Engine Options - anyone help

[sprintevo]

Hi I have 2 x 3.5 litre engines - one and M90 with the 93.4 bore from 1980 the other an M30 from 1988 with the 92mm bore and longer stroke. the M90 needs new bearings and a general overhaul whereas the M30 is in better condition
the M30 has larger inlet valves and wider ports and has benefitted from a little port work and is in better condition plus double valve springs

What are the best options for me with these 2 units - is it a straight forward excercise to swap the longer crank into the M90 and create a 3.7 - would I need special pistons.

Or could I simply bolt the M30 head with the port work onto the M90 block and retain the higher compression or would I need to skim the head - I am sure it has been covered here before but I could not find the thread.

thanks in anticipation

 

[61porsche]

M90 vs. B35 vs. Hibred 3.7 let the debate begin.

1. Not straight forward swap on 3.7. New pistons with shorter height for zero deck.

2. B35 head lowers compression +- .3; would end up at 9.6 cr or so, Euro head gasket needed to match block and head. Confirm- this is with a B34 head. Not absolutely positive with B35 head.

M90s are not high revers, but comes on faster.

First choice would be the B35; higher revs, Second: Rebuild the M90. You're comparing green apples and red apples.

But if you're buying pistons and your budget is healthy- 3.7.

What year M90 and what do the intakes look like? The later M90s had a bigger port; pre B34. AKA; look for the 3.5 stamp on the head; the mystery motor legend continues.

M90s had the better cam- same as the B35 but for distributer.

What induction?

SFDon? Calling SFDon.......:mrgreen:

 

[sprintevo]

M90 b35

Now not looking at stroking as dont have the budget to play with piston deck heights. just getting the B35 head on as it has larger porting valves,better flow and dual valve springs - I want to retain the high CR is possible. Or would porting the m90 head and swapping the dual valve springs over in the rebuild be better. or could skimming the hea don the M30B5 to achive the same head cc as the M90 be the answer? just wondering if it is a simple swap?

High flow stainless exhaust 2" diametr - inlet is Throttle body conversion using webber 45 manifold using DTA engine management

Thanks

 

[x_atlas0]

Now not looking at stroking as dont have the budget to play with piston deck heights. just getting the B35 head on as it has larger porting valves,better flow and dual valve springs - I want to retain the high CR is possible. Or would porting the m90 head and swapping the dual valve springs over in the rebuild be better. or could skimming the hea don the M30B5 to achive the same head cc as the M90 be the answer? just wondering if it is a simple swap?

High flow stainless exhaust 2" diametr - inlet is Throttle body conversion using webber 45 manifold using DTA engine management

Thanks

Does the engine management include spark control? Anything much at or above 10:1 and you will get pinging pretty easily on stock maps/timing, even on premium. The combustion chamber just isn't designed for that kind of CR. The offset spark plug allows for uneven flame front problems, causing detonation.

The larger valves on the B35 are a nice touch. As far as the clearance volume, I think the M90's is less by about 5cc. That is quite a bit to deck off, so I wouldn't do it. There is an excellent M30 FAQ on the firstfives.org website, take a look there.
http://www.firstfives.org/faq/cylinder_head/cylinder_head_faq.htm

 

[61porsche]

DTA- what's your target HP? That system is more race oriented than street or so it seems.

If modifying the M90 to accomidate hub /crank fire is no big deal to you then fine - use the CR. ( 20hp) Green apple.

B35- lower CR, Better flow( 20HP.) Red apple.

2" headers- modify the head, port, cam ( 280-290). Hp is going to shift rpm up, torque down. Usually that size costs you on the lower torque band but probably less so for a 3.5 than 3.0.

There's a couper here that just did the throttle bodies- Henry from DC. Had a Cali shop do it. Never heard the final result dialed in. Just saw the fab - do a search. Interesting though ,since that's what the M6 had and the illustrates the weakness in the single cam head unless you do the Alpina hemi twist that straightened the intake track.

Hennnryyy!

 

[sfdon]

the M90 engine has 1 very nasty flaw....

No rings for sale.....
Only oversize are still available...

http://www.realoem.com/bmw/showparts.do?model=6831&mospid=47183&btnr=11_1669&hg=11&fg=20

You will need to source custom rings.

 

[sprintevo]

Ok so I should be looking to use the M90 head to maintain the compression, swap the larger intake valves over and the double valve prings and look to get some flow work done on the ports. Or work out what 5cc of combustion chamber area does to the compression ratio, anyone know this out of hand to save me doing the calcs

 

[sprintevo]

piston rings

I'm not worried about that as there are plenty of aftermarket and modern alternatives about that will do the job Total Seal etc..- I have a note that a Nissan pickup piston does the job too