Let's see how much m20 heads suck.

[ForcedFirebird]

yeah m54 at peak youre already there iirc, through middle unlikely

done an N52 ?

Not yet, but there's a core sitting on the shelf for whenever I can make time to cobble an adapter and valve opening apparatus together.

[digger]

Not yet, but there's a core sitting on the shelf for whenever I can make time to cobble an adapter and valve opening apparatus together.

my guess its not any better than the m54

[ForcedFirebird]

thats starting to get very good that cracked one you gave me went 200@400 and 216@ 500 +2mm

Valid flow test #10 (at least 10 trips to the bench), currently 195@.400 and 209@.500 :)

Material removal is becoming advanced for little gains. Pretty sure this port is about to stall, finally. The chamber is stock at this point, haven't done any shroud work.

EDIT:

It's officially over for the port. Now the gains will dwindle everywhere except the very high lifts as the port area is getting too great.



Time to do some testing on the chamber, but the 885 has a decent design already, so don't expect chamber gains like I would on the parallel valved domestic iron head.

[digger]

Valid flow test #10 (at least 10 trips to the bench), currently 195@.400 and 209@.500 :)

Material removal is becoming advanced for little gains. Pretty sure this port is about to stall, finally. The chamber is stock at this point, haven't done any shroud work.

EDIT:

It's officially over for the port. Now the gains will dwindle everywhere except the very high lifts as the port area is getting too great.



Time to do some testing on the chamber, but the 885 has a decent design already, so don't expect chamber gains like I would on the parallel valved domestic iron head.

find a good core then rinse repeat 6 times, or get it digitised

[ForcedFirebird]

find a good core then rinse repeat 6 times, or get it digitised

I have several good cores, two AMC castings and a few broken/cracked heads. Will just hang on to this chunk for future reference as I have with all the other makes of heads in the past.

This isn't the first port jobber, but this is one was just to see how far it would go, and didn't have a name attached to it, so there's no qualms about posting specifics (racers tend to be secretive). In the end I was just blatantly removing excess material in the sweet spots - just to find the end. I have never had a "no holds barred" 885 head where money was no object, 90% of head sales are racers with specific rules to go around. I have a customer who wants aggressive porting, so, I would say this is about as "aggressive" as it needs to be. :)

I have a couple more ports to play with from this chopped head, but since this research isn't exactly "billable hours" gotta get back to projects. Two days last week I ran on ~3-4hr of sleep since I do this stuff late nights. :/

[ForcedFirebird]

my guess its not any better than the m54

I have a feeling it is better.

Got to work 1.5hr early today and fired up the die grinders and flow bench. There's more flow in that test chunk of head. Got the loses back in mid-lift with de-shrouding. So, will use another port from the chopped head and get it back to test #9, then do the chamber again.



While working on this stuff, grabbed the n52 head for a quick visual. The n52 port resembles a 400 casting (m/s52) than it does the "D" of the m54. There's also about 75mm of runner cast into the head, rather than be part of the intake manifold. Injectors are in the aluminum and much steeper angle than the previous 24's (as to hit the back of a hot valve). The chambers are actually heart shaped, more than pent/hemi - and there's a TON of de-shrouding. I would imagine the de-shrouding is due to the nature of low lift situations of the valvetronic, but honestly it looks like BMW took some cues from the s54 on the n52. Almost the entire port is machined, very little cast areas exposed.

While it was out, measured the head bolt pattern, and these heads will be a pain to build a jig for - #1 and #6 have different bolt patterns from the center cylinders. So, to flow them all, two jigs will have to be made, one for center cyls, and one for outer that will need to be rotated 180° on the bench (when testing opposite ends) to have the port facing the bench operator.

[ForcedFirebird]

Did this one today. Stock sized valve, no hand porting, only valve/seat machining and SuperTech valves.




and for comparison sake:



EDIT: Went ahead, got greedy, and did a little more, and this is why it's nice to have a bench. :/ Good thing this was just a test on a cracked head to proof concept...

[hasa]

What do you think about the exhaust ports of M20 ? Exhaust port in 885 head has about 31mm diameter where it opens to manifold. Isn't that small?

