Hot Rods 780 Holley double pumper or 800 Quadrajet?

I'm putting a relatively stock 1976 Caddy low-compression 500ci engine in my '49 Hudson. I have an Edelbrock 2115 intake manifold, roller rockers, headers and all else is stock, factory specs, just rebuilt.
I'm not a fan of quadrajets and the one that came with the engine works fine but probably has smog restrictions and I am not putting this together with any smog equipment.
The stock quadrajet is rated at around 800CFM and I have a great condition 1970's Holley 780CFM double pumper that I would like to use if that is possible. Is there any reason this wouldn't work?
Thanks

 

Qjets a better street carb ....

 

I'd rather use the Qjet. But you might like the Holley better. The Qjet will drive better, get better mileage, and perform just as well as the Holley, if you get it set up right. And it will look like crap, if anyone can see it, so make sure to use the original air cleaner to hide it

The carb doesn't have any "smog restrictions" that I know of, aside from being designed to work better than any Holley could ever hope to.

 

I have to agree with them, for this application, the Quadrajet will be the better choice!

 

Quadrajet is my choice.

 

Plus, unless you want to "pop" for a new manifold, you will have to use a carburetor adapter, which screws up the airflow.

 

“ a relatively stock 1976 Caddy low-compression 500ci engine in my '49 Hudson.“
Sounds like a perfect set up for the Qjet to me. I’ve run many of them under similar set ups. The secret is to finding someone who can tune them properly, if needed.

Big air cleaner to hide it, like Jim said.

 

Actually, who's going to see it anyway? The Qjet will probably get 40-50 % better mileage.
The 1.21 venturi 800 has a vapor recovery system, but you don't have to use it. Frankly, I can't even believe we're having this discussion.
Suggest one thing ..If you're not using a factory type A/C compressor in the stock location, then I'd spring for the performer intake..Look on Ebay for a deal..They're pricey.

 

I am using an Edelbrock 2115 alum intake, will that need an adapter to fit the quadrajet?

 

No, that's the Performer. It's made for the Q-jet. Get yourself two thick OEM type gaskets and bolt it on.

 

Another vote for the Q-Jet. Some years back, Hot Rod Mag or Car Craft Mag (I forget which one) did a drag Chevette with a 500 CID Caddy engine, TH-400 trans, and a Ford 8 inch rear end, setup with an unusual 1/2 leaf spring rear suspension. The article is still floating around on the net; article was called "The Bad Seed". They swapped to some small chamber heads to boost the C.R.; do that, and then use the Holley. I am Butch/56sedandelivery.

 

Use the q jet you will get better mileage and will be a much better street carb

 

I am running a 472 built to 1970 specs. In my 57' pickup(avatar). I'm using stock exhaust manifolds, performer intake, 800cfm quadrajet(74 jets) and a Maximum Torque Specialties RV cam. It has turned out to be a very good driver. My understanding is that all Cadillac's had 2:73 gears. I am running a 2:68 10 bolt posi.

 

I put a 75 Caddy 500 that I ported the heads and stock intake. Used a Maximum Torque Specialties cam kit . In an O/T 79 Malibu with a 2.29 gear. I modified the original Qjet and it ran 13's in the 1/4 and pulled down 16 mpg in a daily driver. The slow revving high torque Caddy loves a Qjet. I didn't know Holley made a 780 double pumper ? I thought that was the old 3310 that was a vacuum secondary. I would never run a double pumper on a Caddy unless it was an all out drag car.

 

Looks (beauty) are in the eyes of the beholder

Otherwise, totally agree.

OP - acquire the book on Rochester Q-Jets by Cliff Ruggles. It is paperback, thus not expensive. Sit down some evening and read it cover to cover. Of all the aftermarket carburetor books I have read in the last 55 years, Cliff's is in the top 3 for technical information, and number one for ease of reading. When you are ready to put everything together, give Cliff a call, tell him what has been done to your engine, and the mass (weight) of the target vehicle; and then ask his advice on set-up. Buy the rebuilding kit, and any suggested modification parts from Cliff.

Jon.

 

Hey is this a hot rod forum?

