Custom, Performance Carb Intake Manifolds ( 2bbl / 4bbl )

[A20A1]

A bit off on the placement of the flange but oh well.

The flange is divided down the center so at least that is okay.

[A20A1]

So scared... this secondary is not like what I'm used to... we shall see how things work out.


See something missing ?

their seems to be more to the secondaries than just the venturies... which I don't see.... seems i have a lot to learn.

I removed the upper secondary plates and the linkages and diaphragm that control them... I don't think it's sipmly a choke....

[shepherd79]

well primary looks like they have venturies, but secondary looks like was designed for air flow and fuel dump.
what jets are you going to run?
did you get a car?

[A20A1]

no car yet...

this carb is going to need some work... the fuel and vacuum ports come out of the carb casting... some look like they have been hit. like the carb was dropped on them. I'll see what I can do.

This is such a neat carb though... really worth playing around with.

it's not a vacuum secondary like I thought, not like the keihin or other carbs, but it still seems like the fuel metering is somehow dependant on a vacuum valve.

So as long as it's still load sensitive I'm okay.

[A20A1]

It's heavier than a camshaft... well I think so at least.

[2oodoor]

well primary looks like they have venturies, but secondary looks like was designed for air flow and fuel dump.
what jets are you going to run?
did you get a car?

that sounds like a fair statement, secondaries on Qjet do get some metering/atomization with the M rods connected to the butterflies, according to depth of the plunge. You can borrow different rods/rod seat or jet if you will, from other Qjets to increase or decrease how much fuel by how much throttle. There is also an adjustment on the primarie M rods on the "stepper piston" , you can take out a blocking plate ( most people dont ever do that) so you can adjust the amount of movement the Stepper gets. You can put a tiny hole in the plate and use a very tiny small screw as a 'handle'

[A20A1]

See shep... the choke like plates covering the secondaries... which I had already removed in the first pic... open and as they open there long rods come out of the jets... much like how a needle valve works... there are bobbing rods for the primary and secondary... easy to remove and swap out the secondary ones... the primary ones need the top hat removed... I pushed on the accelerator pump and got a face full of dust... cough cough.

[A20A1]

[A20A1]

busted fuel inlet

[A20A1]

I noticed a problem... I need a new adapter plate for my manifold... it appears that the area between and behind the primaries pick up vacuum, but right now they are on the outside of the wall of the 1" carb spacer that I'm using to mount the carb.

[A20A1]

I just went to measure my intake manifold, not the most accurate
it has two 58.42mm bores and two 35.56mm bores
what ever am I to do?

[2oodoor]

I would not use that carb anyway, it is too old. Those carbs have lots and lots of tiny channels where that corrosion and hardened sediment would likely never get good and clean. You would have to soak it for weeks and even then it is questionable all of it would clear out. Also the casting can loose it's , I dont know what word it is I am looking for, say lubriscity? The metal looses its original oils and binders in other words. I am sure there is a more scientific way to convey that description.
Also on the base plate, some of those you can swap throttle plate. example cadillac throttle plate is not same as sb chevy, but you can use the higher cfm caddy carb by swapping. There are hundreds of RH4bbl apps and part numbers, year models etc. you have to match them up carefully. There are several different casting configs, example, fuel inlet positions and type. The picture you show has hose connection fuel inlet, I have not seen one like that too often, most are screw in with built in filter and flange nut connection.

[cygnus x-1]

Also the casting can loose it's , I dont know what word it is I am looking for, say lubriscity? The metal looses its original oils and binders in other words. I am sure there is a more scientific way to convey that description.

Eh? Oils and binders? Your talking about how the surface gets kinda chalky and pitted? That's corrosion. I think if you were to take a file or sandpaper to the surface you would find that the metal underneath the corrosion is just fine.

But yeah, I noticed the corrosion on that thing. Looks like it's been exposed to the elements for awhile.

And man that carb is HUGE for a 4-cyl. I'll be totally amazed if it doesn't immediately kill the engine when the secondaries open.

C|

[A20A1]

I don't think it will stall with the proper tuning.

Hey roo... the secondaries are supposed to open right? I mean there is a mechanical link... the only thing stopping the air is the second set of butterflies above the throttle plates. The one that has the little spring tension rich/lean bit and the vaccum diphragm to control the opening.

the carb is so damn tall.

[2oodoor]

I told you guys there had to be a better way to describe what I was talking about, yea that thing looks weathered. If an orifice had corrosion on it , in it, that would cause problems.

