Youve got to admit that when we do something we dont half-ass it. We went out to the desert for a to-the-death carburetor shootout and wound up with an oil-soaked wrench on our new boss pile-o-tetanus grease-fest. At least it beat being in the office. Péwé showed up broke and it only got better from there.
The idea was cooler than the Fonz: Take four carbs out to the middle of nowhere, install them on a vehicle back to back, wheel it hard, and see which ones rule and which ones suck. No dyno runs here. We were testing for what wheelers really care about chugging up obstacles at 400 rpm, blasting up dunes at 5,000 rpm, performance over whoops and washboard roads, and ability to stay running at extreme angles.
We called Summit Racing for four of the most popular carburetors. Summit sent us a Holley 750-cfm (PN 3310S), a brand-new model Holley Street Avenger 670-cfm (PN 8067), an Edelbrock Performer 750-cfm (PN 1411), and an Edelbrock Q-jet 750-cfm (PN 1902).
Since we knew wed be wrenching 70 miles from the nearest parts store, we also leaned on Summit, ProForm, K&N, and Edelbrock to send a laundry list of square/spreadbore adapters, fuel line kits, rebuild kits, air filters, and more fuel and linkage fittings than we knew existed. We also wanted a fair shootout, so rather than messing with the carbs we decided the best way to test them was in as-delivered, out-of-the-box form. We couldve lowered the float bowls and tweaked stuff here and there, but 70 percent of you will probably be running them as they come.
Edelbrock Q-Jet (PN 1902)
Since our test mules Buick 455 was already fitted with an old-style Q-jet, we tested the 750-cfm Edelbrock unit first. Although the carb bolted right to the spreadbore intake, we had to bend the choke and throttle linkage in order for them to clear parts of the manifold. Otherwise they hit when the butterflies were opened. Another little annoyance was that the back of the Q-jet requires a 3/8-inch NPT plug (or vacuum nipple if running power brakes) that the carb didnt come with. Since our old-style Q-jet wasnt equipped with one, we pirated the vacuum nipple off our chase vehicle and proceeded. We used an Edelbrock fuel line kit (PN EDL-8135) to connect to our fuel pump and removed and installed the fuel fitting from our old Q-jet.
The new Q-jet fired right up and idled at a smooth 600 rpm out of the box. The first test involved running a rocky, boulder-strewn section of trail. Since faster crawl speeds make it more difficult for a carburetor to keep an engine running, we kept the GPW in 50:1 low range. The Q-jet was able to keep pulling right down to 200 rpm without stalling, and those times it did stall it was quick to restart. The small primaries allowed for smooth increases in power, which resulted in more elegant driving. In the rocks this carb was all about finesse.
Next up was the incline test. We put the vehicle on a series of inclines starting with the passenger side about 45-degrees higher than the drivers side, then with the nose about 65 degrees higher than the rear, and finally with the rear 65 degrees higher than the nose. There wasnt one position in which the carb ran better or worse. It just kept chugging away at all angles. After sitting and idling for a few minutes at extreme angles there was a bit of carb smoke evident, indicating that the plugs were loading up, but this could be cured for a few more minutes with a blip of the throttle.
Bumpies and Sand
We then headed over to the dunes, which involved a blast down a rough whoop-filled washboard road. As the vehicle porpoises, the fuel is allowed to slosh back and forth in the bowls and is more likely than not to cause stumbling under acceleration. Once again the centrally-located fuel bowls of the Q-jet offered miss-free performance. Arriving at the sand, the new Q-jet delivered a noticeable seat of the pants improvement in power over the old carb when climbing. Péwé was as giddy as a schoolgirl, even though the lifters sounded like they wanted to see daylight real bad and the rods are probably held together with chewing gum. The small primaries offered lots of control in the slow portions, but we could really tell when the huge secondaries kicked in.
We followed these test procedures for the rest of the carbs we tested.
Edelbrock Performer (PN 1411)
InstallThe squarebore 750-cfm Performer is based on the ever-popular Carter AFB. It required an adapter to mate it to the spreadbore manifold. We ultimately used a single-plane adapter from ProForm. Unlike the Q-jet, the Edelbrock Performer came equipped with a 3/8-inch NPT plug. Those running power brakes will still need to go shopping for a 3/8-inch nipple. We needed to use an Edelbrock throttle cable stud ball (PN 8016) to hook up our GM throttle and the carb didnt come with an air cleaner stud or gasket.
