Intake design for a mazda rx8

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Keith A. Clayton

New Member
Joined
Aug 31, 2014
Messages
2
Location
Strathmore, Alberta Canada
We have a 2006 rx8 rotary engine installed in a modified JD 2 Dyke delta. Initial tests show the engine not making horsepower expected although it runs well. We modified the intake so it would fit under a plane cowling so the regular engine intake which goes over the engine was replaced with a homemade box attached to the standard intake flange cut just after the fuel injector ports. The standard butterfly throttle body was then attached.

Any help here would be appreciated.

Regards
Keith
 

rv6ejguy

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Joined
Jun 26, 2012
Messages
3,749
Location
Calgary, Alberta, Canada
We have a 2006 rx8 rotary engine installed in a modified JD 2 Dyke delta. Initial tests show the engine not making horsepower expected although it runs well. We modified the intake so it would fit under a plane cowling so the regular engine intake which goes over the engine was replaced with a homemade box attached to the standard intake flange cut just after the fuel injector ports. The standard butterfly throttle body was then attached.

Any help here would be appreciated.

Regards
Keith
If you look around the 'net, you'll see photos showing rather long intake runner designs on most Wankel powered aircraft, usually wrapped around the block. A really short and poorly shaped manifold would lose a ton of power I expect.
 

wizzardworks

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Joined
Nov 8, 2011
Messages
273
Location
murfreesboro NC USA
Keith, There are two points to consider. First is the operating RPM takes a little getting used to. The point where mechanical loads on the rotor/E-shaft are balanced by
gas pressure loads occurs near 5,800 RPM. These engines need a PSRU ratio of 2.85 (Tracy Crook's redrive) minimum although the 3.17 to 1 ratio makes more torque at
take off and climb. Hp is a calculated number = torque X RPM / 5252. What is measured is torque. At 5252 RPM HP and torque curves intersect and are equal. Above 5252 RPM
the HP is higher and that is where Mazda rotaries live. Stock engine redline is above 9000 RPM.
The second thing is your intake is TOO SHORT. Intakes are measured from the intake port on a Mazda (or intake valve head on a piston engine) to the open end of the
intake port. If there is a butterfly valve (throttle plate) the measurement ends there. Mazda intakes vary from 18.5 inches for high RPM (6500) to 22.5 inches for low RPM.
At these lengths you will get volumetric filling of 122 percent of static engine capacity from a pressure wave tuned to arrive at the port just before closing. This is reffered
to as a tuned intake. You can think of the pulses traveling at the speed of sound from port to intake end and reflecting back to the port. The stock intake changes the length
of the runners and number of ports in use to optomize drivability and power output. In aircraft with a fixed length intake you need tuned to the operating RPM.
Low RPM like 4500 and short runners your sound to be 10" (from the base plate of the box to port) you will be in the neighborhood of 140 HP rather than the stock 275 HP.
The tuned runners need as few bends as possible with straight being best, They can come out and turn to the front or back, or have 180 degree bends over the top of the
engine with the throttle body on the plug side.
Being that you have a running engine you MAY HAVE NOTICED how loud and unplesant the exhaust sound is. The cure is to add a turbocharger sized large so as to not
overspeed at altitude and let the impeller chop up the exhaust pulses. This will allow eliminating the muffler unreliability issues and weight which offsets the turbo weight
although the turbo will still be heavier. The turbo can boost or normalize power output. Hopefully you sized the prop for your expected output and it will be capable of
using the 250 HP of a tuned intake normalyl aspirated 2 rotor. If you use the turbo to boost the power you will need a different prop.

wizzardworks
 

Keith A. Clayton

New Member
Joined
Aug 31, 2014
Messages
2
Location
Strathmore, Alberta Canada
Thanks for you comments. I have contacted Paul L. and his comments were similar. I now have to find someone who has taken a six port engine and modified
the intake for high rpm . I have the engine driving a 2.85:1 ( tracy Crook) red rive which appears to be working well.
 

Keltro

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Joined
Sep 30, 2012
Messages
3
Location
Yukon,OK,USA
Thanks for you comments. I have contacted Paul L. and his comments were similar. I now have to find someone who has taken a six port engine and modified
the intake for high rpm . I have the engine driving a 2.85:1 ( tracy Crook) red rive which appears to be working well.
Clayton,
Any progress on your Dyke Delta Renesis engine intake problem??

Kelly Troyer
Delta Project
 

Doggzilla

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HBA Supporter
Joined
Jun 2, 2013
Messages
2,197
Location
Everywhere USA
Some of our members have actually had a good deal of problems with intakes spoiling the flow, including to the point of creating a low pressure area over the radiator. If you are going to run a long intake, try not to position the intake ahead of anything else, especially anything you want to be aerodynamic.

On a side note, since you are already going to make one... might as well put the low pressure to good use somewhere.
 

rv7charlie

Well-Known Member
Joined
Nov 17, 2014
Messages
545
Location
Jackson
Hi Keith,

I'm a bit late to the party (just signed up on Homebuiltairplanes), but thought I'd add my 2 cents. I'm installing a Renesis (4 port) on an RV-7. First, I'd suggest signing up for the Flyrotary email list. Nowhere near as many posts as Lamar's list, but quite a few more members who are actually flying, instead of talking about dreaming of the Next (dis-proven in the last century) Great Idea.

For the intake: The best performing normally aspirated Renesis is almost certainly Tracy's RV-4 (4 port). If the Real World Solutions site is still up, there are some pretty good photos. Here are some relevant points. (my interpretation of Tracy's comments)

Optimum runner length for 6000 rpm cruise is around 16" from the face of the block. Runners can be significantly shorter if they are relatively straight (Tracy's are around 11", and his is the best performing Renesis that I know about). The engine will just come 'on the pipe' at higher rpm, but unless you're racing or climbing out of a mine shaft using a constant speed prop, it's non-critical. The lower restriction of the straight runners makes up for a lot of the tuning loss. Too-long a runner can actually hurt takeoff and cruise performance by tuning at too low an rpm. A throttle body bigger in area than the total area of the input ports won't help, and may hurt performance. Runners should have bell-mouths to improve inflow efficiency. FWIW, one of the Flyrotary members, a retired research scientist flying a 13B powered RV-6 who is obsessed with testing and assigning hard numbers to everything, has a 6 port Renesis running on a test stand at his home airport (~6 or 8k feet altitude in the mountains, or typical cruise altitude for the rest of us). He found that the engine actually makes more power at this altitude if he blocks off the 3rd set of ports, and runs the engine as a 4 port.

If this is helpful, sign up for Flyrotary & talk to guys who are actually flying.

Charlie
 
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