Custom intake manifold for M20

[Elliot]

Have anyone try to build a custom intake manifold for a NA M20?

I am thinking about either this or doing extrude honing. I just think the custom intake will look a lot cooler.

[matt]

Do you really think you can make an intake manifold that will work better than the stock one?

I wouldn't even bother extrude honing.

[Elliot]

I am not a racer car builder but there are equations available to design the intake
just wondering if anyone had tried it before


Elliot

[euroshark]

I've seen it done on cars with forced induction.

On a NA M20 it probably wouldn't be worth the time and effort, unless the "manifold" was simply an adapter for some throttle bodies or triple Webers...

[matt]

It doesn't make much sense on a car with FI either.

Unless you are moving the powerband of the car well outside the stock RPM range of the motor, you will find it very hard to make improvements.

BMW intake manifolds are fantastic. Seriously.

[strad]

Have anyone try to build a custom intake manifold for a NA M20?

I am thinking about either this or doing extrude honing. I just think the custom intake will look a lot cooler.

WTF?? Who cares what it looks like? Be assured that BMW's engineers spent a lot of time fine-tuning the manifold to meet the air needs of the motor within its stock rev range. It is not likely that you are smarter than they are, nor is it likely that you have the resources ($$$$) to make a better manifold.

[dark89e30]

I did a little manifold work. I matched all of the ports to the head (took off quite a bit of material) and tapered in about four inches. In the plenum, I took out all of the sharp edges and made all of the curves as gradual as possible and then polished it. Just use some emery cloth for the runners though, polishing will provide less power. I also removed ALL of the cast marks on the exterior and blocked the emblem and stripes so its all flat and level then polished them and then I flat blacked it. Totally worth all of the time spent (ALOT!). Removing the cast marks really makes a nice difference for appearance. After all was said and done, I got 10 rwhp on the dyno out of it with a nice improvement in throttle response. It would be alot faster with porting bits (I did mine all by hand with files etc.) but you need a really big compressor (at least 60 gal) to be able to not stop and be REALLY careful. But it cost me about $30 in materials. Not bad for 10 rwhp!

[digger]

whats with people thinking that BMW knows best.....these things were designed pre CFD days so it would have cost alot to design, build and test and then design build and test again.............back then so i question how much testing they did and how many evolutions they actually did IMO and it makes sense that it can be improved somewhat.

[matt]

It may be possible, but most of the "custom" intake manifolds I see don't even get the most basic stuff right.

[Andreas]

I agree with digger. I doubt that there was much emphasis on building a good intake manifold in the late 80s. Low to mid range torque was probably their main concern. If you wanted more power, you put in a bigger engine.

Just look at how each runner is sacrificed due to extra material protruding into the runner - this is needed to clear the bottom nuts which fasten the manifold onto the head. Is that the ultimate design ?

Another question. If the M20 intake manifold design was so good, then why did they not use it on later 6 cylinder cars ? I think the basic design of the intake manifold for 6 cylinder BMWs hasn't changed since the E36.

So yes, Elliot go ahead and do something different. While we may not add substantial power to the engine, we can have fun customizing it. Sometimes just being different already makes the effort worthwhile. Be warned though, moving away from the standard intake manifold is quite difficult.

Here are some pics from my efforts for my 3.1 stroker race engine's new intake system. As can be seen from the pics, certain things have to be moved and/or changed to work properly.







A thread for this car currently exists here http://forum.e30clubsa.co.za/viewtop...=1118&start=60

Enjoy your modding.

[rThor432]

This is where I stand on the whole modified vs stock intake manifold arguement...


edit: Not my motor, it's a friends.

[swimstarguy]

rThor432, that's the craziest M20 I've ever seen.

BMW designed the intake mani for a passenger car. Something to get decent enough airflow while not killing mileage. And to not spew pollutants into the rain forest, or something. There's plenty to be had by freeing that up. They didn't design a manifold for a race car.
But...
Even if you have 0 resistance to airflow in that and everything is the proper with and length, you still only have 1 intake valve.


~Zar4

[rThor432]

Yeah it is a great engine. It's a Warsteiner built car. If you think it looks crazy, you ought to see it in person. It belongs to a guy who used to work at the same shop as me. Glad I snapped pictures, because he was let go the next week.

I know another guy with the same Dbilas intake setup on a 2.9 M20. I think it was at 184ish whp before it was tuned for the new throttles. His car had a full Supersprint exhaust and sounded like a Ferrari.

One of these days I'll get one of those individual throttle manifolds, just not anytime soon.

[matt]

I know another guy with the same Dbilas intake setup on a 2.9 M20. I think it was at 184ish whp before it was tuned for the new throttles. His car had a full Supersprint exhaust and sounded like a Ferrari.

Sweet... only 5hp less than my almost stock 2.5.

Probably way less torque also, despite the extra displacement.

I wish you guys nothing but luck, but I wish you would consider a mod that will actually give significantly more power (like a turbo).

[SA E30]

There is a reason this is the M20 forum... cause the guys want to work M20's not swap in a M50... go play in the M50 forum if u feel like blowing smoke up ur own ass.

Now back onto the thread, The M20 intake and head are seriously restrictive, well not for a std 2.5lt , but once you start stroking the motor, the intake is and head is where the bottle neck is... More so the head, as you can only get so much air into the combusion chamber though that 1 valve.

I love the M20, and although I do... I've realised 24v is the way to go, and due to that I am fitting a S50b30euro into my race car... The amount of money I will spend to get to that HP figure asprirated with an M20 is just out of the question.

I think there is a lot that can be done to the M20 to push it up there, the money just isn't viable.