E30 M3 engine

[MONSPORT42]

Pain the rear end I would say. If you haven't already done so, I would park up alongside an M3 and compare the engine compartments side by side. Virtually everything is different. You'd need the gearbox and prop too. The cheapest way would be to buy a crashed M3. But M3 performance is more about the balance between power/weight and handling. I think you would end up with something closer to a 318is than an M3. I had an 85 323 and did a 2.7 conversion which made it in to whole new car powerwise. In fact I still have the same lump running in my Sport now. That route would give you closer to 200bhp for about a quarter of the cost of an M3 transplant and about a tenth of the work!

[Widge]

What specs is your 2.7 monsport? Is it an eta crank in the 323 engine?

[MONSPORT42]

Yep, it has an eta crank. Bexley Motors did the conversion about five years ago, I was already one of their regular customers and still am. For a 2.3 it requires a rebore to get up to 2.7. The 323 conrods are used plus new high comp pistons. I originally kept the 323 head, manifolds and engine management. From memory that all gave about a real world 194bhp. I subsequently bought my current sport and swapped the lump into it but changed the 325 head onto it too (and had it gas-flowed) as it had a better cam and bigger manifolds. Have also had a MAF conversion Zone BBTB and custom RR remap.

[Widge]

So how many BHP now? And I'm surprised the 2.5 head works well with pistons that must have been designed for a 323 head?

[MONSPORT42]

This is the plot from the MAF remap I had. It's been tweaked some more since. Came top in the Zone RR shoot out at Bexley (behind Ian's 332 which wasn't counted) but it only showed 229 bhp on that day but found out that the auto box was slipping badly and since had it rebuilt. Have had 242bhp since then. But it's the torque that makes it.

[Widge]

Can't read any of that, but those figures are awesome man!
So what's the key? Have you got silly high compression? MAF must really be worth it, most 2.7's get 220bhp, are you runing a silly spec cam too?

[MONSPORT42]

Strangely enough the MAF doesn't do a lot for max bhp, it's more for throttle response and driveability throughout the range. Bexley have always been shy about explaining exactly what they did to mine, ( I guess I paid for their knowledge and experience) especially when they did the head swap. The gas flow and porting seemed to make a big difference but I'm guessing that they also upped the compression at that time with a skim. It has however spent hours and hours of development on their rolling road. The cam is the one that was already in the sport when I got it. It's not a Shrick I know but think it's fast road cam of sorts. Am thinking of putting one of Sal's 6 branch manifolds on now that I know they will fit an auto. That should improve the fuelling characteristics even more and give another 8bhp or so.

[Widge]

Then you will be 250bhp from 2700cc! In an M20 that is quite impressive. And is this all with the usual inlet and exhaust manifold?

[MONSPORT42]

Yep, currently 242 ish with standard manjfolds. Hopefully 250 with the six branch.

[Widge]

Friking hell that is impressive!

[bigdek]

what sort of cost are we talking though cos gas flowed heads don't come cheap.

Wouldn't mind it myself though

[MONSPORT42]

Seem to remember the head work was about Ԛ£450 but that was five years ago. Only worth doing really if the head's off and you are doing something else too.