I'm still a bit concerned about the
static MAP readings that I'm getting. This isn't something that
just happened, but rather has been going on for at least the life of this
particular intake setup. At on point, I was almost convinced that the TWM
TB ports were just not providing an accurate reading, but now I'm almost
convinced that they are. Has anyone measured MAP at WOT static?
Yes. As you may recall, I also run with
the TWM TB, and I also see lower MAP than the local atmospheric pressure. That
is quite likely as it should be, or if not; it doesn’t matter. The MAP
reading depends on where you measure it. If you measure MAP behind a big TB BEFORE
the runners, as Tracy (and I guess most others) do; you’d expect to see atmospheric
pressure at WOT. We are measuring it near the ports, and at the very least
about; what 4” down the relatively small TB barrel – a place where
the velocity is high; as it should be.
There may be some error introduced by
the port being just downstream from the throttle plate shaft, but the guys at
TWM say “no”, FWIW. On the dyno at WOT at 5300 rpm with a local
barometric pressure of 29.5”, the MAP reading was 27.5”. At 6000 rpm,
WOT, MAP had dropped to about 26.5”, and it was putting out close to 85
hp/rotor (SAE corrected, which means actual measured of just over 80) with 9.0
rotors. At 7000 rpm the MAP reading was 23.5” and the power was still
climbing at 95 hp/rotor. Not bad for engine with about 2 hours of running since
rebuild. Whatever that MAP reading is, I don’t think that there is a significant
power penalty that goes with it.
Hoping this makes you feel better,
Al
I got the following results in a few
tests the other day:
1- 27.6" This
was with my normal configuration, which is an inlet inside the radiator duct,
feeding a 3" SCEET hose, to a fiberglass duct that covers the two barrels
of a TWM TB.
2- 26.3"-27.0" (erratic
probably due to prop blast across the inlet) This was with the
SCEET hose removed from the TB fiberglass duct.
3- 27.4" This
is with a fairly small K&N cone filter on the inlet to the TB duct where
the SCEET hose normally goes.
From this, I see that the K&N
filter seem to have no significant effect on the MAP, which is good, though I
still don't know if I can fit it in there.
I've got some numbers from Ed, and
also have an idea what Tracy
runs, but those have always been in-flight, WOT, low level runs. I'm
going to try that at about 1000 ft at some point, but would also like to know
what folks run static. Anyone got any readings?
Rusty (not willing to give away free
power)