Megasquirt tuning maps question

tcolt · Post by **tcolt** » Thu Jul 03, 2014 12:44 am

I finally want to install my Megasquirt MSPNP2 ECU and I'm hoping to find someone willing to share their fuel and ignition maps that are already a little closer to what my modified engine B34/ B35 needs than the DYIAutotune start up map that came with the MSPNP2 ECU.

This is basically the engine I have, before I bolt on the Megasquirt: Stock B34 dirty motor block with 10:1 and early euro Motronic 1.0. Add to that Hartge headers and a B35 head and euro B34 cam and stock 3.5L intake manifold and 19 lbs Bosch/ Ford injectors. I machined the head to stick with the 10:1 compression, even with the B35 head, but the performance really didn't seem be much different from the original B34 block and head combo...

I'd like to end up with a set-up without an AFM, but I'd be happy with any fuel and ignition maps to get me started, that are closer than the start up maps from DYIAutotune.

Thanks, Tom Colitt

CabbageFumes · Post by **CabbageFumes** » Fri Oct 09, 2015 5:12 pm

I realize this is an old thread, but to answer your question, by putting a B35 head on your B34, with addition of your "machining", your compression ratio dropped somewhere between a stock B34/35. So your impression of the difference not being much better is right on.

tcolt · Post by **tcolt** » Sat Oct 10, 2015 12:39 am

I appreciate your reply. What reason do you say my engine's compression ratio is lower than 10:1 when I had the head machined down to provide the same combustion volume as the B34 head had?

Thanks, Tom

CabbageFumes · Post by **CabbageFumes** » Sat Oct 10, 2015 11:11 am

Because 10:1 assumes the smaller combustion chamber of the b34 head. When you increase the size of the chamber (b35), including removing additional material from that already larger space, you wouldn't be able to surface the head enough to make up for the loss.

tcolt · Post by **tcolt** » Sat Oct 10, 2015 12:13 pm

That's normally true. I had to take off about 0.7 or 0.8mm to achieve the same CCs as the B34 head. To the point that the camshaft drive chain rattles for a few minutes before the engine warms up because of the excessive slack....
Do you know why BMW went to a lower compression B35 head in the first place and what did they do to make up for the loss in compression ratio on the US spec B35? Does the Euro B35 head have the same CR?

Thanks, Tom

CabbageFumes · Post by **CabbageFumes** » Sat Oct 10, 2015 2:19 pm

tcolt wrote:That's normally true. I had to take off about 0.7 or 0.8mm to achieve the same CCs as the B34 head. To the point that the camshaft drive chain rattles for a few minutes before the engine warms up because of the excessive slack....
Do you know why BMW went to a lower compression B35 head in the first place and what did they do to make up for the loss in compression ratio on the US spec B35? Does the Euro B35 head have the same CR?

Thanks, Tom

To get close, you'd have remove that much or more, then besides having the problem you mentioned, your cam timing will be retarded, so you'd have to get a slotted cam gear to get it back to spec. Plus, by taking that much off, you run a very high risk of valve contact, so you'd have to cut reliefs in the pistons, adding more CC area.
Actually the B35 head isn't "lower compression". The chambers are slightly larger, because the b35 pistons are crowned(domed) to match(9:1), unlike the b34 dished piston (Cat, 8:1). The b34 non-cat are crowned to increase compression(10:1), but the crown is shaped to match the b34 head. These non-cat b34 pistons will hit the b35 chamber, meant for the b35 shaped crown, purposely matched for that chamber. This also make combustion messy.
There are two b34s worldwide: w/cat @ 8:1, w/o cat @ 10:1.
All b35s are the same worldwide @ 9:1.
There is a converter I have somewhere a file that calculates compression for mixing heads and pistons in M30s, I just gotta find it.

tcolt · Post by **tcolt** » Sat Oct 10, 2015 2:30 pm

That would be great if you can find that! Although I can't imagine why anyone (except I) would have attempted to put together a hybrid b34 and b35. BTW, I have no interference with the 10:1 pistons and the b35 head or valves, but of course I did bout in an off-set camshaft key to correct the cam timing. CCs are identical to the b34, which brings the combination back to 10:1...

Tom

CabbageFumes · Post by **CabbageFumes** » Sat Oct 10, 2015 2:46 pm

tcolt wrote:That would be great if you can find that! Although I can't imagine why anyone (except I) would have attempted to put together a hybrid b34 and b35. BTW, I have no interference with the 10:1 pistons and the b35 head or valves, but of course I did bout in an off-set camshaft key to correct the cam timing. CCs are identical to the b34, which brings the combination back to 10:1...