We fired the engine and the carb idled at 1,500 rpm out of the box. We were able to lower this to 650 rpm, but any lower and things werent happy. Heading through the rocks in 50:1 low range was misery! The throttle response was very touchy. Where the Q-jet was more forgiving and lended itself to more finesse, the Performer allowed the vehicle to surge forward with throttle input. The carb would stall when a tire encountered the slightest obstacle or when the vehicle was at an angle. The real bummer was that it was super-hard to restart. It seemed as though the idle was fluctuating by as much as 250 rpm. Things got so bad we threw the GPW in 100:1 just to make it out to the angle test.
Not this carbs forte. Side angles werent miserable, but the engine would load up quickly and then die. However, point the nose or tailgate skyward and youd better be ready to reach for the key. The Performer tended to stall at even slight angles and took several seconds (sometimes up to 15 seconds) of cranking time before the engine would fire, and then die!
Bumpies and Sand
On the washboards the Performer once again exhibited a tendency to load up and stumble as the vehicle porpoised. We suspect we could have alleviated this condition by lowering the fuel float, but this was an out-of-the-box test. However, once in the sand, the Performer showed its stuff. It offered much better low and upper rpm power than the Q-jet. Mashing the gas resulted in good tire spin and snappy throttle response. This carb liked to move, not crawl.
Holley Squarebore (PN 3310S)
Since we already had the adapter bolted to the manifold, installing the Holley 750-cfm on the engine was a no-brainer. However, we had ordered a chrome fuel line kit (PN G-3100) from Summit that didnt quite line up with the fuel bowls. We could have bent the line, but the chrome plating tends to flake inside the tube and clog the carb when the tubing is bent. Instead, we used a fuel line kit with a flexible braided hose that we bought at a local parts store before hitting the dirt. We also had to transfer the ¼-inch ball stud from the Performer for the throttle bracket. The Holley carb was much taller than the Edelbrocks, necessitating a shorter air cleaner stud for clearance. We didnt have a shorter one, so we simply cut the one we were using.
At first fire the Holley idled at 950 rpm. We were able to bring this down to 650 rpm, and we then headed for the rocks. The Holley fared only slightly better than the Performer when encountering an obstacle. The engine would stumble on the smaller stuff, and some throttle input was needed to keep going in the big stuff. However, when the 3310 did stall and die it was very quick to restart.
Again, like the Performer the Holley didnt like angles of any kind and allowed the engine to load up, sputter, and die, although the Holley did let the vehicle idle a bit longer than the Performer. The real bonus was that the engine would fire with only a few turns of the starter. Such a characteristic goes a long way towards helping a driver stay sane on longer trails.
Bumpies and Sand
In the whoops the Holley performed worse than the Performer. It loaded up, stumbled, and even died a few times. However, once in the dunes it kicked ass. The 3310 delivered the best throttle response and power of the testees. It let the GPW really get up and goa small miracle considering the condition of the 45.
Holley Street Avenger (PN 8067)
Holley was very eager for us to try out its newest carburetor design. The Street Avenger is offered in 570-, 670-, 770- and 870-cfm versions, although only the 670-cfm model was available at the time of our testing. The new carb comes with an electric choke, a quick-change vacuum secondary spring, a newly designed power valve guaranteed against blowing out, external float adjustment, and easily tuneable idle circuits.
We simply unbolted the ¼-inch throttle cable ball stud and dual inlet fuel hose from the 3310 Holley and installed it on the Street Avenger. Like the 3310, the Street Avenger idled at 950 rpm out of the box, but we couldnt tune the idle down to less than 700 rpm. Also, the electric choke stayed engaged even with the engine at full operating temperature to keep the idle up around the 950-rpm mark.
Because of the high idle, the rock and angle portion of the tests cant really be counted because a higher idle will allow the engine to stay running longer and prevent stalling when encountering obstacles. Thats just what happened. The Street Avenger motored right over most rocks and obstacles at 950 to 1,100 rpm that the Q-jet had traversed at 200 rpm. When we did manage to stall the carb, we found it started easier than the Performer, but not as easy as the Q-jet or the other Holley.
Once again, the higher rpm let the engine continue running where the others stalled, but the exhaust was super, burn-your-nose rich.
Bumpies and Sand
The Street Avenger loaded and stumbled worse than the Q-jet, but not as badly as the Performer and Holley 3310 probably once again due to the high idle. In the sand the Street Avenger offered the best-of-bunch off-idle throttle response and was a kick to drive, although its smaller cfm rating hurt upper rpm powereven in Péwés timebomb of a 455.
Hands down, it has to go to the Q-jet. Although its the most expensive of the carbs we tested, its still cheaper than fuel injection. So what if it wont run upside down for long and if it felt just a little less powerful than the other carbs we tested? When it comes to chugging away at stupidly low rpm at dizzying angles, this carb has what it takes in spades.