Holley vs. Weber Intake Comparison
The stock carburetors on early Mazda RX-7 rotaries are excellent parts, well designed and well built. However for most performance applications they are too small to meet these demands. This shortcoming can be partly offset by increasing the size of the venturis; however, other problems arise in lower RPM street use, such as poor mixture, spark plug fouling, poor throttle response, and poor mileage. Therefore, even though it is possible to improve power using a modified stock carburetor, we do not recommend it for street use.
Regarding the emission controls that are installed on and around the RX-7 carburetor: In our experience, the only reason for removing them is simplicity, and the reliability this simplification offers. Neither the valves nor the air pump, if operating properly, has a significant effect on mileage or performance. Many of these parts operate only on deceleration or when the engine is shut off. Emission laws and regulations have changed considerably over the years, replacing your RX-7 intake system with an aftermarket replacement may have serious emissions concerns if our vehicle is required to undergo emissions testing and inspection. If so, we suggest you consult with your local testing authorities for more information before altering your intake system.
Replacement Carburetors: Holley or Weber?
We've provided this performance chart illustrating the approximate horsepower comparisons between the Holley and Weber components and complete kits we offer. These kits can be used for RX-7 engine applications, earlier rotary vehicle applications, off-road vehicles, race chassis, etc.. Review this comparative chart when selecting a replacement carburetor system for your specific application.
For many applications, our Racing Beat-modified Holley Intake Systems are understandably a very popular choice. These popular "streetable" intake systems have been developed and tuned by Racing Beat as a complete kit and include a Racing Beat-modified Holley carb, intake manifold, air filter canister and filter element, and complete installation instructions and mounting hardware. Everything you need is included in the kit!
Each Racing Beat-Holley kit has been tuned in-house for a very specific engine application, and should only be used for that recommended engine. Each Holley carburetor that we offer is completely disassembled by Racing Beat, various components machined, jets retuned, reassembled, and then quality inspected. This is not a simple tune-up effort; we've invested years of racing experience, dyno testing, and on-road experience in the development of the specific modifications we incorporate into our carburetor upgrade we perform on the base Holley units.
Attempting to use a specific Racing Beat-tuned Holley kit on another engine application might be possible, but you would need to undertake your own research and retune the carburetor for this other-than-intended application.
Out-of-the-box, ready to install!
Every complete Racing Beat-tuned Holley intake kit comes complete with everything you need to undertake the installation of the kit. We fully detail all required steps and provide all mounting and plumbing hardware - including our exclusive Racing Beat air filter housing and filter element. We've taken all the guesswork and hassles out of the installation effort, if you're looking for a truly integrated and complete kit look no further!
Racing Beat offers complete carburetor kits for both 1976-85 12A RX-7 non-ported (stock) and street-ported (modified engine) vehicles. (Street porting is a technique where the engine is disassembled and the engine intake ports have been enlarged to provide improve air flow.) One of our most popular Holley kit is for the 1984-92 RX-7 GSL-SE (6-port engine), this complete kit can be used to replace a failing fuel injection system on these models.
The alternatives we offer for the Holley system are the Weber 48 IDA or 51 IDA two-barrel downdraft carburetors. These carburetors are useful for racing and certain other specialized applications primarily because of their simplicity, compactness, and excellent float bowl design. The Racing Beat-modified Weber 51 IDA carburetor actually starts as a 48 IDA as delivered by Weber, but further machining and tuning by Racing Beat converts this carburetor to a 51 IDA configuration.
As applied to a Mazda rotary, Weber carburetors exhibit a variety of good and bad characteristics. On a stock or street ported engine, the lack of a choke system on these units makes cold starts very difficult, even in warm climates. However, for some applications, such as off-road, boats, racing, etc., these problems may not be significant. If this carburetor is used on a bridge-ported engine, the only problem is lack of sufficient power, partly because of the modest size, and partly because of intake losses.
Our testing has shown that maximum power from a bridge-ported 12A engine with a Weber 48 IDA carburetor is about 250 HP, while a suitable Holley carburetor on the same engine can produce over 250 HP. The one application where the Weber 48 IDA carburetor is still used is on peripheral ported engines. Here, its relatively small size is compensated by the excellent breathing capability of the porting. Nevertheless, we have found that, by enlarging the carburetor to 51mm diameter (from 48mm diameter), approximately 10 HP more is available. 12A peripheral engines can develop 280+ HP with a Weber 51 mm carburetor.