Hi,

I currently have a '74 400 in my '68 with a '68 intake (#9790140). The engine was rebuilt (stock) before I bought it and now has 20,000 miles on it. I want to swap out the intake with an Edelbrock Performer Aluminum series (#2156). After reading and research, several folks have stated the original cast #9790140 is as good as the Edelbrock. I am also currently running the Edelbrock 1406 carburetor.

Should I switch? If so, what improvements other than weight will I see?

Thanks,
Tom

That would be a big mistake. The two are not compatible. The carburetor is a square bore and the intake is a spread bore. Yes you can get an adapter but everyone knows you lose performance.

You want the two to match. If you wanted to run a spread bore carb the yes change it. But until then keep what you have.

Your wallet will be lighter as well

David

Go with the stock iron mainfold and a stock orignal Qjet! IMO and a lot of what I have read and been told this makes power and it is as good or better if you have a good tune on the Qjet. I have mastered my Qjet and it runs like a beast when floored. A lot of folks, even my brother (long time engine builder) talk smack about Qjets, but once I got my Qjet tuned in I would not go to another carb!!!

Harold B,

Please explain.

Are you saying my current configuration with the Edelbrock 1406 and the cast 9790140 are not compatible?

I called Edelbrock and they recommend the Aluminum Performer 2156 with the 1406 carburetor.

Thanks,
Tom

Your 1406 is a squarebore 4 holes on the bottom of the carb ( like a q- jet) and a matches your cast intake. They are compatible.

The 2156 is a spread bore intake. One big hole. It is not recommended to put a squarebore carb on a spread bore intake. Any engine builder would not recommend it. You would have to use a spacer for it to work which then messes up the plane. I don't know all the details. I just know that it is not recommended by well know engine builders and racers. they advise against it. Always use the same type of carb and intake. If you want a spread bore intake you need a spread bore carb.

I think Harold might have misread your question. Aftermarket carbs are mostly square bore. Stock cast iron 4bbl is spread bore for Q-jets. You need an adaptor to put square bore carb on a stock 4bbl manifold. Edelbrock manifolds will accommodate square bore or spread bore (Q-jet). So if you want to run an aftermarket carb, it bolts right up on an Edelbrock intake. That is the advantage of an Edelbrock intake, along with the weight.

Like you said, according to what experts have written, stock cast iron intakes flow as good as the Edelbrock performer. Q-jets are great carbs but the ones around are usually pretty spent by now and require expert rebuilding and tuning to get them to run well. For amateurs like me, it's easiest to take a new Holley carb out of the box, plop it on the intake, and drive like hell.

Bob his after market carb is a spread bore just like the cast intake according to the specs of the 1406 carb. I just don't recommend putting a spread bore carb on a square bore intake that he wants to get. If he wants a square bore intake he should put on a square bore carb.

I agree with Harold (though his last post said it backwards...) The current setup, and proposed setup, are both a bit of a mismatch. Even though Edelbrock 1406 provides bolt holes to fit on Pontiac Spread-bore manifolds, it is not an ideal airflow. The 1406 is a generic carb, designed primarily as a square bore, that in my opinion should not be run on a spread bore Pontiac intake.

They fit. It runs. But performance will not be optimal.

I feel your money would be better spent keeping your 68 manifold and replacing the carb with a spread-bore carb. If you don't want a Quadrajet for some reason you can buy an aftermarket spread-bore carb...Holley 4175 for example. I believe there are others but I haven't researched it much since I'm a Q-jet guy. I believe you are more likely to notice a slight performance gain with a different carb, rather than just putting another mis-matched intake of a different material & brand name.

That said, I think you may notice no improvements regardless of what you do with carb/intake. I'm not real strong on this type of history, but I believe that a 1974 400 with stock rebuild is simply a very low powered engine. I believe most '74s were rated 175 hp, some were 200, and I think the best was the T/A motor which was 225. It was the first year of the full blown smog era that killed the muscle car. I think they were all low compression, small valves, etc. So you may not notice any change at all with any intake/carb changes because they simply don't move much air. If you are actually looking for a performance increase, you really need different heads. Your current engine, if rebuilt to stock specs as you say, is nowhere near capable of flowing enough air to get the power potential out of ANY 4 bbl carb or intake manifold.

Now the good news is that the 1974 Pontiac 400 block (assuming it's a 481988) is that it is a fantastic block for a high performance rebuild. Many consider it the best of all Pontiac blocks...one of the strongest blocks and favored by builders over the newer ones. If course it'll take substantial $$$$ to rebuild it properly to make it run strong. But even the least expensive of "performance" rebuilds could very easily double the power out put of that engine...

You already have the carb keep it, it's well suited for your 400.
The performer series manifold is made for running from idle to 5500 rpm. If you want to race at 6-7000 rpm use a race manifold. From what I've read the 74 intake was not as performance built as the 60s manifolds, you may find some improvment over your cast iron unit using a performer but may not notice it on the street.