Tom

Tom you probably don't want to hear this, but according to real numbers, by taking off .8mm (.031") off of a b35 head, paired with a Euro "piano top" 10:1 piston effectively gives you 9.77:1, not 10:1. Close,...
Its all in the shape of the piston crown being matched to the combustion chamber. Forget about the c/r numbers being attached to the piston itself. They only mean something in the scenario of matching piston crown to chamber shape.

tcolt · Post by **tcolt** » Sat Oct 10, 2015 3:47 pm

I may have taken off 0.9mm then and not 0.8mm. I went from my memory. That would explain the same CCs. The point is, I don't see how my swapping cylinder heads, plus machining, effectively did anything but increase the size of the intake valve and change the shape of the intake ports (there's a difference between b34 and b35). Except for a slightly rattling timing chain due to the increased slack. The size and shape of the B35 and B34 is virtually identical (after machining) and I didn't change the B34 high compression pistons. Do you agree?... I'd like to see the chart from real numbers that gives you the CR?...

Tom

CabbageFumes · Post by **CabbageFumes** » Sat Oct 10, 2015 5:26 pm

tcolt wrote:I may have taken off 0.9mm then and not 0.8mm. I went from my memory. That would explain the same CCs. The point is, I don't see how my swapping cylinder heads, plus machining, effectively did anything but increase the size of the intake valve and change the shape of the intake ports (there's a difference between b34 and b35). Except for a slightly rattling timing chain due to the increased slack. The size and shape of the B35 and B34 is virtually identical (after machining) and I didn't change the B34 high compression pistons. Do you agree?... I'd like to see the chart from real numbers that gives you the CR?...

Tom

It sounds like you don't like what I have to say.
More truth: The head cc of a b34 is 58, the b35 is 65. Even if you did take .9mm off, that would still leave you with 9.86:1, not enough to make up that difference.
I wonder- have you ever had the head off since the conversion? Most people report the edge of piano top dome of the b34 piston touches the edge of the b35 chamber. Not enough to lock the engine, but you probably had that happen too, unless you have a very thick head gasket.
I guess what I'm saying is, I understand that you say that your head is the same cc as a b34. I'm saying I don't think so.

tcolt · Post by **tcolt** » Sat Oct 10, 2015 6:41 pm

I like what you have to say. Otherwise, I wouldn't keep asking more questions, right?

... Can I get a copy of that CR calculator that you're using?
I don't know what else to add except that I measured the actual volume, but maybe it was off by a little? I haven't had the head off again, so I can't tell you if there was any minimal touching. I don't think so. Maybe that happens to people who don't adjust for the camshaft retarding?... Seems like you said the b35 pistons are domed and mine are flat, so I don't see why they should collide except of the rocker arm geometry opened the valves more which I also don't believe to be happening...

Tom

CabbageFumes · Post by **CabbageFumes** » Sun Oct 11, 2015 12:59 am

The 10:1s are piano top, meaning they are crowned, the difference being b35 crowns look like rolling hills, the b34s have a distinct grand piano shaped crown, the edge of which is the culprit in touching the head(for some).
The c/r calc is an excel file. Not sure how to send it to you.

tcolt · Post by **tcolt** » Sun Oct 11, 2015 5:20 pm

Maybe there were two different versions of the 10:1 B34 engine? In that case, I see how the interference could be a problem. The factory pistons I have in my 1984 Euro spec "dirty" motor, M30 B34 engine are flat top pistons. These 218 HP engines were used in most Euro 535i, 635CSi and 735i engine of the early to mid eighties.

You could attach the Excel file directly to this thread for all members to use or just to my email at tcolt@netzero.com

Thank you, Tom

CabbageFumes · Post by **CabbageFumes** » Sun Oct 11, 2015 5:46 pm

tcolt wrote:Maybe there were two different versions of the 10:1 B34 engine? In that case, I see how the interference could be a problem. The factory pistons I have in my 1984 Euro spec "dirty" motor, M30 B34 engine are flat top pistons. These 218 HP engines were used in most Euro 535i, 635CSi and 735i engine of the early to mid eighties.

You could attach the Excel file directly to this thread for all members to use or just to my email at tcolt@netzero.com

Thank you, Tom

Just for clarification, there are two pistons used in the b34 worldwide. Standard(euro), and "green" motor(used in the US market). Standard are piano top(crowned), green are dished like a saucer. There is no such flat top piston ever available in a b34.

CabbageFumes · Post by **CabbageFumes** » Sun Oct 11, 2015 5:52 pm

B34 Euro pistons. Farah vouches for me:

US and other countries with "Green" b34:

B35:

Are you sure you don't have US b34 pistons in that thing?