Holley Twins Question

[Drew Pojedinec]

Well those are interesting. Don’t look as bad as I’d have thought in regards to the angle.
I am interested in them being made from plate vs one whole piece.
I’d be interested in vacuum testing them. One lil air leak can cause havoc.

Do you still mount the carbs backwards?

[Thumperbird]

Carbs are forward, primary is in the back though.
They are sealed well at all plate interfaces, don't think that is an issue but when I pull the carbs will double check.
Spent an hour or so on the spacers blending all internal edges to nice radii, same for intake.
1" 4 hole sits above them.

About a 48 degree angle, 1" rise over 1.125" run for the offset portion.

Thanks.

[Thumperbird]

Better picture of whole setup.

[e philpott]

You need to let Drew run them on his test engine , that will answer the question on Carbs

[Drew Pojedinec]

Cool, so carbs face forward and primary carb is astern.
That puts the primary Venturi in the middle and away from that 90 degree turn.
Should be ok that way. Interesting. I need to buy one of those intakes and play with it.

[wayne]

offenhauser part 5880 will put holleys on your intake summit racing has them.

[Drew Pojedinec]

Wayne, they already are on.

[Thumperbird]

Did not know those existed, they only provide an inch of spacing though, you need over 2 inches to put twin Holleys on a Edelbrock Air Gap.  Maybe one could stack 3 of them?

[My427stang]

First, your work is beautiful, no critique here, just trying to see why there might not be max power out of these

Although there could be some odd turbulence in the plenum, I don't see this setup being a problem unless you ended up with way too much plenum and fuel is falling out of suspension or there are sharp edges inside causing shear

It could be a carb issue,  still think getting them on something else may be beneficial, but would hate to see you spend a lot of money on carbs if that wasn't the issue.

Also, have you tried wiring the scoop open?  Wouldn't affect much sitting still, but never know what some odd airflow across the tops of carbs will do, and with the butterflies moving with the linkage, who knows what is happening in there

Grasping a bit, but things to consider

[cjshaker]

Just an untrained observation, but with both carburetor airflow streams aimed at each other, where they'll at least partially collide, then get pulled in another direction, I would think that would cause some serious fuel suspension issues. In other words, I'd think the airflow pattern with those spacers is all messed up. It only takes one fat cylinder to make an O2 sensor read rich. If fuel is puddling and getting sucked into 1 or 2 cylinders, then cleans up a bit at different flow rates, that's gonna make an O2 sensor give erratic readings. No amount of carb tuning will cure an issue like that. Just maybe something to consider.

[Thumperbird]

I do see a slight improvement in mixture with scoop removed but not much.
This setup, while reverse from traditional and of course acknowledging the spacers, is not all that much different in relative location of carbs to each other and to the manifold than OE.

Does anyone know what the average velocity is for air in any one intake runner at say 5000 rpm's in a stroker?  Are there any high frame rate videos of clear FE intakes fed with colored air to try and see just how much turbulence is in there and where?

Thanks.

[Heo]

A neighbour had a GTX or Roadrunner or somthing like that
with a Tunnelramed 440 with a scoop like that
When he removed it he saw a big inprovment in performance
i think it was around one sec ET and a bunch of MPH

[cjshaker]

This setup, while reverse from traditional and of course acknowledging the spacers, is not all that much different in relative location of carbs to each other and to the manifold than OE.

It's the spacers I'm talking about. An OE setup is not comparable because of them. I'm not saying they are the problem, just saying they could be. Intake and head porting is all about directing airflow. Because of the spacers, the airflow actually has to reverse direction on itself to reach the front and rear ports. I can't see that as being good.

[Pentroof]

I don't understand why you added 1" straight spacers and didn't use that height to straighten out the angle of the custom spacers? Why not make your custom spacers taller with less angle?

[Thumperbird]

Jim

Had to make the call between carb signal or possible lack thereof and the angle of the spacers/volume right under the carbs.  I felt like, just a guess really, that the 4 hole would be more valuable in providing a stable base for the carbs signal wise, yes at the expense of geometry.

Also, since I was making the spacers at home with a chop saw and table saw and wanted it running this spring, time was tight, I could not make something more fancy in terms of a taller spacer with less slope but with some internal structure, that may be this winters project.  Been thinking about a 4 tube spacer but I need to retain the spray bars.

Like I said, I am not sure how much trouble the spacers are causing, have not had enough time to tweak the carbs yet.  I need to get some more fuel in at WOT and see how it behaves.  It is already incredibly thirsty but oh well.

Until I know more about just what the flow is doing I am going to stay on the carb side of things for tuning for now, hard to believe there is a ton more turbulence in there than normal setups at higher rpm's.  It is very smooth at cruise rpm's between 2000 and 3500 rpms.