Torque drop in various BB engines has me pondering. . .

[shawn]

Hey Chris,
what about exhaust? Do they all use the same header or manifold?We see the same thing in the circle track "over the top" type headers. It allways has a "dip" at the same spot that I've allways attributed to the header.
Shawn

[idunno]

Cross scavaging would be effected by variables in the engines such as cam profiles,hedder effeciencies and rod ratio's.How much of an effect of each one of these possibilites is probably any ones guess being alot on the table here is hypothetical.
Now your probably on to something with the ram effect due to the fact that there is a strong possibility that most of these dyno pulls are beginning around the same rpm's and the pressure change in the manifolds will be pretty consistant on all engines in this arena.As the manifold recovers then the ram effect begins.

[bill jones]

-what have you been using for fuel during all these tests?
-do you know the evaporation curve numbers of that fuel?
-Have you been paying any attention to the fuel temperature?
-Do all these engines have mechanical secondary carburetors?
-I assume you are concerned about the problem when the throttles are standing WFO at 3000 to 3600rpms?
-What is the internal intake port and plenum surfaces like? smooth, as cast or ???

[maxracesoftware]

make a few Dyno tests with the Air Turbine
measuring Volumetric Efficiency % and SCFM

look for Ve% "rate" changes and the actual Ve% value,
if those "Low" values are corresponding to the RPM points of Torque Loss

[Adger Smith]

It could be that you are starting the pull (WFO throttle) at too low an RPM and the air velocity in the intake is to blame. Have you tried starting the pull at or just below the drop point to see if it still there? I have seen the same or similar thing happen in engines with big manifolds, heads & big cams that make their peak Torque & HP at higher RPM.