T-maxx 2.5 tuning ?

[Suade907]

Hi guys I have a general tuning question for those who have experience with tuning a t-maxx 2.5. I just got the kit upon the 4th tank of fuel it seemed like the t-maxx wanted to pull the wheels on asphalt. I finished my tuning and tweaked the top end and then tweaked the bottom end needle for power down low. It didn't seem to be able to pull the front end as easy anymore on asphalt at least. Then in the grass my t-maxx was able to do a wheelie now and then with not too much a problem but after I put the body on the truck it ran a little hot so i tuned it a little fatter on the bottom end and top. It then ran strong as it was all along and would still do a wheelie but after about 5 tanks of gas it couldn't pull the wheelie anymore. It's running great spinning the tires from a dead stop on asphalt but it just won't pull the tires anymore in grass or not.

My questions are.
1. When I tune the 2.5 motor it wants to run best between 250 and 270 consistantly is this normal and is this safe for this motor?

2. Do you guys have any tips for getting this truck to wheelie easier it's a cool thing. In the traxxas video my truck won't come close. THey where doing them on asphault even from a roll. I can't do them from a dead stop in grass anymore.

[robc]

Getting the LSN right on is the key, but you need to watch your temps because the LSN affects the 2.5 temps a lot. I put extra spacers on the rear shock to stiffen them up and wheelied at will. I found that when I changed my suspension settings (lower and wider) it pretty much eliminated most of the wheelies. Probably due to a lower center of gravity. Also, a stupid question. You did glue your tires, right?

[BigBadTahoe]

Isn't the lsn hard to get to on the maxx? I have only messed with the hsn so far and run good but I don't do wheelies even with a stiff rear end. Could it be a loose slipper clutch?

[Suade907]

My slipper is tight as it goes. You are absolutely right about the low end needle it is really touchy with the temps. I have tried tweeking it to death no luck here. Like I said in the beginning I could wheelie every once in a while but now not at all. It's running fast and I'm not really wanting to stiffin my suspension. So tonight I'm giving up. I'm putting a tune on it again to operate between 240 and 260 and leaving it alone. It almost appears in the video that comes with the truck the the truck they use hits really hard from a roll when he wacks it. Mine doesn't do that at all. from a slow roll it just rockets away. You don't hear that wham sound when I do it. Maybe my trans is tighter than the car they used in the video. I don't know. I do know that this truck hussles and I'm happy with everything else I just wished it would wheelie more. Oh well I am going to be setting it up for a track day anyways so it probably wouldn't wheelie with that setup anyways.

THanks guys.

[JoeMAXX]

One of the things I had to do was to remove all the Shocks and fill them up. They come almost full from the factory and this will help to stiffen the suspension without adding spacers.

If the rear suspension is to soft it will not bring the front end of the ground.

You seem to have the tuning thing down and you know the Maxx temp for that engine is 270 Deg. I try to run mine in the 230 to 240 range and once I did break in it flames out at 270 on me. I am 18 tanks into mine and still trying to feel it out.

I think they come with 30w from the factory. I am going to refill mine with 50w in the rear and 40w in the front and replace the shocks with the Traxxas Aluminum Big Bores. From stuff I have read this will help it to handle better because most of the weight transfer is to the rear of the truck in throttle and weight.

[Suade907]

Thanks for the tip. I'll check the oil tomarrow. My suspension is very mushy and I wouldn't normally expect it to wheelie but after seeing that damn video that comes with the truck . It just is getting to me.

Here is a post I put on the traxxas forum regarding my issues. I also have flame out's at around the 270 degree mark. Some of this info might help you with your feeling it out.



"As far as the glue goes I used 5 minute epoxy. I have yet to break a bead with this stuff but I'll check them tomarrow.

But here is the latest. I spent another 90 minutes of tuning to figure out this little motor. I've come to a couple of conclusions that I would appreciate any input on. So far I have gone though 3/4's of a galleon of fuel trying to dial ths sucker in so I wouldn't hit high heat and be able to wheelie. I was able to put a serious tune on the car today where it was ripping up first gear and running second to high r's. Now I was able to get the car to wheelie but only when it was in the 240-255 heat range if it got higher it wouldn't. But with the tune I had, after a few minutes (about 5) the car was hitting high temps in the 270's and low 280's and going up, even if I let it sit and idle the temp would go up. I wouldn't allow it to run higher than this at all. You would think because of this the low end needle was too lean right. Well after richening up the low end needle in 1/16th increments the car got slower on the bottom and still was having heat problems where the temps would go too high after a few minutes. But now I was having engine dieing out problems too even with the idle adjusted properly.

