Best combination of standard M20 parts?

[Brian28]

I'm going to be sticking a standardish 2.5 M20 (can't be a 2.7 and can't be later E36 engine transplant) together over winter. I'm new to the 2.5 M20, and read that there were different versions over the life run of the engine. As the best starting point, should I be looking for an early high compression bottom end, combined with the later head? I read somewhere that the later heads have bigger ports. If anybody has done this, could you post the casting numbers I should be looking for, thanks. Or if it's a bad idea, could you post up a better plan. Thanks.

[gooner1]

Brian, i stand to be corrected here but i thought the only difference
between the early and late engines was the Pistons, internals wise at least.
Engine management electrics and cooling system were also slightly different

[goosiegander]

Mapped motronic 1.3, high comp slugs (special overbore) and 135mm m50 rods for something a little more interesting perhaps,

You might as well pick up a 2.8 crank and custom pistons while you are at it, unless you are fixed on using used parts only its worth a little extra dollar...

hth

[Brian28]

Thanks chaps. Bottom end has to be more or less standard 2.5 (regs), balancing and factory overbore only so custom pistons and 2.8 crank are out the window. The plan is to get a decent engine to start off with and just do a bottom end balance and refresh of bearings and piston rings. I've read conflicting info on the different set ups though, is it just the pistons that are different on the high compression blocks?

Top end is not so regulated so can be flowed and cammed, no ITBs on induction side though. So would be good to have the best head as a starting point if there are already differences in port and/or valve size.

Cheers
Brian

[Jhonno]

Early engine on later management is your best bet then!

Top ends are the same.

[Brianmoooore]

There were slight changes to the casting/machining of the head on later engines. These are identified by 2.5/2.7 cast into them, but AFAIK, they have no advantages over the earlier ones.
There are also Spanish (?) made replacement heads around, which are supposedly less prone to cracking under the cam bearings.

[Brian28]

Thanks again, last question. I'll be using expansion tank etc from a later model, can I change the water pump or anything on the earlier high compression engine so that the water pipes are the same set up as later models? The expansion tank is on the driver side on the earlier models. Thanks.

[daimlerman]

Thanks again, last question. I'll be using expansion tank etc from a later model, can I change the water pump or anything on the earlier high compression engine so that the water pipes are the same set up as later models? The expansion tank is on the driver side on the earlier models. Thanks.

Yes,this is something that I had to do when I built my 2.7.Waterpump mounts in the same way on all the M20 blocks.

Hunt out Hairysceech's thread regarding working on the head,worth a read for the advice available.

[HairyScreech]

id also add to brians bit that i have been working with an early head with a square bit and hollow lug instead of the round 2.5/2.7 lug on the later ones, as far as the combustion chamber and ports go there is nothing to tell them apart.

(and i have a sectioned head now, straight down the intake port )

[Brian28]

Some really good reading on head development there, thanks chaps. Mr Screech, let me know if/when you are ready to do one for sale and I'll happily cross your palm with silver

[HairyScreech]

^^ iv only just made the connection between what your asking here and your pm, iv replied again with some more thoughts.