Cam and headwork

[Farbin Kaiber]

Daniel the "Camera" Colegrove

[nando]

Daniel the "Camera" Colegrove

did you get that from the wiki? :rofl:

ok, enough of this off topic banter, lets try to keep this thread informative. ;)

[z31maniac]

Have you considered an M50 swap? :)

j/k I'd say go with a 272, but seriously, M50....

I've considered alot of things, 24v or turbo M20, or stroker M20.

I like the idea of a built M20 and I know it won't provide as much power or economy as a 24v. But eventually I'll build a bored and stroked M20 and I think it should be the perfect amount of performance for this chassis.

I already have a blast in this car because of how it handles, looks, etc.

I'll buy another sportbike in a year or two once I get this car done to take care of my need for something that is ACTUALLY fast.

nando, thanks for the direction, I know I've PM'd you at length about your build. The car is running great, so I'm going to do a compression test soon and if it turns up good I may look at building a head for it.

Any idea on the stock manifold with a mild cam and headwork, ie when does the stock intake manifold become a hinderance. A guy that races his E30 down here with BMWCCA saw really incredible flow gains from having his manifold Extrude Honed, I think the average flow went from 170s to upper 230s CFM per runner, but I don't what effect it has on velocity.

Any ideas?

[Farbin Kaiber]

I would just go M50/2 You will spend less, and be done faster.

[OrganicMechanic]

there a several Tricks to raise compression--

Facing the piston tops .010-.020 maintain tolerance of +/- .002
reassemble bottom end and measure at TDC deck height to piston top,
disassemble
mill block to .005 deck height

Shave head to preference

[z31maniac]

^You seem to have missed the point. If going to the point of tearing down the motor I'd wait until I have the money for crank/rods/pistons and bore and stroke it.

I would just go M50/2 You will spend less, and be done faster.

No, cause I wouldn't throw in an unknown mileage 24v without at least a bare bones rebuild.

[nando]

I've considered alot of things, 24v or turbo M20, or stroker M20.

I like the idea of a built M20 and I know it won't provide as much power or economy as a 24v. But eventually I'll build a bored and stroked M20 and I think it should be the perfect amount of performance for this chassis.

I already have a blast in this car because of how it handles, looks, etc.

I'll buy another sportbike in a year or two once I get this car done to take care of my need for something that is ACTUALLY fast.

nando, thanks for the direction, I know I've PM'd you at length about your build. The car is running great, so I'm going to do a compression test soon and if it turns up good I may look at building a head for it.

Any idea on the stock manifold with a mild cam and headwork, ie when does the stock intake manifold become a hinderance. A guy that races his E30 down here with BMWCCA saw really incredible flow gains from having his manifold Extrude Honed, I think the average flow went from 170s to upper 230s CFM per runner, but I don't what effect it has on velocity.

Any ideas?

a ported manifold will definitely lower the velocity. It's best coupled with headwork and an agressive cam. But you can still make upwards of 200 at the crank on a stock intake manifold, just having it gasket matched.

The thing is with the M20, unless you put everything together as a system, you will be dissapointed in the results. the manifold alone will probably hurt performance, but coupled with a nice cam, head porting, good headers, a compression increase and of course more displacement, will certainly increase performance. Similarily, any one of the above mentioned mods won't go very far on their own.

I think the main reason nobody bothers building an M20 is because most of these guys aren't interested in building a motor at all, they just want to buy an M50 from the junk yard, slap it in over the weekend and call it a day. Nothing wrong with that, just a different mindset from somebody who enjoys building things and knowing how they work. Of course you can build an M50 in the same way, it's just going to cost even more than building an M20.

[Jesse30]

you can get m50 or m52 motors with known mileage and records. along with carfax.

:D

[nando]

right, but that's still not the same as building your own motor. It's an apples/oranges comparison, I can't explain it. It's not even specific to the M20, most people here don't want to build their own engine at all.

[Farbin Kaiber]

And you can find $400 replacement m50's with 90k on em.

[z31maniac]

Well I'm definitely interested in doing the proper research and building a proper M20, I just read through jixer's thread over on e30tech, and he seems to think the stock manifold is holding back ALOT of HP on the build they completed.

What about BB throttle bodies once you have done these types of mods? I see that Korman sells one for a fairly reasonable price. The car will have 19lb injectors, MarkD 91 octane chip, headers, 2.5" single exhaust soon. After all the debate on the subject I'm now unsure if the M30 AFM is worth doing. I have also considered going MS in the spring on a relatively stock motor so I can learn the inner workings and how to properly tune before an expensive to break built-up motor goes under the hood.

So if the intake manifold and TB aren't the restrictions up to stock displacement and worked head, that's good to know.

[Jesse30]

right, but that's still not the same as building your own motor. It's an apples/oranges comparison, I can't explain it. It's not even specific to the M20, most people here don't want to build their own engine at all.

no i totally get it. i had a 2.7 in my first e30. its a great feeling turning the key on a motor that you tore into and rebuilt. its something that cant really be explained unless you've done it yourself.


im just speaking in a term of bang for the buck

[z31maniac]

Like nando said, this thread is NOT ABOUT M20 vs 24V, its about M20's.

If you think building one up is a waste, then just ignore this thread.

[Farbin Kaiber]

Got ya.

[nando]

And you can find $400 replacement m50's with 90k on em.

which is probably the reason nobody really builds an M50 from scratch either. rebuilding the valvetrain alone would cost 3-4x more than that.