Must have sold a million 1850s, 3310s and 477Xs to guys pitching their Qjets back in the 70s-80s at the speed shop I worked at. They did offer more tunimg parts

I also prefer the Qjet that's on my daily, although I have to say the 780 on my bbc hasn't puked it's gaskets in a few years now.

 

If he was building a hot rod, he wouldn't start with a smogger caddy motor, now, would he? So the Qjet is totally appropriate.

 

Daily driver with a stock setup gets the Qjet. A hot rod built for beating on gets the Holley.

 

I think the 3310 was a 780 cfm "duel inlet" not a double pumper.

 

Yep. We don't know how much he plans on beating on it (yes, stock motors do get beat on, I've done it!).

In my experience, square bore carbs do give better throttle response at lower revs, at least until the secondaries open, and will make even a stock smog motor feel peppier. At the cost of mileage of course, which is the reason the spread bores came to be unless I'm off the mark.

Again I would go with the Qjet unless mileage is not a concern. The Holley is easier to rebuild and tune if needed.

 

I wouldn't say the Holley is easier to tune, it just has more stuff you can play with But it is really difficult to get it to provide the nice mixture curve that a Qjet will, without any tuning.

Qjets seem to be pretty versatile, at least on stock/mild engines. The same carb will work well on a little motor or a big one.

 

The 780 3310 was vacuum secondaries, dual line. If you could find one now that wasn't wore out it'd work great. The 750 that replaced it, 3310, I never liked. They eliminated the rear metering block and it just never impressed me. The QJ would be your best bet.

 

The metering plate provides exactly the same function as the metering block , it is non adjustable , but you can get an aftermarket plate that uses standard Holley jets just like the block. The flow difference between 750 & 780 is in the design of the boosters IIRC

 

Wasn't the 2115 designed to accept both the square bore and the spread bore?

 

Ouch! Maybe not the best choice for a hot rod but I have seen quite a few in them. With some decent heads it's a torque monster that weighs less than an iron big block and about 50 lbs. more than a sbc.

 

I don't think that looks too awful bad on a big inch GM engine. Most of the time it was hidden by a 68 'Bird 400 air cleaner assembly. (it and the HEI )

 

Yes , it was . Still wouldn't put a DP Holley on a cruisin' custom. Actually, wouldn't put one on anything.

 

My dog is bigger than your dog

Lots of folks cut their teeth on Holleys; others, on something else.

Good friend with a race Pontiac 455 ran back to back dyno runs with a professionally prepared 800 CFM Q-Jet and a professionally prepared 850 DP Holley. The Q-Jet won, by 3 HP; basically a dead heat. Probably not going to feel 3 HP even on the strip; definately not on the street.

If the test were run again??? Who knows, the Holley might win, the Q-Jet might win, since they are this close.

Point being that both brands professionally prepared are extremely close on race engines. For street use, the spread-bore design of the Q-Jet is more responsive, and will definitely use less fuel. For circle track applications, the Holley, hands down.

Remember the old cliche about walking a mile in one's shoes. The same thing can apply to carburetors.

Would suggest that those who throw rocks at Holley, might try one, with some tuning help; and those that throw rocks at the Q-Jet, might try one, with some tuning help.

And I still prefer my genuine Carter AFB's and TQ's to either of the above!

Jon

 

Jon, I feel the same was as you do. A lot of stock championships were won using the QJet. I run both, and with my driving style, I get better mileage with the QJet, even though it is on 50 cube larger engine.
The reason I stick with the Holley on the other engine, is that it is original to the engine, and I like Holleys.
Bob

 

Up until this year, the Holley enjoyed a distinct advantage in local availability of parts.

A couple of months ago, I was SHOCKED to find that both local auto parts stores (both major brands), have discontinued stocking ALL carburetor rebuilding kits as well as all carburetor parts, and performance carburetors.

So, at least where I live, carburetor parts are now mail order.

With the proliferation of the internet, pretty easy to mail order parts for Carter, Holley, Rochester, Stromberg, and Zenith. Autolite/Motorcraft is more difficult.

Jon.