intake crossover
Thread Starter
Drifting
Joined: Apr 2004
Posts: 1,433
Likes: 127
From: Mequon WI
intake crossover
I am reinstalling my intake manifold (78 L82 aluminum intake and stock heads). Why do most people seem to recommend blocking off the crossover? Why is it there?
The crossover does have an accumulation of carbon, Is that to be expected?
Thanks
Jim
The crossover does have an accumulation of carbon, Is that to be expected?
Thanks
Jim
1967 Pedal Car Champion
Joined: Mar 2020
Posts: 9,205
Likes: 4,295
From: US-PNW
The cross-over is there for faster warm-ups and choke disengagement. It's totally normal that it's all carbon and soot caked - it's direct exhaust gases going through there. I believe it can be even worse if the heat riser flapper isn't opening correctly.
A lot of folks block them off because of a couple reasons: they don't drive during winter months, so it's not needed for faster warmups; and today's ethanol-laced fuels are very susceptible to the higher heat the cross-over transfers to the carburetor. This extra heat can cause fuel boiling or vapor locking.
A lot of folks block them off because of a couple reasons: they don't drive during winter months, so it's not needed for faster warmups; and today's ethanol-laced fuels are very susceptible to the higher heat the cross-over transfers to the carburetor. This extra heat can cause fuel boiling or vapor locking.
Le Mans Master
Joined: Mar 2004
Posts: 7,507
Likes: 1,513
From: Little Rock AR
Jim,
The crossover will heat the intake, and carb along with feeding the EGR. It's part of the EFE system. You could block the crossover off, but that would require you to also disable the heat riser valve located at the exit of your passenger side exhaust manifold. The heat riser normally closes off the exhaust flow from the passenger side and routes exhaust through the intake manifold crossover to the drivers side exhaust during cold starts. Once it warms up, the flapper is supposed to open and allow the exhaust to flow out normally. The heat riser "flapper" valve can be troublesome as they tend to get rusty and stick in position. Causes a LOT of problems.
If you installed headers, the flapper valve will be gone already. You can leave it in place if you wire it into the open position or you can replace the flapper valve with one from a fuel injected Corvette that has no flapper in it. The Corvette vendors sell them as "spacers".
That intake is not bad, it fits, and you already have it. You might want to keep it. Good gas mileage and more torque below 3500 RPM as compared to the aftermarket replacement that is most often suggested.
The crossover will heat the intake, and carb along with feeding the EGR. It's part of the EFE system. You could block the crossover off, but that would require you to also disable the heat riser valve located at the exit of your passenger side exhaust manifold. The heat riser normally closes off the exhaust flow from the passenger side and routes exhaust through the intake manifold crossover to the drivers side exhaust during cold starts. Once it warms up, the flapper is supposed to open and allow the exhaust to flow out normally. The heat riser "flapper" valve can be troublesome as they tend to get rusty and stick in position. Causes a LOT of problems.
If you installed headers, the flapper valve will be gone already. You can leave it in place if you wire it into the open position or you can replace the flapper valve with one from a fuel injected Corvette that has no flapper in it. The Corvette vendors sell them as "spacers".
That intake is not bad, it fits, and you already have it. You might want to keep it. Good gas mileage and more torque below 3500 RPM as compared to the aftermarket replacement that is most often suggested.
