Let's see how much m20 heads suck.

[4x4_e30]

I got 22deg as well. I have the head reverse engineered to the best of my caliper measuring ability, put a degree finder/ dial indicator on the cam and got a rough profile. Pipemax gives me a target duration at .050" of cam lift, so I was/ still am kind of in the dark as to what that equates to in valve lift. Rocker ratio's are still perplexing me, CAT cams specs show 1.61:1 at max lift, but my measurements on the stock cam/ valve arrangement put me closer to 1.45:1, and my model gives me 1.55:1 ratio.. I pretty much concluded this was all a huge waste of time, and I'll just go with the cam that has the highest lift with least amount of duration.


My computer isn't fast enough to get the mesh settings I'd like so the flow numbers are meaningless, looks cool though.


As far as seat angles go, I went with a Goodson FT-45063U1 cutter per advice from Rama, that is 25 45 60 with a 1.5mm seat width then going to do a 75 deg bottom cut to meet the throat. I got the RHD engineering 44.5mm intake valves, machine shop is putting the bigger seats in next week (SPI SB1812-10) throat will be 39.5mm. I'm leaning towards shaping the roof of the port like the TK head(s), then the rest will be ported to match my target CSA, biggest SSR possible, with a slight taper to the manifold. Hopefully I'll get to >200cfm by the time I grind through my 2 practice heads.

All I need now is someone with a calibrated flow bench to send my orifice plates to...

[ForcedFirebird]

Pretty sure the valve angle is 22*

Finally had a chance to repeatably measure this for a consensus. 22° +/- .3°

Question- Is there a sizable difference between doing a standard 30-45-60 cut with 30deg back-cut valves vs. whatever angles you've come up with?

Short answer, yes.

[4x4_e30]

Question- Is there a sizable difference between doing a standard 30-45-60 cut with 30deg back-cut valves vs. whatever angles you've come up with?

[325e '87]

If this post of mine is perceived as a hijack then let me know, and if there’s a forum problem with you telling us what you do in your shop, don’t let me get you in hot water.

So, mr firebird, I’m taking your thread here to mean that you recondition and assemble heads at your shop?

Also, you seem to have found a formula that provides nice performance gains from a nearly stock m20?

And, the combination of your head assembly and dme chip is a nice daily driver with some solid performance?

I’ve contacted you before wanting to know more about your shop and I’m still wanting to make my 200,000 mile motor like new again, stopping short of building a new engine from another car. It looks to me like you have a way to match heads, cams, valves, and dme chip. I don’t remember if you require higher injector flow than the stock ones.

[ForcedFirebird]

Here's a before/after for an SCCA ITS car. No porting allowed (well, 1" past the gasket only, where it hurts the m20). This was done only with seat angles, back cuts, valve shape, and most importantly, starting with an untouched head that already flowed well for stock...

Lift" CFM before/after
.1" 29/34
.2" 59/60
.3" 114/118
.4" 171/181
.5" 174/185

Just got a report back from this mail order customer. This head with a 2.5 rotating assembly 14:1 pistons (stock dome), and 288 Schrick camshaft made 208whp/186wtq on a MUSTANG dyno with little tuning. Engine has stock intake manifold, stock throttle body, valve and throat cuts only verified on the bench (although this was a hand selected high-flowing stock head from our inventory).



Client's local tuner thinks he can get closer to 220 once dialed in :D

Waiting for a copy of the dyno sheet to add to the M20 dyno thread.

[ForcedFirebird]

It's meant to keep flow stock, but permit certain allowed manifolds and carbs.

This is a very old rule (relatively) that was originally meant to allow carburetor
swaps to try to equalize 1.0- 1.6L
non-crossflow engines in little British sportscars.

t

Thanks for the info. Not much into SCCA, figured it was a rule for domestics for the very same reason.

[TobyB]

sounds like a pretty silly rule, pretty much all the stuff worth fixing is 1" downstream of the gasket. the straightest biggest part of the port is never the most restrictive part so its not a huge limiting factor.

It's meant to keep flow stock, but permit certain allowed manifolds and carbs.

This is a very old rule (relatively) that was originally meant to allow carburetor
swaps to try to equalize 1.0- 1.6L
non-crossflow engines in little British sportscars.

t

[ForcedFirebird]

Pretty sure the valve angle is 22*

Did not measure personally yet. Was going by memory from and article read in the past. Very well may be 22.

[digger]

Pretty sure the valve angle is 22*

[ForcedFirebird]

So, speaking geometry.

If we move the valve angle to correct the seat concentrically, we "should" be moving the curtain in a favorable direction using thought experiments based on data. Many theoretical scientists have been wrong in the past, so I will back my experiment with raw data. This will also give an added benefit of decreased rocker geometry ratio, it's a win-win!

The m20 was designed around tumble and swirl which decreases flow according to modern models. The "ball in sand" shape of the pistons effect the power output unproportionate to standard models.

You have to remember, the m20 was designed in an oil crisis combined with new emissions regulations. As a result, the m20b25 makes as much HP as a C3 Corvette with a v8! Back then we ("we" as in the domestic market) were concentrating on TQ because that's what "felt" fast. :/ My e30 rapes my dads 76 vette except on a dig in a race. Yes, dad is 20 years older than me, my car is 20yr newer than his and handles 2x better, but I can still lap him. :)

[ForcedFirebird]

Will you do a myster-e head? I should add, I can't afford to provide one, sorry. I do like this thread!

I have flowed Bimmerheads stuff as a local;s head cracked a year after purchase and we replaced it with ours. Showing other companies numbers in comparison to mine is not conducive to the community as a whole. If they want to do a public demonstration, that's up to them to produce flow and/or dyno results. We are very different companies with different goals. I prefer to sell a hand full of bad ass heads vs multiple stock-ish heads. ;)

[ForcedFirebird]

All pics are fixed in the thread!

Next up is sectioning an m20 head into single cylinders, changing the valve angles and flow testing results!

Something interesting I found is the 885 head does NOT have the valves perpendicular to the seats!!! BMW "leaned" the valves in relation to the sets by about 2°. Always noticed doing valve jobs that the seat is always thicker near the spark plugs.

From vertical, the m20 valves are splayed longitudinally 0°, and 20° transverse.

Here's a pics of a sectioned head, seat removed, guide/valve reinserted.

As you can see, the seat pocket and valve guide boss do not correlate....

[ForcedFirebird]

42.7cc with .003" (~.7mm) off total deck height, stock chambers, SuperTech Valves (+/-0mm), Bosch wr8lc+ plugs. (EDIT: to add the stock valves actually subtract ~.5cc to the mix with their flat faces)

[ATTACH]119586[/ATTACH]

[digger]

at low lifts it will be the seat and valve

Some quick numbers

1) Port entry size = d37.5mm = 1,105 mm2
2) Port Min area/choke (near guide before short turn) = d34.5mm = 935 mm2
3) Port throat = d36.5 mm (87% Valve Diameter) = 1,010 mm2
4) Flow Aperture / curtain area ( using Gordon Blair formula)
- 0.100” lift: 231 mm2
- 0.200” lift: 548 mm2
- 0.300” lift: 904 mm2
- 0.400” lift: 1,284 mm2
- 0.500” lift: 1,686 mm2

so above 0.300" the port min CSA starts to limit flow and the entry size is 18% bigger than the min cross section

[LateFan]

Good graphic - interesting.

Is it the area just upstream from the seat, or the seat and the valve itself causing the restriction there?