StanJ wrote: ↑Sun May 03, 2015 5:51 pm
gramps wrote:Can someone explain how booster height is measured ? Is there a tech tool that will check this and if so where can one purshase one ?
Right up front, I want to make sure you understand that
IN NO WAY do I mean this as a smart-a$$ answer. There are many sources out there for such gauges; BLP, Tech-Chek, and at least a half-dozen different privately owned machine shops come immediately to mind. Here though - in a nutshell - is the problem with trying to use any sort of booster height gauge to tech a Holley carburetor...
Your first question (or the answer to it anyway) is actually the best place to begin. Booster height is traditionally checked from one of three datums depending on the type of carburetor. Two-barrel carburetors originally produced with choke flap housings (4412-x, 80583-x, 7448-x, 80587-x, and all of their alternative-fuel derivatives) are usually checked with a bridge type gauge that rests on either the horizontal surfaces at the base of the choke horn, with a calibrated plunger that slides down through the bridge to rest on the top of the booster. Some gauges for these carburetors measure this distance from the air cleaner ring surface, and I've seen at least one that measures from the baseplate mounting surface
up to the bottom of the booster. Booster height gauges for four-barrel "non-HP"carburetors with choke housings (too many numbers to list all of them) are of similar design.
Booster height gauges for HP four-barrels (again, a boat load of list numbers) as well as the new "Ultra XP" line of two barrels will typically measure from the top surface of the mainbody casting, but otherwise work similarly to those described above. At least one gauge manufacturer offers booster height gauges that measure from some theoretically-derived plane on the venturi entry radius to the top of the booster.
The unavoidable, totally unaddressable weakness in all of these methods lies in two areas. The first is that like most companies, Holley is in business to make a profit. That's certainly not a criticism, but the fact does bring with it certain economic realities...cost-of-production limits being one of them. In terms of production tolerances from either a
casting or a
machining viewpoint, the cost difference between "+/- .001" (which is about where they would have to be for booster height inspection to be meaningful on the small, ultra high airspeed 390 cfm 4-barrel venturi) and "+/- .004" (which is where those tolerances actually are in the
real world) is huge, and not something Holley can absorb and still make money while also keeping the price of their carburetors at a point that racers are willing to pay. Effectively then, booster height gauges - and in fact all other carburetor inspection gauges - have to have a working "pass" tolerance of .004"-.005", which as any carb guy worth his weight will tell you, is an absolute
football field worth of room in which to play.
The second area of weakness (which compounds the first by orders of magnitude) is the ready availability of the materials in ingot form - Zamac #3 zinc casting alloy, and A356 aluminum - that Holley main bodies and boosters are made from, and the machining skill and expertise that has become commonplace in the racing carburetor industry. Whether by way of modification or complete re-fabrication, there is literally NO surface, much less one of the gauge "reference" surfaces I mentioned above, of any Holley carburetor component that I (along with any one of several other carb modifiers) cannot alter the shape and/or position of while also making it impossible for a "local" track inspector to detect the modification in the amount of time he has to spend on any individual car during pre-race tech inspection, or the amount of time he is
willing to spend during post-race. NASCAR tried for decades to control this, and with all of the resources at their disposal they only occasionally managed to catch the most sloppy examples. This, moreso that all of the other reasons combined, is why Cup cars run EFI now. NASCAR finally realized that they were never going to fully control the amount of air available to the intake ports of those engines, so they opted for the second-most effective thing - controlling the amount of fuel.
I realize that I've rambled a bit here, but the take away point is this: of all of the available methods that a sanctioning body might use to control costs and the general level of competition in a class, attempting to prevent each and every carburetor modification you can think of is both the least effective
and the most expensive to your racers. There are simply too many areas in a carburetor to gain a significant advantage, too many ways to effectively hide those modifications, and too many of us out here with the knowledge, skill, and passion necessary to perform them....and ALL of us get paid. Have someone make a venturi "no-go" gauge for you out of 304 stainless steel that is .025" larger than Holley's stated venturi diameter for the carb you mandate in the class, and a similar gauge for the throttle bore but only .003" larger than Holley's spec for that carb. Let everything else go in the carburetor; the more you try to squeeze there the more you'll be making it easy for some well-funded...but otherwise "no drivin'...competitor in the class to "buy" a season championship. Concentrate on tire and chassis rules that make it difficult to utilize an excess of additional horsepower.
) The meeting of minds came over after a while and said we cannot have any data acq on the car (rules didn't say that). So I replied, then everyone has to take their tell-tach out of their cars 
We we're allowed to run the data acq during practice and heats but not main. 
