I thought I saw one of these for sale recently, but didn't bid.

Did Offenhauser make a dual quadrajet intake way back when? If so, does anyone know anything about it?

I'm not talking about the dual quad square bore which is still for sale. Yes it can be adapted for qjet use.

I imagine such an intake wouldn't fit HEI, but I guess you could a pertronix.

Was just thinking this might be a fun swap and a great way to use up fossil fuel...

cheers
cf

 

Was just thinking this might be a fun swap and a great way to use up fossil fuel...

cheers
cf[/quote]

LOL, i like the way you think.

 

Yes they made a quadrajet base dual quad....maybe they still do??....I had pne and it was not a highrise...very low, never used it and it was sold.

 

Do they make those for SBOs?

 

So it exists. Cool. Looks like no HEI, but would it fit under a stock big car hood, like an Edelbrock performer or is it higher rise?

Just curious in case I see one on ebay again.

thanks in advance
cf

 

FYI, the Offy dual quad intakes are single plane with a single large plenum. They do not flow well at low speeds in my opinion and frankly, it's not clear that the flow that well at high engine speeds, either. There's definitely no work done on tailoring the runners for any sort of tuning. Usually you only see Offy dual quads today as conversions to blower manifolds, where the carb surface is milled and a thick aluminum plate is added as the blower mounting.

 

Even if the intake doesn't flow well it would be cool for car shows. Plus you would get lousy mileage.

 

Hey: I have the same manifold as coldwar has pictured. I pulled it off a 70 supreme back in '84 or '85 and it did have the stock hood but a home made air cleaner set-up w/oai. Car ran very strong best I can remember but had what seemed to be too much blow-by, after further investigating pulled the intake (which had no turkey tray) and found a crack in the heat cross-over. Guy was tired of putting gas in it so I put a manifold and a holley back on it. Still have the manifold (unwelded) was going to use it some day, but I would be willing to part with it. I can have my fab shop weld it or you can have it fixed yourself.

 

If you are willing to part with that manifold then you should take pics of it and post it on our site. Surely someone would be interested.

 

The OTHER intake in those pictures is the old Edelbrock C396, a dual plane dual quad intake for the BBO. MUCH better in my opinion. I ran one years ago with dual 500 CFM AFB carbs and a progressive linkage. Very streetable and decent mileage as well.

 

So the one to go for is the Edelbrock and run dual 500 Carters? I've been through Holley's and gone back to qjets, I'd rather not learn carters too.

The reason I'm interested is I'm familiar enough with qjets to start messing around with dual carbs for fun.

To me it's gotta be very streetable, but with the ability to pull hard all the up to maybe 5500. Am I wrong in thinking a dual carb setup really comes alive >5500 RPM?

The thing is neither of my motors have been specially prepped for high RPM's. Both have been recently rebuilt and are going great at normal street RPM's -- say 800 - 4000. I'm not that much interested in looks. It's really just great off the line and flat torque curve.

Was just thinking it might be some semi-low buck fun. I mean you can get late model Caddy & Olds qjets in the boneyard for maybe $40, get a new or bushed throttle plate and you're good to go if your core was o.k to start.

Noting that the setup is squarebore, would it completely screw upo the manifold flow if you cut out the squarebore holes and made 'em big enough for qjet secondaries?

 

If you can repair and tune a Qjet, a holley or a carter is a cakewalk.
Qjets are a pain because there's so many finite adjustments you can make.

Afb's and Thermoquads are nice and simple.

 

In the context of this thread? Yes, you are.

By themselves, carbs (size or quantity) have little effect on the power curve of a given engine.

I do not know what "great" means, but if it is done with a "Q-Jet" (750 CFM) you have a baseline. If you added a couple more carbs (1500 CFM) you could expect a bit more power, but the RPM range would remain unchanged.

Easier to use a 750 CFM square bore carb, as any power difference would be insignificant.

Norm

 

For some reason, I am fasinated with dual quads. Could Norm or Joe be kind enough to elaborate on the subject a little. I am not clear on dual plane, single plane and the Joe's mysterious dual quad "experimental " intake. I am guessing it has to do with flow to the cylinder banks. I am also guessing that dual quads would not offer much more power unless a complete engine upgrade [cam, values, etc] was made to accomidate the additional flow.

I asked W-machine a week or so ago. Did Olds ever offer Factory Dual quads? Seems like [in my youth] I remember them on Cheby's and Ponchos.


Please be easy on my guys. I'm trying to learn here.

 

A single plane intake has all intake ports in the heads connected to all barrels of the carb. A dual plane intake has two separate sets of runners, with half the cylinders fed from half the carb and the other half of the cylinders fed from the other half of the carb. The theory behind the dual plane intake is that by making the total runner volume smaller, the velocity is increased and the fuel stays in suspension. It also potentially helps with cylinder filling efficiency at lower RPMs, increasing torque. A single plane is usually considered to be a high RPM intake since the runner volume is greater but the top end flow restriction is lower (each cylinder sees all barrels of the carb). Over the years car magazines have run back-to-back tests to either prove or discredit these theories. Unfortunately there are a lot of other details in the engine build that can skew the power and torque one way or the other. Bottom line is that the "better" design will be different depending on the details of a particular engine and what it's used for.

