I flew about 45 minutes the next day. The engine and plane fly fine. I now have 25 flights on the RV-8. Unfortunately, the power lost to the removal of the turbo is significant. I've lost about 40 MPH of top speed!  I hadn't opened up the throttle above 37" manifold pressure for take off, nor about 34" MP at any flight above 4000ft., so I don't yet know what the turbo was capable of providing.

I plan to build an exhaust manifold incorporating a wastegate that has minimal throttling loss when open. I also want to switch from using an 'On-Center' turbine housing to the more efficient tangent style. If I put such a turbine on my existing manifold, the turbo would be touching the cowl. The added benefit of the tangential housing is the V band clamp exhaust coupling, which is easier to fit & align an exhaust downpipe. I would hope to fit the muffler inside the cowl, the drag penalty of an underslung muffler must be great.

I noticed the engine won't start when the EC-2 mode 8 timing is set to +10. I don't know the reason, perhaps the coil dwell is effected or something. When I reset to the default '0', it starts right up, so I'm running it @ +3 which starts & runs fine, and is 23BTDC. I'll try switching from 92 to 87 octane ethanol free mogas, and then bump the timing up to 25 if it improves performance and or decreases exhaust temps.

 

-----Original Message-----
From: Scott Emery <shipchief@aol.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Tue, Apr 22, 2014 1:21 pm
Subject: [FlyRotary] Re: Switcheroo from turbo to not

A quick note from the airport:

I reset timing to 23 BTDC and groomed the injection table for low RPM. 

I'm over propped, but I did fly again, with much better results. Smooth engine again (Mazda goes Hummm).

After I got up to pattern altitude and gained speed over 120mph, climb rate increased to about 1000fpm. After level off @ 2000' speed increased to over 170mph. I quickly re-entered the pattern & landed due to a rain squall headed toward the field.

4375 RPM Static, about 5400rpm @ 170 mph. Fuel burn: about 10.8 gph.

Sent from my iPhone

On Apr 22, 2014, at 9:19 AM, shipchief@aol.com wrote:

OK, I searched the archive, Brian Trubee posted 22-23 BTDC as the correct timing for naturally aspirated operation, so I'll back off the Mode 8 timing to 22 BTDC and test for Static RPM before the next flight.

-----Original Message-----
From: shipchief <shipchief@aol.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Mon, Apr 21, 2014 10:05 pm
Subject: [FlyRotary] Re: Switcheroo from turbo to not

Thanks Dave;

I may end up reinstalling the turbo soon. I use a water cooled bearing, I think the exhaust housing is the only damaged part.

My exhaust manifold has no sign of stress or damage, I'm looking for a way to add a waste gate, not ruin the existing manifold, and fit it around the Fred Breese mount...

Today I completed the transformation to Non-Turbo operation. I replaced the turbo with a cast stainless steel elbow and a Aircraft Spruce 321 SS Ball/Swivel joint and cut/welded to fit the old turbo down pipe. I made up sheet metal heat shields with some blast cooling on the elbow to be on the safe side.

 I checked my maintenance log, and noted that timing had been set @ 18 BTDC, with a EM-2 setting of -2. So I started the engine and advanced the timing to +10, for 30 BTDC. at low RPM, the advance seemed to make the engine run better.

With the CATTO prop I'm using, I could only get 4370 RPM static. I could easily blow thru 4900 static with the turbo. I did a few dry run take-offs with good general engine behavior, so I gave it a flight. RPM increased slightly to about 4400 once I started the take off roll. I took off late & climbed anemically. about like a Cessna 172. I noticed some hiccups even though I was fine adjusting the mixture and watching the O2 sensor output. EGT typically ran 1450 for the take off, and in the 1650 range for most of  the flight, with some 1730F in there too. It never ran smoothly like it has at low power before. I wonder, what should the timing be for naturally aspirated? I thought it's supposed to be 35 BTDC? I set it initially to the turbo setting (19 BTDC) with a timing light at 4000 RPM as per the manual. I didn't quite hit the 19 BTDC in the manual, figuring to err on the side of safety, and add advance later.

So could the hiccupping be retarded or advanced timing, or a semi fouled plug? I didn't expect the non-turbo version to be so weak. The full throttle fuel flow on the EM-3 was about 8.5 GPH, which is only about 100 HP, based on the simple 100HP = 8GPH fuel flow rule of thumb. This was about 5100+ RPM and about 150 MPH @ 2000ft MSL.

14 hours flight time, 26 to go...

-----Original Message-----
From: David Leonard <wdleonard@gmail.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Mon, Apr 14, 2014 8:46 am
Subject: [FlyRotary] Re: Switcheroo from turbo to not

If you want to return to the tubo, consider a water cooled housing like the stock.  Mine is a modified stock housing with a TO4 turbine but still retains the water cooling.  If I am not careful with EGTs I can still melt the turbine blades, but the housing has held up very well.  I also use the stock heat shields.

Nothing like having the extra power!

David Leonard

On Fri, Apr 11, 2014 at 2:51 PM, <shipchief@aol.com> wrote:

I went out to the Hangar last Tuesday to start installing the intercooler. Well, at least to fit a few tubes and hoses, then hold up some parts and make plans.

As I took the air discharge tube off the compressor, I noticed the whole turbo compressor & bearing assembly wiggling around on the turbine housing!

I checked all the mounting bolts and clips, everything was tight.

So I took the turbo off the engine, and realized that I probably cooked the turbine housing. I did see EGT excursions to 1800F. What's worse, I had a new turbo blanket. I think a heat shield would have been better, so some cooling air could pass over the housing, but still block radiant heat.

Bummer.

So I decided to go with Plan B: I ordered the bits and tube bends to switch to naturally aspirated operation. I'm keeping the exhaust header that the turbo sat upon, and replacing everything else past the bottom of the firewall, to the new pipe & muffler I recently added.

I'm retaining the ability to 'Go Turbo' later, but I've become curious about what the turbo must boost to equal full throttle of 'Naturally Aspirated'.

I did build and have been running a tuned intake manifold. The exhaust won't be a tuned header, but it is pretty good, possibly better than the stock exhaust reactor and a whole lot lighter. It has port discharge nozzles (reversion cones) EGT probes and a gentle sweeping shape. Plus it's proven strong while carrying the weight of the turbo beyond 1800F, and it passed inspection. I trust it.

So I hope to run it, find the performance satisfactory, the fuel consumption significantly reduced, and use 87 octane ethanol free mogas instead of 92. (low compression rotors)

Also, I can advance the timing to the NA spec.  

Anyone see a problem or have advise?