Experience with a boosted m30 with 7.45:1 compression

[charofire]

I want to know if anyone on this board can share with me their experience of what it is like to run a b35 head on a 745i block boosted. So anyone with this setup, please share with me if this route was a waste of time or if the spooling of an upgraded turbo made the lower compression less obvious at lower rpm. Thanks.

[winfred]

dead off boost would be my impression, id sooner boost a complete b35 with a head gasket and loose a few pounds of boost on top for some torque on the bottom when the turbo is asleep

[charofire]

Yes, that's what I've read as well; but I would appreciate it if someone with the actual setup could speak to the issue.

[turbodan]

Wouldn't be much worse than a B34 off boost. Wouldn't really be worth doing unless you were planning on running a lot of boost though.

[Cactus]

Don't bother with this setup if you're never going to the track. You'll get worse mileage, you'll see less throttle response and torque off boost, and the head doesn't really breathe that much better than a stock one. If your goal is to run high boost levels at high RPM for extended periods of time, like you'd want on the track, this is a pretty decent setup. Not really worth it otherwise.

[Brad D.]

Higher CR (within reason) for a street car is better for many reasons. I wouldn't run that setup and like Dan said, unless it you were running really high boost, the drop in CR likely offsets any gains from the head.

[Lurker27]

less compression is now and always has been idiotic

these engines want e85 or meth/water injection, because of the heat issues they have in cyl 3/4 and the amount of advance they make best power at

[T_C_D]

less compression is now and always has been idiotic

these engines want e85 or meth/water injection, because of the heat issues they have in cyl 3/4 and the amount of advance they make best power at

What? A m30b34 with 8.0CR is not octane limited. My m30b34 at 19psi reached best least timing before reaching detonation. I have actually ran e85 in my m30b34 and it did not make any more appreciable power than 93 octane.

e85 seems to be great for high compression n/a engines converted to turbo but doesn't seem to offer much advantage for a lowly 8.0CR engine. Better, probably but not enough gain to make the switch IMHO and experience.

[Golosok]

I run b35 block, m106 pistons and B35 ported head.
I think CR should be about 8.5:1

Run 21 psi of boost.

ARP studs, Cometic gasket.

K27 turbo, really big FMIC

Pretty happy with the setup.

[charofire]

I am really confused now. I thought that m106 pistons (which I have) and b34 pistons were essentially worth the same relative compression with a b35 head. So using the b35 block instead of a b34 or m106 block as I have would raise the compression from 7:45 to 8:5:1?
It seems as Todd has mentioned, having the b35 cam is also pretty key.

[Hit Man X]

I drove a 7:1 M102 (Ljet 745i's M30B32) for a while with the 3HP22 + 3.07:1 diff. My old 240D MB with a four on the floor would jump the car from a hole shot... and that car only had 62hp. Yes, it was that slow. I bet its 60' time was in the mid to low three second range.

FWIW, I would just run the entire M106 or B34 and do a few things to its head. B35 dual springs and B35 camshaft for example. Maybe B35 intake valves if you can swing it.

[stefankj]

The Alpina B10BT has a compression of 7.2:1 and that car is not sloppy at all...

[turbodan]

I drove a 7:1 M102 (Ljet 745i's M30B32) for a while with the 3HP22 + 3.07:1 diff. My old 240D MB with a four on the floor would jump the car from a hole shot... and that car only had 62hp. Yes, it was that slow. I bet its 60' time was in the mid to low three second range.

FWIW, I would just run the entire M106 or B34 and do a few things to its head. B35 dual springs and B35 camshaft for example. Maybe B35 intake valves if you can swing it.

Dialing up the ignition advance will recover most of the missing torque. Running injection tuned for a significantly higher compression engine will really make it dog.

[Hit Man X]

Dialing up the ignition advance will recover most of the missing torque. Running injection tuned for a significantly higher compression engine will really make it dog.

I figured there was a pile of response and power left on the table compared to using that stock Ljetronic 745i ECU and harness. It seemed to be either 'on' or 'off' with nothing in between.

Timing was 27° BTDC @ 2300rpm, if it matters. When I bought it timing was down in the upper teens, just putting it back to 24° before a test drive made a huge difference.

But hey, that 745i stuff was never known to be responsive anyway.

[charofire]

Does anyone know my previous question? I just want to make sure I am not misreading previous posts. m106 pistons, b35 block and b35 head equals 8:5 to 1; m106 block, m106 pistons and b35 head equals 7:45 to 1? So the difference between the two blocks, the b35 and m106, equates to a full point of higher compression? And this is using m106 pistons which are approx. equal to b34 pistons...

[turbodan]

An M30 with such low compression would probably be happier with 30+ degrees of advance at WOT/2300 RPM. Possibly as much as 35 degrees.

[charofire]

Dan, that sounds correct; standalone would be necessary to set that kind of advanced timing. Does anyone know the block compression difference like I mentioned in my previous post?

[clongo]

An M30 with such low compression would probably be happier with 30+ degrees of advance at WOT/2300 RPM. Possibly as much as 35 degrees.

Yeah, im running 32 degrees on mine at 2300 RPM.

[turbodan]

Dan, that sounds correct; standalone would be necessary to set that kind of advanced timing. Does anyone know the block compression difference like I mentioned in my previous post?

I believe the blocks are not the difference. Should be the pistons, though I know little about M106 pistons. I do know the B35 head uses significantly larger combustion chambers, accounting for the large drop in CR with the dished B34 pistons.

[charofire]

Thanks, Dan. Can anyone comment on the m106 block/pistons with b35 head? It seems it might be different than the b34 block/pistons with b35 head. Golosok says he has approx 8:5 to 1 compression with m106 pistons and b35 head. That would mean either the m106 pistons with b35 head yield a different compression than b34 block and pistons if the blocks are the same.

[Brad D.]

M106 and b34 piston dish cc are basically identical and have the same CR and the same head cc. I don't see any way that a b35 head with m106 pistons will yield 8.5:1.

[Hit Man X]

M106 and b34 piston dish cc are basically identical and have the same CR and the same head cc. I don't see any way that a b35 head with m106 pistons will yield 8.5:1.

This.