67 L71

[Cliff A.]

I am ready to reinstall the intake manifold on my 67 L 71 engine. The gasket set came with restrictor plates for the exhaust crossover. Is there any advantage or disadvantage in using these plates? Thanks,Cliff

[Dave Stafford]

Re: 67 L71

Cliff, widely held view that this restriction will help alleviate the "boil-over" that you get with big block heat and Holley Tri-Powers. I blocked my passages about two years ago, and it (along with lowering the float level) helped eliminate this problem on my car. You lose the warm up somewhat that trips your fast idle, but I took the trade off.

Good Luck

Dave Stafford

[John H.]

Re: 67 L71

Cliff -

If you block the crossover passage, make absolutely sure that your heat riser valve is either functional, wired open, gutted, or replaced with a spacer. If it's stuck shut or only partially open and the crossover passage is blocked, there's nowhere for the right bank exhaust gases to go.

[Duke W.]

Re: 67 L71

You have a choke stove on the RH side? If so, I'd recommend blocking just the opposite side. This will create a dead end passage and will allow some exhaust heat to reach the choke stove and manifold hot spot, but the amount of heat will be considerably reduced because there is no flow. A carbureted engine does need some heat to promote fuel evaporization at idle and low speed operation for proper mixture distribution and good driveability.

Whether you block one of both sides, like John said you MUST make certain that the heat riser valve NEVER closes.

Duke

[Cliff A.]

Re: 67 L71

Thanks guys. These are restrictor plates with a hole in the center not block off plates.I will put them in.Cliff