July 2012 Chevy High Performance Q&A

Chain Reactions, Part II

Kevin McClelland May 29, 2012 0 Comment(s)
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Tow Beast

I have a ’94 C3500 Crew Cab, two-wheel drive, and want to build a new engine just for towing. I have a three-car trailer, and want to pull it with no problem, but the thing is, I have an LQ9 that I was going to make into a carb 402. I also have a 454 that I was going to turn into a 496. Which engine would be better?

Lee Krucial
Detroit, MI

Well, as we’ve been pushing the LS-based engines, I’m going to have to fall back to “There is no replacement for displacement” adage. To pull around a Crew Cab dualie with a three-car trailer in tow, I would prefer the stroked 454 for this job. Yes, you may get a slight bit of efficiency with the Gen III engine design, but I’ve seen that when you put a ton of load on the LS-based large displacement engines they will eat the fuel also. A good old big-block will kick out tons of torque effortlessly for the long haul.

Make sure that when you spec out your 496 build that you stay on the conservative side and go for maximum torque production. There is no reason to build a warmed-over big-block that is going for horsepower. Go with a good set of oval port (either Gen VI irons or AFR aluminum heads) with a short hydraulic-roller. The GM H.O. 454/502 hydraulic roller would be a great choice as it specs out at 211/230 at 0.050-inch tappet lift, 0.510-/0.540-inch max lift, and is ground on 112 centers. This camshaft is sold under PN 24502611 and in your oval port 496 will make close to 600 lb-ft of torque in the low 3,000-rpm range. It will also make great power to 5,000 rpm. That thing would burn your duals for as long as you wished to keep your foot in it. Make sure that you strap those three cars down well!

Source: gmperformanceparts.com

Get Looped

I have argued this to the death. Now, a lot of guys loop the vent out the top of a fuel cell.

JAZ says do this. Other say not to. A loop can cause a liquid trap (not allowing air to move). Liquid traps are used on an A/C vent to keep bugs and air out. So what’s the deal? Loop or no loop?

Al Smith, SSR Engines & Carburetion
Newton, NC

Al, interesting question. Of all the cars that I’ve built over the years I’ve always looped. I’ve done this to prevent fuel from coming out of the cell during aggressive stops when the tank is completely full. As for preventing the air from getting into the cell because of a liquid lock, as the pump takes fuel away from the tank the liquid lock is drawn back into the cell. This fuel in the vent doesn’t cause much resistance to the atmospheric pressure trying to push the fuel back into that tank when the pump is sending fuel to the engine.

Now that you bring up venting fuel tanks, make sure that you run some type of filter on the vent line into your fuel cell. If you think about it, most of our race cars use anywhere between a quarter to a full gallon of fuel per run; this is after driving around the pits to the lanes, making the run, and driving back to the pits. If you look at the amount of space a gallon of fuel takes up you must bring that much air into the fuel cell. The air that is under your car can be very dirty from the exhaust blowing up dirt off the ground, and the pressurized air under the car as it travels down the track. It’s amazing how dirty my filter gets on the end of the fuel cell vent. It is caked with dirt, which would be getting into my fuel cell, plugging my fuel filter, and even worst, some getting past the filter and into my expensive MagnaFuel pump. A simple universal air filter breather will clamp right on to the end of AN-6 bulkhead fitting. These filters can be washed and reused for the life of your race car. CHP


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