Yet another M20 Stroker config question - CA SMOG legal setup

[RicardoD]

Hello,

I am planning to swap the M10 in my 1982 E21 to an M20B25 stroker as part of its overall restoration project. Looking to build a CA SMOG legal M20 using stock intake, injectors, ECU, new cat... This is for a fun to drive reliable street E21. I am not chasing peak horsepower.


Option 1: 2.9L Mahle (2860cc)
885 head with 272 cam (remember SMOG compliant)
IE Mahle 2.9L Ultimate Street Stroker Piston (85mm bore)
10:1 compression (new to work with 91 octane CA gas)
84mm stroke crankshaft (M52 crank and 135mm rods)


Option 2: 2.8L (2823cc)
885 head with 272 cam (remember SMOG compliant)
86mm bore with Custom Pistons (probably via Top End Performance)
10:1 compression ratio
81mm stroke crankshaft (325e crank)


Anybody with any thoughts or opinions of these two options? I seen a few post indicating Option 2 works for SMOG with a properly rebuilt engine, ECU w/tune, and a new CAT (not one at its end of life from the donor E30). Option 1 probably similar.

My E21 blog is here (just at the start of this project):

https://www.ricardoe21.com

All the best,
Ricardo

[digger]

option 1,

[RicardoD]

So this is essentially the same thread.

https://www.r3vlimited.com/board/forum/e30-technical-forums/engine-drivetrain/m20/9951613-e30-stroker-2-7l-ca-smog-questions

I will update as I converge on a solution based upon conversations with different shops with E30 California SMOG experience.

[digger]

the important thing is the camshaft and tuning, the rest barely even matters

the reason for option 1 was that its the better engine overall and wont impact in any meaningful way on SMOG

[Rev Run D]

the important thing is the camshaft and tuning, the rest barely even matters

the reason for option 1 was that its the better engine overall and wont impact in any meaningful way on SMOG

Can you chip-tune the 2.9? Assuming you can't megasquirt/standalone for smog.

[digger]

Can you chip-tune the 2.9? Assuming you can't megasquirt/standalone for smog.

Yes you can. Quality of outcome will depend on the knowledge and ability of the tuner and to some extent fuel setup and overall maintenance/function of the engine electronics

[RicardoD]

I think 272 cam is the most I would want to temp fate with. Even staying stock is an option. I like the Mahle MS piston setup and that would be my preferred path. In this specific case I will be going from a tired M10 in my E21 making maybe 90hp to a very fresh M20 motor with Motronic. I think I will notice a huge change in the performance of the car even if I stay entirely stock.

And I will end up at the local California Air Resources Board (CARB) referee station undergoing a visual inspection and a tail pipe test since I am doing an engine swap. So visually everything should be stock along with all the E30 emission control bits. Bore, pistons, and crankshaft are obviously not visible.

[digger]

I think 272 cam is the most I would want to temp fate with. Even staying stock is an option. I like the Mahle MS piston setup and that would be my preferred path. In this specific case I will be going from a tired M10 in my E21 making maybe 90hp to a very fresh M20 motor with Motronic. I think I will notice a huge change in the performance of the car even if I stay entirely stock.

And I will end up at the local California Air Resources Board (CARB) referee station undergoing a visual inspection and a tail pipe test since I am doing an engine swap. So visually everything should be stock along with all the E30 emission control bits. Bore, pistons, and crankshaft are obviously not visible.

The stock camshaft is highly underrated for the street. If going with custom pistons then using the 81mm crank is a bit of a waste compared with 84mm and bigger than 84mm ought to be done with a bigger cam and itbs to maintain breathing so a 84 mm stroke is a reasonable compromise / sweet spot.