Posted by zane Most of the older BMW motors keep their specs. I mean, you do check for out-of-round, line boring and deck flatness--these are common machine shop practices. My whole point was not so much having the actual machine work done but only checking things out to make sure that they are in spec. I think most of your power is going to be in that head. Coupled with a good cam, the motor will put a smile on your face. I would leave the engine alone, use the same crank, go a size over with the pistons (if necessary) and put all efforts into the head and tuning phase. Other things aside from the engine (and often overlooked) can give much more seat of the pants results: gearing, for one. So, you see, there are other things that you could do to the car to make it quite fast and, at the same time, have something that will last a long time. If you over bore the block so much, then you can never do a good rebuild later on. But it is your project and you must do what you want. If you so desire to stroke it, poke it and put everything into it, then you must start from scratch and hope for the best. Remember, BMW spent millions in development and used a small army of people to design these engines, so it's a good idea to pay attention to what you already have.
on 1/13/2004, 7:15 pm, in reply to "Thanks Zane - More questions."
12.78.1.128
First of all, any real performance minded person does not care about cost...what it takes is what it takes--period. That's just a blunt truth. It's easy to assume that you could to this or that, but any change in an engine effects many other things. So if you do one thing here, over there it will suffer unless you balance things out.
I've never heard of the M90 block suffering any such ills. But if you bore it enough, then the spacing between the cylinders will suffer and you will have problems. As it stands right now, your current crank and block are "seasoned" together. It is wize to keep up the partenership as long as possible between componants. If you do put other parts in the motor, then you'll have to spec everything out as best as possible.
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