Technical Open adapter on Q-Jet intake?

Need to put a square bore carb on a factory dual plane, four-hole Q-Jet intake. I have an open spacer/adapter that will fit, but not sure about any ill effects from all the churning air in that space (eg manifold secondary bores drawing back from carb primaries etc)

Part of me wants to say it should all even out once air/fuel makes it into the manifold, but I could also see it just not running right.

The alternative would be to pick up a four hole adapter. If I had one of each I’d prob just grab the four hole but I’ve got the open one sitting here on the bench.

Curious if anyone has ever run into this before. Thanks in advance!

(this is a great site! been lurking here awhile, but this is first post)

 

I'd run the 4 hole adapter. I would think you would end up with some cylinders running rich and some lean.

I'd worry about shear and the fuel getting dropped with the turbulence it might cause.

Of course on a street stock engine you might not notice anything but a couple fouled plugs every once in awhile.

.

 

Wouldn't it react like a plenum?(think like a small tunnel ram)
6sally6

 

I ran an open adapter on a SBC 350 with a Holley 600 vac on a cast iron factory intake. Later changed to an E-brock Performer and removed the adapter. Ran much better with the correct/matching manifold. I have no experience with a four hole adapter.

Having done it before, I wouldn't run any adapter (myself), I'd either run a spread bore carb or find a different (correct style) intake.

Given the intake that you pictured, personally I'd run a Q-jet (yeah, I realize you didn't ask ). They really are great carbs and there are a ton of adjustments that can be made to "tune" them. (I am running one on my daily).

 

If the engine is a mild build , I don't think it will make much of a difference which one you run. Engine Masters show tested various spacers on the dyno with a pretty hot engine. The results were that, the engine really didn't care what type of spacer was on it. Your results may differ.

 

Why not run a Q-jet? Awesome street carb, probably the best ever street carb.

 

Second the Qjet recommendation. Unfortunately, I have no idea how to go about finding a good one today. note that Chevy and the other GM brands used different versions, with different fuel inlets, linkage, chokes, calibration, etc.

 

Just for giggles, look for a "square bore" intake. They are not rare and not costly, especially if you can do a trade.

 

Welcome to the HAMB from Illinois.

I don't recognize the intake, but I would lean toward the Qjet also. Find one (by model number) from the early 1980's that was originally on the engine make and c.i.d. that you have.

Don't try to make one for sbc work in your engine.

 

Ford was replacing the spread bore Autolite carbs with a square bore holley at one time. They furnished a flat steel plate instead of a thick adaptor. I have seen them in the aftermarket as well.... Just don't remember who has them.

 

About a 70-72 400, 455 Pontiac that just begs for a Q -Jet. Why in the world would you want anything else? It's not going to work as well on that style intake.

 

Run a qjet or holley qjet replacement.
Ive run both types of adapters , have 2 on cars now , both open , runs great . No lean cyl or other abnormal running.
Remember, air is being pulled into each of the four openings NOT pushed in .

 

If you have the Q-intake, the big opening adapter, and the 4-square carb already, just put them on and see how it runs. It should be very responsive and still fun to drive around town. Low and midrange throttle should blend the air/fuel nicely. But I suspect that the WOT would be less than optimum, however.
Stepping up a half-click with the square-to-Quad adapter should give you back some of that missing top end.
And a QJ carb with no adapter as is being suggested, for a few more bucks should give you the Full Monty.

 

The Qjet is the BEST your going to do . Spend your time and money on getting tuned correctly to your engine and don’t look back .

 

If you happen to follow NASCAR, think restrictor plate racing.

Do the math.

If you have a 750 CFM square-bore carb, it would be 375 primary, 375 secondary.
MOST (not all) Q-jets are 750 CFM; but 150 primary, 600 secondary.

The manifold is designed for the Q-jet. On the primary side the manifold will flow about 150 CFM.
The carburetor has 375 CFM available on the secondary side.

The manifold limits flow on the primary, and the carburetor limits flow on the secondary.

PRESTO: You are a magician! With your adapter, you have converted a 750 CFM carburetor to functionally flow 525 CFM.

Suggestion: run a spread-bore (Autolite, Carter, Holley or Rochester- your choice) on that manifold.
If you want to run a square-bore carb, change the manifold!

Save the adapters for the ssssnnnnaaaaaakkkkkkkkkkeeeeeeeee oil salesmen!

Jon

 

I’d never go against @carbking , but here’s a thought:

Engine Masters usually uses Holley carbs and not a spread bore, but in their spacer tests they found that for a dual plane manifold with a 4-hole top an open spacer did best because there was some ‘talk’ between the sides. Likewise on an open plenum manifold a 4-hole did best.

I’m not going against carbking, just sayin.

John

 

@carbking , is this carb a candidate for the OP to have serviced for this application?
https://www.jalopyjournal.com/forum/threads/holley-spread-bore-650.1264573/

 

We don't know the application here, but I'd guess , with a cast iron factory dual plane , we're not dealing with a race car here.
DP's aren't much of a candidate for anything practical

 

At what RPM would that be?

 

I used the 4 hole adapter you posted to run a square bore carb.
Did ok. Beware that ya need to double check gasket surfaces. Make sure it seals properly.
Running a q-jet now. Works great other than fuel evaporating if it sits for a while.

 

We don't know the exact application, so do not know. The second line in my signature block is applicable

Jon

 

Put a GM linkage Carter Thermoquad on it! carbking agrees-right?

 

The TQ is a great carburetor, as is the Q-Jet.

My comments on this thread are directed at the mis-match of intake and carburetor as to style; not at what carburetor to use. Would need to know exact application for that suggestion.

Jon

 

We need to slow down on suggestions until we hear back from OP. He has not yet viewed most of the comments.

 

Unless you're looking to set the NHRA Q/S Natl record what's the worry? Will it idle, run, start in the morning and get you to work? Fuckin eh. What will you notice? I'll raise a rt hand to NOT A FUCKIN THING except the dickin around with line and linkage. "WTF Jocko, how can you say that?" Cuz I've done it a time or 3 my damn self. Is it the end-all do-all move? No, gets the car running with what you have on hand. Fire away, kick me in the balls, I challenge anyone to call it bullshit but tell me why.

 

Not calling it BS, by any means. I would call it speculation, like a lot of us have done. We don't know if he wants to try and outrun his buddy at the next nostalgia drags. We've had those threads before.
Some of us are trying to get him the best drive-ability and performance for the least amount of $$$.
Yes, it'll get him to work with a 56 Ford percolator-firetrap Holley adapted, but as of yet, we just don't know.

 

I did it on a 460, dropped an Edelbrock on an open adapter. If anything that one ran better. Others just ran, no issues at all. Dropped one on a stock-ish 350 too, square bore carb, spread bore aluminum intake. No difference, except the carb issue that made me do it was gone. Then I got around to rebuilding the spread Holley and put it back on, happy days...

 

As I recall is was throughout the RPM range of the dyno pull, likely 3000-6000? YouTube might have the episode. Pretty interesting really.

John

 

Much thanks to all for the responses! I’ll try to give some more context here…

This is going on a fairly stock Pontiac 400 automatic that sees exclusively street/cruiser duty so responsiveness & drivability from idle-mid range are more important than what happens up top.

Long term, it absolutely deserves a proper Quadrajet but just trying to get going with parts on hand for now. I’m sure it will suck gas & air just fine and run, but wanted fish around for any potential nagging issues I might chase with the carb for months only to figure out it was that goofy adapter with this intake.

 

Here's the Pontiac quadrajet guy:
https://www.mountainmanfuelsystemsllc.com/

He can help with other auto brands of quadrajets and parts also.