intake vents?

[cdixon4950]

I have a 40 nissan and noticed vents in the intake manifold maybe for equalizing pressure btw the carbs?? Do i need these on a modified motor? It looks as if i could block them off and smooth out the flow into the reeds. Also, what is the small hole next to the top bore in the intake, looks like it goes from carb and bypasses the reeds?

[cdixon4950]

anybody???

[Fastjeff57]

It's there to prevent a gas cloud in front of the carbs at certain rpms. (The phenomenon is technically known as a 'reversion pulse'.) That's also the main reason for the "silencers" you see on one carb per cylinder engines--to contain that mess.

When two cylinders breath through one carb, the other cylinder "sucks in" that gas cloud, making the "silencers: unnecessary. But when there's only one per cylinder, a gas cloud the size of a tennis ball will form before the carb at low rpms--a scary sight to behold, as
I witnessed that on my homemade 30 cube Merc with external reeds.

To answer your question, you can probably remove that piece, but not the "silencer" if you intend to run with the hood on. Doubt if there would be much performance improvement, however.

Jeff

PS: The below photo shows a 40 hp Yamaha twin's intake set up. Note the size of the "equalizing (pressure) tube".

[cdixon4950]

Yes sir, thats the info I was looking for. I appreciate it

[fyremanbill]

For high performance use, you really are better off with it on. When each crankcase intakes, it will "see" 2 carb venturis instead of 1. Same concept as the cross drill on a Merc V6 intake.