Rebuild M90 block

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84E24

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Looking to rebuild a 1980 M90 block.

Is there that much benifit in going with 10:1 pistions vs the stock 9.3:1 ? Looking at cost of pistions vs performance. Is it worth it ?

My plan is to have the Metric head, Mallory mechinical dist, triple DCOE 40's with the M90 block, 5 speed 265.


Thanks, Steve
 
All things considered, you're looking at roughly a 10% bump in hp.

The cost.... well I figure 800- 1000 bucks for custom pistons.

A few build ups have used Mahle VW big bore pistons- you have to buy two sets to get 6 with 2 left over. But again the cost gets close to the lower end of the custom.

Some recently have stated Toyota fits... don't know much about that but someone here has done it.

The real difference is the M90 feels and comes on a bit quicker than a B35 for street.:-D

If you're planning on 8000 rpm... well you better start from scratch and all bets are off.:twisted:

One final comment- carb cam is a little different; slightly more overlap; if you're going for best performance. ( Alpina, yada, yada.)
 
M90 rebuild too

I would be interested to know which Toyota Pick up or VW pistons do the job too
 
I too would be rather wary of a MM head. I have heard far too many horror stories from various BMW/MM owners about MM's engines and heads. Their transmissions used to be quite good while Blanton was there, but apparently since he went and started his own gig, that too has gone downhill.

The one MM M30 engine I have heard good things about (meaning it didn't explode in a firey conflagration) produced power far below the promised spec when it came from MM, much less after 30k miles.
 
I just had the M90 in my 635 rebuilt. The shop that did the work used J&E forged 10:1 pistons. I think the cost ran about $850 including wrist pins and rings. My valves were good, so I just had them ground. I had the head ported and all manifolding port matched. The cost for the head work ran about $850 and included surfacing, as it had a slight tweak in it. I also used a Schneider reground cam to 284 spec. If you are running Ljet, 280 is probably the max you should go on the cam unless you use a stand alone injection system or switch to Motronic. My car, which is an 81 euro, had factory Motronic. My total cost including balancing and assembly by the shop ran about $3100 and was done by Basko machine in Gilbert AZ, one of the highest ranked shops in the Phoenix area.
 
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