Vacuum on a '66 Riviera converted to EFI

[66GS425]

Hi.  I have converted my '66 Riv to an EZ-EFI system.  I am hoping to correct less than optimal performance by switching out the original Quadrajet manifold, which is very restrictive, particularly on the primary side, to an earlier square bore manifold, which I had milled to match Doc's intake treatment. 

 

The square bore manifold has no vacuum port on the passenger side rear to connect the steel modulator line to, only a brass connection (female, for which I assume I can swap the male on the Qjet manifold) for the vacuum advance line. 

 

Can someone in the group suggest an alternate location on the manifold or possiby the base of the EFI unit which has two blocked ports in addition to the power brake and PCV ports.  

 

There is an aftermarket Vintage Air system for what that is worth to the equation.  

 

Thanks all. 

 

 

 

[NTX5467]

There is a reason the primary side of the spreadbore carburetors are smaller than normal.  NOT "restrictive" as such.

 

That reason is to get higher velocity through the primary throttle bores and the special triple-booster venturis for better fuel atomization and efficiency.  The secondaries are larger to compensate for the smaller primaries in total WOT airflow, which is used much less frequently than cruising on the primaries on the highway or at slower in-town vehicle speeds.

 

What intake manifold are you desiring to use?  Just a normal Buick dual-plan 4bbl "square bore" manifold would work just fine.  There are still some around used or possibly new in Edelbrock.  All of the stock-oriented manifolds will have one hole in a runner from which intake manifold vacuum can be sourced.  GM used a plethora of vacuum fittings for this function, over the years.  One plug could have several nipples or varying diameters.  Searching the salvage yard works good, too!  Some were brass and others were "pot metal".   The number of ports could range from "1" to "4" or more.

 

What about vacuum for the power brakes?  That should be on its own separate fitting.  Vacuum for the hvac system can run from that one plug in the intake manifold runner, too.

 

I'm suspecting you might have chosen an intake manifold based on "size" rather than having an rpm range the engine normally operates in on a daily basis?  It doesn't matter if the EFI can flow 800cfm, if the engine only needs 500cfm, that's all that's going to happen . . . the "restrictive" carb you're replacing is rated at 750 cfm IF the secondary air valve opens all the way (on the 1980s versions that don't open all the way, 650fm, which is plenty for a good street motor).

 

The advantage of electronic EFI is not power per se, but throttle responsiveness and modest gains in highway cruise fuel economy.  It's just another way of atomizing fuel going into the engine than an "analog" carburetor.  "Keep your foot out of it" and fuel economy will increase but also with good acceleration in the process.  EVERY time your throttle foot presses on the gas pedal, MORE fuel is added to the mix.  Conversely, when you coast, the fuel trims back to right at "zero" (99mpg on modern trip computer readings), which helps fuel economy, too.

 

On the EFI unit itself, there might be several vacuum taps.  One for the PCV valve.  One for manifold vacuum?  One for "ported vacuum" for distributor vacuum advance . . . all noted in the instruction manual for the unit.  The whole situation might be easy to install, but you'll need to do some fabrication for your particular application.  Use an OEM-quality base gasket on the manifold, too!

 

Please keep us posted on your progress.

 

NTX5467