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Chris,
The attached image shows a comparison of RPM vs MAP for a 13B on an engine test stand for a turbo installation, a supercharger installation, and a normally aspirated setup along with the data you reported. The test stand prop was the same for each installation and the same intercooler was used with the turbo and the supercharger. The altitude here limits the NA MAP to 23" Hg. No claim is made that the turbo or supercharger installations were completely optimized, however the trends should be valid. The NA intake was the dynamic chamber intake as found in a 1986 RX7 car. The NA installation had the turbo and supercharger completely removed: that is, the turbo was not connected to either the intake or exhaust system, and the supercharger was not being belt driven and was not connected to the intake system.
From the data you reported, you got similar max static RPM with the turbo with about 6" less MAP than normally aspirated (similar situation at 5000 RPM). That is difficult to accept since it takes energy to drive the turbo in the form of increased exhaust gas backpressure which would raise the MAP requirement rather than decrease it.
If your data for the turbo and normally aspirated cases were reversed, then the data makes sense. If the normally aspirated MAP was limited to 24.5", the max MAP of 29.8 would correspond quite well with boost being limited to 3 psi by the wastegate spring. The turbo system would appear to be working correctly if this unlikely scenario were to be the case, but unfortunately, the indication of a free lunch would be gone.
Steve Boese
RV6A, 1986 13B NA, RD1A, EC2
________________________________________
From: Rotary motors in aircraft [flyrotary@lancaironline.net] on behalf of Chris Barber [cbarber@texasattorney.net]
Sent: Monday, August 20, 2012 7:17 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Turbo question.
As I have mentioned I have had what I think are incongruent readings regarding my manifold pressure (mp)and engine rpm. It seems I am getting quite low mp as I add power to higher rpm.
I am not well versed in this area but my thought is that as I add power, even with slight boost (currently using a 3 lb spring in my wastegate) eventually my mp should raise a bit more.
Today I did some static test. I recorded engine RPM with the turbo hooked up and recorded the mp at 1000 rpm increments. Then I removed the turbo plumbing from my intake and recorded the same info My results currently confuse me.
With the turbo hooked up I am getting
RPM. MP inches
2000 - 14.0
3000 - 15.5
4000 - 19.3
5000 - 21.6
5700 - 24.5 (topped out)
With the turbo removed.
2000 - 15.8
3000 - 15.3
4000 - 19.7
5000 - 24.8
5833 - 29.8
Is this indicative of restriction in my plumbing? Perhaps in the inter cooler? A dirty air filter? A bad pop off valve or a leak not allowing the air pressure getting to the intake. Or????
I am uncertain what other permitters I need to check and provide. I am just starting my diagnosis in my Phase One testing. I only have 1.6 hours in the air so far. I value ya'll's direction and input.
Heck, perhaps this is working properly but it just doesn't seem right/comfortable.
Thanks folks.
Chris Barber
Houston
Velocity SE
Rotary 13b turbo (?) :-)
Sent from my iPhone 4
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