m20 with small mods: what gains can be expected?

[iXguido]

So I'm looking into some mods for my m20 right now. The motor was supposed to have been rebuilt by BMW by the PO and has a little over 40K miles on it now. I am thinking of:
Miller MAF and WAR chip
Schrick 272 cam
Already have Racing Dynamics headers, but not installed
ITB setup from a euro s50 that I already have and am going to try and custom fit

My question is does anyone have any idea what kind of power I would be looking at making from this setup? Also if anyone has any suggestions for additions/subtractions/changes to this list, I would appreciate it

Thanks r3v,
Willy

[Wh33lhop]

If you tune it right, all of that should be a pretty noticeable improvement and will shift the powerband up a bit, if your M20 is indeed healthy you'll probably be looking at 175ish whp, give or take. The ITBs won't really give you much of a boost, but they will give you 6 throttle responses.

Also, take a look at the Schrick 284/272 cam. You'll want to check your valve clearances before bolting your head down for good, but it's a bit more aggressive than the 272 and doesn't require aftermarket valve springs.

[iXguido]

So with the 284/272 cam that would keep the intake valves open longer correct? Does that mean that the m20 has more problems with intake than exhaust? Also what about bigger injectors?

[Wh33lhop]

Problems? That's not exactly how I'd put it. But yes, the 284/272 is a dual-pattern cam. I'd get some slightly bigger injectors, 17.5lbers out of an M50 or 19lbers from a Mustang will do fine and help a bit with atomization because of the multi-pintle design.

[iXguido]

Okay what I really meant was more restrictive intake than exhaust. what is a multi-pintle design?

[u3b3rg33k]

My money is on you losing torque (area under the curve) by deleting the stock manifold. I'd consider extrude hone before deleting it, unless you're going to build one with similar runner lengths/volumes (18-19" long runners).

There's a thread 'round here bout a guy that did the dbilas ITBs. definitely disappointing results.

So with the 284/272 cam that would keep the intake valves open longer correct? Does that mean that the m20 has more problems with intake than exhaust? Also what about bigger injectors?

Problems? I don't think that's a good word to use.
Compare the M20B25 to a modern run of the mill 2.5L. I'd say bmw did a pretty decent job with their design in the 1970s. Subaru gets 170hp out of a 4 valve / cyl 2.5L N/A engine. I think 168hp out of an ancient 2 valve / cyl 2.5L is pretty good. the MAF should make it feel more responsive, and hearsay says it helps with midrange torque.

[iXguido]

My money is on you losing torque (area under the curve) by deleting the stock manifold. I'd consider extrude hone before deleting it, unless you're going to build one with similar runner lengths/volumes (18-19" long runners).

There's a thread 'round here bout a guy that did the dbilas ITBs. definitely disappointing results.



Problems? I don't think that's a good word to use.
Compare the M20B25 to a modern run of the mill 2.5L. I'd say bmw did a pretty decent job with their design in the 1970s. Subaru gets 170hp out of a 4 valve / cyl 2.5L N/A engine. I think 168hp out of an ancient 2 valve / cyl 2.5L is pretty good. the MAF should make it feel more responsive, and hearsay says it helps with midrange torque.

I don't disagree that the m20 makes very good power especially considering its age. The word I meant to use was restrictive instead of problems. I understand what you are saying about losing torque, but I really want to get rid of that ugly starship enterprise manifold sitting on top of my engine. Is there anyway to do that without sacrificing torque? That guy with the dbilas ITB setup you are referring to, did he have dyno results? Do you have a link? I have always heard ITB/short runner intakes reduce power at lower rpms and increase at higher rpms...

[nando]

the powerband you get from a schrick 272 or 284/272 isn't suited to aftermarket intakes. a mildly ported stock intake would be plenty. You'll only lose all your mid range, and gain almost nothing in the top end (especially since those cams will peak way earlier than an ITB setup is usually designed for).

then add all the custom work and expense. It's just not worth it. I'm not saying there is no value at all in an ITB setup, but there really isn't on a mild/street M20. Especially the very oversized (by about 10mm) and expensive Dbilas ITBs. The more I read about them the less I like them. If I got them for free I wouldn't use them. The manifold they come with sucks even more..

