Amateur BBC 781 Intake Valve Shootout

[BobbyB]

Does anyone think back cutting the other valves would increase their low lift flow without losing high lift flow?

I believe so...but who knows unless you test. My experience is with Ferrea only. I tested 30 degrees at a few different widths.

[1980RS]

Was this test done on the good port or bad port?

[rapidride2]

Was this test done on the good port or bad port?

It was performed on a good port.

[rapidride2]

Does anyone think back cutting the other valves would increase their low lift flow without losing high lift flow?

I believe so...but who knows unless you test. My experience is with Ferrea only. I tested 30 degrees at a few different widths.

I was thinking of a 30 degree back cut at maybe 30 to 40 thou. wide.

[1980RS]

Was this test done on the good port or bad port?

It was performed on a good port.

Last year I flowed a 781 on the good port with a GM factory 2.19 on the good port with no back cut. It went 316@600 lift. Would have liked to tried a few different valves like you did but we ran out of time. Good work on the testing.

[BOOT]

Don't forget to CC them in the chamber

[GARY C]

Several test have been done over the years that show a back cut increases low lift flow on the bench but hurts power on the dyno, possibly due to reversion, lack of fuel sheer or both. If it reduces reversion then it would allow more duration and lift than normal.

[1980RS]

That picture of the oval port head on the bench looks like the intake ports are way bigger than the most 781's. Almost looks like a rounded Sq. Port head to me.

[BILL-C]

That picture of the oval port head on the bench looks like the intake ports are way bigger than the most 781's. Almost looks like a rounded Sq. Port head to me.

Intake port matches mr gasket 107 intake gasket for stock location oval ports

[BILL-C]

Absolutely try a back cut on all of those intake valves. I haven't done a back to back test on dyno with and without back cut intake valves on #781 equipped BBC, but on the engines I have tested the back cut valves always made more power.

[vortecpro]

Absolutely try a back cut on all of those intake valves. I haven't done a back to back test on dyno with and without back cut intake valves on #781 equipped BBC, but on the engines I have tested the back cut valves always made more power.

Nice job on that CNC program, I always back cut the valve on a BBC myself. Every time I have get into that porting room and grind I'll be thinking of that Centroid grinding away. What kind of flow were you getting on the short port, 4.310 bore?

[rapidride2]

Here's a question, as the results stand for now...is there any reason the PBM/Erson Comp series valve couldn't be trusted?

My buddy/machinists' discount made this a sub $14 valve WITH a factory back cut and so far it's betters than the other big name valves.

Anyone with real world experience with PBM/Erson valves?

[cgarb]

I have had zero issues with any of the PBM/Erson valves I have used. Not that I use 300 sets a year, I'm sure others here have that input but not me. I probably have at least 10 sets of heads I have done with those valves and all are still running without issue. Some of them I see back on a regular basis for freshen ups in bracket race sbc's and they look good with no abnormal wear.

[rapidride2]

I have had zero issues with any of the PBM/Erson valves I have used. Not that I use 300 sets a year, I'm sure others here have that input but not me. I probably have at least 10 sets of heads I have done with those valves and all are still running without issue. Some of them I see back on a regular basis for freshen ups in bracket race sbc's and they look good with no abnormal wear.

Nice to know just in case. Thanks

[BOOT]

Vortec factory heads came with back cut valves I think.