Question for engine gurus

[tw1980]

I ran across the "roll on wheelie"thred by Big Red.He reported that after replacing the stock valves with polished stainless ones from OMP he noticed a substantial increase in power.Could someone explain how changing the material the vales are made of increases performance. Thanx Terry

[Ken Talbot]

Maybe just a comparison of the 'after rebuild' performance to the 'just before rebuild' performance? If you freshen up a motor with a properly done top-end rebuild, it should be much better then just before you rebuilt it. I think it would be a bit tough to compare the 'after rebuild' performance to the performance it would have had when brand new.

JAT...

[crazy steve]

The material a valve is made of wouldn't have any effect on performace, but if you changed the shape of the valve, you could see a increase...

[petejw]

the angle of the valve face can
affect flow which can improve performance.

also on the older valves could have carbon build up
from leaking valve seals
which again would also affect flow.

[tw1980]

Glad to hear from you Pete.I was afraid you may have been swept away by the flood waters over there.I hope you're doing well. Terry

[petejw]

all good here Terry, im in a different state,
no where near me thankfully, cheers.

[Poprock]

Me and Tony think the OMP valves show increased bottom end performance because they are not only stainless, but they are polished, very smooth. Compared to a new "stock" type valve which has a rougher, mill finish, non-polished surface, it must flow more air at the lower velocities. As rpm increases, the effect diminishes, but it is noticeable on the low end (i.e.) roll on wheelies. Worked for me.

[79XS11F]

Installing new valves that would also involve re-seating them or at least cleaning everything up and lapping them in would increase performance. The same effect can be obtained by doing this with the stock valves. An even bigger increase can be obtained if new rings are involved with a rebuild.
Rob

[DGXSER]

I would agree that the effect being noticed here is the sealing of the new valve faces, the clean valve surfaces and cleaned up mating surfaces.

While it is true the smoother surface will offer less drag to the air flowing across it, I would bet if you dyno an engine with the stock valves cleaned up and the new valves you would see very very marginal differences. So small that it might show in tenths off a 1/4 mile run, but nothing you can physically feel in normal street riding, even street ripping (would not want to call it racing, the po-po frown on that.)

[TADracer]

I cannot see how just the change in material would affect the low end significantly but who knows? Any real increase in performance might be part due to everything being put back in a more fresh condition and maybe partly to the shape of the valve between the seat and the stem of the valve. Even slight changes in the shape of the of the valve there can affect performance so if the new valves are not exactly the same shape everywhere as the OEM valves then they may act differently.

Case in point, the valve seating surface is at 45 degrees from the stem and the stock seat contact area should be about .045" thick (the grey part seen on the valve after you lightly lap it). My stock valves have had a 30 degree back cut done on them and in conjunction with that being made on the valve, the seat contact area was changed to about .035". This small machining function can give an increase in 'gas passed' by the valve of up to 10% mostly in the mid-higher RPM range. And yes, you can feel it, but not on the low end.

All valve measurements being the same, the SS valves would affect the top end more significantly since they are probably a bit lighter than the stock steel valves. Kinetic energy and all that stuff. But, I am sure the better performance does exist with the new SS valves. After all, they are newer technology over the 30+ year old valves most of us are using.

In any event, if you feel it and it feels good, it is worth the effort.

[tw1980]

Thanx Mike I like your explanation.I think you just talked me into ordering a set. Terry