There's nothing wrong with the stock manifold. The Helmholtz tuning produces a very strong and relatively flat torque curve from 3500-5500rpm, and it can still flow plenty of air for a 7krpm redline, especially ported. If you want to "upgrade" because it's ugly (I disagree, but that's beside the point) then maybe you want to upgrade for the wrong reason.

I'd sell the euro S50 intake and use the money to have your stock manifold worked over. extrude hone is nice but I don't know if it's $700 nice. I think bottlecape30 does a ported M20 manifold for about $350.

[nando]

My money is on you losing torque (area under the curve) by deleting the stock manifold. I'd consider extrude hone before deleting it, unless you're going to build one with similar runner lengths/volumes (18-19" long runners).

There's a thread 'round here bout a guy that did the dbilas ITBs. definitely disappointing results.



Problems? I don't think that's a good word to use.
Compare the M20B25 to a modern run of the mill 2.5L. I'd say bmw did a pretty decent job with their design in the 1970s. Subaru gets 170hp out of a 4 valve / cyl 2.5L N/A engine. I think 168hp out of an ancient 2 valve / cyl 2.5L is pretty good. the MAF should make it feel more responsive, and hearsay says it helps with midrange torque.

you know everyone talks about the M20B25 as if it was designed in the 1970s.. but it really wasn't. The block was, kinda. But if you want to say the block was, then basically all the M20-M50 motors are basically the same. You wouldn't say an M50 was designed in the 1970s with the original baby six. The important parts of the M20 (mainly intake/head) were designed in the 1980s, and as far as 2v heads go, it's among the best.

[Wh33lhop]

Helmholtz tuning

Bah. You're just talking about basic resonant tuning here, nothing fancy :p (I suppose for it's time..). That kick we get from that at about 3500rpm is very nice though.

I remember you saying you had a good bit of power choked up in your stock intake (not really the manifold) after the build. What did you wind up doing with that intake?

[u3b3rg33k]

The important parts of the M20 (mainly intake/head) were designed in the 1980s, and as far as 2v heads go, it's among the best.

Good point. Otherwise one could make the same claims of the S14.

Personally, I find the M20B25 intake manifold to be aesthetically pleasing. No sharp bends, apparently equal length runners, and metal. Not that aesthetics really come in to play here.

[iXguido]

Lot's of usefull information here. My number one reason for upgrading is definitely not looks, haha. I am not looking for a flashy engine bay and nothing else, I am just not a huge fan of the intake manifold. But, if it is the best performance option, then I will keep it. So what's the difference between extrude hone and porting? Also I've heard that it's better to port and not polish vs port and polish, is there any truth to this?

[nando]

well the thing about hand porting is you can't really get very far inside. you'd have to cut the manifold up, port it, and weld it back together. extrude hone gets all the insides. The disadvantage is you don't have a lot of control over where the porting happens.

but you can do a "decent" job at hand porting, still improve airflow, and not break the bank. Or pay somebody else to do it. :p

[nando]

Bah. You're just talking about basic resonant tuning here, nothing fancy :p (I suppose for it's time..). That kick we get from that at about 3500rpm is very nice though.

I remember you saying you had a good bit of power choked up in your stock intake (not really the manifold) after the build. What did you wind up doing with that intake?

the manifold or the airbox?

the airbox is unfinished. It's an open K&N filter at the moment. It works as long as I'm moving, but obviously heat soaks when I'm sitting still for a while. That will be fixed soon though.

I haven't done anything with the intake manifold yet. I've got one I'm going to hand port as much as possible though. Basically clean it up, gasket match, and clean up where the TB enters. The entries inside the manifold look pretty good. I'll probably see some gains just by having the 1/8" thick crust of goo and crud cleaned off the runners. :p

[iXguido]

Okay so I'm thinking of getting new pistons for my m20 to add to this list. However, I'm thinking of raising the CR to 11:1. What do you guys think about that? An m20b25 with 11:1 CR and the previously mentioned mods minus the ITB's. ANy suggestions? I have also decided on extrude hone for my intake, and maybe some head work, but that is yet to be decided.