M102 or Franken-B32

[Fedaykin528e]

I have recently landed a complete M102, with the intention of putting it in the 633CSi. That will no doubt be fun, but since I’ll have it apart to do the head gasket some thoughts occurred.

As far as I’ve been able to tell, the downside of these engines was poor off-boost performance, corrected in the M106 by increasing compression. Since I have a b32 sitting in the six already, I’m thinking through the possibility of stripping that block and M102ing it, ending up with a 8.8:1 turbo motor. This will no doubt be challenging to tune but I’ve started to nerd out on Megasquirt already.

I’m totally green to the world of turbocharging, but am a third of the way thru Corky Bell’s book, and have done quite a bit of forum trawling already. Can’t find anything yet on this particular swap, but everything seems doable until preignition enters the equation.

So my question to you, has anyone seen a build thread like this? Should I enter the rabbit hole and end up with one fun frankencar, or should I just deal with in-town pokeiness and stick the whole M102 in this car? Cheers!

-L

[marc79euro645]

Forget the m102! I had one as my 1st turbo motor, super lame. High compression is your friend, especially with a small stock compressor. I think all you need to do is address the exhaust manifold studs, and turbo oil return. You'll probably need to pull the motor I would use the larger studs from the m102 and drill and tap the existing head, then just bolt it all on.
I'm still using the m102 charge piping and recirc setup with my current m106 bottom end.
good luck

[Fedaykin528e]

That seems to be the word on the street, that the M102 is kind of a dog.

I was thinking I’d bolt the M102 to my block and port the block for the oil return. I’m not sure what if anything is standing in my way. With the head off the b32 block I could even drill piston oil channels mapped from the M102 block. Or wait that only the M106. Dang. Someone has to have a jig for that.

[Hit Man X]

First off, is this a pre or post 09/81 Ljet? Static compression came up 0.5:1 in the mid gen ones.

Next, has anyone on here actually driven a dialed in Ljet? Good injectors, correctly tuned AFM, non worn out head, factory 10psi, timed to spec? They run nearly the same as a Motronic car, the trans is geared the same also sans OD. Motronics boost quicker as they have an electronic boost system, that is about it and have knock control to dump boost. Total power output is the same. Sure it is 0.5:1 higher static, wow! More important is the increased displacement via the bigger bore. There are two folks in the US I know that can time an Ljet properly, the scribe of this is one of them. The other taught me. My 12/82 had 19* only at purchase! Think about that. Spec is 27*. Car ran shockingly different once timed properly.

Word on the street is full of sofa mechanics that have no real world experience with them, just like the claims of 500hp with it. That is all there is to it. Even Motronics run like shit out of tune, go drive one in safety mode at 2psi and let me know how responsive it is for you.

Expecting much from a 47mm compressor wheel is futile. It is out of steam at 13psi area, dynos about 275rwhp and falls off hard once it peaks. 15psi wastegate springs tend to do 8-10psi tops by 5500rpm. IATs are spicy at that point too. Regardless of what you do, the head is what makes and breaks power. Expect smoked exhaust guides at least and probably a wiped camshaft.

I would just take that M102 block and overbore to 92mm for US B34 pistons for perfect bores again. There are a sets around that people would probably give you. Another option is just to hone it to help knock the shit off the walls and freshen them up, then put the rest of cash in that cylinder head. You are dealing with a 40 year old engine.

[Fedaykin528e]

This is great, thanks. This is my first L-Jet car, and I know nothing about it other than it's an L-Jet and the DME has '81 written on it. Is there a way to date it without the VIN?

[Hit Man X]

My M102 actually had the last seven of the VIN on the block above the starter pad. 787xxxx was mine. 12/82 build. Unsure if the pre 09/81s had this as they are not common.

-124 was the early ECU, -127 was the late (09/81-05/83). -012 early AFM, -017 was late. Just because that came with your engine does not mean much, I have seen all sorts of hackery bullshit on these cars over the years with wrong ECUs and crap piggybacked. US ECUs in them, US AFMs on them, US spark plugs in them. Stuff that makes you laugh, then cringe.

I built an M106 last summer that had a 3.0 bar FPR (spec is 2.5) and basically belched black smoke at idle. Pulled a steller 10" of idle vac. AFM was FIVE clicks too rich, think about that. It has US spark plugs in it, luckily the AFM and ECUs were correct in it. Tossed in correct plugs, leaned AFM by ear, got it to 16" of smooth idle with a bad camshaft and some vac leaks still.

[Nebraska_e28]

If your b32 is healthy, I'd vote boosting that. You wont complain.

[Fedaykin528e]

If your b32 is healthy, I'd vote boosting that. You wont complain.

This is the path. B32 w/M102 head, with a goal of a reliable 10 pounds o' boost. Lotta learning to do!