Boost Referencing Question

What is the preferred method? Holley version doesn't work with my base plate. Drill thru the side of the body or go with the metering block method?
Holley 750 double pumpers.....what say the pros?

Lumpy said:

What is the preferred method? Holley version doesn't work with my base plate. Drill thru the side of the body or go with the metering block method?
Holley 750 double pumpers.....what say the pros?

Click to expand...

What does not work with your baseplate ?

I drill into the baseplate into the primary power valve passage thru it .

This keeps the boost signal in just the 'PV bell area' .

AzGeo said:

What does not work with your baseplate ?

I drill into the baseplate into the primary power valve passage thru it .

This keeps the boost signal in just the 'PV bell area' .

Click to expand...

Confused...please elaborate.

This is what Holley sent me....

View attachment boost%20ref.pdf

Looks nothing like my baseplate.

Looked at other versions...drilling thru the side of the main body or channeling a small portion of the main body allowing vacuum from a modified metering block.

Sorry about the pdf...

from the front side of the base plate (above the lower vacuum fitting in the Holley diagram) .

Drill it directly into the vacuum port for the Power Valve signal .

I epoxy in a brass tube, let it dry over night .

Then I re-drill only down (halfway) to intersect the brass tube .

This now allows the Power Valve 'bell' (cavity) to be powered by whatever hose is attached to the brass tube, and not by the carb base vacuum .

If needed, this can be done to both Power Valves, (primary and secondary) if needed .

I then use 2 pieces of .041" stainless safety wire, bound around the hose and brass tube (like hose clamps), to hold under boost conditions .

modify it to have less function .

When I did this to my 'draw thru turbo' BB dually (1979), I needed 'carb base' and 'ported' vacuum sources to keep all the 'cruse control','canister/tank vents', 'AC doors', 'T-400 shift modulator' working .

Using what Holley shows in their diagram would not have allowed my truck to run really great for 497,000 miles .

My baseplate looks nothing like the diagram above. I opted to go thru the body with 3/16 bit and block off the original signal hole.
Thanks for the info....all good stuff:thumbsup

Lumpy said:

What is the preferred method? Holley version doesn't work with my base plate. Drill thru the side of the body or go with the metering block method?
Holley 750 double pumpers.....what say the pros?

Click to expand...

By far the most effective is to utilize the metering plate especially if your 750 already has a side port (as a guide). This way you can easily drill and tap a NPT thread and use AN fittings etc. Be sure to block off the port under the throttle plate; best practice is to use a small set screw (not a plug); tap and Locktite it. Lastly be sure to validate your work with a hand held vacuum pump.
Hope it helps,
197