M106 comparison question

TamperedWith · Post by **TamperedWith** » Dec 06, 2015 1:13 AM

Hey fellas! Now I've done a little research and what seems to be the most popular setup is b34 block with b35 head, however I have the opportunity to buy a complete m106 from a 745 for less than what it would cost me to get a b34 (I'm in Hawaii btw). If I can get the m106 is it worth it to buy that instead with intentions of using a b35 head with custom Pistons to dial in the c/r? I haven't read many threads with people using the b35 head on the m106 block but I imagine that would be the most ideal setup if cost is of no issue (yes I understand the b34 block can handle it). Any input would be appreciated!

P.s. The car is an 83 533i so I'll probably be using the lighter flywheel and the hotter cam from the b32

charofire · Post by **charofire** » Dec 06, 2015 12:52 PM

Get the least abused m30 motor you can. That will be your best bet unless you plan to strip it down and rebuild. A b34 block with a b35 head gives you around ~7.45 compression, which means your car will feel slow until it spools. B35 head on a later 745i block will still have yield less than 8:1, so not ideal.

Cactus · Post by **Cactus** » Dec 06, 2015 10:25 PM

What's your power goal? Is 93 octane available or are you stuck with 91? What sort of Engine management are you going to use? You can run a positive pressure 12:1 compression engine if you have a sufficient octane rating and the ability to put the timing where you want it.

TamperedWith · Post by **TamperedWith** » Dec 07, 2015 2:18 AM

Power goal around 500 whp, 92 octane fuel probably megasquirt management and now I have 3 engines available to me to mix and match how I please the m106, the b34 and the b35. Custom Pistons will be used to bring the c/r to around 8:5:1 ideally

charofire · Post by **charofire** » Dec 07, 2015 2:28 AM

User M106 used a 745i engine with custom cam, s38 ITBs, and a big turbo and standalone to get some crazy rwhp #'s. You can find his build here:
http://www.mye28.com/viewtopic.php?f=7&t=129886
"its a stock m106 bottom, and modified cylinderhead with another camshaft, rockers, valvesprings etc
m5 e34 b38 itb
precision 6265 turbo
precision fuelinjectors 1260cc
its runs on e85 and have 655whp @ 6200rpm and 853wtourqe @ 4400rpm on 1.4 bars =)

Shadow · Post by **Shadow** » Dec 07, 2015 12:45 PM

Hey this might sound like a dumb question but what engine will make more power?

7.4:1 or 9:1 on the same 91 fuel?
What I'm saying is the super low compression worth the sluggishness?
Will it be able to run like 10psi more making 100hp more then the 9:1 one?

offroadkarter · Post by **offroadkarter** » Dec 07, 2015 5:31 PM

Shadow wrote:Hey this might sound like a dumb question but what engine will make more power?

7.4:1 or 9:1 on the same 91 fuel?
What I'm saying is the super low compression worth the sluggishness?
Will it be able to run like 10psi more making 100hp more then the 9:1 one?

If two engines are the exact same, except one has higher compression over the other, the higher compression engine will always make more power.

As long as you keep the tune in check, I wouldn't be afraid to run 9:1 at all.

Shadow · Post by **Shadow** » Dec 08, 2015 9:56 PM

Then why the low compression. Why do people lower compression then.

offroadkarter · Post by **offroadkarter** » Dec 08, 2015 11:18 PM

Shadow wrote:Then why the low compression. Why do people lower compression then.

Because its safer against knock especially if you get one bad tank of gas. Older EFI systems also couldn't compensate as well as something newer. A lot has changed basically.

TamperedWith · Post by **TamperedWith** » Dec 09, 2015 1:00 AM

Shadow, no offense dude but that's a very easy subject to acquire info on and you totally hijacked my topic rather than posting your own new topic, please post a new thread asking such a question. Thanks!

TamperedWith · Post by **TamperedWith** » Dec 09, 2015 1:04 AM

charofire wrote:User M106 used a 745i engine with custom cam, s38 ITBs, and a big turbo and standalone to get some crazy rwhp #'s. You can find his build here:
http://www.mye28.com/viewtopic.php?f=7&t=129886
"its a stock m106 bottom, and modified cylinderhead with another camshaft, rockers, valvesprings etc
m5 e34 b38 itb
precision 6265 turbo
precision fuelinjectors 1260cc
its runs on e85 and have 655whp @ 6200rpm and 853wtourqe @ 4400rpm on 1.4 bars =)

That's pretty cool, but the itbs are a little much for me

charofire · Post by **charofire** » Dec 09, 2015 1:59 AM

Yep, that's the real deal right there. Buy a TCD kit and you'll be a happy man.

wkohler · Post by **wkohler** » Dec 10, 2015 2:42 AM

I'd go for the M106 in your position. Those blocks have some nice things that might make your life easier. Oil squirters for the pistons and the block is already tapped for an oil return. Especially if it's less than it would cost to get the B34. It is for all intents and purposes a B34. You could get a B35 head and pistons and use the 9:1 CR with a TCD kit.

Everyone always discounts the 745i stuff but there have been some pretty good builds out there with it. One problem is that it doesn't fit the E28 without modifying the support on the right inner fender, but if you aren't looking to create the fastest car ever made, I don't see what's really wrong with it other than the turbo will need work, everything is old and dirty and the manifold is probably cracked. Still...

The M102 cars had the low CR but higher boost. They didn't have the knock sensing capability the M106 cars did so that was probably part of the reason.

stoney · Post by **stoney** » Dec 10, 2015 4:50 PM

My RB26 in my R34 skyline, runs a 9.5:1 CR and over 500hp, making 1 bar of boost by 3000rpm (redline 8500rpm), but it is a much more modern design motor and i'm running a ViPec ECU to control things.

But basically the higher the comp ratio, the earlier your motor will spool the turbo, however the main risk involved is detonation, if you have to retard the timing too much with a higher CR motor to prevent detonation, then the added benefits are all but lost.

What ECU and tuning aids are you planning on using, as well as what fuel quality? these factors will (or should) play a big role in deciding on a final CR

charofire · Post by **charofire** » Dec 11, 2015 12:54 AM

I built my 535i with a 745i block + the 9:1 pistons + b35 head. I also have the original KKK27 turbo and manifold, which are less than ideal. The modification needed to make it fit on the passenger side is fairly straightforward - I used a 533i or s38b35 passenger motor mount, and a few washers, and I was able to clear everything. I am assuming you would roll with a better manifold and turbo though. If you are going to R&R the engine, then the 745i block is nice for what Chris mentioned.

TamperedWith · Post by **TamperedWith** » Dec 11, 2015 5:03 PM

Wkohler I think that's what I'm going to do at this point, except I'm not a fan of kits, I'll more likely build a custom setup to my liking after its running and driving on the refreshed stock m106.
Stoney I'll probably run some variation of Megasquirt, Hawaii is limited at 92 octane so that's why I figured I'd shoot for somewhere in the mid 8's for c/r which should keep me happy enough with the power/spool balance.
Charofire I plan on doing something very similar to what you did, likely with less compression. I'll probably flip the tb on the b35 intake manifold and use a Rapidspool turbo manifold

ZenitramNaes · Post by **ZenitramNaes** » Jan 02, 2016 12:00 AM

I love my megasquirt and I love my m106. I'd pick it up anyway, complete motors with the turbo setups are hard to come by.

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