Originally Posted by funola (Post 3267568)

mach4, do you know about the mod to get rid of the VCV? It is not needed for the tranny to shift properly and may eliminate a potential vacuum leak source.

Originally Posted by mach4 (Post 3267572)

You mean the one where you install a 5-speed manual? :D

If not, I'm listening....

Originally Posted by mach4 (Post 3267414)

Of course.... but what would be the fun of that :) I stated earlier in the thread that this isn't being done as a "solution", but rather a learning project and a proof of concept. Learning is always best when working on a real project...and boy have I learned a lot.

Originally Posted by BillGrissom (Post 3267490)

I also don't think the fairly small volume of the transmission modulator requires more flow than the pump can deliver. I suspect the flow restriction of the VCV is the main limiter in how fast vaccuum is applied to the modulator. Before adding a reservoir, try a simple test. Disconnect the tube to the modulator and turn on the vacuum pump. Measure the vacuum pump outlet pressure vs the VCV outlet at various "throttle" positions. If the pump keeps up, even at wide-open-"throttle", a reservoir wouldn't help much. 1985 cars got a "vacuum amplifier" (blue moon) to account for the VCV restriction (and to process a boost signal).

Originally Posted by mach4 (Post 3269642)

Well it now appears that as long as there is a VCV required for proper transmission shifting, the use of an electrical vacuum pump to replace the engine driven pump on an automatic 617 is not a viable option.

With a setup consisting of just the vacuum pump, a check valve and a small reservoir (7 fl oz), the pump pulled 22" in about 5 seconds and with the pump off, held with no discernible leak-down.

I then hooked up the electrical vacuum pump in a test that isolated the VCV system as shown below. With the VCV in the circuit, the pressure went to 12" and held. There was enough leakage that it could not get above 12". Activating the throttle linkage showed the pressure dropping to 1" as it should, obviously dumping all vacuum above the 1" level.

http://www.peachparts.com/shopforum/...1&d=1389477120

So this is definitive confirmation that the VCV does constantly bleed all vacuum above it's set point (12" at idle and 1" at full throttle") and behind the restrictor. The restrictor ensures that the amount of vacuum leaking does not overwhelm the engine driven pump, which clearly has significant excess capacity and is designed to run constantly, but would be a serious problem for a relatively undersized electrical pump. Note: I took my pressure readings upstream of the restrictor, so at no time was the electric pump able to pull more than 12". Translated, that means that the brakes would never have more than 12" available for boost.

My conclusion: The use of an electrical vacuum pump would be a solution for a manual transmission vehicle, and should someone desire to use a microcomputer controlled system to control the pump, that would also work, though probably overkill as a simple pressure switch and relay would do the job.

It was a fun project with an unfortunate ending... unless of course there is a way to modulate the transmission without vacuum, then maybe it would work.

Originally Posted by OM617YOTA (Post 3269645)

Dang! You put a lot of work into that!

Originally Posted by mach4 (Post 3269642)

Well it now appears that as long as there is a VCV required for proper transmission shifting, the use of an electrical vacuum pump to replace the engine driven pump on an automatic 617 is not a viable option.

With a setup consisting of just the vacuum pump, a check valve and a small reservoir (7 fl oz), the pump pulled 22" in about 5 seconds and with the pump off, held with no discernible leak-down.

I then hooked up the electrical vacuum pump in a test that isolated the VCV system as shown below. With the VCV in the circuit, the pressure went to 12" and held. There was enough leakage that it could not get above 12". Activating the throttle linkage showed the pressure dropping to 1" as it should, obviously dumping all vacuum above the 1" level.



http://www.peachparts.com/shopforum/...1&d=1389477120

So this is definitive confirmation that the VCV does constantly bleed all vacuum above it's set point (12" at idle and 1" at full throttle") and behind the restrictor. The restrictor ensures that the amount of vacuum leaking does not overwhelm the engine driven pump, which clearly has significant excess capacity and is designed to run constantly, but would be a serious problem for a relatively undersized electrical pump. Note: I took my pressure readings upstream of the restrictor, so at no time was the electric pump able to pull more than 12". Translated, that means that the brakes would never have more than 12" available for boost.

My conclusion: The use of an electrical vacuum pump would be a solution for a manual transmission vehicle, and should someone desire to use a microcomputer controlled system to control the pump, that would also work, though probably overkill as a simple pressure switch and relay would do the job.

It was a fun project with an unfortunate ending... unless of course there is a way to modulate the transmission without vacuum, then maybe it would work.

Originally Posted by funola (Post 3269648)

Don't give up just yet. VCV is not needed for proper transmission shifting and can be eliminted. Did you look at the thread link I posted? Brian Carlton gave a good step by step description on eliminating it.

Originally Posted by mach4 (Post 3269702)

I read the entire thread and didn't see anything about removing the VCV. He did talk about removing the 3/2 and egr stuff but never the VCV... at least that I saw. Can you reference a specific post?