|
|
Building A Blow-Through Carburetor - Feeding The FireBuilding A Bulletproof Blow-Through Carburetor From the June, 2010 issue of Chevy High Performance By Henry De Los Santos Photography by Henry De Los Santos
|
|
When it comes to supercharging, carburetors have been given an ill rap for a number of years-at least until recently. Most naysayers would spew out the negative connotations with little knowledge of how carbs really worked. The truth of the matter is, carbureted blow-through technology is much more advanced than they're given credit for and The Carb Shop has proven time and time again that its carburetors flat-out work. If you weren't aware of how far back this technology goes, we'll start by saying The Carb Shop first tried the blow-through setup back in 1977 on a twin-turbo boat application. In the automotive sector, it was in the early '90s they outfitted a '69 Camaro with a ProCharger system. On the dyno, the numbers were impressive, but The Carb Shop later learned through extensive testing on the road and at the dragstrip that it's important to size up the intercoolers properly, as they themselves can be an added restriction. Over the years, they've had an extremely successful track record with a number of fast heads-up cars, all of which has trickled down to the street-level consumer. Can you say 1,000-plus horsepower with no driveability issues whatsoever? For those of you who are still up in the air, we're more than happy to report that we've used nothing but The Carb Shop's carburetors on our blow-through builds, including a 383ci small-block along with a 496ci and a 502ci big-block, all of which have generated big numbers on the engine dyno. Once it's down to the bare... Once it's down to the bare housing, every carb is checked for casting flash. In our case, everything looked good (no flash), so on to checking the sides for a smooth surface. This month, we're going to go through the motions of how these carbs are built; granted, some of it's proprietary information, so you won't get the exact dimensions on certain components. However, it's a good overview to showcase the amount of detail that goes into them. If you're looking for a complete kit to build one for yourself-you can forget it. Honestly, there are way too many variables and you're much better off purchasing one custom-built for your application. For those of you who are looking to put in your orders, expect to wait 7 to 14 working days and pricing is contingent on the power level you're trying to achieve. Of course, you can save a few bucks if you already have a carburetor to send in, but even if you don't, we're sure you'll agree that the price is more than reasonable for the results that can be achieved. Quick Notes
What is it
Custom-built blow-through carburetor by The Carb Shop What we did
Modify a Holley 950 HP Price (Approx)
Starts at $480 if you supply the carb; $1,600 for a ready-to-run, custom-built piece  Most of the blow-through setups...  Most of the blow-through setups are built with these annular boosters, which have been proven to move a lot of air. The signal is good, and responds well to jet changes. For lower-horsepower applications in the neighborhood of 450 hp, The Carb Shop uses dogleg boosters in the primary with the annulars in the secondary. For 700-plus-horsepower applications, they use nothing but the annulars.  Both primaries and secondaries...  Both primaries and secondaries are installed using a special tool. This tool secures the booster in place by expanding its pot metal.  With the boosters in place,...  With the boosters in place, the body is then machined to eliminate any rough edges from the sides. Once completed, the top and bottom areas were also checked to ensure a perfectly flat surface; Often times, cutting 0.007-inch seems to be the norm, but this will also promote a better seal for the gaskets. Note: this process is vital on older carbs, especially since you never know how much the bolt holes have been pulled in from constantly removing the bowls. This ensures no leaks, which is detrimental to a blow-through setup.  For the next step, each hole...  For the next step, each hole is deburred for a nice, smooth edge.  A little epoxy is used on...  A little epoxy is used on the edge of the new boosters to keep them in place.  Next, the throttle shaft entrance...  Next, the throttle shaft entrance on the base was machined. The machined portion will allow seals to be pressed in, keeping the fuel from getting out under boost. Without this proces when lifting off the throttle, the leftover pressure will force fuel out of the throttle shaft. People tend to think it's leaking, but the fuel is actually forcing its way out. Also, it's a good idea to spray a little WD-40 occasionally to help keep the seals fresh. With the seals in place, the throttle shaft itself has to be machined on both ends to fit properly.  During reassembly, the factory...  During reassembly, the factory throttle blades were swapped out with a set from The Carb Shop that eliminates the holes in the factory setup. Originally, the holes were there to make tuning easier by the idle circuit and helped the transition to be a little cleaner, especially to keep the end user from opening the throttle blades too far. Removing the holes makes the idle air bleed a bit more sensitive but allows the caburetor to be custom tailored based on engine specifications.  From here, it's time to secure...  From here, it's time to secure the base back on by placing the six Phillips screws with Loctite.  Here, the idle fuel restrictors...  Here, the idle fuel restrictors are removed, which gives a general fuel curve with a little adjustability. In place of it went in an allen set screw that will allow for additional adjustments when needed.
|
|
|