The Air in There

Our Bracket Brawler project...        read full caption Our Bracket Brawler project GT has been depending on a Holley HP-series 750 carburetor to get the job done and it has done just that running consistently in the mid 10-second zone. Always looking to go faster, we replaced it with an AED 1050-cfm small bore Dominator to see if the bigger breathing carb would drop our elapsed time on the race track.

Our 393-ci stroker motor was...        read full caption Our 393-ci stroker motor was relying on a Holley HP-series 750 and had run in the 10.40s with it onboard. It has 80 primary and 88 secondary jets and a 6.5-inch power valve, both of which the engine seems to work best with. Note the manual throttle stop on the carburetor linkage that we use to slow the engine down when running in the NHRA 10.90 Super Street class.

We were curious to see if...        read full caption We were curious to see if a bigger carburetor would pick up the power level of the engine and decided to swap the Holley HP 750 for an AED-built Dominator. The Dominator is known as a small bore design and has a flow rating of 1050-cfm. Note how much bigger the bores are in the Dominator as opposed to the smaller 750.

Our AED Dominator is equipped...        read full caption Our AED Dominator is equipped with 12 adjustable air bleeds that help the engine run and perform better and smoother,especially at idle and part throttle.

All AED carburetors come with...        read full caption All AED carburetors come with a calibration sheet such as this one that tells the consumer all about the type of carb he is using. The sheet will display the carburetor jetting, the primary and secondary air bleed sizes, the power valve sizes and the squirter selection. It will also tell the consumer if the carb is built for gasoline or alcohol and shows that it has been flowed and tested prior to shipment.

Our Bracket Brawler drag car...        read full caption Our Bracket Brawler drag car runs in the 10.40s but we need to slow it down when running in the NHRA Super Street class, which is a heads-up class with a 10.90-second breakout. To slow down the engine we use this simple Moroso manual throttle stop that prevents the engine from achieving full throttle. After numerous runs down the quarter-mile we have figured out that, on our engine, every full turn out will slow the car down approximately .08-second.

With the carburetor studs...        read full caption With the carburetor studs loosened and the two 6-AN fuel lines removed we lifted the HP 750 from the intake manifold. We are currently using a wooden 1/2-inch four hole spacer and a 1/2-inch open spacer underneath it but will have to change this in order for the Dominator to fit on the 4150-style intake.

You have all heard the term "bigger is better" over 1000 times, but that statement is far from an absolute. When discussing the power potential of an engine, sometimes bigger is not the answer. Picture this: what will happen if you stick a set of NHRA Pro Stock cylinder heads on your mild big-block engine? The end result will be a guaranteed loss of horsepower. Why?

Engines work as a whole; no one part will make it exceptionally better. Granted, nitrous or a big blower will prove that theory wrong, but in most cases, a normally aspirated, internal combustion engine needs to have all of its parts working in harmony with one another in order for it to perform at an optimum level.

Cylinder heads can and will upgrade the power level of most engines, but using a set with a port design that is way to big for the camshaft configuration and the compression of your engine will more than likely do more harm than good. The engine can't take advantage of the bigger and higher-flowing ports of the new head design because the remaining hardware is not designed to do so and the end result will be less airflow and a reduced signal from the ports. Of course, stepping up to a bigger cam and more compression will help but now you're into juggling the whole combination around, which is not what most racers plan on. Carburetors fall into the same category and there has been a lot of talk lately about what type of carburetor will best suit a specific engine. A large number bracket and heads-up racers use the very popular and proven Holley 4150 setup. These are the standard "Double-Pumper" carbs that we are familiar with and come in sizes ranging from 575-cfm to over 1000-cfm, depending on the size and the modifications they have. These designs have been proven for many years and are perfect on top of most racing and street engines.

Jason Keener of Advanced Engine Design Performance (AED) in Richmond, Va., had been following our Bracket Brawler project in MM&FF for the past year and wanted to design a high performance carburetor that he felt would add to the horsepower of our engine. Our current powerplant consists of a DSS Inc., 393-ci Windsor that uses a set of Canfield high port cylinder heads and a Holley HP-series 750 carburetor. The mill has a .600-inch lift camshaft and a conservative 12.1 compression ratio.

With this in mind, Jason recommended that we try out one of his AED-constructed Holley Dominators to see if the bigger and better flowing unit would help reduce our elapsed time.

Stepping up
The 750-cfm Holley HP series unit we're using has adjustable air bleeds on the main carb body and no choke horn. It is a race-only piece and, with 80 primary and 88 secondary jets, has yielded a best run of 10.47 at 127 mph. "The Dominator we constructed for your car is what we like to call a 1050-cfm, small-bore design," stated Keener. "It is smaller than a conventional Dominator carburetor, but should still outflow your 750 by quite a bit. We started off with 93 jets in the primary and secondary metering blocks and feel that the 93s would be a good starting point for your engine. It should pick the car up on the track right away."

