Hot Rods Carter AFB / Edelbrock 500 CFM Dual Quads for Blower?

Hello,

Does anyone have any experience with modifications and tuning 500 CFM Carter AFB’s or Edelbrock dual quads for a roots-style draw through blower (471/671) on a small displacement SBC?

Thanks for your time!

Jim

 

Even on a small displacement, the 500s might not be enough. It depends on your overall combination.
My 389 Pontiac had two 600 Carters and was super lean on the dyno. A pair of 750s fixed her right up.

Your results might vary...

-Abone.

 

Thanks for the reply. I am using the standard formula that seems to be the standard for supercharger shops. I do know that this is a simple guideline, and understand that many members here may have more applicable experience and information. I am new to supercharging, so this is really all I have to use as a starting point.

I appreciate all comments.

Here are the calculations:
Maximum CFM Required = ((Engine CID x maximum RPM) / 3456) x ((max boost / 14.7) + 1)
Engine CID = 311
Max RPM = 7,500
Max Boost = 6.0
Result = 950 CFM total (7,500 RPM / 6 PSI Boost)
996 CFM total (7,500 RPM / 7 PSI Boost)

 

311 is about 3/4 of 435, and I'm running a pair of 1990s Carter 750 AFBs on my 435 ci 427 on a 6-71.

So yeah, the 500s might be just a little small on yours.

Mine have almost stock jetting (slightly leaner cruise on the metering rods), making somewhere around 6 psi or so. Lots of miles and lots of p***es on the combo, it works.

 

I had two 500s on a a 6-71, on a 354 Hemi. It was totally fine. They were, of course, boost referenced (yes, this can be done with a Carter, or an Edelbrock.

I swapped for Carters, only because I wanted the look.

 

Thanks, Jim! I would like to run 600’s or 650’s, as the availability is better. From the research I have done, It would be better to run rich than lean (essentially detonation vs. fouled plugs).

It’s a new rebuild with an extensive list of expensive parts. I would like to run dual carbs, and keep it as simple as possible to ensure a good break-in period. I expect that a bench tune or even a full pre-tune will still require some work to get it right for my specific build, but I want to be as close as possible to make that as simple as possible.

 

I learned how to boost reference these from Ago.

His tech can be found in this thread: https://www.jalopyjournal.com/forum/threads/tech-week.365678/#post-3962288

 

“gimpyshotrods” - thanks! I have done the research on boost referencing and will either do this myself or order carbs that have been modified. I have read some varying information about the AFB’s/Edelbrock’s not requiring boost referencing. Nothing definitive though.

 

The modification is not largely done to the carburetors. You need to simply epoxy up a slot next to each barrel.

The mod is done to the carburetor adapter. Essentially, what you are doing is redirecting the vacuum source from just under the carburetor, to the plenum of the manifold.


Ago's adapter has 8-holes, and has vacuum p***ages through from one side. Mine has 4 vacuum ports, and two big holes. I sized-up my openings, so that I could run the largest carburetors made, just in case. He has an enormous number of miles on his car, so it for sure works.

Incidentally, carburetor CFM has little to do with rich or lean conditions, up to a point. That is jetting, metering rods, step-up springs, etc. CFM is just where the peak efficiency falls off.

 

You can boost reference the carbs if you want, but it's probably not necessary. I've put a lot of miles on a couple different engines without doing so, no problems with leanouts. If you like doing that sort of stuff, it will be fun work.

 

Thanks for that info. Are those adapters available? I think that I could build one.

 

Hand made. You can make one with a drill press, hole saw, various bits, taps, and some transfer punches. There is not much to it.

I CNC machined mine, because I have access to those tools.

 

For the street?

 

I am well versed in CAD and have access to a 5-axis CNC and operator. I will take a closer look at design criteria. Thanks!

 

Street/strip.

 

My experience, if the carburetors are for naturally aspirated engines, the fuel bleeds will be too small. The p***ages may also be too small if you are running much boost.

My best recommendation, is go, FIRST thing and buy an air/fuel gauge.
Don't leave it to..."I think", or "he said", or "this should"...
I've two cars with Innovate gauges in them. A REALLY accurate way of tuning any engine. No guesswork involved.

Mike

 

I tuned my setup with a wideband O2 sensor, and Ago did his with one, too.

Neither of us guessed.