General Category > Quadrajet Carb Talk and Tips
Fuel pumps
hiy_po:
yes it runs at 1psi at cruise. Its a draw threw turbo system.
My theory about that is my extremely low compression ratio.
It seemed like a good idea to invest in a 72cc Aftermarket Alloy turbo head, and bolt it onto a fresh bottom end with dishtop pistons and standard deck height of around 0.040'. o.040' copper head gasket.
I should have used flat tops and decked block so pistons came out 0.005' Maybe next engine.
Would go from 7:1 now up to about 8.5:1 and run a better tune.
Pic is in top gear at about 50mph.
Cliff Ruggles:
The factory routed the vacuum supply to the power piston in externally for "pull-thru" turbo set-ups and put a check valve in line so the PP was not boost referenced or at least no boost to the PP.
This can be done to the later baseplates without much effort, blocking the internal hole and drilling in from the front for external vacuum supply to the PP.
I've done a few pull-thru turbo set-ups but really don't have a lot of time spent with them.
Another option is to eliminate the power piston and pull straight off the jets. These carburetors work fine like that an the A/F ratio will still change proportionally to throttle position and engine load. Rochester even set up the 1970 Olds W-30 4 speed carbs to run straight off the jets......Cliff
hiy_po:
Cliff what fuel pump would you chose??????
My Carb is boost referenced power piston to Inlet manifold after the turbo and I do run a check valve.
I am surorised by how many Holley users dont reference there Holleys. A low pressure under the carb when turbo is spooled is not what these carbs were manufactured for.
lightning boy:
hiy-po, how much horse power is your engine making?
hiy_po:
Its a fresh build. Boost is turned down to 7 psi and rev limit is set at 6000rpm. Once I get a few more miles on it I will turn it up and see how it feels.
Last Dyno run I had was 10 years ago plus. Was same turbo setup but was using twin 1 3/4inch SUs.
Had a GM cast Iron 12 port head I opend the chambers from 56cc to 62cc by removing material from the spark plug side. Ran a huge exhaust valve slightly bigger Inlet valve, 5 angle seats, pocket port and short turn opend and ported roof. I do all my own port work.
440 lift cam on a 112 lobe centre. Compression about 8.5 maybe 9 to 1
Pulled 233 rwhp then 235rwhp @ 10 psi
https://www.facebook.com/112808622092369/videos/1501437580981/
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