Port velocity average target fps?

-
273

273

Well-Known Member
Joined
May 14, 2012
Messages
8,160
Reaction score
5,298
Location
Ontario
What average target fps should you be shooting for and how much for different levels of builds like daily driver street to like pro stock?

Is there kind of formula or guild or rule of thumb for target fps?

So far mainly from Speier Racing Heads that he seem to target 310-350, he stated 350 fps is like a a Pro Comp engine and 330 fps for bracket racing didn't say what 310 fps was for.

How to figure needed cfm and csa was given but not target fps (velocity),Formulas given.

Min CSA = b x b x s x rpm x 0.00353 / 613.8
Cfm demand = cid x rpm x 0.0009785 / 8
Average CSA = port length x 16.387 / port volume
Average fps = cfm x 2.4 / CSA




On a side note what I find keel piece of info found a long the way looking into this was, max tq per cid was 1.67 which is about a max 135 VE% and max hp for a cylinder head is about 2.5 hp per cfm and to get max hp is by moving max tq per cid up in the rpm range to get max peak hp on wedge is in the mid 9,000 rpm then you have to go staggered & canted to go high 9,000 rpm to 11,000 rpm, the straighter the high rpm which ends at the Hemi head for 12,000 + rpm for around max hp per cid is around 3:1. Seems to be the limits of NA gasoline engines at the moment.

​

 
Last edited:
chad speier is in that top 1% club of head porters/engine builders. His work speaks for itself. That being said, 1.67 torque per cube is astronomical, very few folks can reach those numbers. If you can, you are gifted. The R&D needed is overwhelming. Those are the guys that grind and dyno 50 or more cams for their race engines. David Vizard says most really good engine builders reach 1.45 tq per cube.

David and Charles servedio both strive for 300 fps in a performance street strip engine. When checking air speeds, it is done in 5-6 different areas in the port. Remember there is no such thing as perfection as you are always porting a head as cast. The port has to go around bolt holes, pushrod holes and water jackets. Unless you are casting custom heads, you have to work with what you got.

Then you have to figure in intake manifolds and carb/FI. You wouldn’t believe how much all single four barrel manifolds choke flow.
 
ch1ll said:
chad speier is in that top 1% club of head porters/engine builders. His work speaks for itself. That being said, 1.67 torque per cube is astronomical, very few folks can reach those numbers.
Click to expand...
I know that's out my league :), I'd be happy around/above 1.25 lbs-ft per cid just thought the limits are interesting.
ch1ll said:
David and Charles servedio both strive for 300 fps in a performance street strip engine.
Click to expand...
That's where I was thinking the average build should be but just want to know for sure, hard to find much info on fps/velocity compared to cfm and csa.
 
Charles servedio on YouTube. Must watch porter, student of DV. Been porting over 40 years. DV described him as “when the student surpasses the teacher.

His current project, even though they are Chevy heads, is killer. Plenty of mopar stuff on there as well.
 
ch1ll said:
Charles servedio on YouTube. Must watch porter, student of DV. Been porting over 40 years. DV described him as “when the student surpasses the teacher.

His current project, even though they are Chevy heads, is killer. Plenty of mopar stuff on there as well.
Click to expand...
I've watched a bunch of his videos especially the mopar ones, but I watch on any engine there's a lot of overlap between engines.
 
Eric kind of answered my question this video or at least got me closer, I think I heard Darin Morgan say similar 285 ish fps but now kind of confuses me why Speier is shooting for 310-350 fps in his examples.





 
273 said:
What average target fps should you be shooting for and how much for different levels of builds like daily driver street to like pro stock?
Click to expand...
Where in the intake cycle? At the start, middle or the end?

When you open the intake valve what's the pressure in the cylinder?
 
Hysteric said:
Where in the intake cycle? At the start, middle or the end?

When you open the intake valve what's the pressure in the cylinder?
Click to expand...
It would be the average fps of the port measure on the flow bench.
Chad Speier was saying and gave examples how to figure needed cfm and csa but was vague on average fps but said you should have a targeted fps from the start, I imagine most his builds are race or serious street strip. He mention you could go as high as 350 fps Pro Comp so I imagine that's all out, said 330 fps for bracket racing. He started with 310 in his example but didn't say what type of motor that would be. When using the calculations for cfm and csa seems like those heads would give a 300-310 fps. But Darin Morgan and Eric Weingartner where saying like high 200s, I've heard Darin say you need over 250 fps to keep fuel suspended. I'm assuming an average dude build is like around 300 fps but don't know for sure.
 
