ported heads vs HP gain

[gtxrt]

if you have a stock engine with decent flowing heads from the factory and then take the stock heads and mildly port them. then put them on the same stock engine will there be a HP gain and or will the peak TQ and HP move to a higher rpm.

 

[BSB67]

Is this a hypothetical question? The specifics of the “decent” head and engine details matter.

I have taken off a set of decent heads, and had them professionally reworked (no porting) and track data suggests that it added 20 to 25 hp.

Then I had the heads professionally ported (260 cfm with the 2.08” intake) and added another 30+hp.

This with a stock-ish 440 (small cam, 6 pack, and 2 1/4” exhaust with manifolds).

So, I would say, depending on your starting point and finishing point, 20 to 60 hp. Probably closer to 20.

 

[gtxrt]

Is this a hypothetical question? The specifics of the “decent” head and engine details matter.

I have taken off a set of decent heads, and had them professionally reworked (no porting) and track data suggests that it added 20 to 25 hp.

Then I had the heads professionally ported (260 cfm with the 2.08” intake) and added another 30+hp.

This with a stock-ish 440 (small cam, 6 pack, and 2 1/4” exhaust with manifolds).

So, I would say, depending on your starting point and finishing point, 20 to 60 hp. Probably closer to 20.

it must move the peak power to a higher rpm ?

 

[lewtot184]

I did a pocket port on some 906 heads with a somewhat similar engine as BSB67. I can't exactly quantify power gain but power peaked at the same rpm. To move the power peak up may require more than some basic head work with a given package.

 

[BSB67]

it must move the peak power to a higher rpm ?

Probably not in your case. The hp curve will generally move up the y axis. So you should make more hp at each rpm point. That’s the beauty of porting, you’ll make more hp at both ends and in between,3000 rpm to 5500 rpm. Peak hp rpm will stay about the same

 

[33 IMP]

I think cam timing will be more important to WHERE power is made than headflow. Headflow will influence how much power can be made. (The general rule of thumb I've seen is 2hp/1cfm improvement. Still a wild-*** guess, imo)

 

[Geoff 2]

You have asked a really good question & I think it is very hard to answer. I would think you would get a small increase in tq & hp, assuming that the 'porting' actually improved flow...where the flow was needed. Enlarging a port reduces velocity.

Many years back before all the aftermarket alloy heads became available, I had some 906 heads. I brazed up the outside of the intake ports where the prod pinch was. Spent hrs & hrs on it. Moved the prods & rockers over. Was able to pretty much grind out, straighten & eliminate the prod pinch.
After a few months on the car, engine started to use oil; brazing had cracked.
Had a set of later heads. Did a mild port job, more of a clean up, smoothing sharp edges.
These performed better everywhere up to 6000 rpm!
The lesson I learned was: the prod pinch does not become flow restriction until the rest of the port has been substantially ported/enlarged. All my brazing did was reduce velocity which in turn reduced the amount of air entering the cyl.