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Old 04-16-2007, 02:03 AM
no4 no4 is offline
Join Date: May 2004
Location: A small island, somewhere in the South Pacific
Posts: 119
Default Manual Wastegate

Quote from John Slade

"Just as a data point, I took the Kitty up to 190 kts (220 mph) indicated at 11,500' (straight and level) incrementing by 5 knots then testing for flutter all the way. There was no sign of flutter whatsoever, in fact the engine seemed to hit a sweet spot as it got to 6100 rpm and was quieter and smoother than usual. I think I got to around 6200 or 6300. (2.17 ratio) I had plenty of throttle left and, if I remember right, was running at about 43 MAP. After a minute or two I decided that was quite enough for one day and throttled back."

I find it interesting that you have gone to alot of time and expense to compress air using the exhaust gases, only to restrict that compressed air from entering the manifold using a throttle body.

If you have the throttle closed 50% and are still indicating 40 "inches MAP, then the turbocharger is generating perhaps ??" inches. At 11,000 feet the air is around 20" inches MAP, and thus a compression ratio of perhaps 4:1. Which I believe will put the compressor into or close to overspeed and surge. A larger turbo has of course alleviated the problem, by increasing the "thumb print" of the compressor map, and thus bringing the line back on to the graph.

If the throttle was fully opened first, followed by the wastegate, then the pressure and temperature passing through the exhaust gas turbine will be reduced, leading to a reduction in turbine RPM, and thus wear and tear.

Two levers, very simple.

This is the system fitted to TIO - lyconentals in birds such as the Piper Seneca.

My 20 Pence ...
I would be interested to hear thoughts on this ...
all the best

Last edited by no4 : 04-16-2007 at 02:29 AM.
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Old 04-16-2007, 09:30 AM
John Slade's Avatar
John Slade John Slade is offline
Flying TurboRotaryCozyIV
Join Date: Apr 2004
Location: KWST
Posts: 3,836

Welcome back, No4.

The flight I described was back when I had the stock turbo and was using a manual wastegate. (no - this wasnt the flight when the turbo blew).

I discussed the issues in detail with a member here, RV6guy, who installs turbos on airplanes and seems to know his turbo talk. On his advise I installed a large automatic external wastegate along with the T04 turbo and disonnected the manual boost control. The wastegate reduces the speed of the turbo compressor, so I dont have to deal with it manually.
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Old 04-18-2007, 12:49 AM
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rv6ejguy rv6ejguy is offline
Join Date: Dec 2004
Location: Canada
Posts: 578

Most turbos are limited to a pressure ratio of between 2.8 to 3.6 to 1. At say 18,000 feet where air density is about half of sea level, your PR is about 2 to 1 to maintain 30 inches Ab and about 3 to 1 to maintain 45 inches.

Last edited by rv6ejguy : 04-18-2007 at 12:01 PM.
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