I was wondering if a restriction, in the intake or exhaust, is pressent at only certain pessures? We all know that even the LS6 intake is a restriction to a ported set of LS1 heads. But, is that restriction only present at certain pressures or is it present all the time? We know that the pressure inside a engine isnt always 28", and that is where the heads are flow for a standard, and was wondering if the pressure an engine experenced was directly related when the intake becomes a restriction?

Thanks
Jeremy

 

The "restriction" is always there, but becomes more important as the flow and velocity increase. The restriction tends to limit the maximum flow and therefore maximum power.

Engines which use restrictor plates to limit maximum horsepower usually have normal low and midrange torque. Torque (and therefore power) only drops off when the flow limit of the restrictor is approached.

When Winston Cup restrictor plate engines were allowed unlimited static compression as much as 17+:1 was used, I hear, because by the time the engine got to hp peak rpm the effective compression was down to normal ranges. Unfortunately, under perhaps 5000 rpm WOT could cause severe detonation because the flow for max VE was still low enough that the restrictor wasn't a factor. In other words, if a given restrictor will allow 400 cfm, and the plate engine only needs 400 cfm @ 5000 to get 100%+ VE, a 17:1 engine goes boom when driver goes WOT al low rpm. That made if fun coming out of the pits.

My $.02