I got the math blues... reading hurts your brain.

[MR P-BODY]

Ahhhhhh, now we are making progress. It would be nice if they published minimum cross sectional area information. Instead they've started giving us port volume. A large volume with a small pinch point, is all about the small pinch point.

Mr. P...stuff you've read, or stuff you know?

Both... I talked to alot of the head guys (head lab at work) plus seeing
those results on my own junk.... the 300fps is a pretty decent number
but I'm sure there is some variance in it(one number never fits all)

[quick 52]

I would call 300 ft/sec a "happy safe" number. Some engines may like as low as 250ft/sec and on up to near sonic choke at 350ft/sec. Alot of the Stock and Super Stock heads are borderline sonic choke cause they are required to have a poured stock volume that limits what you can do. A newer head like the LS3 for example may be in the 270 ft/sec territory. That's where people like myself have to sit down and calculate "targets" for a given combination. I base alot of my work off of these calculations and tweek from there until I'm satisfied with the results. Wallace Racing, Stan Weiss's Website, Pipemax, Dynomation, and some personal Excel Spreadsheets are what I typically use to get a feel for an engine's specific need. Problem is you can dive even deeper with calculations from an engineering point and that is where your head starts to spin!

when all else fails use bar math

[MR P-BODY]

I would call 300 ft/sec a "happy safe" number. Some engines may like as low as 250ft/sec and on up to near sonic choke at 350ft/sec. Alot of the Stock and Super Stock heads are borderline sonic choke cause they are required to have a poured stock volume that limits what you can do. A newer head like the LS3 for example may be in the 270 ft/sec territory. That's where people like myself have to sit down and calculate "targets" for a given combination. I base alot of my work off of these calculations and tweek from there until I'm satisfied with the results. Wallace Racing, Stan Weiss's Website, Pipemax, Dynomation, and some personal Excel Spreadsheets are what I typically use to get a feel for an engine's specific need. Problem is you can dive even deeper with calculations from an engineering point and that is where your head starts to spin!

Yeah I use the Pipe Max alot for this type of data

[DanStokes]

It's great to hear Nick bring up choke flow (as we called it at EPA). I've tried to discuss this with a few hot rodders over the years and they mostly refuse to believe in the concept. Truth is, there's only so much air that you can stuff thru a hole of a certain size and the question is does the engine want more than that.

Dan

[BOSSMAN]

That LS3 head responds to a better valve job, a little chamber work, and bowl work really well. You can gain 40-50 cfm pretty easy on those.

[BKBridges]

Now adays its soo much easier to put a design into a CAD model and tweak with computational fluid dynamics programs (verified in practice by guys like Nick) that it only takes a few cubicles worth of engineers to design something good. Some of us dont even remember the math behind it much. Theres probably some low hanging fruit on the HO head, not so much on the LS3...

[Beagle]

Bob, not sure how serious you were but I'd take you up on that. I just priced a couple of SAE papers and how the treat OUTSiders... Cough. Choke. lol.

Thanks guys for the input. I'll keep it in mind while I'm screwing up all the work the Ford guys put into this HO head.

[Bob Holmes]

If you like calculations, I've got a Gordon Blair book you could read. LOL

Actually its loaned out at the moment, but it has plenty of formulas that will eventually go in an excell sheet.

[BOSSMAN]

According to a lot of the stuff I've read you want 300fps port velocity
on a port

I would call 300 ft/sec a "happy safe" number. Some engines may like as low as 250ft/sec and on up to near sonic choke at 350ft/sec. Alot of the Stock and Super Stock heads are borderline sonic choke cause they are required to have a poured stock volume that limits what you can do. A newer head like the LS3 for example may be in the 270 ft/sec territory. That's where people like myself have to sit down and calculate "targets" for a given combination. I base alot of my work off of these calculations and tweek from there until I'm satisfied with the results. Wallace Racing, Stan Weiss's Website, Pipemax, Dynomation, and some personal Excel Spreadsheets are what I typically use to get a feel for an engine's specific need. Problem is you can dive even deeper with calculations from an engineering point and that is where your head starts to spin!

[Bob Holmes]

/edit - the reason I'm asking all this is because I'm thinking CFM numbers are fine sales tools ,but do not represent the full picture on what is happening in the port or really tell the whole story on what a set of heads are capable of supporting. I know there are some "generalized" estimations, but I got curious about it and you know how that goes... plus, the flu has me stuck on the couch with a less than fully functional brain.

Ahhhhhh, now we are making progress. It would be nice if they published minimum cross sectional area information. Instead they've started giving us port volume. A large volume with a small pinch point, is all about the small pinch point.

Mr. P...stuff you've read, or stuff you know?

[MR P-BODY]

According to a lot of the stuff I've read you want 300fps port velocity
on a port

[Beagle]

just general information .. I found another one here that was a lot simpler.

http://wallaceracing.com/lpv.php

I think the point was that your LPV has to do with area and now matter how efficient the port, you're gonna hit a limit with accelerating, stopping, accelerating, stopping air? IE, you're not gonna have enough time during the air movement event to accelerate the air to the speed it would need to travel in the port for the size of the cylinder, no matter how much volume you can move in a period of time?

What is considered too high for port velocity? I'm getting the feeling for a 7k mill that I should be looking for 400 ish fps? I'm just playing with stuff in my head here, wanting to get a little better understanding of this "Mach number" thingy. Thanks!

/edit - the reason I'm asking all this is because I'm thinking CFM numbers are fine sales tools ,but do not represent the full picture on what is happening in the port or really tell the whole story on what a set of heads are capable of supporting. I know there are some "generalized" estimations, but I got curious about it and you know how that goes... plus, the flu has me stuck on the couch with a less than fully functional brain.

[milner351]

Reality is a good equation in and of itself.

Beags - you maybe looking into this a bit too far? Please tell me you're not committing this kind of brain power to a rusty old set of E7's with out the benefit of a flow bench?

The constant is probably the result of another pile of equations, ideal gas law, density of air and standard atmospheric pressure and temperature, etc, etc, etc.

[TheSilverBuick]

Come on Nick, don't let reality get in the way of a good equation.

[BOSSMAN]

I'm reading up some stuff - words and everything, no pictures. NOT my favorite kind of reading. Anyway... here's one I was looking at recently. You guys ever get carried away with this crap?
To calculate the limiting port velocity: LPV=(.00353*RPM*S*B2)/CA Where:
S = stroke (in)
B = bore (in)
CA = minimum port cross sectional area in sq./in.’s
RPM = peak power rpm
LPV = limiting port velocity
For peak power at a target RPM the minimum port cross-sectional area can be calculated: CA = (.00353*RPM*S*B2)/690

For the maximum RPM that a particular set of heads is worth: RPM = (CA*Kn)/(S*B2) Where:
Kn = Constant 184136 for endurance race roller cam
Kn = Constant 195558 for pro-stock type roller cam
Kn = Constant 177780 for flat tappet cams

I came up with 1.89 x 1.1 - roughly 2.08 sq inches csa minimum from intake pinch point - anywhere from intake to valve. Too much? It's on a SBF, target 6500-7000

I stole it from TMoss who liberated it from Neil Erickson who got it from somewhere else I'm guessing? Tmoss won't answer me here even though he has an account.

Your digging pretty deep there, don't over think it. You can get lost in calculations.......