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Thread: 3.3 High Temps

  1. #1
    RC Qualifier nebulous.cow's Avatar
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    3.3 High Temps

    Hey folks, and all you nitro heads out there,

    I've seen a lot of people mention how hot their 3.3's run, and mine is starting to get that way too.

    Now that I'm coming up on probably 1/3 to half a gallon on my Revo, the motor is starting to really finish break in, you know how just one day the motor starts to really scream? Well today was that day for my Revo. I could really start leaning it out more and it makes much better power! It's actually running really nice, when my tank lit doesn't leak lol.

    But dang, the temps are high. Well over 300 high. I think it hit like 330 peak today, according to the telemetry sensor. I've read some discussions online about the accuracy of the temperature sensor, and it reading high potentially. But I think it's pretty accurate, when at room temp, the sensor reads almost exactly my thermostat temp. I used my new separate temp gauge today as well, but can't get accurate readings at the plug with the EZ start wire in there. Took some temp readings from the crank case and side of the engine head, ranging from 260-270. So it very well could be 300+ at the head/plug.

    It runs really good. no bogging, a good trail of smoke all the time when on the throttle, nice high RPM at top speed, and good wheel spinning action at low speed. If I didn't have the temp telemetry, I would not think it was so hot at all.

    I know I know, you're not supposed to chase temps, a good running motor is usually a good running motor, leave it. But my god, 300-320? I feel like I'm gonna warp some metal parts or something! If I richen it, it can barely get to 2nd, and bogs a lot. If I was tuning for power, I would have kept leaning, it was getting better and better. I think there's still more power to be made if I leaned it more. Haven't killed a single plug with it yet either, no signs of any leaks anywhere too except a bit of moistness around the front bearing, but I take that as normal.

    Without the body it runs 260-290 depending on the driving. It's about 75-90 degrees here as well, and I run 30% VP race and Byrons Race Gen 2.

    Part of me says just send it if it's running good, but the other part of me knows that when you see temps above 300, something can go wrong pretty fast.

    Any advice? Especially those of you who have used a lot of TRX engines, I've owned a ton of nitro motors over my years, but only 2 TRX engines, this being my second.

    Thanks in advance!
    -Mike

  2. #2
    RC Champion grizzly03's Avatar
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    A good mod to help with the cooling is to cut a hole in the windshield to allow more direct air to hit the engine. I don't put much faith into the accuracy of the telemetry temp sensor. If the sensor is turned into a different position on the head it will get a different reading. If the sensor is above the exhaust outlet it will read higher than what the engine is. I had to turn my sensor around to get it to read close to what my handheld was reading.

  3. #3
    RC Qualifier nebulous.cow's Avatar
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    Hey that's a good point. I will do that too.

    I do have the hole in the windshield and it helped some. I have also enlarged the hole around the engine head in the bed of the body area. I also then lowered the body more to expose more of the engine head to the air. Still runs crazy hot.

    Although yeah maybe you're right, it might be picking up more EGT than engine head temp, good call. I'll rotate the position of the sensor to the carb side of the motor and see how it does. Still though, my handheld was reading pretty high, even at the crank case...

    -Mike

  4. #4
    RC Champion grizzly03's Avatar
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    I get nervous too. I ran my revo with the OS21tm and I was hitting in the 270's. Plenty of smoke and no cutting out at RPM's. Left it alone and had some fun.

  5. #5
    RC Qualifier nebulous.cow's Avatar
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    Ahhh you're making me want that motor even more haha. Everything about it sounds better.

    Plus I'm sure it has an affect, but I am at 5500 feet altitude in the mountains here, so in general, the hot, thin air makes for a suuuuper lean mixture to run at peak performance. So it really doesn't help me. I figured too the slightly bigger motor would make more torque without needing such an aggressive tune too.

    Seems like in general, bigger motors suffer less from the thin hot air than the small ones. With nitro RC, as well as automotive and motorcycles. My 300cc bike had an INSANE gain in power when I would ride it down to lower altitude, but my 636cc supersport (that i unfortunately folded doing stupid young man stuff lol) didn't have an as extreme gain in power when going down to lower altitude, because I suspect it made more of its potential power at altitude than the smaller bike did.

    Same with nitro motors, my small blocks suffer terribly up here, but my big blocks still rev and pull pretty dang hard up here.

    That motor is so tempting I might just have to buy it. Gah. lol. Everything about it is better than the 3.3 except the price so it seems.

    Grizzly, you living at any altitude in your area, or are you closer to sea level?

    -Mike

  6. #6
    RC Champion grizzly03's Avatar
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    I'm only at 1,000ft. I never had to deal with elevation problems some of you have to. Glad to hear your still enjoying nitro rather than getting frustrated and switching to all electric. I tip my hat to you.

  7. #7
    RC Qualifier nebulous.cow's Avatar
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    Ahh, got to join up with the RC squad today. Went out to our favorite expired motocross track for some good ol bashing.

    Tuned the motor and just sent it all day, never had any issues, didn't even bother to check the telemetry temp readings. I used my handheld gauge a few times with promising numbers.

    Also discovered my temp gauge is like, less than 45 degrees off the exhaust header. So no wonder it reads real hot, I haven't moved it yet. She needs a good cleaning before I go in there, not sure what a good full-car cleaner is for my needs yet though.

    I think I just need to worry about it less. It appears to be running great, so I think most of the worrying was just bad temp sensor position. Still haven't burned a plug yet!

    I love this truck! But man, I trashed the body shell a ton in just one day... The whole rear end is just crumpled and folded in and crushed from some 12 o'clock wheelies and good tumbles. Bummer.

