Amateur BBC 781 Intake Valve Shootout

[rapidride2]

The AMATEUR is me.... I am no pro here...

I Just thought I'd contribute my findings today on a good friends' flow bench of B&L engines out of Cahokia, Ilinois who was gracious enough to help me do some flow testing of valves.

Flowbench: Super Flo Sf-600
Heads: 781 GM iron CNC ported by Carlquist engines out of Oakville CT. (BiIl C.) on here.

All intake valves tested were 2.250 x 11/32" stem diameter.


1. Manley Super Duty 11850-1...My price $32 E-bay

2. REV Extreme Duty. (Part no?) My price $25-$30???

3. Ferrea FERF 1223P...My price$38 E-bay

4. PBM/ERSON Competition Series ...My price $16.31 PBM


Valve weights.

1. PBM/Erson Comp Series. 127 grams.

2. REV Extreme Duty. 133 grams.

3. Ferrea 1223p. 150 grams

4. Manley Extreme Duty. 143 grams





My Results of flow in CFM of one of the better

-------------PBM/Erson---REV------FERREA---------Manley
.100-----------65--------------65------------74----------------74.3
.200----------150------------136----------138---------------123
.300----------221------------208----------209---------------208
.400----------280------------271----------273---------------273
.500----------317------------311----------311---------------309
.600----------336------------334----------334---------------333
.650----------339------------338----------338---------------337
.700--------‐-337------------339----------339------‐--------337


Notes:
The PBM is the ONLY valve to have a back cut.

[rapidride2]

Excuse the valve titles being off line. It looked fine in my draft until posted....

[rapidride2]

Questions:

Does back cutting valves generally improve low lift flow?
Does it impede high lift flow? Or?

(I've heard the Manleys don't allow much material for back cutting)

What is the consensus on backcutting the other valves?

[patrickonb]

Awesome info, thanks for sharing!

Carlquist is only about 10 hrs from me, maybe I can take my 781's to him, and get them CNC'd
this summer sometime. Looks like killer results!

It's always been my understanding, that back cutting your intake valves will generally help low
lift flow, but I am no expert on heads. Hopefully one of the other folks with more experience will
weigh in here.

Patrick

[rapidride2]

Awesome info, thanks for sharing!

Carlquist is only about 10 hrs from me, maybe I can take my 781's to him, and get them CNC'd
this summer sometime. Looks like killer results!

It's always been my understanding, that back cutting your intake valves will generally help low
lift flow, but I am no expert on heads. Hopefully one of the other folks with more experience will
weigh in here.

Patrick

Bill was great to work with.

His bench offered better results than mine but for an apples to apples comparison on the different valves tested, I used my local bench.

[rapidride2]

Valve weights. (Wrapper weights were tared)

1. Manley Extreme Duty. 143 grams

2. REV Extreme Duty. 133 grams.

3. Ferrea 1223p. 150 grams

4. PBM/Erson Comp Series. 127 grams.

[mag2555]

The PBM valve with its nice flow gain at .200" and .300" will greatly help the peak hp the motor makes to not nose over as fast as the others will.

Thanks for the effort and funds you put into doing this !

[rapidride2]

Screenshot_20230315-053038_Gallery.jpg

[rapidride2]

Intake valve seat angles are

45* at the seat.

35* at the top,

And 60*, 75* and 82* at the lower.

[KnightEngines]

Nice test, thanks for posting.

[rapidride2]

Correction.
Manley 'Severe' duty...not extreme duty valve.
Still part no. 11850.

[panic]

Better low-lift flow (assuming the lift occurs within the overlap duration) also improves the overlap window area slightly.

[rapidride2]

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

[BobbyB]

Awesome info, thanks for sharing!

Carlquist is only about 10 hrs from me, maybe I can take my 781's to him, and get them CNC'd
this summer sometime. Looks like killer results!

It's always been my understanding, that back cutting your intake valves will generally help low
lift flow, but I am no expert on heads. Hopefully one of the other folks with more experience will
weigh in here.

Patrick

I my limited experience, backcutting intake valves helped low lift flow. Back Cutting intakes hurt high lift flow a very small amount. Good test. Thanks.

[SupStk]

I'm somewhat surprised the Ferrea was so much heavier than the others.