The next thing I did was change the glow plug to a Mcoy MC59. The car ran like a rape dape again wheelieing in the 240-255 heat range and then getting hot, with the heat climbing uncontrollably. But it was not dieing out. I tried fattening the top end but it didn't matter. If I richened it up a about 1/8 turn it would run to fat and run really crummy. I really didn't have the top end too lean.

Then next thing I tried was a Mcoy MC9 glow plug. Again with the same results as the MC59. The car would wheelie between 240-255 and after 5 minutes exceed the safe heat zone.

I have never used a motor that was so sensitve and not cool off at a idle.

The final step I tried was a Mcoy MC8 glow plug and that one fixed the heat problem. I'm now able to run the car in the 240 to 260 heat range safely with semi decent performance but no wheelies. I leaned on my settings a little to see if I could tweak it out but to no avail the car would start to run too hot. With the MC8 glow plug I cannot do wheelies and suffer a little bit in the performance department but get nice safe heat ranges. And now the Truck will cool down slowly at idle. very slowly.

I ran all my tuning in 75 degree heat with 20% fuel. And 1/3rd the front window cut out for cooling and part of the body directly in front of the motor.

The conclusions I have come to are that. At least on my car.
1. The TRX 2.5 motor is very very touchy. It's very difficult to control the heat.
2. The motor has a very hard time cooling itself down at idle when properly tuned. With my motor and a normal or hot glow plug it is impossible to cool it down.
3. With my motor and using any heat range glow plug HALF throttle will yield a very rich midrange that will deliver less than stellar results. A half throttle run with a change to full throttle will deliver a slow transistion in speed change because of the rich midrange. I cannot dial this rich midrange out, Even when the truck is running very fast.

Questions to you guys.
1. Anybody know if they make any parts to aid in cooling this engine. Like a new head or something.
2. Anybody know if they make a new exhaust maifold to adapt a CVEC exhaust too.
3. Will the stock drivetrain survive with a wimpy .21 motor. like the ofna force P4?

Thanks for your help guys. My car just won't operate in a safe heat range to get the performance I would have liked to see. Unfortunate for me to say the least. I still love the truck but with a engine this touchy. It almost makes me want to put in a .21.

Any feedback is greatly appreciated."

[chriscrash28]

I would agree, this little engine is a pain to get it to run in a safe temp! I have tried 15 tanks of fuel triing to find the right settings. I am also using the MC-9's as TRAXXAS them selves recomended it. I would also like to know if there is anything else I can do to get the temps down? I have cut holes all over the place triing to get this thing cool. Surely other guys are having this trouble.
Any help at all would be appreciated....

[JoeMAXX]

Here is another thing I noticed on mine which may help you. My LSN was too lean from the factory and I had to richen mine by 3/16 of a turn counter clockwise. Then I went back and retuned my High end.

This helped me to get my temps down, I can run mine down to about a 1/4 tank before it gets lean from all the bouncing around and added air in the lines.

I can pull a wheelie from a rolling start on grass and hard dirt. It will not wheelie on the road and soft dirt. I have mine tuned pretty good and I have to play with it a little everytime I run but that is a nature of the slide carb and weather conditions.

In my experience Rotary Carbs are less touchy to weather conditions and require a little less maintenace if you are going to bash. The Slide Carbs are little more touchy but to obtain the HP and they are definitaly better. It just takes a little more attention but they built the new TMaxx as a competition race Truck so that is why your are having a few problems. I have seen them compete with the Savage .21 at the local LHS track and they compete very well against it if setup properly.

Yes to can convert to a .21 with a conversion kit the best engine is a Sirio .18 direct replacement.

Few more thoughts

[Suade907]

I just bought a Golden horizons cooling head. I'm gonna give that a try tomarrow. Has anybody ever used this type? It looks big and high quality. I hope it works. My LHS didn't have a large selection and the guy helping me was an moron. We'll see if it works I'll keep you guys posted with my results.