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Old 05-02-2008, 08:40 PM   #11
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Quote:
Originally Posted by bonny99
The carb i am talking about came from a 1977 pontiac grand prix with a 400 big block, the carb is of big block calibration.I am asking if we tuned it right would it work on a 1974 small block which had a rochester on it.
Ok, I'll reiterate myself...without the part number off the carb, you have no idea what you have in hand.

The motor it came off of wasn't much of a performer as it left the factory. 1977 was in the bad old days of low hp, emmissions strangled motors. For the Pontiac 400 motor, which was never intended to be a hot rod motor, you are talking about very, very, mild street manner (ultra smooth idle, tons of low rpm torque, nothing up top in the HP department.) The factory carb didn't need to flow much to keep up with the motor'* cam and induction.

The good news is that the carb in question is probably a M4M Q-Jet...one of the easiest to recalibrate. If you look on the casting, you should find an 8 digit number stamped into the casting. If the carb really is off a 1977 Pontiac motor, it should start with "17056" or "17057" and the next to last digit with be a "6" or a "7"... That works out to a 1976 or 1977 Pontiac use M4M Q-Jet. (The M4M wasn't a "high performance" carb, but it does have a large bore casting and the adjustible part throttle tuning feature added in 1975..so it has a fair amount of potential to be anything you want it to be.)

If it is in good shape, it should fire a mild 350 "as-is". Probably well enough to drive the car around. After that, you will be spending a lot of time messing with it to get it to run the 350 in high rpm.
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Old 05-03-2008, 07:46 AM   #12
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Default Re: rochester 4barrel

Quote:
Originally Posted by bonny99
Does anybody know if a 1977 rochester 4 barrel will work on a 1974 350?
Yes, if it has a 4 barrel manifold you can make it work, or you can trade the core to a qualified rebuilder who can set it up for your specific engine application. My local carb shop charges around $140 to rebuild a Qjet, with base and air filter gaskets and a warranty. I can't buy the parts and do it myself any cheaper than they can.

And just for what it is worth, the Pontiac community doesn't refer to a Pontiac V8 as a big block. The terms big block and small block are generally used to distinguish between different engine families of the same manufacturer, such as Ford, Buick, or Chevrolet. All the V8s made by Pontiac Motor Division from 1955-1979 had very similar block dimensions, except for the 301 and 265 which were short deck blocks, so they were slightly shorter, but definitely not a "small block". For the most part, when those of us in the Pontiac community use the generic term big block and small block, we are referring to Chevrolet engines, which are definitely different than Pontiac engines. Yes, a Pontiac block is bigger than a Chevrolet small block, but not as large as a Chevrolet big block.
When trying to identify a specific engine in a car of this era that could have had an engine from almost any one of GM'* divisions in it, it is too vague to simply classify it as a "big block" and can be misleading to someone who may think you know the difference and you have verified that you actually have a Chevrolet big block retrofitted into your car.
Having said that, there is not one generic carb tune for large engines and another generic carb tune for small engines. Qjets were used on a very wide variety of engines and each engine got a Qjet that was tuned specifically for that model of engine.
If the carb you have that you want to use is in good shape and not leaking, I'd say stick it on there and see how it runs, you will know in short order if it will do what you want it to do.

Maybe this comment was limited to the 1977 model, in which case it is understandable, but still inaccurate...
Quote:
Originally Posted by clm2112
the Pontiac 400 motor, which was never intended to be a hot rod motor
I'm not sure what you would classify as a performance engine then. Sounds like you aren't familiar with the Ram Air (especially 4!) engines, and probably the history of Pontiac V8 engines in general if you really believe that. In the late fifties and early sixties the really serious hot rodders knew that whatever sort of vehicle they were building, if they wanted to go really fast, they would swap in a Pontiac V8. The 400 replaced the 389 in 1967 for the express purpose of making more power in the muscle car era, specifically for the GTO and the new Firebird . Google "Pontiac Ram Air IV" or check out the Street or Race sections on Performance Years Forum to find plenty of people that get very respectable power numbers and verifiable track times using classic Pontiac V8s. It'* just that they do it by making wicked torque and horsepower across their entire power band, instead of just concentrating on peak top end horsepower.
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Old 05-03-2008, 10:03 AM   #13
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Bastard, what he'* talking about is a very MELLOW carb setup for fuel efficiency and emissions in 1977. Most here aren't old enough to remember the reason for this, much less remembering that they did.

The engine itself was fine, but was held back by other means......the very carb he'* considering using.

