M20 Build Options - Please Advise

[Jon_E30_vert]

Normally you choose FI or NA and build to suit but since you aren't after anything extreme I'd get some better 24V rods, a set of forged slugs and m52 crank as foundation for the build that works for both NA or FI. Don't go lazy on the CR maybe 9.5:1 is a good balance that will work with either config.

I like this idea and am leaning this way, thank you for the feedback and suggestion sir!

[Jon_E30_vert]

Meh on forced induction. Turbo cars are never "done". It's a constant fiddle, which is fine, and can be rewarding. My vote goes to N/A for a simple car you can enjoy with relatively low hassle and good power. If you do go FI, you don't need 400hp in an E30. Some head studs and an MLS gasket on an m20b25 with an efficient snail goes a long way. Tune well and you don't need a built bottom end for that.

Alternatively, m20 stroker motors get pricey, very fast. To make power from an m20 the "stroker configuration" is only part of the equation, as a ton of your power will come from the upper half. And you can EASILY have $3K+ in the cylinder head alone, just to make 200-220whp. Not to mention the bottom end.

But regarding the bottom half, an N/A m20 build has many "tiers", before you even get into FI.

-M52b28 crank with 130mm rods and "i" pistons is a "budget" 2.8L, but requires machine work to the counterweights and/or piston skirts, plus crank snout adapter, plus slight block deck, aka $$ in machine work and extra stuff, but using cheap used parts. Still 84mm bore


-M20b27 crank with 130mm rods and "i" pistons is a similar compression 2.7L and doesn't involve any of the machining that the above does outside of decking the block 2mm, and uses cheap-er used parts. Still 84mm bore


-M52b28 crank with 135mm rods and the 2.9L IE "ultimate street stroker" Mahle pistons works well, but then introduces high piston costs among other things


-But then s52b32/m54b30 crank works without modifying counterweights, so if you're already going to spend $1200 on pistons, it makes sense to use an s52 crank instead for more stroke and use that $1200 and get custom slugs made to fit your exact application for the same price.


So, either go big or go small. A healthy 2.7L with the above formula is proven to make a healthy 180/180 by ForcedFirebird, and most of the other random configurations above that cost more only make ~20hp/tq more and cost 6x as much.


The stock intake manifold sucks, so to extract solid power out of the above options, ITBs should be on your list, which is another large sunk cost. The bigger the motor, the more important the head work and supporting mods will be.

MY VOTE:

Build a simple 2.7L per the above, but assemble with ARPs and an MLS gasket. Get your car running really well on Megasquirt N/A, and once you're tired of it, go turbo.

Awesome feedback, thank you for your feedback and vote!

[Andre3127]

Curious to know - why is 400hp a goal? Personally for what you describe (vert, street, someone else doing the engine build) - I'd go for a 240hp 2.8 and call it a day. Sounds great, plenty of power for the street, close enough to stock the other parts of the car don't need doing, way less hassle...still M20. or 2.9 if you want to do custom pistons. If you use the car currently, try keep it on the road and enjoy it. 400hp sounds like a lot of heart break to play out over the next 5 years. I can only tell you what I would do in the same situation so do whatever you can afford and makes you happy.

It's all personal preference. My car is around 170 crank, but I've driven 350 crank e30's. 300 wheel is super fun, and that's where my car will end up for now, but 400 would be the sweet spot for the car. A bit overpowered, but not uncontrollable with good suspension (like my car and the turbo car I drove had).

[Gus]

To give some context behind the question, my Alpina M52 is putting out 260 hp and you start running into issues with injectors, fuelling and brakes/tyres taking a hammering (on track) - plus the M20 is cool and in some ways I wish I never went down the rabbit hole involved...more time driving the car would be better! To AWDBOB's point - Turbo cars are never "done". I am nearly nearly there but still a couple of things to go.

Having said that - I just sourced a later manifold to fit the 540/740 Throttle body so what do I know. Thought that was mainly because talking to someone who has the same engine ITBs are just a whole lot more fuss and cost and seemed a relatively cost effective 10hp or so

For the 2.8 recipe I was thinking this: -M52b28 crank with 130mm rods and "i" pistons is a "budget" 2.8L, but requires machine work to the counterweights and/or piston skirts, plus crank snout adapter, plus slight block deck, aka $$ in machine work and extra stuff, but using cheap used parts. Still 84mm bore

If you use the early pistons you get pretty high comp, put a 288 or similar cam in there and fine someone to tune (which is harder than it sounds) and you're good. Unsure if the injectors will be close to maxed but everything else should be OK. And that seems farily DIY to me. E30Zone has some good stroker info in their wiki. To get to a proper 240 you would probably need a good (BTB) exhaust manifold and some head work...but all achievable.

[Jon_E30_vert]

To give some context behind the question, my Alpina M52 is putting out 260 hp and you start running into issues with injectors, fuelling and brakes/tyres taking a hammering (on track) - plus the M20 is cool and in some ways I wish I never went down the rabbit hole involved...more time driving the car would be better! To AWDBOB's point - Turbo cars are never "done". I am nearly nearly there but still a couple of things to go.

