 is the worst!

???????Why would a M106 be third? The M30B35 does not have pistons designed for turbo (thicker crowns and piston rings spaced farther apart)...............nor does it have the oil jets for piston cooling. The M106 has this, designed by BMW for turbo. The CR for a M106 (8:1) is better too.

Do you know something that I don't? Educate me on you sources of info and theory.

[T_C_D]

???????Why would a M106 be third? The M30B35 does not have pistons designed for turbo (thicker crowns and piston rings spaced farther apart)...............nor does it have the oil jets for piston cooling. The M106 has this, designed by BMW for turbo. The CR for a M106 (8:1) is better too.

Do you know something that I don't? Educate me on you sources of info and theory.

I assumd we were talking about stock used motors. Clearly the b35 is the superior motor. No argument there. Second the m102 has none of the items you mentioned to increase longevity. It's just a 3.2L with 7:1 or 7.5:1 depending on the year. Both are lethargic slugs off boost.

Now as for the m106 vs the m30b34. Given two motors with the same mileage. I'll take the m30b34 slap a headgasket and studs on it and boost to my hearts content. No reason to use a motor that has seen boost it's entire life. And believe me, an automatic 745i lives alot of time under boost just to move out of it's own way.

Todd


[Edit by TCD on [TIME]1107900093[/TIME]]

[Duke]

I assumd we were talking about stock used motors.

Now as for the m106 vs the m30b34. Given two motors with the same mileage. I'll take the m30b34 slap a headgasket and studs on it and boost to my hearts content. No reason to use a motor that has seen boost it's entire life. And believe me, an automatic 745i lives alot of time under boost just to move out of it's own way.

Originally posted by TCD

Lets talk NEW or rebuilt engine, same group. I would stay with my decision to use a M106 block and pistons. Think NEW, not junkyard beater.

[Jeremy]

You're changing the question, Duke. The original question concerned used motors. As for what you're saying regarding new or rebuilt, didn't you have to add those piston oil sprayers to your M106 because they weren't there from the factory? If we're talking a built motor, then JE forged pistons with wider ring spacing and thicker landings would be the way to go IMO, better and stronger than anything stock, even BMW stock, and the m30b35 simply flows better in the head, so it's the logical choice since you'll get more power per psi of boost. Compression ratio for the pistons would depend on the desired boost level. 9:1 is good for 15psi or more when intercooled, which is right about where I'd want mine to be if I were building a motor from scratch. Your motor is built for different purposes though, hence your different approach to the problem.

Just tossing in my .02

Jeremy

[Edit by Jeremy on [TIME]1107898455[/TIME]]


[Edit by Jeremy on [TIME]1107898514[/TIME]]

[T_C_D]

Originally posted by TCD"]Lets talk NEW or rebuilt engine, same group. I would stay with my decision to use a M106 block and pistons. Think NEW, not junkyard beater.

m30b34 block
s38b38 crank
Forged 8:1 pistons
m30b35 head

Todd



[Edit by TCD on [TIME]1107900063[/TIME]]

[DMNaskale]

For a used engine, it is hard to argue with Todd, he has proven the plain old B34 or B35 is up to the task. If you are talking about building up a motor, the M106 is block is first choice because of the oil jets and the oil return fitting, but a solid B34 or B35 block is fine too. Forged pistons are very nice for the strength, and the weight is a huge factor that doesn't get enough attention. You save around 5 ounces per piston in reciprocating mass using forged pistons over stock 745i pistons, and you can name your CR. For the head, the B35 is the obvious choice with custom pistons. For my car I am going to run my original tight sub 100,000 mile B34 engine to get my feet wet and get my system sorted out, and I have a M106 block and a B35 head for the build up to replace my original engine. I am planning on running forged pistons at 8.5:1. I think this is a very good all around setup, the stock B34 runs nice with just 8:1 and no boost.

[Velocewest]

Well, I asked...

I think I might go with the 745i engine anyway, because, and Daryl puts it, "I'm getting my feet wet". I'll be out around $800 when the car lands in my driveway, throw in another $500 to $600 to complete the swap. Under $1500 to get 300 hp is pretty reasonable. OK, I know the Roadflea turbo board would flame me and tell me I could scavenge junkyard parts and do it all for $500, but I actually do have a life outside my engine compartment...

[Craig -535i- Seattle]

Clearly the b35 is the superior motor.

[T_C_D]

Well, I asked...

I think I might go with the 745i engine anyway, because, and Daryl puts it, "I'm getting my feet wet". I'll be out around $800 when the car lands in my driveway, throw in another $500 to $600 to complete the swap. Under $1500 to get 300 hp is pretty reasonable. OK, I know the Roadflea turbo board would flame me and tell me I could scavenge junkyard parts and do it all for $500, but I actually do have a life outside my engine compartment...

That will work well for you especially since you have an e12 and the 745i stuff just drops right in. What year is the car?
Todd

[Velocewest]

Nineteenseventyfive!

[T_C_D]

Nineteenseventyfive!

The 745i not the e12.

[Duke]

You're changing the question, Duke. The original question concerned used motors.

Not one word in the original thread indicated anything about a used motor.

OK, I drink my TCD kool-aid daily and I know an M30 is a completely satisfactory base for a turbo project. But if I can get a good deal, is there any real reason NOT to use the M102?

"Base" engine what was being referred too.

didn't you have to add those piston oil sprayers to your M106 because they weren't there from the factory?

Yes, only because it was a BMW test engine. All m106 production engines have them.



[Edit by Duke M535Ti on [TIME]1107928864[/TIME]]

[Velocewest]

The 745i not the e12.

I don't actually know... Sounds dumb, but this offer just came up and I haven't had all my questions answered yet.

What month/year did the M106 start?

And I didn't really specify rebuilt, new or used, but in my case the 745i engine is used and the M30 would be freshened -- tanked, new rings and bearings, new guides and seals, 3 angle, etc. Basically a nickel rebuild, and it's a 3.3 block with an '85 head. The 3.3 is being finished either way, if I don't turbo it I'll put it in my e9.

[Velocewest]

Engine is an '86 M106. Duke, isn't your bottom end M106?

[Duke]

Duke, isn't your bottom end M106?

Yes.