273 said:
It would be the average fps of the port measure on the flow bench.
Click to expand...
The flow bench is not a running engine.

Here's some thing to think about. What is Darren talking about when he says keeping the fuel suspended?
 
I know a flow bench isn’t a running engine but obviously these people are seeing some kind correlation. Trying to seeing what it is and does it have some merit.
 
Hysteric said:
Here's some thing to think about. What is Darren talking about when he says keeping the fuel suspended?
Click to expand...
Just say what you got to say don’t want to play guess your point :)
 
273 said:
Trying to seeing what it is and does it have some merit.
Click to expand...
Wouldn't you need to understand why they target FPS in the first place to be able to figure that out?
 
Hysteric said:
Wouldn't you need to understand why they target FPS in the first place to be able to figure that out?
Click to expand...
You know you come off as condescending, obviously I understand why it's important to keep fuel suspended in the air and that fps plays a role but still doesn't give the target average fps for builds were generally talking about. I understand why you don't want to go to high or low but what is just right? For now I'm working off the assumption of around 300 fps until I find out better.
 
Hysteric said:
And if you don't what happens?
Click to expand...
If you want a proper conversation fine but I'm not playing these games, your not a teacher, I don't need to be lead into a conclusion. I know your overall point your always trying make.
 
273 said:
I know your overall point your always trying make.
Click to expand...
Do you? Looks like Chad doesn't have a problem maintaining homogeneity even @ 350 FPS when others might........
 
Hysteric said:
Do you? Looks like Chad doesn't have a problem maintaining homogeneity even @ 350 FPS when others might........
Click to expand...
Get to the point instead of asking questions to the questioner looking for answers.
 
273 said:
Maybe you have an amazing insightful point beyond the obvious direction that your questions are leading to, but I'm betting you don't.
Click to expand...

It's always the same game, it never goes anywhere.

To get an average fps air speed you can take the flow rate in cfm, divide by 60 to get per second and then divide by the csa in sq ft. There's 144sq in per sq ft.

So if you have 300cfm and a 2.0sq-in port, you have 5 cfs (300/60 = 5) and .014 sq ft of port (2/144 = .014).
5/.014 = 357 ft/s. Obviously I just made up the numbers, but the same can be done with any data.

This is just rule of thumb of course, but it will hold at any given cross sectional area. There will be local high and low velocities of course, caused by the interaction of the boundary layer and wall inflection.

When the area increases velocity decreases. Velocity and pressure are related, p1v1 = p2v2 (all other things equal), when velocity is reduced the pressure goes up which can cause vapors to condense. This is one of the reasons water boils eaiser at higher elevations. There is some chemistry happening too since evaporation of the fuel will cool the air and also increase the density. This can either increase velocity or pressure depending on port geometry and the Mach # of the flow.

Bernoulli is a lot more complex than this, and when you take all the variables into account and keep the units matching it should be possible to calculate general ranges for a lot of parameters. If you can get real world data and compare it can give a bunch of insight.
 
273 said:
Maybe you have an amazing insightful point beyond the obvious direction that your questions are leading to, but I'm betting you don't.
Click to expand...
Imagine doing a study where you test what size fuel droplet best follows the induction path. They found it to be in the microns. Obviously the size of the fuel droplet is affected by the speed at which the air is travelling since it carries more weight so therefore it has a harder time turning corners.....If it doesn't turn corners it will coalesce making larger droplets that burn as well and require heat from the flame front to convert them to a burnable state.

Dry Flow vs Wet Flow....
 
Hysteric said:
Imagine doing a study where you test what size fuel droplet best follows the induction path. They found it to be in the microns. Obviously the size of the fuel droplet is affected by the speed at which the air is travelling since it carries more weight so therefore it has a harder time turning corners.....If it doesn't turn corners it will coalesce making larger droplets that burn as well and require heat from the flame front to convert them to a burnable state.

Dry Flow vs Wet Flow....
Click to expand...

Stating once again something every goddamn person knows already, in a way that helps exactly no one. Not to mention it has zero to do with OPs question. We call that a derail, or put another way: a dick move.
 
You must log in or register to reply here.
-

Back
Top