Port velocity average target fps?

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?

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.

There is not an easy answer to target velocity. It depends on the head. For instance, a head with a 10 degree valve angle and a high port should be able to handle higher velocity than a head with a 23 degree valve angle and a low port. The 10 degree head would have a more favorable short turn and better pressure recovery in the chamber.

Another difference between race heads and street heads is valve lift. A race head with 0.800” or greater lift is getting most of its cylinder fill after the venturi convergence point. A street head with 0.500” lift is getting most or all of its flow before the venturi convergence point.

For example, an 18 degree small block mopar head on the street needs to keep the air attached to the SSR for the entire lift curve, so the port will need to be designed for less than 300 fps. If the same head were to be used for racing, the cam would be more aggressive (faster opening) and higher lifting. Now, the SSR would be laid back more and the the port designed to shoot the air over the top of the valve, so higher air speeds can be tolerated.

I think when these head porting experts are put on the spot, they have to give a conservative answer for the max safe street velocities.

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