Although there are many things to consider when building an engine combination, few are as critical or mysterious as selecting the proper carburetor. After all, there are dozens of possible candidates for your engine, from vacuum-secondary spread-bores to 4500-series Dominators, not to mention multiple-unit options. Rated by cfm (cubic feet per minute), carburetors significantly determine your fuel curve and engine efficiency. Too little carb, and the engine will starve for air/fuel power at the top end; too much carb, and it won't flow air fast enough to properly atomize the mixture.
This story is a continuation of our slick budget small-block series, which will be familiar to former readers of High Performance Mopar. We built a low-budget 360 and installed it in a Dodge Challenger. This is a street-strip machine, so after consulting with Holley's recommendation chart for size and style of carb based on combination, we selected a 750-cfm double-pumper for the combination. After some baseline testing, we found some significant gains through tuning and spacers. The car uses a stock Edelbrock Performer RPM intake and a set of mildlly ported heads.
But there was more to the story than simply swapping on the new juice pot. The Challenger's gas tank had numerous rust spots and leaked, a dangerous situation in any regard. It was decided that before we began the real-world testing, this E-Body was going to need some upgrades. To that end, we secured a replacement gas tank and 3/8-inch pickup from The Paddock, prepped it with restoration coatings from Eastwood, and installed it. At the same time, plans were made to install a new 3/8-inch fuel line and a Holley electric pump in the rear; time constraints prevented that from happening for our first test, which, in turn, skewed our baseline results to some extent.
Getting back to carb selection, race-only cars normally run huge carbs because they're lighter, have high-stall converters and steep rear gears, and don't have to be concerned about part-throttle driveability. On the other hand, cars like the ones we use (the Challenger and a '67 440-powered Coronet R/T) see many street miles. Indeed, they're driven more than 90 minutes each way to the test sessions we hold at Raceway Park in Englishtown, New Jersey, so streetability is critical. Strip-testing has proven that better 60-foot times will translate to increased throttle response on the street.
Here's where it starts. The...
Here's where it starts. The Paddock sent us a new gas tank and a 3/8-inch pickup, which will increase the fuel flow over the 5/16-inch stock version. One additional thing to consider when redoing the tank is to replace the filler neck in the trunk floor as well. Again, The Paddock had what we needed, since our originals were shot. A little petroleum jelly on the tank filler neck will prevent the new neck grommet from sticking when doing the install.
While a given motor/carb combo may seem very good on the shop engine dyno, it may be lacking in street manners. For example, a heavy (3,800-pound) car with a stock converter and 3.23 gears will be a candidate for a vacuum secondary carb, since the engine's response will have a softer upswing; too much fuel here, and the engine will choke trying to catch up. Take the same engine and swap it into a 3,200-pound A-Body that stalls at 3,000 rpm with a 4.10 gear (still streetable, but not as pleasant a cruise ride), and a double-pumper is the way to go; it'll take all the fuel now, thank you. Like any other component, carbs should be selected based on your complete combination. Our 12-second street/strip machines have responded well to Holley double-pumpers. Optimum tuning has been with No. 37 squirters on the 360's 750 carb and No. 40 squirters in the 440's 850 unit.
On The Dragstrip
Before going any further, we'll tell you right now that our fuel-delivery problems affected our initial test. The 5/16-inch line, mechanical pump, and hot summer humidity led to fuel-starvation problems at the top of every pass. As a result, our times were off, but the baseline 750 we normally use gave us a 12.84 best. Holley sent us three others: an 870-cfm Street Avenger and a pair of HP-series carbs in the 750-cfm and 950-cfm versions, but the baseline carb was the best. We gave up and returned to the shop to finish our fuel-system upgrades.
Looking good! Here is the...
Looking good! Here is the tank installed; we sandblasted the straps and painted them Chassis Black. We left the EEC (Evaporative Emissions Control) intact in case we ever went back to stock. With the old fuel line removed, we also gave the frame areas normally hidden by the lines the Corroless/Chassis Black epoxy treatment.
Leave it to Eastwood to have...
Leave it to Eastwood to have the materials we need to do the job right. After we scrapped and wire-brushed the underside of the truck pan, we sprayed on their PRE-Paint Prep for proper surface prep. Next, we added a layer of Eastwood's Corroless Rust Stabilizer to prevent future problems, then hit the area with Chassis Black to finish it. The latter two paints combine to form an epoxy bond against rust, chips, salt, and other road hazards. We repeated the process on the top of the pan. Then, to prep the tank before installation, we sprayed it with PRE-Paint Prep as well and finished the job with Eastwood's Tank Tone, which has a nice hue and contains zinc for rust prevention.
Before getting down to our...
Before getting down to our second day of testing, we upgraded the rest of the fuel system as well. Shown here is a roll of 3/8-inch line, a Holley Red electric pump, an inline filter, the dual-inlet carburetor line, and a pair of good air cleaners. Replacing the fuel line can be a bear; the old line needs to be examined and the new 3/8-inch line carefully bent with a tubing bender to match. Take your time here, because one bad kink can ruin your whole day.
If you want to do it the easy...
If you want to do it the easy way, you can order a complete 3/8-inch prebent line from The Paddock (shown, right) like we did. Install the line using the OE loops in the body. Mount the filter between the pump and the pickup to keep contamination to a minimum, and check the filter periodically, especially if you're using a variety of pump gasolines.
Fuel System Follies We found...
Fuel System Follies
We found that our stock fuel system was going to need some work if we wanted to get honest results. The gas tank was basically junk (it had an inch of rust and slag at the bottom) and we wanted to upgrade the fuel lines and fuel pump for performance. Here's a brief overview.
Here's our selection of Wilson...
Here's our selection of Wilson spacers. Three varieties: open (for increased plenum volume and power in the midrange), tapered four-hole (for better air/fuel distribution to each intake runner-best in single plane applications), and untapered four-hole (for low-end response and increased throttle response by increasing venturi signal). Wilson spacers are CNC-machined from billet aluminum. When hood clearance isn't an issue, 1.25-, 1.5-, 1.75-, and 2-inch varieties are available as well.