M20 Cam charts?

[SeatTime]

I see there are a couple of aftermarket cams out there for the m20. Is there anywhere with some specs on the cams? Maybe someone has the info from the cards that came with them? Lift/duration? Max speeds?

[Simple_Smith]

I believe these were posted by digger a while back, please correct me if i am wrong. hope these help out

[digger]

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

[MonkeyMan]

these are money..
I'm no expert, but it looks like the Schrick 288 is in a totally different league than the others and would not be at it's best unless there's porting in the mix.. the MM and dbilas also should benefit from porting also, but look like they're more likely designed to compensate for the stock head's intake vs exhaust differences..

I'd like to see a Schrick 272 in there (I'm sure as would others), as it seems it would totally split the difference between the stock vs wild cams. It's one that always comes up on the forums because of it's 'I-just-want-a-little-more-poop-than-stock-while-still-passing-smog' effect.

I'm about to get into a stock-ish motor rebuild pretty soon, but I have an extra 885 head that I've been working on.. I'm contemplating going with either a Schrick 284/272 if I were to leave the ports alone, or a Schrick 288 if I were to port the exhaust side.. problem is, it's gonna take a lot more time and money if I were to go with option B, plus I'm having a hard time thinking it will be worth it on a 2.5 bottom end..

any advice/thoughts on this?

[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!

[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!

[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

[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.

[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]

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.

[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]

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....

[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]

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]

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".