Let'* get the part numbers of both the original carb and the intended replacement please.
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Old 05-03-2008, 01:40 PM   #14
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Default Re: rochester 4barrel

Quote:
Originally Posted by bastard
Maybe this comment was limited to the 1977 model, in which case it is understandable, but still inaccurate..
I stand behind my comment 100%. Did Pontiac soup up some of them in the 60'*. Sure, so did every other division of GM. The norm for a Pontiac V8 as it left GM was geared for moving 4000lb sedans, which is what they were designed to do in the mid 50'*.

The worst examples are from the mid 70'* to end of production in '79. (Yes, if you have the coin, and plenty of it, you could get the Super Duty block from Pontiac Performance parts all the way into the late 80'* and build one heck of a motor.) GM killed the Pontiac V8 off for a reason. It had a high production cost, and didn't do anything better than either the SBC or BBC...it ended up as a motor without a mission.

If you have the brand loyalty bug that insists you must have a Pontiac motor under the hood, then hot rod it. Otherwise, there are far easier and cheaper ways of building a hot motor than starting with a Pontiac V8.

Meanwhile... I'm looking forward to hearing what Q-Jet the fellow really has in hand. I think the basic casting for the M4M will be fine, as they are not sized by CFM like Holleys (Rochesters are mechanical secondary carbs...by the time they got to the M4M they all had the same airflow capabilities, which * considerable...but some were limited via the linkages for use on motors with smaller airflow demands.)
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Old 05-03-2008, 01:54 PM   #15
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I cannot find the serial numbers on the carb, im positive its from a grand prix because i the one who took it off and it was the original carb.
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Old 05-03-2008, 02:14 PM   #16
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Quote:
Originally Posted by bonny99
I cannot find the serial numbers on the carb, im positive its from a grand prix because i the one who took it off and it was the original carb.
If it is original, It will have a number. Look again on the casting for numbers punched in. Even when Carter was making Q-Jets for GM they had numbers punched in just like the Rochester made Q-Jets.

While you have it in hand, you can do a little evaluation of what condition it is in. First thing to look at is the throttle shafts. The should turn smoothly and not wiggle in the bores...that'* the first place a vac leak starts. Next take a peek at the top air-horn area and look for the anti-tamper caps covering the APT. If the caps are there, then nobody has ever dicked with the carb. That'* a good sign. If it runs the 350 well enough, then you can pop that cap yourself for adjusting the midrange fueling later.
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Old 05-03-2008, 09:05 PM   #17
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clm2112, I'll guess we'll have to agree to disagree on this one. Pontiac'* image was the Performance brand back in the fifties. So even then it was a cut above the other GM brands engine-wise. And when GM Powertrain designed the LS series, which was truly their first "corporate" V8 engine, It was related to a Chevrolet engine in outward dimension only with the internals more closely resembling the best design characteristics of Pontiac and Oldsmobile engines. I know that the Chevrolet crowd can't accept this but that doesn't change the facts.
apple v orange again.


Part number on the driver'* side of the carb toward the rear:

Regarding the carburetor numbers, here is a page from a Buick site showing where the part numbers are supposed to be.
http://www.buickperformance.com/qjet.html
And here is what the numbers mean:
http://www.4wheelnoffroad.com/qjetid.html
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Old 05-03-2008, 09:19 PM   #18
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quadrajunk............buy a holly you will be much happier...............
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Old 05-03-2008, 09:36 PM   #19
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Quote:
Originally Posted by Daver
quadrajunk............buy a holly you will be much happier...............
Only for people that never learned how to fix a Qjet. But if you are the type that just likes to throw money at a problem rather than fix it correctly then by all means give up on the Qjet. And you know what they say about opinions...
This topic isn't about which brand to use it is about whether or not the Qjet he already has will work on the engine he has. I guess if money was no object he could put fuel injection on it.

I still say if your carb is in good condition, stick it on there and try it. Since we know it is mismatched it won't deliver the optimum mileage or performance, but it should function adequately to get you back and forth to work, or to get the car running well enough to sell it. as long as it isn't leaking or clogged.
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Old 05-04-2008, 11:16 AM   #20
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Holley is like Nike. Cooler name, but is it really any better than Adidas?

Qjets are fine if you know what you're doing with them. Holley doesn't do you any good if you don't understand them, either. I'll take a Qjet any day over a holley, and I've owned several of each.

Why? Because I know how to rebuild Qjets, and make them work like they're supposed to. Even after 20 years, I got right back to it like the last one had been yesterday.
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