The Stovebolt Site Forums The Shop Area Engine Shop 250 upgrade

I am considering putting on an 4 bbl carb on my 250. An Offenhauser intake is readily available. I can get it from JC Whitney or PAW. Both also list a Holley #8007, 390 CFM carb. I don't see an edelbrock carb that small listed in the catalogs. Does anyone know of one? Is this one Holley pretty much my only readily available choice? Am I going to have much trouble fabricating linkage? It's going in a '63 c-20 that is pretty much a stock setup.

PAW also lists some mild performance cams. Would one of these do any good? They have one listed with about 195 degrees of duration, and one with 224 degrees of duration. Advice would be appreciated.

i bought a edlebrock power package for a 231 buick.it came with a 500 cfm edlebrock carb.

A power improvement is a give and take operation. If you improve one area you give up another. The engineers at Chevrolet just didn't throw this stuff together, true, they could of worked a little more on the intake system, but all in all,it works pretty good. A "bigger" camshaft will increase torque and horsepower if it's designed correctly. But for that to happen you must give up some, and that means low rpm power. A camshaft is a good way to improve power, but you will have to increase the rpm to use it. Same holds true to the bigger intake and carburator. Ever see a really low rpm race engine? Check out some of the high performance books on the 6 cylinders. The engines they build are 6000 to 8000 rpm motors. If it was easy to do Chevrolet would have done it! Joe

I have got two problems with the stock set up. I'm running headers, so therefore I don't heat the intake with exhaust. Its a dog when cold. I have to leave the choke half out to take off from a start (when its cold). Once it has had some time to warm up, its accelerates o.k. I have plenty of power (torque) at low rpm's (after its warm), but not much at higher rpms. It will pull anything you put behind it, if you are not in a hurry. Would the 4 barrel holley and Offenhauser intake help this? I've adjusted the one-barrel soup can every way I can think of with minimal results.

Glen E.

My opinion is that the Offy and a nice 2 barrel would probably give the best results for your application. The one barrel just doesn't allow enough air into the engine to produce any decent power at sustained higher RPMs (which for a stock 250 like you have is 3000-3500 RPM).

The 2 barrel with the Offy would give you better low end torque, compared to stock, because of the additional airflow for the stock cam/head combo. And the 2 barrel (350 cfm max for your app) would not flood the engine with too much air/fuel.

There is a really good section of a book written back in the 1950 by "California" Bill Fisher (called "How to Hop up Chevrolet Engines") that discusses in detail (and shows a graph of) the power differences in a 235 with a stock 1 bbl carb versus a 235 stock with 2 1-bbl carbs. There was about a 12 HP gain in going with an extra 1 bbl carb. That's HUGE for a bolt on mod on an otherwise unchanged engine. Not only was there an improvement in power, they also note how the peak RPM curve moved up slightly. They added a third 1 barrel carb and there was yet another increase in peak HP as well as a slight increase in the peak RPM curve. The improvement in going from 2 1-bbl carbs to 3 1-bbl carbs was not nearly as great as going from a single 1-bbl to 2. The author noted that the increase in power in the 3 1-bbls was only significantly noticed once other power equipment (hotter cam, headers) were added.

That's why I think you'll get the most bang for your buck with the 2 barrel. On the smaller six, unless you're going to beef up the camming, the airflow (by way of headwork), the compression and ignition, then the 4 barrel would not compliment your engine as much as the 2 barrel.

-ftyler

Any ideas on what 2 bbl to use. Is there one readily available that will fit the Offenhauser intake? thanks.