Note also that Offy sold some manifolds called 180 degree intakes, where instead of the runners being divided four and four, it had two stacked sets of single plane runners. All eight cylinders were fed by the primary side of the carb in the upper set and all eight were again fed by the secondaries on the lower set. This is similiar in theory to the variable length runners used on newer EFI cars but never really proved itself in the Offy implementation.

The only factory multi carb setups sold by Olds were the J2 in 57-58 and the L69 in 1966. There were no factory 2x4bbl intakes. Chevy, Buick, and Caddy DID offer that design at various times. I'm pretty sure Pontiac stuck with the 3x2bbl (and the early Bonneville fuel injection in 1957 or 58).

 

I recall there was a post some time ago where an Oldsmobile enthusiast was having an aftermarket run of the L69 intake manifolds cast. I wonder if he ever got enough interest to have them cast?

 

Depends what one has, and what it is being replaced with.

If more carburetion is needed, in a particular application, the logical choice is to use a larger carb. If one is not available, the addition of a second one would be the only alternative. Before the advent of the 4 barrel (actually two 2 barrel carbs, in one package) the use of multiple carbs was the only choice.

Today we have carbs (as well as intake manifolds) that flow four times as much as those that were available in '52.

Norm

 

Thanks, Got it [or some of it anyway]

 

I would think dual Q-jets would be a real PITA to keep from bogging. Or don't you whop the throttle wide open?

 

Oh heck yea I'll take one for $63.95

 

Could you immagine a 330 trying to use all that CFM?

 

How would one setup the linkage on this intake? I imagin you wouldn't want progressive linkage. It would be better to setup both carburetors to open together and open the secondaries at the same time. I guess...

 

I have this setup on a 425, both carbs are linked together by a straight piece of linkage/rod. The back carb has the regular-stock-modified rod from the firewall which actuates both carbs simultaneously. It worked well for me but do not really know if the setup is any better or worse than a single 4bbl.

 

One thing is for sure... it is alot cooler than a single 4 barrel.

 

Depends on the car, its use, and the owners preference.

Norm

 

I cannot imaging a carb (or carbs) supplying more CFM than an engine can use.

Norm

 

My point was it would be WAY overkill and that much CFM couldn't be used by a 330 (unless it was spinning 9000 RPM or more). It's more of a "look what I've got" type of thing.

 

I think there were quite a few 455's used for marine speed boats had all sorts of carbs and blowers on them. Or are these a different design to allow more water to flow through the block ?

 

I can, it's called a bog. Most usually too big a carb or the secondaries coming in too quickly. Dual Q-jets would be very tricky to tune I would think. That's a whole bunch of cfm when the secondaries come in to play.

 

No different than a single carb.

A simple adjustment of the secondary air valves and the "bog" goes away.

Norm

 

Norm,

I don't believe I reading your post correctly.

I can understand how [or at least I think I understand ] that the number of carbs doesn't matter.

But I am thinking 380 racer is referring to the engine getting too much gas/air mixture. The assumption I am making here is that the engine is stock and just adding more flow [ be it one bigger carb or two or three carbs] without other modification would be a waste and the engine would "Bog"

If a simple adjustment eliminates the "Bog" wouldn't that same adjustment also eliminate any benefit?

Be easy on me, I'm just trying to follow and learn something.

 

Norm is correct in that it is the engine determines the flow rate. Using a carb that's too large will result in inadequate signal in the venturies and thus the bog. If the carb has an air valve or vacuum secondaries, it can be adjusted to better match the needs of the engine. Accelerator pump shot can also be increased to cover the bog, but that's really just a bandaid. The fact remains that too large a carb is less than ideal.

 

In this case, it would be too much air and not enough fuel. As joe_p stated, air valves limit the air volume (or accelerator pumps supply extra fuel) as required.

Depends on the combination. If one is looking to increase power at WOT, many stock engines can benefit from some extra flow.

By eliminating the "bog" the "benefit" is enhanced.

In this case, the addition of the second carb would double the pump shot.

Optimum carb size varies according to the application and the owners preference.

Norm

 

So you want to "tune" the carbs down to 2-2bbls by calming the secondaries down and maybe never fully opening? Having a very high winding air pump (the engine) to use all the air capabilities? Gotta be all bling.

 

Already covered in post #29

Norm

 

On SB applications, the secondary air valve may need to be adjusted down so tight that it may not open the secondary butterfly's to their full extent. The engine would only draw in what it could use, once a proper adujstment has been obtained.

I have, however, always wondered how a dual (2X) 2bbl rochester setup would have worked on a 330/350. They are damned near indestructible, and always run very well for many many years, until the accelerator pump gives out on extreme high mileage applications.
And I think this could actually be made into a decent appearing intake setup, unlike most of the others out there. They should spend more time on asthetics. Admit it...the Holley manifolds in particular, (yes, they work very well) are plain FUGLY.

I know-just run a single 4bbl.