...the journey of a '77 bmw 320i from its home in california through a mild "frame on" restoration in the midwest...
Wednesday, April 6, 2011
M10 Engine Rebuild/Upgrade
The "perfect" engine build is different for each person and application-it still requires compromises. Having said that I will post my personal "recipe". Though I have done it in the past it continues to evolve.
84mm stroke (s14 crank) counter weights coated with oil shedding coating
92mm bore forged flat top pistons set at .000" deck height, skirts coated with dry film lubricant (DFL) and tops with ceramic heat reflective coating.
Bearings coated with DFL
Reworked stock connecting rods coated with oil shedding coating (I would love a set of 5.7" custom H beam rods but the cost outweighs the benefits)
A light weight dampener/pulley with 36-1 tooth wheel attached
Lightened stock flywheel
All reciprocating parts static balanced to within .5 gram and rotating parts dynamically balanced.
Milled for combustion chamber volume of 50cc (a compressed head gasket thickness of .035 and zero deck height will give 11-1 compression)
Mildly ported head with DFL on intake valve stems, ceramic on valve heads and combustion chamber
Elgin 284 X 10.47mm valve lift cam coated with DFL (this cam should perform in a 2.2L engine much like my current Elgin 278 does in my 2.0L)
rockers with shaft and bushings coated with DFL
Titanium valve retainers
Valve springs with "just enough" pressure to control the valves with that cam.
Single row timing gears/chain
Distributor hole plugged
4-2-1 header, 1 5/8" primaries 18" long into 1 3/4" secondaries 20" long, merged collectors used throughout and a venturi on the last one to a 2.5" exhaust using mandrel bends, one Edelbrock RPM oval muffler and exiting through the body behind the passenger seat.
Fabricated intake with 15" intake runners (plenum to valve head length) not sure on the plenum volume yet
65mm throttle body
MS efi with EDIS ignition
29lb injectors at 48psi rail pressure
aftermarket external fuel pump
1/2" steel supply lines
3/8" return lines
As you can see there is much more than most people think, an engine is a system and EVERY part must be considered when modifying it.
Compromises with this configuration:
single stage oil pump with wet sump vs. 3 stage oil pump with dry sump
5.315" rods instead of 5.7" rods
Crank is heavier than I would like
Lightened steel flywheel vs aluminum flywheel
These compromises save about $2000 in parts and labor cost but don't reduce power much.
This engine should easily push 200hp and nearly equal torque in the mid range. In a 2200lb e21 it would have 11lb per hp. The e46 M3 6 cyl (333hp) has about 10.5lb per hp and the 3.2L e36 m3 has about 10lb per hp so it would be pretty easy to startle those drivers. A properly set up e21 would be more fun anyway...