    Nitro is my only way haha. Saw only one other guy out there today out of maybe 15 dudes with nitro, bummer how few there are. But the all electric guys got a kick out of the revo, and I got to show them that you can actually have a full day of fun with no real issues, and not need to charge a single thing. I love it!

    I'll move the temp sensor around and see if I can get better numbers, and get all the dust off the truck too.

    -Mike

  8. #8
    RC Champion grizzly03's Avatar
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    I got the rear wing for mine, it works great for saving the body. Sounds like you had a blast! It sure is fun to do a quick fuel refuel and keep going, no battery swap.

  9. #9
    RC Qualifier nebulous.cow's Avatar
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    So funny story, I thought I just banged up the back of the body. Turns out, I broke the silicone exhaust coupler, and it was spewing hot exhaust gasses at the body, and it melted it a bunch. What the heck lol I've never ever broken one of these silicone couplers before. Didn't even notice, the truck was still screaming and wheelies and running good the whole time too. Temps were good.

    Had to drop the motor out to clean the truck. The exhaust mess was awful, got everywhere. Tore down the engine while I'm at it to check it out and see how it's wearing.

    My engine has maybe half a gallon through it, and it's got very little pinch left at all. Bummer. Everything inside the motor is immaculate. No scoring, no burnt spots, all the friction zones are mirror finish, and the piston looks almost new. But it's lost almost all usable pinch already, that sucks. It still runs alright but kinda bummed how fast it's wearing.

    My kyosho and OS engines last so much longer, running the exact same fuel and tuning the exact same way. Kinda bummed about the trx motors in general, both I've ever had have just been strange and problematic, compared to all the other engines I've used. My 2.5r did the same thing, had a great deal of pinch at first, and quickly loosened up and power and tuning went out the window.

    I think next paycheck, I'm going for that os21. I just need to bite the bullet.

    -Mike

  10. #10
    RC Champion grizzly03's Avatar
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    As you probably know, with a broken coupler it causes the engine to run lean. It can even fool you into thinking the engine is running great. Actually act like it has more power.

    I don't know if you have the bolt on or spring mount header. I switched to the spring mount header and have had better luck with not cracking/ripping the coupler or breaking the header itself.

  11. #11
    RC Qualifier nebulous.cow's Avatar
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    Interesting. Yeah my tune was okay but had some rough spots when driving yesterday.

    They make a spring style header for the 3.3?? Why wouldn't they just use that stock... Bolt on headers are a pain and break.

    -Mike

  12. #12
    Marshal Double G's Avatar
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    Just look up spring header or Platinum Revo header or put an "X" after the stock number (if I remember right). Then buy two springs for it.
    The Super Derecho

  13. #13
    RC Qualifier nebulous.cow's Avatar
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    Found it! I'll have to gather my pennies and head to the hobby shop. Hopefully the rubber coupler won't break again. It wrecked my body shell, kinda bummed. It was perfect that day when I got out there, and trashed by the end.

    Might have a fun painting project in the near future then too. Thanks for the suggestions guys! Should be running pretty good after all this.

    -Mike

  14. #14
    RC Champion grizzly03's Avatar
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    If I destroyed a body I'd be bummed too. But, also kinda happy at the same time. It would mean I had one heck of a time.

    I try and look at the bright side. You seemed to have a fun filled day. Showing the electric guys the nitro side. You could have been on the sidelines watching, wishing you could join in. Plus now you could design your own paint job if you went with a clear body. It's a Win-Win in my book.

    Too bad we don't have bumpers to put on bumper stickers. "Nitro rules-Electric drools"

  15. #15
    RC Qualifier nebulous.cow's Avatar
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    Hahaha. Couldn't agree more. One of these days I'll find a new shell and some paints. It's been at least a decade since I painted one, should be fun!

    Picked up the parts for the exhaust at the hobby store, as well as the jato that's been sitting in their shelf for a long time. Super hyped about that, now I'll have a couple off road and a couple on road nitros to play with!

    Jato will need some tires, I'll find those later. For now I'll play with the anacondas and have some fun.

    -Mike

  16. #16
    RC Turnbuckle Jr. Nitronaught's Avatar
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    Any change to exhaust or air filter re-tuning is highly recommended. Do not forget to tune the LSN with the pinch test, if you do not tune the LSN right the HSN will not be right either. They depend on each other. I will bet dollar to dime if you follow this information in this thread, you will find your tune and a long engine life. I average 7-8 gallons before I start seeing considerable performance issues. I've ran TRX engines up to 12 gallons before they just were not worth running without a rebuild.

    https://forums.traxxas.com/showthrea...ul-Tuning-tips
    All Lives Matter
    United We Stand, Divided We Fall

  17. #17
    RC Qualifier nebulous.cow's Avatar
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    This engine had the bearings go bad FYI. Already sold the parts.

    I'm quite confident in my tuning abilities, this particular engine just didn't work out for me. The 3.3 in my jato runs great and so far has no issues. The OS 21tm I just put in the revo has been running really well, with no issues.

    I'm pretty sure part of what I was experiencing was manufacturing variations in the plastic Traxxas carb bodies. The jet is made of plastic, and the LSN physically prevents the carb from even closing all the way at stock setting.

    To me it just seems really hit or miss with the Traxxas motors. My OS motor in my t Maxx has seen at least 20 gallons in its 10 year life, and runs great still.

    I posted pictures of the engine internals on my FS thread on here as well, if you go look you can see how good of condition all the parts were after my running it.

    I don't think I was having tuning difficulty related to lack of understanding.

    -Mike

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