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Discussion Starter · #1 ·
What is the easiest way to run with a vacuum modulator with an engine that runs boost. Is there a way around it or is a manual valvebody the best way. Would it even be possible to have auto shifts?
I believe there is a way using 2 one-way valves in the vacuum line ,but once boost came in and the signal to the modulator is lost would the trans hold on to gears?
 

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I just left mine alone and had great results. That was on a turbocharged 302/C4. The only time it was under boost was at 1/2 throttle and above anyway.

Once the mod. vacuum signal is gone, the trans reverts to using the governor and throttle valve for shift timing control. Doesn't matter whether it's a naturally aspirated engine or a boosted engine it works the same way.

Mine was 24 psi (the highest I ever ran it) and it always worked great.
 

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Discussion Starter · #3 ·
Mmm,thats interesting,so a transgo 40-3 manual kit should work fine.It still uses the modulator to control line pressure to a point at part throttle, but under boost modulator will just act as though it has no vacuum and will just run full pressure .I'm about to do a C4 now to run behind a turbo 6 so will see..
 
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