Let's see how much m20 heads suck.

[hasa]

welding ports (for relocation) requires probably unused raw head?

[ForcedFirebird]

Not at all. I've welded used heads, oil pans, thermostat housings etc. The bigger issue is the water jacket just above the port.

[digger]

Here is a couple of ported exhaust ports i have. One is a BMW OE cast 885 (LHS) and the other an AMC spanish casting (RHS)

Unforuntelty i dont have stock ex port mould hand.

they are identifical volume. the BMW has much deeper bowl so a bit more CSA around there but the exit is almost stock where as the AMC has a slighy larger exit

[Tom Galloway]

I don't get it - Don't we know ( from HVAV, plumbing, physics) that the most volume is in the center ( of the duct, pipe, runner). If so any of this "porting" seems to be of little consequence barring some unlikely engineering mistake from the "mother ship".

tg

[digger]

I don't get it - Don't we know ( from HVAV, plumbing, physics) that the most volume is in the center ( of the duct, pipe, runner). If so any of this "porting" seems to be of little consequence barring some unlikely engineering mistake from the "mother ship".

tg

Not really, the velocity is much faster than an aC duct so the air straight lines the port (think line of sight) so follows the roof and does not follow the curvature

[hasa]

Not at all. I've welded used heads, oil pans, thermostat housings etc. The bigger issue is the water jacket just above the port.

Okay, I only listened some talks on pit. People say that the contaminated oil and other residuals in the casting are problem for the welding process. Specially for the exhaust side.

Is it problem for engine cooling if one welds the coolant chamber closed and lift the port (specially the inlet port) ? I assume that it is required if one tries to achieve the CFM needed for best power above 8000rpm on a stroker M20.

[ForcedFirebird]

I don't get it - Don't we know ( from HVAV, plumbing, physics) that the most volume is in the center ( of the duct, pipe, runner). If so any of this "porting" seems to be of little consequence barring some unlikely engineering mistake from the "mother ship".

tg

Near sonic fluid reacts far different than a squirrel cage fan. To put things in perspective, you need about 500cfm per 12,000btu to cool/heat a home. A 2500cc engine moves .88cf every other rotation. At idle (~800rpm) you need 350cfm. When air starts moving at much higher speeds, it "acts" more dense. This is why satellites fall when the atmosphere expands, or they lose a little altitude, why supersonic planes need heat shielding etc.

Also, at those speeds the Coriander Effect is huge. You can demonstrate this in your kitchen sink. Turn the water on a slow stream and touch your finger to the edge. You will notice the stream makes a turn where your finger touches it (imagine this is the short side radii). Turn tap to flow more and repeat. The faster moving fluid will move further away from vertical.


So, in short, yes, flow does have an effect on power output. Otherwise, manufacturers wouldn't have gone to 4 valve heads ;)

[e30davie]

or 5 valves! though there aren't many of them.

I have always wonderered how steady state flow testing relates to real world flow in regards to reversion and accoustic effects. as in real life the air flow in an engine is quite the opposite of steady state. OEMs spend a heap of time tuning intake manifolds for pulse resonances, get a bit more air shoved in with the returning pressure wave. if you say increase the steady state flow bench results by X%, i suppose any resonance effects also take advantage of this. but perhaps not always? maybe if you make the port too big with favourable flow bench results, but the resonance effects are reduced?

[digger]

or 5 valves! though there aren't many of them.

I have always wonderered how steady state flow testing relates to real world flow in regards to reversion and accoustic effects. as in real life the air flow in an engine is quite the opposite of steady state. OEMs spend a heap of time tuning intake manifolds for pulse resonances, get a bit more air shoved in with the returning pressure wave. if you say increase the steady state flow bench results by X%, i suppose any resonance effects also take advantage of this. but perhaps not always? maybe if you make the port too big with favourable flow bench results, but the resonance effects are reduced?

Oem generally don’t optimise ports and valve jobs well because it is too expensive to mass produce and they are not trying to maximise power. There is always heaps left on the table.

flow is from the variables: CSA, discharge coefficient and pressure ratio.

flow bench testing is improving discharge coefficient and/or CSA. Wave tuning wizardry is improving pressure ratio

[Tom Galloway]

Thanks, I knew there were some smart guys here.

[mikey.antonakakis]

flow is from the variables: CSA, discharge coefficient and pressure ratio.

flow bench testing is improving discharge coefficient and/or CSA. Wave tuning wizardry is improving pressure ratio

Perfectly described. I miss having a free license in Ricardo WAVE and VECTIS (1D engine modeling that can couple to 3D CFD). EngMod is amazing bang for the buck, though. Thinking about getting the 4T license.

[ForcedFirebird]

Oem generally don’t optimise ports and valve jobs well because it is too expensive to mass produce and they are not trying to maximise power. There is always heaps left on the table.

flow is from the variables: CSA, discharge coefficient and pressure ratio.

flow bench testing is improving discharge coefficient and/or CSA. Wave tuning wizardry is improving pressure ratio

OEM "didn't" then, but now they do. Pretty sure Honda broke the mold on the NSX with CFD.

Modern cylinder head ports are CNC machined, die/spun cast, etc. We cannot compare what BM did in the 80's to today's tech. Also, cannot forget the e30 came at a time when emissions was a folly. My pop's 70's Corvette makes 10bhp more than a stock m20 with his 350 and "rock crusher 4 speed" lol.

I started my engine modifying career with GM v6's. With the 1991my+ 3x00 series we are in the 240cfm intake range on 2v heads with 44mm valve (GM 3100, 3400, 3.5vvt etc). Could you imagine my surprise when the m20 885 head flowed ~170-ish? lol

[82eye]

OEM "didn't" then, but now they do. Pretty sure Honda broke the mold on the NSX with CFD.

Modern cylinder head ports are CNC machined, die/spun cast, etc. We cannot compare what BM did in the 80's to today's tech.

no kidding. my m20 is a dinosaur. on top of it as a single cam 2v per cyl engine it was just waiting for the asteroid to hit. i still love it though lol.

[digger]

OEM "didn't" then, but now they do. Pretty sure Honda broke the mold on the NSX with CFD.

Modern cylinder head ports are CNC machined, die/spun cast, etc. We cannot compare what BM did in the 80's to today's tech. Also, cannot forget the e30 came at a time when emissions was a folly. My pop's 70's Corvette makes 10bhp more than a stock m20 with his 350 and "rock crusher 4 speed" lol.

I started my engine modifying career with GM v6's. With the 1991my+ 3x00 series we are in the 240cfm intake range on 2v heads with 44mm valve (GM 3100, 3400, 3.5vvt etc). Could you imagine my surprise when the m20 885 head flowed ~170-ish? lol

44mm valve stock ports 240cfm ? The irony is they make SFA power relatively speaking but knowing GM they probably use circular cams.
A 44mm valve m20 will probably top out at 230cfm max but be capable of 350bhp or slightly more

[ForcedFirebird]

There's enough room to put a 46/36mm valves on stock seats in those heads (bore is 92mm). Canted valves, pushrod engine, fast burn. The next gen 3900 heads flowed well into the 260's CFM bone stock.

Kind of a tangent here, but to put things I perspective, an iron head domestic of the m20 era had heads with straight valves, are also in the 140-180cfm range, and those iron v8's would HP at 180, but have gobs of torque.