I cannot seem to find a 4 barrel carb for my 69 OCH 6 that is reasonable.
Could anyone tell what CFM (flow) was used on this carb. I can buy new carbs with 390, 400 CFM.
Please let me know.
I have two 68 Firebirds: 68 convertible ls2, auto 4L60E, red interior, white/black power top. I have owned since 1971. 2) 68 coupe, aqua/white tope. aqua interior, 350 4 speed. I am restoring this car and it will be for sale. Before paint or after.
The Rochester Q-Jet only takes what air it needs, so the CFM rating of the Q-Jet is no different than the rest of them from 1966-1969: about 750. The difference is that the OHC only uses about 2/3 of that.
Many people run the 390 or 450 Holley on them, with mixed results. You can put almost any Q-jet on and it will perform, but there were distinct changes to the base of the OHC Q-jet. I do not know for sure what's different.
Also, if I recall, you are running the 1-bbl head with the 4-bbl cam/intake/exhaust, right? The stock Q-jet would still need some tweaking to run right in that respect. Most of the Q-Jet books I've seen don't even list the jet and rod combinations for the OHC, so it's a guessing game. I have an original 1968 Q-Jet, so I can get the combo from it, and you could just have a garden-variety Q-Jet set up and running, with just some minor jet and primary rod tweaking being all you'd need. I was going to run a Chevy 7029202 on mine with the jets and rods from a 7098261.
You might want to seek the advice of a few of the OHC gurus about the differences in the OHC Q-Jet, though. I really don't know for sure what all the differences are, and how they affect the performance of the motor.
My 67 Sprint carb has a fuel inlet like a Chevy v8 Q-jet.(side inlet) Not like the typical Pontiac v8 Q-jet inlet.(center inlet) I will have to investigate a little to see what the base differences are, as I have no idea. I think one could rebuild a just about any q-jet to work fine on the OHC 6, as it will use what it needs. (as any engine) May have to play with jets, rods, hangers, etc......
they also use a 3hg power piston spring (7029922).
the secondaries, near as i can tell, were a BE, or BF. sensative to small throttle increments, but without much flow until full open. BG appears to be available. i want to check the dealer on a BE kit (7034377).
i've had some carb. people tell me that a v8 q-jet wont work, but i am going to try it. they want to sell me a holley. mine runs w/ a 350 carb on it, but it is rich as heck.
i was also told that only the B-series primary metering rods are available, but i dont know what that means. all i know is it means the primary rods i want for my '68 are listed as 42B.
I know a guy in the San Antonio, TX area that specializes in Q-Jets. If you know the carb number, I will give him a call and see if he has it or send me a PM and I will give you his phone number and you can call him direct. I also know a guy north of Detroit that may have the correct carb.
Anyone familar with these numbers and would this work on the OHC 6 (with adjustment).
Did Carter build any 4 barrel carbs for OHC 6?
Thanks, Grant
I have two 68 Firebirds: 68 convertible ls2, auto 4L60E, red interior, white/black power top. I have owned since 1971. 2) 68 coupe, aqua/white tope. aqua interior, 350 4 speed. I am restoring this car and it will be for sale. Before paint or after.
Are you sure about that number? It should start with 70 ... something like 7029268 or 7040268. 20268 might be the part number of one of the castings.
As for whether or not it will work with adjustment, the answer is probably "yes," but as Scott mentioned, the right components to make a V-8 Q-jet work on the OHC might be a problem if the primary metering rods are not available.
All OHC 6 Sprints had Q-Jets from the factory. I do not think Carter made a OHC 6 carb, even in aftermarket. Didn't the Q-Jet debut on the Sprint in 66?
As far as Primary and secondary rods: Some part numbers/sizes may no longer be available new. But one could do as I am doing and pick up parts carbs at swap meets for ~ $5. I have the a small assortment started that includes various Primary and secondary rods, hangers, and jets.
Sixstarved: I have some of the rods that you are looking for. I would start with the #42 rods if the #42B's aren't available. The only difference is in the double taper.
To put things in perspective: One could build or buy a carb and the engine still may not perform up to potential. The fuels that we are using today is a lot different then 35 years ago. (Octane level, Specific gravity, etc.) I started collecting parts and obtaining carb books for the purpose of tuning my engine. No one is running a stock engine, with a stock exhaust, using original fuel. A stock carb set up will get you close.
BIRDSPRINTER, what does the double taper do? more flow when the power piston is fully up?
i may take you up on the #42 rods. the place i found with the 42B wants so much i was considering getting 43 or 39 from carbsunlimited instead. but like you said, who knows what my engine will actually want?
as i understand it, the higher the # the thicker the rod, and leaner the mixture. is this right?
I spoke with a friend/co-worker of mine (former GM tech) and he indicated the step was for some "fine tuning". Looking at a double tapered rod: it appears that the engineers were trying step down the rate of flow. (a little leaner than a straight taper) He indicated that a 42 would be a good replacement for the 42B. He also re-iterated that the original carb settings were "middle of the road" calibrations, meant for 49 states using the fuels of the day. You are correct in that the higher the number primary rod, the leaner the mixture. I may have the primary and secondary rods you need. Send me an e-mail if you are interested. What does your current carb have in it? (jets, rods, etc.)
