Jim Rosenthal
Supporter
We are getting close to starting up the engine in my GT40, probably a few weeks away, and this seems like a good time to post a question and solicit opinions. The question is about cam selection and carburetors etc
The engine in my car is a 302 which was built with AFR heads, about 9.5 compression, and a flat-tappet hydraulic camshaft picked by the engine builder based on my request for an engine with a broad relatively flat torque curve, 350hp or so, and good idle and tractability. These cars are light enough that I did not need huge torque in the lower range, but smooth power delivery would make the car more fun to drive. The engine was run in and several dyno runs showed peak hp of about 355, I think at around 4000 revs, and peak torque of about 380 ft/lbs. Redline was 6000. This was done with a 650 Holley mechanical secondary carb. I had intended to fit Webers, but that was not possible at the time, and so the engine was run in, and then drained and put away until it was installed into the car. It has not run since then. During the most recent phase of completing the car, the Holley carb and manifold were removed and the 4x44IDF setup that I bought from Chuck Schmidt on this forum was installed, and also the crossover exhaust system which I did not have when the engine was originally tested. Chuck was kind enough to send the cam that he used with the Webers in his engine, but I have not installed it into the engine. I went with 44IDFs because I thought 48IDAs would be too much for a street car, based on the experience of others and my (very) limited experience with original cars.
My question is this: what is different about a cam that is intended for use with Webers, particularly small Webers such as the 44IDFs? I recall reading that Webers rely on a strong vacuum to work properly; I don't know what "strong" is, and what sort of cam profiling and lobe separation and timing work well with Webers. It would be a relief if the engine runs well with the current cam and the Webers (the current cam is a fairly conservative hydraulic flat lifter cam, or so the engine builders said at the time- someplace I have the cam card and grind number, and I am looking for it). Changing the cam in my car would not be impossible without pulling the engine, just a pain in the neck I would just as soon do without.
So- with all that- what cam characteristics make a cam suitable or better for use with Webers, particularly the individual-runner kind of setup which my engine now has? Suggestions and experience and reference sources cheerfully acknowledged. Thanks in advance for help/encouragement.
The engine in my car is a 302 which was built with AFR heads, about 9.5 compression, and a flat-tappet hydraulic camshaft picked by the engine builder based on my request for an engine with a broad relatively flat torque curve, 350hp or so, and good idle and tractability. These cars are light enough that I did not need huge torque in the lower range, but smooth power delivery would make the car more fun to drive. The engine was run in and several dyno runs showed peak hp of about 355, I think at around 4000 revs, and peak torque of about 380 ft/lbs. Redline was 6000. This was done with a 650 Holley mechanical secondary carb. I had intended to fit Webers, but that was not possible at the time, and so the engine was run in, and then drained and put away until it was installed into the car. It has not run since then. During the most recent phase of completing the car, the Holley carb and manifold were removed and the 4x44IDF setup that I bought from Chuck Schmidt on this forum was installed, and also the crossover exhaust system which I did not have when the engine was originally tested. Chuck was kind enough to send the cam that he used with the Webers in his engine, but I have not installed it into the engine. I went with 44IDFs because I thought 48IDAs would be too much for a street car, based on the experience of others and my (very) limited experience with original cars.
My question is this: what is different about a cam that is intended for use with Webers, particularly small Webers such as the 44IDFs? I recall reading that Webers rely on a strong vacuum to work properly; I don't know what "strong" is, and what sort of cam profiling and lobe separation and timing work well with Webers. It would be a relief if the engine runs well with the current cam and the Webers (the current cam is a fairly conservative hydraulic flat lifter cam, or so the engine builders said at the time- someplace I have the cam card and grind number, and I am looking for it). Changing the cam in my car would not be impossible without pulling the engine, just a pain in the neck I would just as soon do without.
So- with all that- what cam characteristics make a cam suitable or better for use with Webers, particularly the individual-runner kind of setup which my engine now has? Suggestions and experience and reference sources cheerfully acknowledged. Thanks in advance for help/encouragement.