Having said that - I just sourced a later manifold to fit the 540/740 Throttle body so what do I know. Thought that was mainly because talking to someone who has the same engine ITBs are just a whole lot more fuss and cost and seemed a relatively cost effective 10hp or so

For the 2.8 recipe I was thinking this: -M52b28 crank with 130mm rods and "i" pistons is a "budget" 2.8L, but requires machine work to the counterweights and/or piston skirts, plus crank snout adapter, plus slight block deck, aka $$ in machine work and extra stuff, but using cheap used parts. Still 84mm bore

If you use the early pistons you get pretty high comp, put a 288 or similar cam in there and fine someone to tune (which is harder than it sounds) and you're good. Unsure if the injectors will be close to maxed but everything else should be OK. And that seems farily DIY to me. E30Zone has some good stroker info in their wiki. To get to a proper 240 you would probably need a good (BTB) exhaust manifold and some head work...but all achievable.

Thank you! This is the way I am kind of leaning.

thanks again!

[digger]

Thank you! This is the way I am kind of leaning.

thanks again!

what are you goals and expectations for a NA M20 though? you need to have realistic expectations

[Jon_E30_vert]

what are you goals and expectations for a NA M20 though? you need to have realistic expectations

I have update my goals a bit.

1) 200+ hp,
2) drivability and reliability are key factors and goals
3) keeping it as “original” looking as possible

[JehTehsus]

I have update my goals a bit.

1) 200+ hp,
2) drivability and reliability are key factors and goals
3) keeping it as “original” looking as possible

This should be very doable. A stroker kit with higher compression/custom pistons and head work (cam, etc aimed at a fun street profile) and maybe some exhaust changes will probably put you in the 200WHP pretty easily. If you want to drift a bit from a stock look ITBs would be a (relatively) big jump as well.

Just the stroker and head can be done and the motor would look completely stock and could get into the 200WHP range without getting too crazy.

[e30davie]

I see mention you want to keep "driveability". Just remember that the wide open throttle tuning "dyno graph" is the easy bit. cold start, hot start, accel enrich, idle control, idle up. These take forever to tune to oem standards. very rewarding, but if you've not done it before (like me) its a iterative learning curve that takes a while to perfect. 200hp that idles/starts/drives like oem is way better than 400hp that drives like a dog and never idles properly.

[digger]

I have update my goals a bit.

1) 200+ hp,
2) drivability and reliability are key factors and goals
3) keeping it as “original” looking as possible

200 flywheel is achievable with the looking original and reliability requirements. 200whp is a bit more involved as you need decent headwork or bigger cam

[Jon_E30_vert]

200 flywheel is achievable with the looking original and reliability requirements. 200whp is a bit more involved as you need decent headwork or bigger cam

Thank you for the feedback sir!

[ForcedFirebird]

Yup, 200hp seems to be the hurdle. Takes a lot more $$ to get that last 10whp to go from 190whp to 200+, than it does to go from the stock ~155-190.

I chased that 10whp to break 200 several years ago experimenting on a client car:

https://www.r3vlimited.com/board/for...-rotating-assy

It's crazy how building m20's regularly for another ~6yr we can now do 180whp using mix-matched used m20 parts, stock single throttle, and not too long ago broken 200 with a stock manifold/throttle and b25 rotating assy (12:1, big cam, our flow-tested valve job, though).

Since there are no cam blanks left in the USA right now, am working with a custom cam maker to see about having some more cam options for these typical m20 combinations we have been building (less off-the-shelf generic).

[digger]

The same issues people have faced in the past still apply, all that's changed in the last 10 years is people are making bigger power numbers these days pretty much because of the better intake manifold (ITBs style shorter runner better flow) and to a smaller extent better control over the tune with standalone. That's provided a decent incremental gain of around 20-30 rwhp

When i say realistic expectations i mean there's been a couple of threads recently with people that seem disappointed with the results from strokers with basically stock head, mild cam and stock intake. Maths and physics tells you a mild stroker with stock induction parts is in the ballpark of

155 whp x 2.8/2.5 = ~175whp +/-

which is about what an Alpina 2.7L made in the late 80's early 90's 200-210bhp flywheel. if you build something along those lines that's what you're going to make.

[ForcedFirebird]

^^^ agree/disagree.

Read a long (overdue continuing education), article about gas porting, effects and vs racing rules. Many classes don't allow gas ported pistons, so the new "cheat" is to use gas ported rings (rings are open in most classes, even "spec".

Conventional rings came in last, even though the gas ported pistons was considered the "base".

Results were:

Run 1, gas ported pistons = xxx bhp
Run 2 gas ported rings/conventional pistons = xxx+2%
Run 3 conventions pistons, conventional rings = xxx - 3%

Doesn't sound like much, but 3% at 200hp is 6 of those 10 we are looking for.

[ForcedFirebird]

To add, an optimally built stock-spec m20 only using standard rebuilding procedures, and stock ECU /components produce closer to 160-165whp. PB is 171. One client claimed 179 on his spec engiine we built (got a custom tune and headers tafter the fact), but wasn't there to verify. When our car was 167, he was leaving us on the straights, even with a better exit on our part.