Q-jet Carb and Intake manifold

[james Kekeisen]

I'm in the process of bringing my 1969 350/350 engine back to nearly stock. I've picked up a 3927184 cast intake manifold with a casting of D25 9 which I presume is April 25, 1969 but what does the "CONV4" stand for?

A friend has given me a Q-jet carb numbered 7045213 which was from his 1975 with a manual transmission. My question is whether it will work on my 69 (also manual) which I believe should be the 7029207. Will there be a fit or performance difference? It has additional markings of "F6" and "YA".

Thanks, Jim

[Clem Z.]

Re: Q-jet Carb and Intake manifold

the 7045213 is a 1975-76 350 HD truck carb. should work fine.

[Joe L.]

Re: Q-jet Carb and Intake manifold

James----

I've not seen a GM #3927184 casting which has the sequence "CONV4" on it. I've looked at quite a few of these over the years. The one on my original 69 300/350 (which also used the same manifold) and which was cast in August, 1969 does not have this on it. Is this a debossed sequence (like the casting number and date) or is it embossed (stamped in)?

The manifold should have a 3 character sequence debossed on it which will be "GM" followed by a number (e.g. "GM 4"). This identifies the mold number for foundry quality control purposes.

[Clem Z.]

Re: Q-jet Carb and Intake manifold

CONV 2 is found on BB block castings as posted farther down on this page.

[james Kekeisen]

Re: Q-jet Carb and Intake manifold

It does have a "GM 5" casting right below the main casting number.

On a similar line to the left of the date casting is the "CONV4" which is the same type and size of casting as the date casting. If you are interested I can post a picture?

Jim

[Joe L.]

Re: Q-jet Carb and Intake manifold

Jim-----

You needn't go to the trouble of posting a picture; your description is excellent. I don't know what it is, though. Mine definitely does not have it. Is there a "T", large or small, anywhere on the manifold?

[Clem Z.]

Re: Q-jet Carb and Intake manifold

joe was not this manifold sold as a service replacement and could have a different casting symbols.

[Joe L.]

Re: Q-jet Carb and Intake manifold

Clem------

Yes, this manifold was sold in SERVICE under GM PART #3958624. However, I would expect that PRODUCTION or SERVICE examples dated correctly (in this case early 1969) would be exactly the same. Later SERVICE examples, with incorrect dates, might have different and unusual symbols, markings, etc.

This particular manifold was a one-year-only item, however. It was used for 1969 only although it was used across the Chevrolet car lines for 350s equipped with 4 barrel carburetors and cast iron manifolds. It was discontinued from SERVICE in May, 1972.

[james Kekeisen]

Re: Q-jet Carb and Intake manifold

Yes a big "T" below the main casting # and a big "R" on the plenum on the otherside of the carb just below the casting listing the firing order.

[Joe L.]

Re: Q-jet Carb and Intake manifold

James-----

OK, now I think that we've solved it. This is one of those exact situations that I was discussing in another post on the board recently. Most Tonawanda cast parts had the "2 digit" year dating, but NOT ALL Tonawanda cast parts used that system. You have a part that represents one of the exceptions. The "T" on your manifold indicates that this was a Tonawanda cast piece. Originally, it was used on a 350 with 4 barrel carburetor installed in some other Chevrolet car besides Corvette. The "R", as you might expect, denotes that the manifold is for a Rochester carburetor.

Apparently, the "CONV4" casting mark was some sort of quality control casting mark used by the Tonawanda foundry. Each foundry had their own particular procedures which were not "standardized" across the Central Foundry operations of the time.

If you wish, and inasmuch as your manifold has the "single digit" year system as was used by Saginaw, you could carefully and cleverly grind off the "T" and "CONV4" and no one will ever know the origin of this manifold.

[james Kekeisen]

Re: Q-jet Carb and Intake manifold

I was going to try my hand at a carb rebuild. Does anyone have a suggestion for a good rebuilt kit and where to get it? Or maybe I should send it out and have it done professionally?

[Clem Z.]

Re: Q-jet Carb and Intake manifold

i have used "hygrade" kits with good results. if you want to send it away i would suggest lars grimsrud at V8fastcars@msn.com he is in colorado and the guys over on the corvetteforum have great luck with him on Qjets.

[Clem Z.]

PS

lars does not restore or replate carbs he just rebuilds them.

[james Kekeisen]

Re: Q-jet Carb and Intake manifold

The groove in the carb mount that runs side to side of my intake manifold has plugs in the holes that say "3/8" with what looks like sealer holding them in. I have another identical manifold but the holes are unplugged? Which is the correct configuration? Why would they be plugged. The one with the unplugged holes is also missing the heat shield that is typically riveted to the underside of the carb area. Is the heat shield necessary and can a new one be purchased. Those rivets look like they could fall out and into the engine?! In fact the manifold that has the heat shield has one rivet missing. thanks

Jim

[Joe L.]

Re: Q-jet Carb and Intake manifold

James------

On one of your manifolds someone has plugged the carb heat groove. Actually, I HIGHLY recommend doing this and whichever manifold you use, I'd plug the groove. Drill and tap the holes in each end of the groove for 1/4" NPT allen head pipe plugs. I don't think that the sealer is necessary, but you can use it if you want. These heat grooves are a MAJOR destroyer of carburetors, causing the throttle bodies and float bowls to warp, even when the stainless steel heat shield is used between the carb gasket and the carb base. Chevrolet abandoned the use of heat groove after 1969.

The heat shield is really a good thing to have on the manifold if you maintain an active heat riser crossover passage (which you must if your choke is to work properly). These shields are no longer available from GM for your manifold. However, you have several choices: you can obtain a used shield from a junk-yard manifold and transfer it to your manifold; it doesn't need to come from a manifold exactly like yours as just about any 68-69 small block shield should do. Or, you can obtain a shield for later manifolds which is currently available under GM #6271071 for $8.14 and re-work it to fit you manifold. It doesn't need to be pretty, just functional; no one will ever see it.

The special serrated studs that hold the shield to the manifold are actually quite tenacious and reliable. However, once removed, they cannot be reused if their reliability is to be maintained. A new stud MUST be installed. These special studs are currently available under GM #10229247 for $0.53/each. If you still feel uncomfortable using the studs, though, you can CAREFULLY drill and tap the stud holes for small machine screws. Install the screws with Loctite and you're all set (this is actually what I've done in the past).