M20 Cam charts?

[digger]

of course a uniform velocity gradient is the goal, minimize dead/slow areas and too fast areas and the port works better at higher average speeds and pulsed flow so can be kept a bit smaller than would otherwise be the case.

in the first pretty picture you can see the high speed area over the short side. i'm sure if you widened that area or layed back the radius better it would be a whole lot better and the air would turn better

at peak hp the cylinder pressure can be 150-180" below ambient so you can never test at too high of a depression

[ForcedFirebird]

The flow bench won't tell you the correct size because if you keep making the port bigger and bigger in an efficient manner the flow keeps going up in proportion to the size increase this is due to the fixed test depression.

There's more to the flow bench than just the flow numbers. Using other tools in combination, you can find dead spots, where the velocity is etc. And I don't just use 28", it's just a number that is industry standard, so numbers correlate to one another. With the 2 vacuum motors here now, about ~24" at 200cfm is what I can achieve, but lower lifts can generate in the 40's. Would be nice to have a 6 motor setup with electronic depression control. :devil:

[digger]

The above plots show what happens with a steady state scenario kind of like a flow bench. All you can do here is try to maximise flow per square inch of area. This comes from having as uniform velocity gradients across each cross section and efficient transition shapes.

However you also need to target an absolute size that provides the best cylinder fill. this is dependent on engine parameters bore, stroke, rpm etc etc . At any given rpm a 3.2L engine will pull harder on the port than a 2.5L so in a stock head the velocity will be higher with the bigger engine. as the rpm rises the bigger engine may pull too hard on the ports and the head wont function well at the higher airspeeds if the head isnt ported properly. this is why a big stroker engine without a proper ported cylinder head doesnt make hp up top there isnt enough area to feed the engine. So it is the absolute size is what governs velocity in the running engine. The flow bench won't tell you the correct size because if you keep making the port bigger and bigger in an efficient manner the flow keeps going up in proportion to the area increase this is due to the nature of a fixed test depression. a given bottom end will pull a variable depression on the port with differing rpm and for the same rpm a different capacity bottom end will pull differently on the head.

So first thing to work out is how big does it need to be then maximise the flow without going bigger than that size.

[LateFan]

Those are great. So that's cut though the center of the valve stem....I wonder how you could visualize the whole 3D flow around the valve.

So are you not trying to maximize flow, but maximize velocity?

[digger]

This just tickled my ear. Amazing how many people think more flow means more power, but in reality it's the "proper" flow we are looking for.

It gets tedious at times flowing heads, that is until you can go back and show why things are the way they are. I have made good use of flow balls and string. :)

EDIT: I would love to have those pretty pics like Digger. :(

yeah more flow is more "power potential", there is a big difference between "power potential" and actual "power".

[ForcedFirebird]

note the bigger the pipe the more it flows which can be misleading in terms of which would produce more power

This just tickled my ear. Amazing how many people think more flow means more power, but in reality it's the "proper" flow we are looking for.

It gets tedious at times flowing heads, that is until you can go back and show why things are the way they are. I have made good use of flow balls and string. :)

EDIT: I would love to have those pretty pics like Digger. :(

[digger]

Does it cause a turbulence or tumbling at the step? I've always assumed you want your intake port / gasket / head port to be a continuous surface.

EDIT - Coandă Effect... interesting, I'd never heard that word before. So a small turbulence at where the shelf drops off.

So I whipped up these diagrams to ask you more about not needing to port match. Each is a different situation. When do you match or not match?

[ATTACH]116150[/ATTACH]

it certainly does add some turbulence (energy loss) and a vena contracta (partial size reduction) and also changes the flow bias onto the valve and can affect how well the air turns the short side radius

but it depends how close is the size to the optimum size to start with as to whether it is an issue. it

some pretty pictures, each case the cylinder port is identical and arranged in terms of steady flow highest to lowest

note the bigger the pipe the more it flows which can be misleading in terms of which would produce more power









note the gasket projecting into the port is a bad idea, the air wont recover intime to turn the radius and so you arent utilizing as much or the circumference of the valve as possible

[ForcedFirebird]

There are a lot of thing that are assumed in fluid dynamics, but it's not always true. Take 90% of those "DIY porting" guides and disregard most of it, specially for the m20. Do a search on Coandă Effect and Boundary Layer - there's so much involved, it would deserve it's own thread....

[LateFan]

Does it cause a turbulence or tumbling at the step? I've always assumed you want your intake port / gasket / head port to be a continuous surface.

EDIT - Coandă Effect... interesting, I'd never heard that word before. So a small turbulence at where the shelf drops off.

So I whipped up these diagrams to ask you more about not needing to port match. Each is a different situation. When do you match or not match?

[ForcedFirebird]

A step or bump almost always helps a short side, on almost any head.

It's called the Coandă Effect.

Much like people asking why we don't polish the ports. Polishing decreases the effective diameter due to lack of boundary layer.

[digger]

quoted an old post but anyway it is spot on, never gasket match anything, who says the gasket is the right size?

match porting will likely be a waste of your time to, it just isnt the restriction on anything south of 300hp and even then the minimum area is still going to be in the straight part of the port at the entry to the short side radius near the guide protrusion because of casting limitations. even a step down in area isnt as bad as people think depsite the air seeing sharp edge.

i updated an earlier post with some graphs

[ForcedFirebird]

Bigger issue than the porting is the flow from manifold to head (port match).

Not true with the m20. The angle of the intake gasket compared to flow direction makes gasket matching useless. They flow extremely well for stock valves, but can gain a little if you know what you are doing, but as Digger said, you need flow verification or it's a crap-shoot. Oversized intake valves are the way to go, but again, just going to a machinist and asking for the larger valves to be cut in will actually hurt your head, not help. There is additional work to be done to take advantage of the larger valves.

[zaq123]

can we see these one more time? looks like links are broken

these are the latest ones, you can also refer to the schrick, dbilas, catcams catalogues

[digger]

IMO there is little to be gained in port matching, a nice multi angle seat and a general clean up will not hurt anything. anymore work than this requires a good operator to make changes for the better

the inlet exhaust flow ratio means the inlet and exhaust lobes should have similar duration, something like a 284/272 does not suit this but is still a good allround cam but usually the topend power is plateud more than what you'd get with say a 284/284 but the better manners at low end would make it a sensible compromise for the street.

The MM cam has the ICL too high/wide IMO, while it is good for topend but makes compromises elsewhere. Also the exhaust lobe is too small so you'd need an exceptional exhaust port and system to get rid of the residual gas. MM dont pay enough attention to the exhaust side of things and they give up alot as a consequence. it is fine to strive for low emmision and nice idle but you are either building rally / race engines or you aren't, and with fixed cam timing you cant have your cake and eat it to!

[SeatTime]

AWESOME!

Let me put some thought into these.

On first look, that MM rally cam is pretty intense. The flat nose on the profile scares the crap out of me and would warrant pretty serious springs to keep things from coming apart.

I think you can expect a pretty lopey idle on the Schrick too.

Just initial impressions. Porting just makes it easier for air to get into the chamber. It's advantageous on both sides and for any cam. You can change how the air spills into the cylinders too via porting, but without a lot of knowledge, you can do more damage than good, making combustion more difficult.

Bigger issue than the porting is the flow from manifold to head (port match).

Thanks all for the data!