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PostPosted: Thu Jul 19, 2018 7:13 pm 
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Joined: Wed Oct 28, 2009 8:24 pm
Posts: 152
Location: Phoenix, AZ
I’m trying to help my neighbor tune his rotary powered tube frame race car. It has a street port 13B engine with a Weber 48 IDA carburetor and stock distributor with mechanical advance only. We tuned it on a roller dyno with an air fuel sensor. The car has two EGT probes about 12-13 inches from the exhaust ports. It ran fine on the dyno but when we took it to the track the EGT on one rotor got as high as 1800 degrees and the other got to 1600. Is there supposed to be a difference between the two? What is the target EGT for a rotary engine and at what temp should we back off/shut it down? Are monitoring EGT’s the right way to do it or should we install a wideband oxygen sensor? Will a wideband oxygen sensor work with gas/oil premix? For reference it has 42mm chokes, 145 main air jets, F7 emulsion tubes and 235 main fuel jets. I have a large selection of jets and emulsion tubes to choose from.
Thanks for any and all advice, I know very little about rotary engines.

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PostPosted: Thu Jul 19, 2018 8:42 pm 
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Joined: Tue Aug 20, 2002 10:01 am
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Location: Belmont, CA
What was the A/F ratio on the dyno, and what were the EGT's on the dyno?

I use both A/F and EGT's when at the track. My EGT readings are going to be WAY lower than your rotary, so I wouldn't even have a guess as to what the EGT's should be.

Jesse Prather would be the guru to ask.

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PostPosted: Fri Jul 20, 2018 4:20 am 
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Location: Topeka, Kansas
Usually on a rotary your looking for between 1500 and 1600 on the egt's. That being said, I've gone away from egt's as they can be a bit unreliable and now run an oxygen sensor in each primary pipe so I can watch both banks of the carb. Air/fuel should be in the mid to upper 12's. It's common if you have an air box to have to rejet at the track. Also check the ignition timing as this can make a big difference in the tuning as well. I would normally run about 26 degrees on leading timing and a few less on trailing. The dyno will tell you what the engine wants. The air/fuel works fine with the premix however I do run a stand off to keep the sensor from getting too hot.
Good luck!

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PostPosted: Fri Jul 20, 2018 4:58 am 
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Location: Huntsville, AL
If you are not very familiar with tuning a rotary, stay on the conservative side of ignition timing. If the engine has carbon seals, even a little detonation can destroy those seals.

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PostPosted: Fri Jul 20, 2018 10:20 am 
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To echo what Jesse said, I've done the same thing he recommends and it works well.. when my EGTs were working, I'd see 1600-1650F with the sensors about 3" from the exhaust port. with the engine running 12.5-13AFR. I suspect your ETGs will be higher because of the distance from the engine giving the exhaust more time to burn. I've noticed exhaust surface temps under my car are higher than stuff right at the engine (i.e. even with 3-4 layers of thermal wrap on exhaust and floor, it still burned the paint off inside the car right next to the passenger seat).

I suspect the EGT sensors just get cooked quickly with that much heat, as the probes never lasted me more than a few races and I gave up on that bill and the effort to replace them each time. My A/F gauge was also giving me an error toward end of races and troubleshooting manual said it was due to sensor overheating. I stuck in a little spacer / standoff like Jesse mentioned and the error messages went away.

Regarding the jetting, those numbers sound quite similar to what I'm running on an identical setup (SP 13B w/ 48IDA and 42mm chokes). Louie Rivera does my engine work and tuning, but I remember those being what we talked about for an initial setup. I bolted it all together, then took it to Louie to set up the carb and timing, and the car has run fine on track with good AFRs, so I've never bothered with dyno tuning.

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PostPosted: Fri Jul 20, 2018 8:49 pm 
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Joined: Wed Oct 28, 2009 8:24 pm
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Location: Phoenix, AZ
Thanks for all the replies, I appreciate all the good information!

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