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I'm thinking of incorporating a heat shield on my build. It's an L20B, and now has a Cannon intake with dual Webers. Just resourcing a smaller diameter b/booster for better fitment, air filter clearance is the issue here. Any ideas regarding which heat shield to use with said configuration?
Make your own out of sheet aluminum or header wrap the exhaust manifold.
I don't believe anyone actually makes a heat shield for dual side drafts. I have made them in the past and they serve two functions: A - to isolate the carbs from the high heat of the exhaust just below. And B - to tie the carbs together when using a centerpull linkage (to avoid the single twisting linkage to cause them to go out of synch.)
A - you can build it to isolate just the heat at the front of the carb opening or you can build it to curl under the carbs to keep the underside of the float chambers from getting hot.
B - if you are using soft mounts between the carbs and intake (which I highly recommend) and a centerpull linkage, you will need to tie the carbs together somehow. The frontal heat shield kills two birds with one stone.
I do have a template that was designed by Datsun Comp back in the day, and I have used it to build many heat shields, but it does not fit all manifold configurations. And there are no mounting provisions on most intakes, so mounting the shield gets tricky. Back then, they simply used springs wrapped around the intake runners to tie it to the intake. We also sandwiched a sheet of asbestos cloth in between two sheets to help further isolate the carbs from the heat. That worked really well.
Hope this helps. Good luck.