e12 or e24 block for turbo best?

[Grapedude]

Hi, new here from the Big coupe site... I'm just starting the turbo process and have an '86 E24. Its auto so I bought an '81 manual wreck (imported from UK in case anyone wants to track it I have orig ownership papers) thinking i could swap, with out understanding that the engines internally were slightly different in dimensions. So my question is; better to just swap gearbox and work with later e24 engine OR swap engine and box (which would be easier?) and turbo the older motor M90 which has shorter stroke and wider bore? Any opinions on this? The pro's and con's of each? thanks you in advance!!

[tschultz]

My hesitation on turbo charging the M90 is the bore and piston spacing. It should be doable, but being in the US, it makes a lot more sense to turbo the B34 since it is lower compression to begin with.

Being in europe, lower compression make more sense for you...

I finding pulling engine+trans is easier. Pulling the trans isn't fun and I did it with a 265 box with removable bell housing...

[Grapedude]

Sounds like the M90 might be better suited to N/A use and the M30 the turbo. cheers!

[marc79euro645]

+1 on not turboing the m90. There is about 3/16" between the bores. Headgasket failure will be your biggest issue turboing any motor. good luck!

[CSBolger]

Any M30B34 will be easily replaced and super-sturdy. I'm in the process of moving my M30B35 rotating assembly into an M30B34 block for its thicker deck. Got the infamous cracks between the coolant and oil passages on my B35 block.