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In a message dated 9/14/2003 12:18:49 PM Eastern Daylight Time, 13brv3@bellsouth.net writes:
Here's my question- Is my above assumption correct? I've tried to follow
some intake flow discussions in the past on the RX-7 forum, where they were
stating that pressure isn't everything. The idea (as I think I understood
it) was that having good pressure registering on a gauge didn't guarantee
anything, since the gauge isn't fast enough to show you what's really
happening. They said that if the pipe was restrictive, or there was some
other obstacle to flow (throttle butterflies half closed), you wouldn't get
the power you should, because the pressure would drop instantaneously when
the ports opened. When that happens, I guess the engine doesn't get the
charge that it would appear to be getting from the gauge. Is this more or
less what you're getting at when you say I need to be a WOT to get good
power? Thanks for all the thoughts.
Rusty (still baffled)
All of the air that is available to the turbo must pass through the butterfly. For the sake of argument, say that the turbo will double the pressure in the intake between the butterfly and the turbo. That would suggest that the turbo engine would need an air supply nearly twice the volume of the nonturbo engine. It can only compress what it can get passed the butterfly. So the operation of the butterfly on a turbo engine produces a more nonlinear outcome relative to power. The partial throttle operation should produce an output below that of a nonturbo. There is little exhaust restriction in a nonturbo. But once mass flow through the butterfly gets high enough, output comes up very quickly. Maybe even alarmingly fast. So to balance this act with the butterfly, and keep it in a narrow range seems to me very difficult. Wouldn't it be better to watch boost, inlet air temp, timing and mixture and not track MAP?
How much boost did the stock Mazda run on the street? How much advance did the street cars have dialed in at full tilt? I don't know much about turbos, even though I have a new RayJay in the barn, I have nothing to try it on right now.
Once you get the boost under control, you could have over 200 HP on tap. When the prop stalls it suddenly becomes inefficient at moving air so it "unloads" the engine and the engine revs up without a change in throttle setting. Gaining more air speed, (airspeed controls the relative angle of attack of the propeller blades) or pulling off some throttle will unstall the propeller and the engine RPM will slow just as suddenly.
Perhaps a small manual waste gate to get into the range. Or a popoff valve in the intake ahead of the injectors. Whatever it takes, you will get it right. Lynn E. Hanover
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