Admittedly, this question isn't precisely GT40 related...but I've noticed over the years that many of you here have a lot of practical experience using Weber carbs, and I hope that I can benefit from some of that experience. I recently undertook a project to design and develop a plenum-style intake manifold and related parts for an inline four cylinder engine used in a CORR Pro-Lite off-road race truck. The class requires the use of a pair of Weber 48 DCOE side-draft carbs. With the current IR-style intake manifold and using 42mm (max allowed) venturis in the carbs, the engine produces a peak of 320 BHP at 7100 rpm. My customer routinely operates the engine in excess of 8500 rpm however, and lately has been getting spanked by the factory-backed trucks which have better heads, camshafts, and exhaust systems. When you determine the RPM at which the current intake flow path length (17.4") "tunes", a big part of the problem becomes apparent. We've improved the cylinder head quite a bit and the new manifold design (along with revised valve timing/ header dimensions to compliment) should bring the power up to around 395 at 8100 with no reduction in "bottom end" (in this case 6000 rpm) torque. Now to my question...
The old design utilizes rubber-encased (for vibration isolation?) carb mounting pads approx .875" thick. Generally, how necessary are these? Granted, an inline four cylinder tends to be a bit more "buzzy" vibration-wise than a typical V-8, but is it a given that they need these isolators? In conjunction with the new manifold design, that .875" puts the air cleaner just far enough "out" that a tube in the truck's frame will have to be moved. My customer is willing to break out the hot-wrench if he must, but I'd rather not make him do that if he doesn't really need to.
The old design utilizes rubber-encased (for vibration isolation?) carb mounting pads approx .875" thick. Generally, how necessary are these? Granted, an inline four cylinder tends to be a bit more "buzzy" vibration-wise than a typical V-8, but is it a given that they need these isolators? In conjunction with the new manifold design, that .875" puts the air cleaner just far enough "out" that a tube in the truck's frame will have to be moved. My customer is willing to break out the hot-wrench if he must, but I'd rather not make him do that if he doesn't really need to.