Going smaller on an exhaust valve.

[gordonr390]

    Has anyone installed smaller exhaust valves, seats and some welding? Say between 1.55" to 1.58". I ran some scenario's on a couple programs I use and found running these sizes on a mild cammed (no headers) unported 390 @10.5 showed gains. In the Harley world I have been involved with, shrinking exhaust valves does improve power. For the 390 the trends show from 3000 rpm and up tq and hp gains up around 30-34 points with the low end numbers (1000rpm to 3000) staying the same on my modeling.  I looked at a few aftermarket heads and found most all exhaust valves are about the same size. 1.65".

[e philpott]

maybe would work with something that has a great exhaust port to begin with , sounds like a lot of work that probably won't help as much as a ported exhaust port with stock sized valve

[Joe-JDC]

Yes, but not on the FE heads.  Some years ago, folks trying to use existing heads for Stock or Super Stock builds would braze up the void under the exhaust seats and reshape the exhaust port to try to get the flow up to make more horsepower.  It was an expensive process requiring heating the heads hot enough to accept the brass rod and get it to adhere to the void under the seats.  Today, the aluminum heads from several manufacturers have gone to a 1.580/1.560/1.550/1.500 exhaust valve to give them more room for a slightly larger intake valve in the same casting.  I did it with a set of the Mummert Y-block aluminum heads by changing the 1.940/1.600 to 2.00/1.55.  Most of the Yates/Motorsports heads now have 1.560 exhaust valves.  Did the exhaust flow change?  Not much, if any.  Sometimes we overthink what Ford or someone has spent years developing, but sometimes we stumble onto something that actually works and a fad develops.  Joe-JDC

[cjshaker]

   For the 390 the trends show from 3000 rpm and up tq and hp gains up around 30-34 points with the low end numbers (1000rpm to 3000) staying the same on my modeling.  I looked at a few aftermarket heads and found most all exhaust valves are about the same size. 1.65".

I would find those numbers pretty ambitious. That would equal nearly a 10% gain in horsepower. Not very likely in my opinion, but I've been wrong before. I'm always pretty suspect about computer programs though.

[gordonr390]

The last V-twin engine I was involved with ran a 2.220/1.590 in a 120"na (cast heads). On 106 octane it made 187hp and I went to Bonneville as crew. The bike set its class record. Before and after that experience I worked with this head porter for many years running calculations to find the best trends and also backed them up with the dyno results.
 
Most including myself believed going smaller ex valve made no sense on a performance engine. It was the belief to get a larger intake in the combustion chamber the exhaust would have suffer by going smaller. But as I explained before the smaller exhaust valve in a "cammed" engine will make more power. It will promote better cylinder fill on the overlap by providing a much stronger low atmospheric pressure or vacuum created in the exhaust pipe. Large exhaust primaries slow the exhaust speeds down after exiting the exhaust port and cause weak cylinder fill also. The Bonneville bike had 1 7/8" primaries.
     
Welding up, machining and porting is a lot work but I was curious if work like this had been kicked around on FE's

[machoneman]

My 2 cents. I don't see how a smaller valve in an FE would do much unless the entire port was reshaped, among other things. 

On the legendary C302A-B-C series of SBF heads, Ford made 3 what of I'll term major versions and a very few more with minor reshaping. One head having the smallest exhaust port volume apparently was tested with a less than the norm 1.60 valve. Yet, this post Trans-Am (re: Boss 302) head still reverted to the standard sized valve as the port was so good it more or less required a larger valve.  Interesting too that Pro Stock crowd learned long ago that shrinking the exhaust to allow a bigger intake was the way to go.

In both cases though the heads for these race engines were optimized for port location, height and shape to maximize hp. FE heads, "as is" were not and even the famed Hi-Riser and Tunnel Port heads retained pretty much the same port shape, height and volume as many more run-of-the mill heads and all retained the more standard exhaust valve size. I still wonder why the HR and TP heads didn't receive some serious exhaust side port work from the Ford engineering folks.

So many variables not even related to valve size exist makes me think it would take some long and serious experimentation to the basic FE exhaust port in order to bring about some serious hp gains. Ford learned this with the prototype 427 SOHC that had the D-shaped port exit turned 180 degrees from the much more powerful final version. And yes, the interior of that prototype port has a bad dog-leg bend that was also taken out of the final product so it was an all-hands effort to maximize flow.     

It would be fascinating to see a FE head with say a BBC style exhaust port or better, a raised and re-shaped port also eliminating the R-L-L-R orientation of the ports as viewed from the top of a head. Ford essentially did this with the A-460 and B-460 race heads (essentially a BBC port) while Blue Thunder did the same but took it a step even further. Maybe someday........
 

[gordonr390]

My 2 cents. I don't see how a smaller valve in an FE would do much unless the entire port was reshaped, among other things. 

On the legendary C302A-B-C series of SBF heads, Ford made 3 what of I'll term major versions and a very few more with minor reshaping. One head having the smallest exhaust port volume apparently was tested with a less than the norm 1.60 valve. Yet, this post Trans-Am (re: Boss 302) head still reverted to the standard sized valve as the port was so good it more or less required a larger valve.  Interesting too that Pro Stock crowd learned long ago that shrinking the exhaust to allow a bigger intake was the way to go.

In both case though the heads for these race engines were optimized for port location, height and shape to maximize hp. FE heads, "as is" were not and even the famed Hi-Riser and Tunnel Port heads retained pretty much the same port shape, height and volume as many more run-of-the mill heads and all retained the more standard exhaust valve size. I still wonder why the HR and TP heads didn't receive some serious exhaust side port work from the Ford engineering folks.

So many variables not even related to valve size exist makes me think it would take some long and serious experimentation to the basic FE exhaust port in order to bring about some serious hp gains. Ford learned this with the prototype 427 SOHC that had the D-shaped port exit turned 180 degrees from the much more powerful final version. And yes, the interior of that prototype port has a bad dog-leg bend that was also taken out of the final product so it was an all-hands effort to maximize flow.     

It would be fascinating to see a FE head with say a BBC style exhaust port or better, a raised and re-shaped port also eliminating the R-L-L-R orientation of the ports as viewed from the top of a head. Ford essentially did this with the A-460 and B-460 race heads (essentially a BBC port) while Blue Thunder did the same but took it a step even further. Maybe someday........

I lot of information there to digest. I assume on the Edelbrock head could be ordered with an unfinished exh port?

[57 lima bean]

Seeing legal FE heads years ago was always a hoot as the thickness of the exhaust flange was almost half of stock.An earlier exhaust opening will take care of the (small) issue.The sound of a local guys SS sbf is awesome.Honestly I could pick his engine out over any other at the track.When I asked why his car had such a wild cackle told me of the early opening.With the "to the moon" launches(stick car),the engine got almost quiet.
    Another project for Jay.