Are they both M10's?

Are they both 1.8's?

Didn't the earlier e21's come with 2.0 liters and the latter with 1.8's?

Are any parts interchangeable between the two? (Specifically pistons)

Does the e30 have "that" much better head flow? Can you drop an e30's head onto an e21's block?

Anything else I ought to know about the differences?

Thanks!

1. 84-85 318 = m10
2. yes, its a 1.8 just like the 80-83 320i
3. yes, the 2.0 have different heads, crankshafts, and pistons (not sure what else)
4. pistons should be interchangeable between 80-83 320i and 84-85 318i
5. e30 head-flow should be exactly the same as the 1.8 320i's. The big difference between the 1.8 320i head and the 1.8 318i (e30) head is that the e30 doesn't have the holes for the k-jet fuel injectors. Conversely, it does have holes for L-jet fuel injectors in the intake manifold. So, you can drop a 318i head on an e21 block, but you'll need the injection system to accompany it (or some other solution).

Some claim the 1.8L head casting flows better than the e21 head casting because it's a more open chamber design which unshrouds the valves. Nobody has produced any flow beach data to support that claim. There is more to a good head than big flow numbers. Getting air in is one thing, burning it efficiently is another.

The 1.8L head is an open chamber design with no flat spots facing the piston-it's nearly a Hemi shape.

The e21 casting has a fairly large flat section facing the piston top. As the piston reaches top dead center the air fuel mixture that is between the piston and this flat spot gets "squished" into the combustion chamber creating more turbulence which in turn mixes the air fuel mixture a little more. This helps the air fuel mixture burn more effectively.

Some older heads used on the 2002 have two flat sections, one on each side of the combustion chamber which works even better. Some of these heads have smaller valves though.

It's a balancing act between flow and combustion efficiency. For piston "squish" to be effective the piston crown MUST get as close as possible without actually hitting the cylinder head. Anything over .050" shows a dramatic drop in the effect. I shoot for .035" to .040" which is about the thickness of a compressed head gasket so your piston should be set flush with the cylinder block. If your piston is "in the hole" you should have the block cut the correct amount to get it flush. I don't rev my engine past 7,000rpm EVER and generally not past 6500rpm, if you plan to rev your engine higher than that you may need a little more clearance.

Most engines in the '80s had open chamber heads to reduce compression ratios and improve emissions. With the advent of EFI and more understanding of the combustion process most engines have gone back to small closed chamber heads like the Chevy vortec and LSx heads. Even the new Hemi does NOT have a real Hemi combustion chamber.

ken

I don't rev my engine past 7,000rpm EVER and generally not past 6500rpm, if you plan to rev your engine higher than that you may need a little more clearance.

ken

Hey I can tell you for a fact that an M10 will rev to at least 9200 RPM. When I got my car I didnt know that the tach was WAYYYYYY off. From what I can tell it's meant for a 6 cyl. car. So...... it took me a while to figure out why my car stopped pulling after "4000 rpm". LMAO

As long as we're talking about an '84-'85 e30 318i, the engines are exactly identical save for the fuel injection. The head isn't milled for the k-jet injectors, but the bosses are still there and it is stamped 1.8i. Cam, crank, pistons, all the same.
--dennis

i know that an e30 m3 engine will fit perfectly into an m10 compartment.

Pre 80's 1.8L m10's are pretty weird. They have the same crank and connecting rods as the post 80's 1.8L m10's. The pistons and head are different though. I have not taken my head off so I don't know what the pistons look like or what the combustion chambers look like. The head does have smaller valves though. Intake 42mm Exhaust 35mm compared to most of the other m10's Intake 46mm Exhaust 38mm. The early heads also have smaller ports to go along with the smaller valves. With smaller valves and exhaust ports the motor produced 98hp where the later e21's made 101hp with bigger valves and cis.
I'd much rather have a rare engine and simpler fuel system than have that extra 3hp.

But it gets more complicated than that, the 316 engine was actually 1.8 (same bore and stroke as the 318) but the early ones only had 75hp. What did they do to make it so low?

There was a 1.6 m10 also. 1573 cc, if I'm not mistaken.

But it gets more complicated than that, the 316 engine was actually 1.8 (same bore and stroke as the 318) but the early ones only had 75hp. What did they do to make it so low?

It was a low compression variant for a stripper model.

There was a 1.6 m10 also. 1573 cc, if I'm not mistaken.

You're right, but that was in the 315, not the 316.

Whoops, my bad. It was the E30 that had - here in Europe - both 1.6 and 1.8 m10 engines, under the same designation, "316".

But it gets more complicated than that, the 316 engine was actually 1.8 (same bore and stroke as the 318) but the early ones only had 75hp. What did they do to make it so low?


Yes, they are the same bore and stroke. The difference is in the pistons and head. I believe the only difference in the head though was the shape of the combustion chamber. The combination of different pistons and combustion chamber gives the 316 motor a lower compression ratio than the 318. I'm not positive about this but I believe the 318 had 8.3:1.

I own both 2.0L and 1.8L e21s and I also have an e30 318. With all of this discussion of which M10 is what and who has the better whatever is a mook point. Both are slugs in stock forms.

Well I found an '83 320i engine for core value ($100). I don't know how good it is, or how many miles. So I gave the junk yard $40 as a down payment to get them to drag it out of the top of their storage barn. Unfortuneatly, it has been there some time, so there are lots of other engines stacked in front of it. When I get it, I'll clean it up, toss in the 8.5:1 pistons, and rebuild the head.

Couple more questions for the turbo e21 guys.

Any place make forged rods?

What cams are you running with your turbo cars? OE NA cams?

Any other misc suggestions?

Which 8.5:1 pistons would those be? Stock is 8.8:1 which is fine to turbo. For more power though, you could install a 2.0 crank with flat top pistons and run higher boost. Besides the longer stroke this will drop your compression to about 8.0:1.
Forged rods: Carillo makes them and there is another brand on e-bay all the time, but both are ultra expensive.
OE cams do work, the 2002 turbo had the same cam as all other M10s, but there are special 'turbo grinds' that would get a bit more out of it. A performance cam designed for N/A is not recommended.
Misc suggestions: Make a turbo header, don't waste time with the old log manifolds that don't fit any decent turbos. Use megasquirt EFI!!

The pistons are JE's.

^ I have a 1.8L for sale if anyone needs one for a core to build. 1983 - 180k and it runs