The Stovebolt Site Forums The Shop Area Engine Shop 454 4 Barrell Carb question

I,m having my engine rebuilt. I was wondering which is the best over all carb to put on it. Its in a bus that gross weights out at 22,000 lbs. It has a 5 speed split shift. Also what CFM would be right to be economical etc. Thanx. Cheerz !

General Motors designed the ideal carburetor for that one in about 1965. It's called a Quadrajet, and it came as original equipment on that engine. Anything else will be a poor substitute for the right carb, either from a power or fuel economy basis, or maybe both!

Definitely a driveability compromise will have to be made if you get away from a stock carb and intake manifold. The 3-stage primary venturis and the air-valve controlled secondaries make for very smooth operation from idle to full throttle with no bogs or flat spots. Just be sure to get the correct part number carb for the application, as there are at least 200 different versions of the Q-Jet that I'm aware of.
Jerry

GM didn't put the Q-jet on trucks larger then 1 ton. The spread bore doesn't work good on heavy duty trucks. They used either large Roch. 2 barrels or Holley 4 barrels. I would use a Edel. Performer or Holley.

Then again they didnt put 454s in large trucks either

I really like the Edelbrock carburetors for what you are asking to do.Call summit racing and talk to one of there tech guys to get the correct one for your application.

Anything you run on something with that many gears needs a rev limiter or a governor incorporated into the system. A big engine with lots of torque and a 4-barrel can jump into dangerous RPM territory in the lower gears in a hurry. The popular choice for dump trucks, buses, etc. with V-8 4-BBL power back in the 60's and 70's was a governor-equipped Holley carb in combination with a special distributor that got into the rev-control business along with the carb. I'd still reccomend the Q-jet, set up to optimize low-speed and mid-range performance, but I'd also include an electronic rev limiter with a "soft" RPM control that gradually reduces speed as the limit is approached, not a sudden speed cutoff.
Jerry

I think the Q-jet also is a very good carb for the 454 as well

A long time ago, my Dad had a 454 in a 1981 Winnebago gross weight approximately 15,000 pounds. We used to use it to tow my Carburetor Shop van (loaded, approximately 9000 pounds) to Hershey.

454 came from the factory with a 800 CFM Q-Jet.

Power through the mountains in Pennsylvania using cruise control was terrible. Often the cruise would kick out, and we would be down to as low as 20~25 MPH when we crested the mountain. Heat gauge would be maximum. Of course, it would cool off going down the other side.

My theory was the primary side of the Q-Jet (spread-bore, little primary) was insufficient for the load.

I custom built a genuine Carter 750 CFM AFB (note smaller overall) and installed it on an Offenhauser intake.

I did not have a dynamometer, but power on the "power hill" seemed to be improved.

Next year, same roads, same load to Hershey. 20 hour trip reduced to 18 hour because we never got below 50 MPH in the mountains. Temperature gauge never rose above center of "normal".

Fuel economy INCREASED from 6.1 to 6.4 MPG loaded, and from 9.0 to 10.4 not towing my van.

For a vehicle with this much weight, the square bore is the way to go.

Jon.

And I agree the Q-Jet is an awesome carburetor (although I prefer the Carter TQ) for a 454 in a passenger car or even a pickup. But the 22,000 pound bus requires more airflow on the primary side.

Yes, my opinion and others will differ; but the Winnebago incident proved it to me.

If anyone is interested in the carb I used, it was a Carter 4760s Competition Series to which I added: automatic choke, fast idle, and secondary lockout. I also spent a few hours in calibration.

Jon.

Jon.

I really favor a holley carb, personally, for its ease of tuning. However, for passenger cars that need a good low-end torque boost with good power when the secondaries kick open, I always liked the old Quadrajet too. I can see how it can be a deficit on a 22,000 pound vehicle however.

When you need a lot of airflow, I would favor a square bore Holley. You could use either a mechanical secondary or a vacuum secondary, however, for that large of a load, the vacuum secondaries would be opening up all the time anyway, so I don't know if there's any advantage to it. Usually, V-secondaries are a little better at fuel economy, but they say go with a M-secondary on a manual transmission.

Another option I don't see mentioned much here is the Barry Grant line of carbs. They resemble Holley carbs and even use some Holley parts, but are not Holley carbs. They used to be known as the Silver Claw and the Gold Claw, but are now sold under the Demon line of carbs.

What makes a BG carb different is that it has 4-corner idling and you set the jets on all 4-corners the same, whereas on a Holley, the secondaries are usually about 10 steps richer than the primaries. It's more of a 4-barrel, with all 4-barrels doing the work, instead of 2 barrels with a pair of secondaries. Like a full-time 4-bbl, if you will.
You might consider trying a BG Demon carb. Might work best for you. Just be careful not to tune it like a Holley. Keep the above tip in mind.

Wow,..great advice. Thanx.