[skot917]

I hate to ask a stupid question, but feel it is moronic not to ask if you don't know.

What do the rpm ratings on intake manifolds mean? I.e., Weiand Stealth High Rise is rated for 1500-6700 rpm.

Thanks,
Scott

[curtis73]

there are no stupid questions, just stupid people

Intake port size and flow is set up to provide a range in which it will make its best power. Small runners will mean that the flow will reach high velocities earlier in the engine's RPM range.

Basically an engine operates based around several compromises. Peak velocity is associated with maximum cylinder filling and turbulence which means it helps torque. Peak flow is associated with how much air it can move and therefore HP. Selecting an intake for your engine is as simple as selecting a runner flow that won't choke it on the top end, but isn't so big that it kills velocity. Its always a trade off.

The published RPM ranges are very general (sometimes exaggerated) numbers that help you pick which one you need, but its important to note that those numbers are usually based on a common engine. An RPM range for an Edelbrock Performer for a small block chevy might say 1500-5500, but that is usually a guideline based on a 350. That optimal RPM range on a 305 might be 2000-6000, and on a 383 it might be 1000-4700.

[red65mustang]

just a different way to express Curtis's info?:

"ALL" the parts must be chosen to have the same operating range for them to work best...

illustration:
a open plenum "race" intake rated at 2500rpms "minimum" operating range doesn't work on a stock cammed motor and stock stall convertor that lives and operates at 500-2500 rpms daily...

different cams reach their initial HP peak at different rpms...
you don't want say a Performer rated for max 5500rpms if your cam peak starts at 6500+...

if your cam HP peak shift point is 4800, and the heads are rated for only 5500, a 6500 rpms rated Stealth intake won't make more HP/TQ and may lose a little low rpms TQ...

the stock oem intake 500-5000 is designed biased for max street rpms acceleration force TQ,,,it can be the best choice(!!!) depending on the whole car parts combo and goal...

a favorite so true so often Max Keith (a member) saying: "ALOT more gooder is not always more good!!!"

there are so many different markets (off road/road race/strip/etc) and gazzillion possible car combo's,,,it's tough for the mfg to give more specific info

[skot917]

Thanks for the info. It makes sense unpon explanation.

[Cape Cod Bob]

A lack of knowledge does not translate into stupidity.