80Stang
Well-known member
A question for those who have installed the new head: what happened to your vacuum figures?
Mine dropped to a tiny 5-6HgIn at idle with the 274-110 Classic Inlines / CSC cam. Yes I still have a few hours of tuning to do but this is the first impression that I'm down on vacuum big time. Well the new head and intake are much more volume on on the intake side, and kind of "single plane" setup so I do expect somewhat lower figures at low rpms. While steady driving I see pretty much the same values as it was before. Low vacuum seems to cause troubles at idling and low at rpms when transition to the main circuits are happening.
I'm running the new head on a 200, CR about 9.5+, headers & 2.5" exhaust, 390cfm 4V Holley with 61/59 jets and 6.5 PV. The 390 carb was fitted with Quick Fuel secondary metering block, which utilizes normal holley jets for the secondaries, thus my secondary jets are now easily changeable and does not change the appearance of the carb any way.
After the first ride it seems like the previous ignition setup actually was damn good (Duraspark + MSD6A + Motorsport SVO coil) and very possibly I'm swapping back to it from the DUI tomorrow, changing secondary jets up to 63 and maybe I'll need to play with secondary spring a little as the thing goes way lean at the point it starts to open the secondaries. I'll also swap the PV down to 5.5. It runs on the lean side all the way at the moment, so I'll richen it anyways.
On Sunday we have a day at the race track, so if I'll get it tuned better tomorrow I'll give it a heavy foot at the track and can compare to previous times at the same track. Now I can rev this thing way more
as the weak valve springs are history with the log head and I fitted the alum head with 302 exhaust valves, getting 90lbs seat pressure and adjustable valve train. Today at the first test drive I let it ring to 6K and it did it easily.
Mine dropped to a tiny 5-6HgIn at idle with the 274-110 Classic Inlines / CSC cam. Yes I still have a few hours of tuning to do but this is the first impression that I'm down on vacuum big time. Well the new head and intake are much more volume on on the intake side, and kind of "single plane" setup so I do expect somewhat lower figures at low rpms. While steady driving I see pretty much the same values as it was before. Low vacuum seems to cause troubles at idling and low at rpms when transition to the main circuits are happening.
I'm running the new head on a 200, CR about 9.5+, headers & 2.5" exhaust, 390cfm 4V Holley with 61/59 jets and 6.5 PV. The 390 carb was fitted with Quick Fuel secondary metering block, which utilizes normal holley jets for the secondaries, thus my secondary jets are now easily changeable and does not change the appearance of the carb any way.
After the first ride it seems like the previous ignition setup actually was damn good (Duraspark + MSD6A + Motorsport SVO coil) and very possibly I'm swapping back to it from the DUI tomorrow, changing secondary jets up to 63 and maybe I'll need to play with secondary spring a little as the thing goes way lean at the point it starts to open the secondaries. I'll also swap the PV down to 5.5. It runs on the lean side all the way at the moment, so I'll richen it anyways.
On Sunday we have a day at the race track, so if I'll get it tuned better tomorrow I'll give it a heavy foot at the track and can compare to previous times at the same track. Now I can rev this thing way more
as the weak valve springs are history with the log head and I fitted the alum head with 302 exhaust valves, getting 90lbs seat pressure and adjustable valve train. Today at the first test drive I let it ring to 6K and it did it easily.