Calling all EGT Tuners! Newbie has ?'s

[IDoSeaDoo]

Hey guys, I recently bought a set of Koso EGT gauges for my 787 Challenger. I plan on tuning all my skies with this gauge, but currently am starting with my boat. I have a fresh rebuild on this motor, pressure tested to hold 10psi. Standard bore, with some chamfering of the case and cylinders. I just basically cleaned up the casting marks and smoothed some edges. The probes sit about an inch away from the Y-pipe gasket and are right in the center of the port. When I fired the engine up, I get a reading that my Mag cylinder runs quite a bit hotter than my PTO. Like 100degF hotter. I feel that this is worthy of action. This persists through all bands of RPM and I was not able to tune it out with needles. I haven't taken carbs apart yet, but did look and see that the linkage was adjusted. Judging with the eye up close to the carb, they seem identical, but is there a better method of verifying? Is it common to have one cylinder run this much hotter? What's an acceptable differential gradient? Would pop-off pressure affect the fuel delivery at all RPMs?

Thanks!

 

[IDoSeaDoo]

Also, forgot to ask this: can anyone tell me what my EGT should be at idle on say a 70degF day? How can I tell if I'm running rich at idle? My highest temp at WOT was about 1070 on the MAG, PTO was 100degF less... At idle, I think it was in the high 400's, again PTO reading quite a bit less.

 

[IDoSeaDoo]

Well I finally got a chance to rip the carbs apart, and like the PO said, the MAG carb is new. Couldn't verify the jet sizes on it (stripped screw), but the pop-off registered at a nice 30psi. Next, I verified the settings on the PTO. The jets were 147 and 70, which I think is what the book calls for on a 97 challenger 110. The pop-off was only at 18-20. So this thing must've been running quite a bit richer, which is consistent with the readings I got. The PTO cyl was almost constantly 80-100degF cooler than the MAG. I found a new spring in my carbs bin and put the pop-off to 30. Reassembled and plan on testing today. On my last trip out, I did notice a peculiar symptom: If I rev it from low speed, it would smoothly accelerate to the top RPM (didn't look to see what that was) and stay there for a second or two, but then slip into a slightly lower RPM and sound rough. My buddy thought it was a lean condition, but I thought it was raves. I popped the cap off the raves and they move up and down all the way. No binding, and the resistance is what i'd expect. I know that 1030degF isn't too hot for this engine, and that's what my leaner piston was running, so I'm going to try it with my new carb settings. I still have pre-mix gas in the tank, and I'm running injection. Can't wait to burn through this tank to see what my actual EGT numbers will be.

Offtopic: I recently bought an Arduino. It's a $15 microcontroller which you can program to do all the things these $350 EGT gauges do. All you need are a few thermocouples and a bit of ambition. Everything is on youtube. I am no programmer, but I feel that this will be a fun and easy project In the end, I hope to read EGT, Water Temp, RPM, Volts, and low oil. Eventually, I may even play with the notion of converting to fuel injection. I know it's been done before on a car.

 

[Guest_User]

from what I understand the MAG cylinder does run hotter than the PTO. you have the flywheel/electronics/mag housing all collecting and absorbing heat, so heat transfer and temps will be different. I do not know the exact temp differences, but as long as your carb settings are good to go and plug color confirms along with good performance you should be fine...

 

[IDoSeaDoo]

Does anyone out there know what stock idle temps should be at 1500 rpm? I have no idea if I'm running too rich or too lean at idle. I do quite a bit of idling, and don't want to constantly kill plugs. Is there even a way you can damage the engine at idle, or would it just run too poorly that would happen? I don't trust the book's specs as I did a bit of chamfering/cleaning the case of casting marks and rough edges. I feel that it flows better than a totally stock motor, but the ports are all stock. When reading plugs, when do you do this? New plugs seem to take forever to take on a hue...

 

[IDoSeaDoo]

Well, after equalizing my Pop-off pressures, the PTO is still running 70-100degF lower, and that seems consistent across the entire throttle range. My Mag cyl is only getting up to 1000-1030degF and I'm only hitting like 6500rpm. I'm thinking I may have my water reg tuned too far out. I think I need to screw it in as I may have screwed it out too far last time I was messing with it. Anyone know of anything else it could be?

 

[IDoSeaDoo]

Check out these plug readings please

Well, I screwed the water reg adjuster in to the point where I couldn't keep my hand on the lower E. Pipe. I backed it back out one turn in fear of melting my oil line. I made sure my linkage goes all the way to WOT and have put in new plugs to get a reading. How long am I supposed to run it before I get a reading? I took some pics this time, hope you guys can tell me. The first pic is of me doing a WOT run for about 5 min. EGTs were 930's PTO and 1030's MAG, RPMs never went above 6600. Top speed was lacking. The second pic is of idling at around 1600RPMs for 5 min. Egts were in the 4-500 range

Please let me know what you think about the color of the porcelain, and the color of the electrode. Which am I supposed to go off? Could my rotary valve timing be off?