Question: I've been reading your magazine for a few years now and just love it. First off, those who write in and complain about way too many Jeep articles and tech info can shove it. The way I look at it is that it's obviously who is doing the most writing in requesting the info, so just follow the trend!
What is the proper way of setting up dual carbs on my Chevy 350? All that is done right now is a set of Edelbrock headers, an MSD ignition, dual 231/44-inch exhaust with 4-inch jet boat bottles on 3-inch tips. The truck is an '85 Chevy 31/44-ton 4x4 regular-cab longbox with an 8-inch Skyjacker lift with reversed shackles residing on 44-inch TSL Swampers, with 4.56:1 gears on Dana 60s. I like the 350 that's in it, but just need to squeeze a li'l more power. Would there be any benefit to putting on a Six-Pack, or are there other solutions other than dropping a new engine in?
Robin
via fourwheeler.com
Answer: Well, to start with, you're right. The majority of the letters we get are from Jeep owners, and the majority of the vehicles on the trails are Jeeps, but that doesn't make us Jeep-biased. That's what our sister magazine, Jp, is for: "just Jeeps." We try to cover all vehicles.
Anyway, what's really hurting your performance are those 44-inch tires and only a 4.56:1 axle ratio. That's about the same as running a 31-inch tire and 3.23:1 gearing, but worse! Worse because the truck also has to push much more air out of the way due to the lift and the added rolling resistance of the tires due to more contact area as well as their weight. You actually need an axle ratio in the 5.38:1 to 5.86:1 range, as this will put the engine back into the right rpm range where it can develop some horsepower and torque. Changing to this new ratio will make it feel like you added 100 hp to your engine.
As for the dual carb setup-well, you pretty much have the correct carburetor right now with the four-barrel Quadrajet. It's an excellent all-around street and trail carburetor. Most likely, it needs a complete makeover to bring it back to a performance level. One place to check out is i-5 Automotive (800/526-9952, www.i-5automotive.com/page5.html) for a replacement or a rebuild of yours.
I believe you could pick up an honest 10-plus more horsepower by swapping over to one of the performance manifolds. Edelbrock has its Performer that's good from idle to 5,500 rpm, and the RPM Performer that produces power from 1,500 to 6,500, if you should decide to go with a cam change. Weiand's Action Plus and Holley's dual-plane are also good choices. If you don't want to keep your present carb, Holley's Truck Avenger works quite well. Just make sure the manifold you pick will match the square-bore bolt pattern. I have used both a modified Quadrajet and the Truck Avenger, and found them both to work quite well-even on steep sidehill angles.
As to your question on dual carbs, well, with modern manifold design, it has been found that a single four-barrel will generally outperform both dual four-barrel and multi two-barrel carb setups, plus you don't have all the linkage hookup problems.
If you also think that you want to make a camshaft change for even more horsepower, be sure to make the axle gear swap first. If you think that your truck is underpowered now, going to a performance camshaft with your present gearing will almost make it undriveable. Whatever you decide on doing, don't "over-carb" or "over-cam" thinking that bigger will be better-in most off-pavement situations, it's not.