Jim Hand, who knows more about Pontiacs than I ever will, has done extensive testing and found no inprovments in E.T. or speed on the 1/4 mile track using the Performer over the iron intake.
But he drives a full size station wagon, results could be different with a lighter car. He does use an Edelbrock intake on his car, so do I. I got 365 RWHP using an Edlebrock carb and Performer intake on a mild build 428. I used a 3/4" aluminium spacer. Since then I've rebuilt and use a performer rpm intake. I had to lose the spacer and get a drop base intake to fit under the hood with the rpm as it is taller.

If you want to change the intake you have to the performer because you think it will give you great increase in performance, don't. It wont. If you want to change it for some other reason go ahead it will work.

The performer isn't just a big square hole, it is divided just like the Q. Jet stock intake. There are two rectangular holes left and right just like the q. Jet right under the top plate of the intake. The holes in the stock top plate match the bores in the carb but it is open under, just like the performer.

If you get ahold of Jim's book 'How to Build Max-Performance Pontiac V-8s' check out the manifold section and see some of the modified intakes he's made.


Just my opinion.

Also Performer intake seals to the newer 72 and up heads, earlier manifolds require modification. Is yours modified already or do you have early heads to go with your 68 intake?

What kind of mods are needed to put a 68 manifold on 74 heads?

Later heads have an opening above the exhaust crossover that causes an exhaust leak with an older manifold. Several different cures available.

Is that why there is two different sets of intake gaskets in the set, one tall cross-over and one short? Or are there just tall and short cross-over ports?

Tom68bird,
Was the Edelbrock carb on when your engine was rebuilt or did you remove whatever was on and install it yourself after you bought the car? There should be a spacer/adapter between the square bore Edelbrock carb and the spread bore Quadrajet manifold, something like the one in the pic I'll attach below.
If not was the 68 manifold modified?
You could take off the carb and place a gasket over the bottom of the bores just to be sure there is no restriction of flow from the carb bores to the intake. If not you're good to go. If so you could modify your intake with a die grinder, install an adapter or install the Edelbrock manifold.

I wasn’t going to add to this thread because Ordy put out the end-of-discussion-sign; after all, what else is there to discuss? The way this thread has unfolded, OP isn’t going to know which way is up.

First, the 9790140 is one of the best intakes ever manufactured. To this day, no one has manufactured a better one, maybe ‘as good as’ but not better. It’s 100% unbiased, documented fact, the reason you hear strong feedback. One of the no-brainers is its design. See how much additional cooling area your intake has than other intakes? Cooler air = denser air; denser air = bigger bang.

Second, stock Pontiac intakes are spread bore intakes. Spread bore means big bores in the back and smaller ones in the front, meaning a spread bore carb is a direct bolt on. There isn’t an upgrade for your intake, so it’s moot to discuss square-bore anything.

A Felpro #1233 gasket allows you to bolt any year heads to any year intake. Although it’s not included in gasket kits, it doesn’t cost any more than buying intake gaskets by themselves, and it’s amazing that the pirates don’t cash in on this one!

https://www.google.com/search?q=picture+...344&bih=716

Avmervo,
I agree, you are correct about the intake.
But it kind of is not moot to discuss square bore anything, as Tom states in his OP he is using an Edelbrock square bore carb not a spread bore Q-jet. Thus the need to use an adapter.
It's just that someone got it backwards as to which was square bore and which was spread bore.
Now as you say spread bore carbs, such as the quadrajet, have big secondary bores and smaller primary bores. The bores, front to back, of the Quadrajet are on the same centerline. The center of the back bore is in line with the center of the front bore, the distance between the front bores is spread to line the centers with the rear bores, thus spread bore. If the carb is a square bore and the manifold is a spread bore an adapter is used to flow the air/fuel from one type to the other. A conduit from one hole size and location to another of different size and location.
Of course I could be wrong.

[img]http://s1078.photobucket.com/user/raguza...acb01c.jpg.html[/img]
The picture above in the link is a Square Bore manifold, if you look under the Edelbrock you'll see the bores closely match the openings.
The manifold in the picture is a Pontiac 326 from 1967 for Carter AFB's and Edelbrock carb's only.

Yes I think Ordy says it best. I was just showing a Square bore manifold,
The 2156 is both a Spreadbore manifold for Qjet's, if you want to use a square bore Edelbrock Carb's they make a square plate to bolt down under the carb., I ran a 2156 and a 1406 for 13 years with no air leaks.
The 9790140 is a great manifold too, I bought one to keep in storage, I plan on putting a Qjet on top of it, do not sell yours.
It was said a 68 9790140 shouldn't be on a 1974 engine, the crossover leaks out on the 1974 engine, thats why Edelbrock"s 2156 made the flange wider there to block it off, if you look at the picture.

Tom,
A lot of info being tossed about here. Did you get an answer to your question or do you think you opened a can of worms?

Here's an article on what they are talking about, the opening on the crossover:

http://www.highperformancepontiac.com/tech/hppp_1301_pontiac_cylinder_head_modification/