At what point is a high flow power valve required?

[Paul_G]

I have been getting this new to me carb dialed in on my 505 stroker. Bought the carb used and rebuilt it. The carb is a Holley based custom built 950 by Pro Systems. It had 76 jets in the primary with 7.5 PV, 90 jets in the secondary with a PV plug. MY AFR's were showing mid 14's at half pedal/low vacuum when the primary's should be at full flow. I drilled out the PVCR to the next larger drill size, went with an 8.5 PV to get the fuel a little sooner as well. I should have measured the drill bit but I didnt. I want the additional fuel coming from the PV, because cruise and light pedal AFR's are around mid 13's. Bigger PVCR helped a little but still lean. I went to 80 jets in the primary. My half pedal AFR's are now low 13's. acceptable for now. WOT AFR's are low 12's. nice and safe.

The engine; 505ci Trick Flow headed, roller valve train, Comp roller cam 234/240@50 .542/.539 lift with 112 LSA. Stock 4 speed, 3.23 gears, 255/60-15 tires, 26" tall

 

[68 HEMI GTS]

Depends on the size of the PVCR. I think it’s safe to say once you get in the >.060 range you should be running a high flow power valve although .070 seems to be the hard number I’ve seen. Sounds like you’re pretty decent on the tune up. How’s the low speed cruise?

 

[Paul_G]

Low speed cruise bucks a little bit. Running in the high 14's afr. They have drilled plugs in the Transition slot feed hole in the primary metering block, might need to open those a touch.

 

[68 HEMI GTS]

Yep, you bump those a drill size she’ll come right around.