The Stovebolt Site Forums The Shop Area Engine Shop Going from 2 bl. to 4 bl. on 283

I am thinking about changing from a 2 bl. to a 4 bl. carb. in my truck. I have a 65 chevy 283. It is stock except for a pro-street harmonic balancer, HEI, holley 2bl., front disc brakes and dual flowmaster exhaust. The mechanic that updated my brakes also changed out the rear-end to match the bolt pattern of the up-dated front end (1975 parts) but instead of the original 3:73, now it is geared kind of weak on the take off, but it drives posted speeds with no problems. The mechanic swears that the 75 rear end was the same, he said that he counted the teeth and the bolt pattern is the same, but I know its not. It is a daily driver that I use for work. It is going to be pulling a 10ft. and 16ft. light duty trailer sometimes, not to exceed 3500lbs. (thats what my truck is rated). I hope that the new rear end ratio will take it and not give me clutch problems! Any suggestions on what carb I should use? I'm thinking about a quadrajet because if I'm not mistakin', the four only kicks in when you need it. I already have a OE quadrajet manifold that has the oil filler hole in it so that I wan't have to change my valve covers. Has anyone already went fom a 2bl. to a 4bl. on their 283? Thanks.

I'm a big fan & user of the Q-jet carb but pulling the kind of loads you are talking about with that small engine, I think a square bore would be better. With the tiny primary side bores of the Q-jet you will be back & forth out of the secondaries. That is why the big trucks used big 2 barrel carbs or squarbore Holleys. I would also use an aluminum manifold as long as I was changing. I think an Edelbrock carb would be best.

I did it many years ago. I did the heads and put in new rings and rod bearings along with the manifold and a Holley carb over a weekend in probably 1973 or 1974?

The carb was tiny like 400 or 500 CFM and the heads were Power Packs. It was a very responsive motor when done and I was very pleased with the results. It was in a '62 Impala though, not a truck, and it never pulled a trailer or any other load expect passengers and in those days I was a lot thinner.

My truck bumper had tow ball on it when I got it, also the first guy had a large cab over camper on it for several years. These trucks were made to work. My father had a 64 GMC when I was about 11. We worked it every day on our tobbacco farm in N.C. We haul loads of tobbaco to the market and pulled trailer loads of hogs in it too. Maybe I should be more concerned about the transmission. I'd like to put a 5 spd. in it, but I hate to let go the money. Thanks for input.

I would go for an aluminum manifold but I really hate to have to change my valve covers too because my valve covers don't have an oil port. Thats why I picked up the quadrajet manifold because it has the oil filler hole in it and would look original on the engine, and it has the original chevy red color. The numbers on it are 3875954, then in another place it says GM3, then a letter "T", and in another place, A126. Is anyone familar with this? Thanks

Many edelbrock manifolds have the boss on them for he oil filler/breather tube. Cut a hole and stick the tube in.

I am going to disagree mildly with some of the above posts.

First, on a basically stock 283, whether you use a square bore or spread bore is not going to make much difference for the following reasons:

The original 4 barrel (Rochester 4-jet) used on the 283 truck engine was about 400 CFM (about 180 primary, 220 secondary).

The Q-Jet is 750 (150 primary, 600 secondary). There is not a lot of difference from 150 to 180. The 800 CFM Q-Jets (newer) were used on 454 engines up to 1 ton chassis.

With a basically stock 283, you won't use all of the CFM available from any of the above.

I definately would NOT go with an aluminum intake for your application. Every test I have ever read or conducted show the cast iron intakes perform better at lower RPM's (torque area). If you are going to run above 4000 RPM all the time, then go with the aluminum intake.

As to carburetor, my choice would be an original Rochester 4-jet square bore if you can find one WITH the original cast iron square bore manifold. NEVER make the mistake of using one of the square bore to spread bore (or vice versa) adapters.

Jon.

I read your post 3 times and I'm thinking you are considering replacing your 2bl with a 4bl to make-up for some possible differences in rear end ratios. I don't believe a 4bl is going to achieve your objective, in fact I'm thinking your are better off with your current carb if the rear ratio is more highway friendly.

What I would suggest is to nail down exactly what the new rear ratio is. Then you will have a starting place of what direction to take to prepare the truck for your intended use.

Please consider this as friendly input and good luck with whatever choice you make.

In terms of answering your question, I couldn't come up with more wisdom than Carbking.

What tranny have you now?
I think you should re-evaluate your gearing first.

cm

I fully agree. If you are intent on going to a 4 barrel carb I would suggest using an Edlbrock RPM Air Gap, and a Holley 500-600 CFM Vacuum secondary carb. Easy carb to tune an rebuild.

I despise Quadrajets, have had way too many issues with them. After hours of rebuilding, adjusting floats, tuning them I gave up. Throw a Holley on it and be done..LOL

I appreciate your knowledge concerning this matter. Also, I like keeping a cast iron intake. Thanks alot.