Those plates above the secondary throttle plates are called air valves. When the primary throttle is open about 35 degrees the secondary throttle starts to open but no air flows through until the vacuum is strong enough to pull the secondary air valves open. The air valves will stay open until the primary can handle the air required by the engine. The opening rate is also controled by a damping diaphragm and connecting rod so bogging does not occur. Opening of the sec. air valve lifts the tapered metering rods attached, and pulls additional fuel thru the jets, the reduced tapering rods meter the amount from various positions as they pass thru the jets.

A good start may be to find a Q jet off of the smallest displacement motor they come on. such as 2.8, 3.8 v6. or possibly a Pontiac 301 or chevy 262 V8.

[shepherd79]

Mike, i know you love the idea of a big carb, but i think that one is a little rusty.
see if you can find this one http://www.carburetorfactory.com/expvw26.html
it looks like it has equal barrels.
i am sure it will still give you a kick in your pants.

[2oodoor]

4GC will be a tough one to get, they stopped making them in 1967. The Qjet was supposed to be the new and improved verision.
I was wrong about the Pontiac 301 and Chvy 262, they used what was called a dualjet, a QJet minus secondary. I forgot about those, yes Im looking at my Rochester book I do think that I have seen a Qjet on a 2.8 v6 in an s-10, I know Ive worked on them on a 4.3 s-10 and 3.8 buick motors.
Don't be intimidated by the size of those air valves, it only looks like a monster. Consider though your choice of 4bbl, do you really need dual bowls, four idle air jets? Q jet may just be one of the more adaptable choices, there are dozens and dozens of internal setups to make the carbs fit application.

[cygnus x-1]

Hey, I used to have that Rochester book back when I was driving an '86 Cutlass. It had a computer controlled version of the Q-jet. The primary mixture needles were connected to a solenoid that would open and close depending on what the oxygen sensor thought the mixture needed to be. It was quite a piece of engineering. I remember rebuilding it once. There were so many little pieces and parts it was amazing.
Eventually I got rid of the car and started driving an import ('89 Nissan, fantastic car). So I sold the book figuring that I would never see another carb again. What was I thinking?

I'll admit it would be cool as hell to see a Q-jet on a 4-cyl.

C|

[2oodoor]

Hey, I used to have that Rochester book back when I was driving an '86 Cutlass. It had a computer controlled version of the Q-jet. The primary mixture needles were connected to a solenoid that would open and close depending on what the oxygen sensor thought the mixture needed to be. It was quite a piece of engineering. I remember rebuilding it once. There were so many little pieces and parts it was amazing.
Eventually I got rid of the car and started driving an import ('89 Nissan, fantastic car). So I sold the book figuring that I would never see another carb again. What was I thinking?
I'll admit it would be cool as hell to see a Q-jet on a 4-cyl.
C|

yeah it is an excellant book. I have rebuilt several different apps of Qjet, but I had to pull out the book again to refresh on some things.
I am a little curious how this will work though, Hondas have short strokes and these carbs need gobs of vacuum to maintain.. this is interesting.
I know the secondaries on the 4gc are smaller looking compared to Qjet, but I think the Qjet needs that size as an engineered factor because of the upper air valve, not necessarily that it is all that more cfm.
I think maybe if you can use the four barrel, the secondaries will not be able to stay in long...on the same point, you dont hang around 8K rpm long anyway.
EDIT: also A20A1 if your looking for another core, that carb was also used a lot in marine apps., v6 inboards for example.

[A20A1]

Well thats the point... have the carb that can open the secondaries if it needs to as much as it needs to.

But it was a big shock to lift the Air Valves open for the first time and see a very large fuel tube instead of the boosters.

[A20A1]

http://www.popularhotrodding.com/tec...boosters_tech/

I'm so happy it hurts

[dat]

nice carb lookin there.....

[A20A1]

dear lord, this is a beauty
http://www.popularhotrodding.com/tec.../photo_03.html
















had to go looking for a broken link
http://www.popularhotrodding.com/tec...ech/index.html

[DDRaptor]

Holy Progressive Carbs, Batman. That's a mean beast too bad it would flow way to much for our small engine.

[cygnus x-1]

Holy Progressive Carbs, Batman. That's a mean beast too bad it would flow way to much for our small engine.

Well, not necessarily. The article says 500-1000 CFM depending on the venturis. For a fully worked over A20 (ported head, cam, header, high compression) 500 CFM wouldn't be out of line. Side draft carbs are still better though since the head ports are on the side. That way the air flow doesn't make any bends before head.

C|