Many inline enthusiast use aftermarket Carb adaptors to install a two barrel carb to the integral log intake, replacing the anemic one barrel. There are many different types of adaptors, so you'll need to make sure you purchase the correct adaptor for your application and choice of carburetor. Most of the adaptors offered are for Weber carbs, however there are those that allow Holley and/or Autolite 2V carbs to be adapted to the log intake. The most widely known adaptor, from Offenhauser, allows the use of triple one barrel carbs.

While the adaptors seem straight forward, they are not. Not only do you need to make sure you purchase the correct adaptor, there are other issues you need to consider. Some adaptors require a spacer, which is used to square the carb orientation (making it perpendicular) to the crankshaft. While the spacers are not absolutely required, the end result without a spacer, will result in a misaligned carburetor as seen in the picture below.

Stacking up adaptors and spacers may result in inadequate hood clearance as well. To compensate, you must use drop base air cleaners with narrow elements, or a carb hat with a remote air filter. In most cases you will need to switch to a throttle cable as well, which needs to be custom fabricated for your application, as there are no kits currently available.

Upgrading to a two barrel carb over the one barrel definitely offers improved performance. However, the increased air flow is funneled into the integral log intake through the existing one barrel opening, thus limiting the full potential of a two barrel carburetor. If the motor is not properly built, this may also create hesitation and flat spots under acceleration. For more info see the dyno results we got, when we tested three 2V carbs mounted via an adaptor. You might also want to read our tech article on Selecting the Right Carburetor.

Another method of upgrading to a 2V carburetor, which has become popular amongst the FordSix Performance forum members, incorporates mounting a custom carb adaptor to the log and then hogging out the carb opening. Depending on the design, most adaptors allow the use of the popular Holley and Autolite carburetors, which offer improved hood clearance and substantial increases in power and torque. This method was also tested when we did our dyno sessions last summer.

The only drawback to this method, is that the intake manifold needs to be milled flat, which means the cylinder head must be removed for machining, and reinstalled. To mount the two barrel carb, you'll also need a custom 2V conversion adaptor. Most machine shops can make one up, but be prepared to pay a little more for a one-off adaptor, verse an aftermarket adaptor, such as Classic Inlines Billet 2V Conversion Adaptors. At the present time we only offer Autolite/Holley conversion adaptors, but there are plans to make one for a progressive Weber in the near future. We're also working on Phenolic carb spacers to reduce heat transfer to the carburetor.

Prior to milling the manifold (carb pad), the low spots on the intake manifold need to be built up. This is accomplished with furnace brazing or by using some sort of permanent metal filler. Once the low spots have been filled in, the manifold is milled flat so the adaptor can be mounted. Most conversion adaptors are fastened to the modified log manifold by drilling and tapping three to four holes. Gaskets, high temp silicone, or JB Weld are used to seal the adaptor plate to the manifold.

HINT: We like to make a light pass over the log first, which helps to identify the low spots, then do a final pass after the metal filler (or brazing) has hardened. In the photo below you can clearly see where metal filler was use to fill in the low spots, as well as the hogged out carb hole, which was port matched to the custom adaptor (as seen in the photo below).

(click image for larger view)

More Photos

milled intake

homemade adaptor mounted

homemade adaptor - with three mounting screws

another homemade adaptor - with four mounting screws

here, a spacer was used between the adaptor and the carb

carb mounted and plumbed

here's a good shot of a throttle cable set-up

here's another throttle cable set-up, with a carb hat.

clean and simple, yet very effective

Nice shot of a custom made adaptor (click image for larger view)

Classic Inlines - Black Anodized Billet Conversion Adaptor .