Do you enlarge the exhaust ports when prepping heads for race engines?

[digger]

What do you think about the exhaust ports of M20 ? Exhaust port in 885 head has about 31mm diameter where it opens to manifold. Isn't that small?

Do you enlarge the exhaust ports when prepping heads for race engines?

The exhaust port is terrible but the exit size is the least important part of the port to address that. The short side radius needs to be fixed foremost . Just like the entry of the inlet port is the least important part.

[fiftytakedowns]

Such a beautiful thread, Digesting information here when it's time to refresh the head on my IX.

Cliff notes I've picked up for highest ROI is:

+1 Valves
Higher lift
3 angle valve job

[Digitalwave]

Hey John. You're doing God's work here. I have a Schrick 284/272 that broke in between cylinders 4&5. Would the 2 pieces of it be helpful to your testing? I can mail down to you if so.

[I_DRIVE_E30S]

John,

if you're still replying to this I have a few questions about the eta intake you mentioned early.

1. is the intake length benefit related to the stroke and the added velocity from that?
2. is this impacted by running a turbo specifically on the eta/885 combo? For instance, would the longer runners benefit spool and below boost driving?
3. would the added torque extrapolate as rpm increases under boost?
4. would the intake giving up past 5500 be a huge impact?
5. how much hotter did it make the intake charge?

lastly, thanks for taking the time in doing the digging and then posting your results. The back and forth between a few of the members and you on multiple threads is incredible.

[ForcedFirebird]

What do you think about the exhaust ports of M20 ? Exhaust port in 885 head has about 31mm diameter where it opens to manifold. Isn't that small?

Do you enlarge the exhaust ports when prepping heads for race engines?

Fig. 10.10. The more poorly the turn into the valve throat area is, the smaller the valve appears to the port, and therefore the port needs to be smaller in cross section to keep a lesser amount of air up to speed for inertial ramming of the cylinder. As the port inclination becomes steeper, it is able to utilize the valve better and the valve appears to the port to be bigger; hence, a bigger port is optimal.

Seeing a stock exhaust valve is 36mm and the port angle is ~60° (floor to valve),BMW did a good job at sizing the exhaust port IMO. In stock form the exhaust already flows ~80% of intake, which is a good ratio. Even increasing valve size to 37mm, the port shouldn't be much larger than ~33mm. The minimum CSA is actually a bit smaller, and just before the short turn.

Now you have me thinking. I have done similar ports in my early days that piked up a but by raising the roof, but the m20 doesn't have much room to do so unless the primaries are moved, or oversized, might not even be worth exploring.

[digger]

the exhaust port exit is the least important part of the port (just like the inlet port entry size is on the inlet side). IMO the stock ex port is fairly rubbish in absolute, definitely not compared to other heads of same era, though that's a low benchmark. The short turn area is terrible just run your finger over it. You can tell a good port in about 2seconds by feeling it. if it is not smooth/ gradual it simply wont work at 1000ft/s as seen in the operating engine. Making the exit bigger or "Gasket matching" is not the answer though.

Take a port mould and slice it up. the smallest area is at the short turn near the guide where the height is restricted and the path is sharp radius so this is a much more critical area than the exit. The focus should be on between the following areas:

• 0.5" before the valve i.e. the chamber
• 0.5" after the valve so up to and just after the short turn in particular the roof of the port as the bottom part of the main section of port is a dead area in reality.

Unless you've properly addressed these then you can start to think about the exit. You can get an idea of the exit size based on the correct sized header which is simply a function of hp:

• On a mild engine (99% of m20's) sub 280hp you only need 1-3/8" OD header off the head (assuming stepped design and not garbage quality) so 31mm stock port is fine as you do NOT want the step change in area right at the head as you are wasting the energy of the exhaust flow by slowing it down
• If you are using a 1.5" in header (again stepped and not garbage) it will easily support 350 flywheel hp then no need for port to be more than 34mm which is about the gasket size coincidently.

[ForcedFirebird]

^^Didn't have to mold, have a sectioned head sitting on my office desk lol. Yes, the design is horrible, the short side especially. The whole port needs to be raised and the floor filled.