Blocking the Intake Manifold Exhaust Crossover

[Christopher R.]

What is the thinking now on blocking the exhaust crossover passage in an intake manifold? This is on a C1 with no smog equipment.

What difference does any of the following make?
1. cast iron vs. aluminum manifold
2. cross over exhaust pipes directly after the exhaust manifold
3. use of an FI spacer in place of a heat riser valve
4. car is only driven in mild weather after some warm-up.

[Clem Z.]

Re: Blocking the Intake Manifold Exhaust Crossover

(1) do not do a cast iron as it takes too long to warm up. with a aluminum intake it will help prevent carb percolation because the aluminum intake transfers heat to the carb. if you have a choke operated by a bi metalic spring in the intake you will have to disconnect it because it will now have not heat source. (2) the exhaust will not be as loud if you have the crossover in the exhaust system.(3) you can just wire the heat riser valve open for the same effect. (4) i ran all my aluminum intake manifold corvettes and other hi perf cars i owed with the crossovers blocked to get the performance increase and to prevent the carb percolation problems and i drove them all the time. it is a problem in cold weather if you have to disconnect your choke but if you have a electric or exhaust manifold heat tube to the choke there should not be a problem. it also may hurt your fuel mileage