We felt that running the two carburetors on the car on the same day would give us the best results and cruised over to Raceway Park in Englishtown, N.J., for the testing. We began by making a test run with the car exactly as it was and, on this day, it ran a 10.651 at 124 mph. The temperature was in the mid 80s and the track had a nasty headwind. With the base number in hand we began our conversion project.

The first step was to remove the 750 from the intake and after removing the two 6-AN fuel lines from the float bowls, it came off in a matter of minutes. The Dominator would be a very easy part to install but we would have to replace our 1/2-inch, 4-hole spacer and 1/2-inch open spacer with a Dominator adapter in order for the bigger bolt pattern of the unit to fit. For this, we called upon Wilson Manifolds in Fort Lauderdale, Fla. Shop owner Keith Wilson makes a trick CNC machined spacer that enables you to mount a Dominator carburetor on top of a standard (4150-style) intake manifold. Wilson Manifolds can custom-fabricate virtually anything you can think of for a racing engine and specializes in carbureted intakes and nitrous systems for high horsepower engines. The spacer fit with no problems whatsoever under our Cervini's 21/2-inch cowl induction hood. However, if you are running a stock hood on your pony, you might have no choice but to replace it with a raised design as the clearance of the Dominator is a bit tight. With the spacer/adapter on we were able to bolt down the AED Dominator to the engine. After hooking up the two fuel lines and reconnecting the carburetor linkage, we started up the Windsor and checked for fuel leaks and the proper idle quality.

"You can adjust the way a carburetor acts during idle with the adjustable air bleeds on the main body of the unit," explained Brockwell, the Dominator expert at AED. "Your combination should idle well, but if it doesn't we can make you some smaller intermediate air bleeds, which should help the idle quality and the overall torque of the engine. Air bleeds are just like jets but flow air and, just like with jetting they can be adjusted to tailor a certain engine." Keep in mind that the Dominator can get away with much bigger jetting because it can flow a much larger amount of air. If the Dominator was able to absorb the extra air that it is capable of doing, but was not able to balance that with the required fuel volume, the engine would be dangerously lean. We made our first pass with the new carb and noticed in the burnout that the throttle response was a bit weaker but the overall feel of the engine was noticeably better, especially after half-track, where the Dominator really started to shine.

On the very first run the car picked up a full .10-second and ran a surprising 10.559 at 125 mph. The 60-ft. was the same (1.49 on the footbrake) but the extra mid range and top end power was evident right away.

We tried bumping the timing up (from 38 to 42) but it didn't seem to like it as it lost .02-second on the very next run. Since this testing, I have tried running the 750 HP once again just for kicks and, just as expected, it lost almost .10-second, running a 10.64 just a few days later under similar conditions.

Most of us at the MM&FF headquarters thought that the AED Dominator would be slightly big on top of our 393 but, sure enough, the car picked up and ran quicker and faster in the quarter-mile. In the coming months we will be performing even more testing with our AED Dominator and will be trying out different jet sizes and spacers in an attempt to go even faster. In this instance, the "bigger is better" mantra holds true.

For the Dominator install...        read full caption For the Dominator install we chose to use a 11/2-inch spacer from Wilson Manifolds in Fort Lauderdale, Fla. Dominator carburetors have a bigger bolt pattern than a standard Holley 4150 design and will require the use of this spacer/adapter to work.	Our only other choice was...        read full caption Our only other choice was to install a different intake manifold that is designed just for a Dominator but the spacer is cheaper, much easier to use and works perfectly.	Note how the Wilson spacer...        read full caption Note how the Wilson spacer is tapered on the inside. The HP 750 has a smaller base plate and smaller throttle bores. The Dominator uses a wider bolt pattern (to tailor to the bigger bores) and uses a bigger base plate because of it. The Wilson spacer bolts to a standard 4150-style intake and allows a Dominator (4500-style) carburetor to be mounted on top of it.
With the spacer bolted to...        read full caption With the spacer bolted to the intake we placed the Dominator on top of it and connected the two fuel lines to the float bowls.	Our old setup required four...        read full caption Our old setup required four 2-inch studs that allowed us to use our old spacer arrangement but the Wilson spacer requires four small bolts to mount the Dominator to it.	We hopped down to the local...        read full caption We hopped down to the local parts store and picked up the four required bolts to replace the studs.
With the Dominator on and...        read full caption With the Dominator on and ready to go we primed the fuel pump to check for leaks and then reconnected the carburetor linkage.	Note how much bigger the Dominator...        read full caption Note how much bigger the Dominator bores are as compared to a more conventional HP 750. The boosters have a smoother design and the four bores are tapered on top to help improve the overall airflow of the unit. Another thing to keep in mind is the hood clearance. We are using a 21/2-inch cowl hood as opposed to the stock steel version and that seems to help. With the 11/2-inch spacer/adapter underneath the carburetor, the stock hood may wind up having aclearance issue.	With the Dominator on and...        read full caption With the Dominator on and ready to go we started it up and checked for fuel leaks. After running the car for the first time we ran .10-second quicker on the quarter-mile and 1 full mph faster as well. We then tried bumping the timing to from 38 to 42 degrees but it didn't seem to help. On the next pass it slowed by .02-second.