The Stovebolt Site Forums The Parking Lot Big Bolts Dual carbs on big bolt 235 - am I crazy?

Hi all,

I've finally got my 51 4400 road worthy after most of a year and have had a chance to drive it a bit. It's apparent after driving it a bit that the overdrive tranny I had planned for it would be useless without more power. I'm having to downshift a lot to take hills and with overdrive I wouldn't be able to maintain highway speed on much of a grade. Is this typical? The engine is a '58 235 and has good compression, no smoke, and good oil pressure.

My question is whether there would be anything gained with multiple single barrel carbs (or perhaps an Offy/Holley 390) on a vehicle this heavy (5600lbs)? I'd like to keep this engine, as it's in such good running condition but I need to be able to drive it on the highway (55 mph) for it to be useful. I don't need to go fast, just get it up to speed and hold it there.

I'm going to have my friend put it on his Sun engine analyzer to make sure that timing, ignition, fuel ratio, etc are OK. Hopefully, there's a bit more power to be gained through tuning.

I think that your wishing for more speed than your truck is going to allow because of the rear end gear ratio. Back when these trucks were new most of the speed limits for trucks was 45 mph tops. My '53 6400 is happy as can be going 45 mph. If I have to pull a hill with lots of grade I usually will drop a gear, or at least shift the 2 speed into low range.

Don

An improved carb setup and headers will definitely give you more power out of a 235.

Without the overdrive it won't matter, as Don states the gearing will keep it around 45 mph.

If you do the overdrive keep in mind how your going to stop the darn thing. That's one I haven't figured out yet so I just drive 45 and keep to back roads.

Yep, that's definitely still on the top of the agenda. After I've gone through all the brakes on this thing, it's not too bad... if you're Paul Bunyan. A power brake conversion is the next thing I'm working on. I'm going to fab up a bracket and mount a 9 inch dual diaphragm booster with a drum/drum 1 1/4" dual master cylinder on the frame rail. If anyone is interested, I can probably dig up the part number for that MC.

I have plenty of power but the rear axle gearing(2 speed rear axle big bolt) doesn't allow me to use what power I have with one carb. I'm going to say two is just a waste of fuel and money. just my opinion..

If anything, the dual carb setup will make the problem worse, not better. The only place you'll gain any improvement will be at maximum RPM, and once the engine lugs down, even a little bit, the power will simply evaporate. If you want a little more carburetor, you might consider going to a 2-barrel Rochester like the one that was used on a 265 or 283 V-8. (Not the bigger 2GC model used on Pontiac engines, Chevy 350's, etc.) Even that one would require some major machining and welding to the manifold for a proper-sized flange to eliminate the choke point that would be created by using an adapter plate.

Bottom line- - - - -pick a gear that lets you pull the load without downshifting any further, and keep the RPM's up near the maximum horsepower point. That's probably close to 4,000 RPM, maybe a little less. If you can stay at the max-HP engine speed without losing road speed, that's all the performance you're going to get, regardless of the carburetion you have. Any more power will require a bigger engine (261), more compression, or a camshaft that's able to produce more bottom-end torque.
Jerry

I was never a believer in aluminum intakes or headers until my son's 85 Ford F-250 4 x 4 with a 300 6 developed carburator / computer problems. We didn't want to buy a new 1 bbl and deal with the computerized carburation crap, so we replaced it with a Clifford 4 bbl intake and headers that we found used, and a new Holley 4160 390 cfm carburator. Fuel mileage was about the same, but the truck ran much better with alot better acceleration and alot more power. In fact it would spin the tires in 3rd gear on pavement if you got on it. We're planning on doing the same thing to his 69 Ford 240 this winter. They sell stuff for Chevys too. I think everything they sell is for inline engines. They sell direct. www.cliffordperformance.net