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Old 02-10-2004, 10:49 PM
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"Dry" Intake Manifold Question

I was (once again) tearing into the intake manifold on my 1997 5.7 vortec when I began to wonder about the design. All the CSFI and MFI models use a dry intake...the intake only delivers air and the fuel is injected directly into the runners. Basically, the intake is a big, empty box...sort of a massive single plane...with the injector plumbing snaking around inside.

So...why isn't the intake design critical as it is with a carborated system? At least no one seems to be offering any aftermarket MFI or CSFI manifolds so I am assuming the design isn't important. What is it about "wet" intakes that makes design so critical to performance, and why isn't design important in a "dry" intake??

Just a thought.....

Dave
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Old 02-10-2004, 11:02 PM
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intake design

this is because(in part) there is no mixture to keep in suspension. the old carb intakes had to have the runners designed not only to flow well, but also to prevent fuel seperation. if u want to look, check the edelbrock sie or catalog. i think they are starting to make these manifolds.
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Old 02-10-2004, 11:05 PM
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bluesman123,
On engines that have carburetors the air and fuel need to be mixed and the runners need to be equal so this can happen. When two cylinders that are side by side fire one right after the other in the firing order the first cylinder will get a better mix of air/fuel than the second and will cause the engine to sort of pulse because the first cylinder has a stronger power stroke than the second because the first cylinder took more of the air/fuel first. So, long story short, by having a dual plane manifold most of this pulsing was evened out. On some of the nascar engines the firing order has been changed to help produce a better power flow at higher RPM where the amount of time the valve is open is less than a nano second, so by changing which cylinder fires first more power can be had. This is also true for cylinders that share an intake runner but are on opposite sides of the engine.
I hope this made sense.
Scholman
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Old 02-11-2004, 11:59 AM
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It does make sense! I can see that keeping the fuel/air mix just right is more important than just feeding plain air to the runners.

So...Edelbrock may be making TBI intake manifolds?

Thanks,

Dave
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Old 02-11-2004, 12:12 PM
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I think they already do.
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