Cam and headwork

[DCColegrove]

Actually making the manifold ports smaller and the right shape and surface finish is the trick... Cutting the manifold in half and then welding it back together is the biggest bitch... I hate port work... It's tediouse mind numbing...

But you can make big power with an M20...

But as Nando stated it take a "holistic" aproach.

[nando]

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.

there is an easy way to measure the TB and see if it is a restriction. You would need two map sensors - one measuring vacuum inside the manifold, and one just before the throttle inlet. if there is a significant pressure difference (intake pressure lower than before the TB), then the TB is a restriction. Measuring the manifold itself would be more difficult. Actually I would like to try this on my own engine, I just need to get some extra vacuum hose.

I still don't like the M30 AFM "upgrade". It's never going to run correctly, one part of your map will always be off, be it part throttle, idle, or full load. Most people "tune" the thing by the seat of their pants and pray to god nothing breaks.

As far as MS, it's a great way to learn, and it's a nice match to the M20. It will get hated on a lot by the r3v crowd but that's why there are guys like Mark D who will do this stuff for them. Ditching the AFM altogether makes a big difference in power through the entire RPM range, but motronic works really well for a cruiser/DD (any idiot can tune WOT, but getting the part throttle/cruise area smooth is very time consuming and difficult). It's up to you - but beware you will find those 19#s are too small if you switch to standalone.

[DCColegrove]

...
I still don't like the M30 AFM "upgrade". It's never going to run correctly, one part of your map will always be off, be it part throttle, idle, or full load. Most people "tune" the thing by the seat of their pants and pray to god nothing breaks.

....

^^^^^

If nothing else...

Pay attention to this.

EDIT: It's Daniel (please) and the aditional C is because I stutter. :p

[z31maniac]

ok I'll ignore any thoughts about the arm. What size injectors are you running?

Any idea if the 19s would be enough for the headwork and cam, or would it be best to step up to a standalone at that point?

[nando]

42#, but I got them with only 1500 miles and cheap, and I've had thoughts of boost. They are definitely bigger than I need, any bigger and I wouldn't be able to tune them (my idle PW is barely more than the injector opening time). I think 24# are a good match with a bit of room left over, 19# are enough if you are running motronic and less than 200bhp though. I had 19# before and I was at 90% duty cycle with about 210bph, which is too high.

[z31maniac]

Good to know. I don't know if I'll bother with the effort of doing a head and cam on a stock 130k mile bottom end, but if I did I wanted to know if it would be worth the effort.

Related to a stroker.

Any input on S52 vs M54B30 crank? They both have the same 89.6 stroke, correct? Are they the "same?" IE, same construction/weight, is one preferred over the other?

Is there one block that is better than any other to begin a stroker build with? Or are the similar enough that it doesn't matter?

[nando]

the S52 crank has the same stroke. I think the M54 is basically the same, but it might be trickier to bolt the M20 VR wheel to it, but it's certainly possible. I would ask hoveringuy about that as he has experience with the M54 crank and getting it to work with the ODB1 VR circuit, which is the same as the M20B25/Motronic 1.3.

I don't think the blocks are much different. However, the earlier blocks have a 360 degree thrust bearing, later blocks only have 180 degrees. The earlier block can probably handle higher RPMs better than the later ones because of this (i've heard the S50s are subject to crank walk at high RPM?). They also have a 360 degree oil groove on the thrust bearings. Jixer says there is more clearance inside the early blocks, but I have no idea if this is true. But I would still prefer the early block because of the better bearings.

[z31maniac]

Pre 9/87 blocks, or even earlier? Do you know?

[nando]

I think that's about the right timeframe. I think my block is a 7/87 ('88 ix) and it has the early bearings. It should be pretty easy to find an early block though.

[BMWLA]

are the early blocks a lot tougher than the b25s ? no one seems to be able to tell me here

[z31maniac]

are the early blocks a lot tougher than the b25s ? no one seems to be able to tell me here

Read post #37.

[BMWLA]

Read post #37.

isnt he talking about M 50 on ?

I mean the m20 b27 compares to m20 b25

[z31maniac]

No, this thread is about M20s.

We are talking about early M20 blocks (which would be pre 9/87 M20B27s) vs the later M20B25. And the different bearings being the main difference.

[nando]

No, this thread is about M20s.

We are talking about early M20 blocks (which would be pre 9/87 M20B27s) vs the later M20B25. And the different bearings being the main difference.

this applies to early M20B25s as well.

I don't think one block is inherrently tougher than the other. the biggest difference seems to be the main bearings.

[z31maniac]

Ooops, forgot there was an '87i/is.