Let's see how much m20 heads suck.

[xxlbimmer]

Cool info. Where would I find a 731 head casting?

[Scallywagon]

With respect to the numbers shown, what rpm range( normally aspirated) would the 885 head flow to. Before it became the limiting factor.
Looking at building a 12:1, 13mm lift M20 for racing.

I would say you need to look for a 731 head and do your research on how to work the bowl, and the combustion chamber for larger valves, or hire someone who gets it.

I believe the 885 will absolutely be a limiting factor (literally a bottle neck) for your desired range.

[xxlbimmer]

With respect to the numbers shown, what rpm range( normally aspirated) would the 885 head flow to. Before it became the limiting factor.
Looking at building a 12:1, 13mm lift M20 for racing.

[cashsterling]

Also love this thread, as an engineer... very cool to read page one, start thinking whilst reading the rest, and see that things seem to moreorless work out as fluid mechanics would predict

[Simple_Smith]

Did you ever get definitive flow/velocity numbers for the modified eta manifold on an 885 head? Basically wondering if it'd be worth it to port match an eta intake for an I throttle body and 885 head.

[digger]

at low test pressure the air will have no problem attaching to a tight radius and thus will not separate, if you correct the CFM measured at low pressure to the more commonly used 28" using the mathematical equation you could get a different (higher) result to that seen if a true 28" pressure is used.

[AlphaE]

Smart guys??!!

[AlphaE]

at the end of the day the peak hp numbers correlate well to hp potential on a good port, given a stock or basic modded head flows 175-180cfm +/- is only good for 260-280hp ballpark

i am not convinced that on a 100% stock head this would be realized, there seems to be lots of thoughts that alot of flow separation occurs on the M20 which need to be addressed to access all that flow. so addressing this separation may not always produce big CFM gains but you will start reaping the benefits of the CFM you have by being more efficnet head on a running engine.

When testing at lower pressure benches like 10" and then calculating flow at 28" only works if the port is good, velocity and velocity profiles are good etc.



the same analogy applies to testing at 28" and wanting to correlate to hp potential if the port is crap its not gonna work under higher pressures that it encounters in running engine and 10% more CFM may not give any extra hp.

More infor on flow seperation please. is this air in the intake/head pulse due to cam profile and rpm? or whats this about?
And the bits about 10" and 28".. is that inches of merc? so they'd have a direct bearing on MAP and air velocity? or am i way off?

lovin this thread!!

[LJ851]

We back our findings up with dyno runs. Last one was 10whp gain by swapping on our porting only, not even a map adjustment in the PCM.

I like your logic john! So many folks living in theorecticalville these days. Dyno proves all, keep at it i love the proof.

[ForcedFirebird]

We back our findings up with dyno runs. Last one was 10whp gain by swapping on our porting only, not even a map adjustment in the PCM.

[digger]

at the end of the day the peak hp numbers correlate well to hp potential on a good port, given a stock or basic modded head flows 175-180cfm +/- is only good for 260-280hp ballpark

i am not convinced that on a 100% stock head this would be realized, there seems to be lots of thoughts that alot of flow separation occurs on the M20 which need to be addressed to access all that flow. so addressing this separation may not always produce big CFM gains but you will start reaping the benefits of the CFM you have by being more efficnet head on a running engine.

When testing at lower pressure benches like 10" and then calculating flow at 28" only works if the port is good, velocity and velocity profiles are good etc.

the same analogy applies to testing at 28" and wanting to correlate to hp potential if the port is crap its not gonna work under higher pressures that it encounters in running engine and 10% more CFM may not give any extra hp.

[downforce22]

i've got a cracked 885 if you need one, and a 200 head that i was going to recycle

[ForcedFirebird]

So to put that into moron friendly terms, if you wanna throw money at a head, do a cam and bigger valves?

Does the story change any when you go to a bigger bottom end? MM somehow squeezes a claimed 240HP out of their beast "M20B31".

No, we aren't done with research. The 885 head will probably need to have material added and reshaped to gain in the low lifts, but time will tell. We have hundreds of flow tests in and are using up all our cracked/damaged heads. Since we are putting time/effort/money into the research with no immediate returns, the process will be slow since it's being done after shop hours/weekends etc.

I can see 240hp no problem if you are talking at the crank, many guys including Digger are over 200 at the wheels which would be near 240 at the crank.

[u3b3rg33k]

So to put that into moron friendly terms, if you wanna throw money at a head, do a cam and bigger valves?

Does the story change any when you go to a bigger bottom end? MM somehow squeezes a claimed 240HP out of their beast "M20B31".

[ForcedFirebird]

Yeah. It's easy to gain flow in high lifts on m20 heads, like well beyond usable cam lifts.