426 Street Hemi intake manifold question ?

Anyone know the reason for the plenum notch under the primary bores of the rear (primary) carb?

For drag racing 4 speed cars
If your driving it on the street mainly don't do that

No this notch or cutout is about 1/2 inch deep connection of the rear carb only primary bores and is on all stock factory street Hemi intakes. I tried to post up a picture but had an issue.

That is used to have the same amount of vacuum to both idle circuits on the rear, primary, carb..
I thought you were referring to removing that divider all the way to the plenum floor like Mopar use to recommend for 4 speed drag cars, sorry

Thanks!

Nothing to do with vacuum. EDIT. little to do with vacuum.

It was done to correct fuel distribution problems on cylinders 5 & 6.

Winner Winner, and from what I read Chrysler never got it right

Distribution seemed to be all over the place on mine, but likely aggravated by a pretty big cam profile.
We ended up with pretty much every corner being different, but after that it ran clean & mean.
Could arguably have been better with a single big carb, but I wanted a stockish look.

There was three distinct “curves” for distribution depending on engine speed using the stock manifold.
Chrysler was locked in on the manifold design for 1966 due to planned launch dates.

I was always surprised they never did anything to further improve on that manifold design for the street.
Maybe subtle carb changes gave them what they needed.

The people who bought the Hemi didn’t care too much about running perfect as long as it did well with foot to the floor imo.

There's truth in that - the thing was really happy wide open above 3500.
Idle & low RPM was pretty fat until my guru tweaked on the carbs.
Seems to me any 2x4 setup is a compromise at other than full throttle.

Do you have any technical notes on what the engineers were doing? I have wondered about the evolution of the carb jetting over the years. I get non emission/emission carbs, but Air bypass until 68, then some jet changes even on the 70 carbs.

All I have access to is the 1966 Hemi Engine Development report/book.

And bits and pieces from discussions with some of the Chrysler engine guys back In the 60’s and 70’s.

I once saw what I assume was the first street hemi intake manifold. It was a work of art. It looked like a regular street hemi intake but was made out of steel tubing. Man those guys had fabrication skills. I guess this was used to test the idea on the dyno.

This one?

No, this one was made out of steel tubing and of course covered in light surface rust.

The marine manifold has that on each carb?

Yes, if I remember correctly the "marine" intake is similar to the 67 RO/WO and Vanke intake.

That is steel. Just painted. So you mean steel tubing, not steel sheet.

Yes, it was steel tubing, not fabricated. I was wondering how they got that tubing to bend so tight.

Here is a Vanke. It’s my understanding they did not come on any production vehicle.

I'm getting old but I think those came on 67 RO/WO cars. I could be wrong.

Then Eldebrock stepped up with the Rat Roaster, 2 4s and single 4 tops.

Come to think of it they had to come on the RO/WO cars or the throttles wouldn't have opened. Street hemi holes are too small the way I remember it.

But my understanding is NHRA did not allow the cheater carbs and the 67 cam with Street hemi carbs. Vanke mode was after market with a venturi, jet, meter rod change.

What does the engine development report say? Is that available in pdf to read?

Hemi carbs are the largest ever offered except the TQ. The cutouts were for better distribution

I am assuming (there's that word again) that is is the paper being discussed. I have not bought it yet but I plan to.

SAE Hemi Paper

While the mentioned book is great reading it isn’t the one I reference.

The book I reference focuses only on the street Hemi release. All kinds of development work, dyno runs, etc.

Which Hemi carbs are you talking about? The Holley cross ram race carbs or Carter Street Hemi carbs?
The 1964 426 wedge cross ram carbs were the biggest Carter carbs I've heard of on production Mopar motors in production cars

I was wrong. I checked it out. I was thinking the 67 RO/WO cars had the bigger carbs and the Vanke manifold but they didn't. I've studied 68's and 65's but never really paid any attention to the 67's. I was just thinking that was correct.

My understanding the Carter carbs all had the same size butterflies even the Hollys, 1-11/16, (big engines only)

All the stock street hemi carter carbs I've seen, 1966 up to 1971 all have the smaller primary throttle blades than the rears. I'm thinking all of those carbs. flow around 600 CFM, both the front and back carbs, maybe not
When Mopar put the new E series Carter 3705 AFB on the 1964 Max Wedge motors that shook the Hi Po world up and made those cars with those motors noticeably faster than the 1963 motors with the smaller 3447 ABF carbs
G.M ended up dropping out of the Hi performance cars wars in the spring of 1964 is what I'm remembering now. Ford had brought out the 427 ford Thunderbolt Fairlanes and those cars gave the M. W. B body cars a run for the money so Ma Mopar came out with the 426 Hemi motors for racing only in the first part of 1964 for both drag racing and NASCAR racing back then

What is the ISBN on the book you have?

This book was never intended for release outside Chrysler.
It’s an internal technical report.

I was lucky enough to find it squirreled away in paperwork found when I purchased a car from a Chrysler Engineer who had passed away.

Would you be willing to share it via making a pdf file?

You’re right cab, I checked the Hemi carbs again in fact I looked at all of them, AVS looked to be the largest

Carter came out with the D and E series AFB in either late 1962 or maybe mid 1963, the 1964 M.W. cars came with the Carter # 3705 "E" series carbs that had the same size throttle plates front and rear.
I'm not sure if they flowed as well as the later bigger AVS carbs on the 1968 and later 440 motors that had no venturi in the rear to impede air flow

How 'bad' is the stock street hemi intake compared to the dual quad single plane version that I have from Edelbrock for my 572 with a manual transmission? Goal is a nice running street engine, not interested in what it does at 7500 rpm....

Thanks
Craig

One would assume the dual plane would be better for that but that doesn't mean anything.

I guess the answer is no.

I have back to back dyno results on Indy single vs dual plane intakes. But that is for single 4500 manifolds. Maybe not applicable on this. Anyway, the dual plane only lost about 11hp up top but made over 30 more foot pounds of torque. 540" with a mild FTS cam which peaked at 6,800.