Thread: SBC - Crate Vacuum Question

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Yo All - Am interested in putting the ZZ4 Chevy Crate Motor in my '46 Ford 2dr Sedan - Question is: With the Hyd.roller cam(.474"/.510"lift and 208/221 degrees duration) will I have enough vacuum to operate accessories? How Much vacuum will I need for the brake booster, etc.? And should I upgrade the convertor from stock? ('86 700R4 tranny/stock Camaro Convertor).This engine advertises 355 HP @5250rpm/405ft.lbs.@3500. Many Thanks in advance. Charlyg

Hi Richard - I suppose the finalOD gear in the 700R4 is a basic lockup! - ?maybe? - anyway thanks for the info - I've been told to expect no more than 12-15 inches of vacuum from this combo - does that mean I may have to use a booster? thanks again!
Charlyg

Originally posted by Charlyg
Hi Richard - I suppose the finalOD gear in the 700R4 is a basic lockup! - ?maybe? - anyway thanks for the info - I've been told to expect no more than 12-15 inches of vacuum from this combo - does that mean I may have to use a booster? thanks again!
Charlyg

the stock 700r4 uses a lockup converter. it is locked via the engine computer. you can spend a small amount of money ($75 to $150) to buy a kit to eliminate the computer OR do this:

there are 3 wires on the trans plug - pin A (pink wire i think) got to ign hot (12+). the other two wire get tied together. there ya go. now to get fancier, you can get a delco switch that will unlock the converter when vac drops, but if you have only 12-15 in to start it may not ever lock up. You can also run the +12 wire through the brake light switch so that the circuit is broken when the brake pedal is pressed. I have not done that and have no problems - when i slow down, the trans downshifts and unlocks...simple easy!

Operation: one wire in the trans grounds when the trans is in 4th. the other one is the - lead to a solenoid. so when the trans goes into 4th, the converter will automatically lock up, and when it leaves 4th it unlocks.

if you do not lock it up, at 45+ mph in 4th you will see a temp rise of 30-50 degrees - the trans will overheat and die.

You should be have enough vacuum with that cam. I have had larger duration cams than that and the power brakes have worked ok, not like stock but worked. A friend of mine is running the Edelbrock performer RPM package on his car and has about 9 to 10 inches of vacuum, his power brakes work fairly well.
As techie said you can get one of those vacuum resevoirs for pretty cheap if you need one. I would try it without any extras first and go from there. That way you didn't buy something you may not really need.