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T-maxx 2.5 techie questions - 12/16/2003 6:12:37 PM   
Dale Gribble



Posts: 3838
Joined: 9/17/2003
From: Pittsburgh, PA, USA
Status: offline 		I have the motor disassembled right now. I had a few ???'s that maybe someone can answer-

I know based on exp with real cars, that head gasket thickness can have a big effect on compression
(and performance- good or bad). So I am going to get the cooling head gasket set from Traxxas with
three sizes of gasket-

0.15mm
0.25mm
0.35mm

I am guessing on this small of a motor, the thickness will make a big difference in performance.
I am instantly thinking the thinnest gasket for highest compression, but I wanted to see what others
said first. Typically the main threat to high compression is if the piston ring can take it, but since
this motor doesn't have a piston ring, I figure the higher compression the better- unless temperature
is an issue.

Also, what is your FAVORITE glow plug for this motor? My Maxx runs good with decent
power around 220-240 temp range, but I just don't feel it is as fast as it should be... I only
have maybe 2 quarts through it, so I wouldn't think I am losing compression yet. As
a matter of fact, the piston definitely wedges snugly in the sleeve.

I will do a search and check, but in a one liner, what mod helped you realize the most power
the the 2.5? I am willing to give up some top speed RPM's for some more low end umph.

Finally, what is your favorite pinion/spur gear combo?

Thanks!
       Post #: 1

RE: T-maxx 2.5 techie questions - 12/17/2003 1:25:23 AM   
overrev


 

Posts: 158
Joined: 10/19/2003
From: auburn, WA, USA
Status: online 		I'm running my engine with the traxxas optional tune pipe,hardcore munant head and 18 tooth clucthbell and 72 tooth spur. I really like this set up, the truck will wheelie when ever I want it to. The glow plug I use is a Mccoy59.Hope this helps. mike

< Message edited by overrev -- 12/17/2003 3:49:54 AM >

(in reply to Dale Gribble)
       Post #: 2

RE: T-maxx 2.5 techie questions - 12/17/2003 7:27:43 AM   
Dlock



Posts: 427
Joined: 12/11/2002
From: Moscow, ID,
Status: offline 		One of the biggest things you can do to your truck to get the most out of the engine, is learn how to tune it properly. I don't know your background, but learning how to tune is a big thing. Like you said earlier, since these things are so small, the slightest change in temperature, humidity, elevation, barometric pressure can have major effects on your performance.

If this is your first nitro rc then I suggest leaving it stock for a while. If you only have 2 quarts through your engine, then you are really only part way there until your engine is up to maximum performance. These things take a little longer than the recommended break in period. I started seeing the true power of the trx 2.5 after about a gallon through my motor. I suggest getting atleast that far, and then change some things if you want a little more umph.

A couple different ways to get more umph is through changing the gear ratio. I run 18/72. I have not had it on there for very long, so I can't tell you how much low end power it added. Also a good aftermarket pipe will give you either more low end, more high end, or a smoother power band. If you want low end, check out the Ritter Steel or Ritter Carbon Fiber pipes. I have had the CF pipe, and it definitely gave me more low end.

I also rune the McCoy 59 plugs. I like these better than the OS #8, and the Traxxas brand plugs.

Hope this helps....

_____________________________

"If it aint broke, then it's time to upgrade....."

(in reply to overrev)
       Post #: 3

RE: T-maxx 2.5 techie questions - 12/17/2003 8:03:46 AM   
godlyone



Posts: 167
Joined: 12/22/2002
From: Vancouver, WA, USA
Status: offline 		My experience with head shimming is to do anything but shim the head until the engine itself begins to wear out. Call me lazy. You can change the combustion timing with other simpler methods such as different glow plugs and nitro/oil contents. You can even change the combustion timing by tuning your exhaust. I know guys that will shim their heads before break-in but I just can't justify that amount of enthusiasm into my schedule.

I have never had any problems with the Traxxas standard long plugs in these engines. Depending on what time of the year usually dictates what plugs I run and it's been the McCoy MC-8 or MC-9 for sure.

The 2.5 performance mod "one-liner" you requested: [insert drum roll here] Sorry dude, I run my 2.5 engine bone-stock! The engine was designed to have excellent power through the entire band, it does just that and I like it the way it is.

Gearing: It's all about what you want/need. Stock gearing +/- a tooth or two is as close to best overall setup you could want. If you find yourself racing around in large open places then a larger clutchbell and smaller spur gear may make things seem to happen faster for ya. If you are confined to a smaller area with a nice 60 foot back stretch and lots of little turns and jumps in your foreground than maybe an 18/70? If you really have the time to try out different gearing than by all means take advantage of this time. Nothing anyone can say beats actually seeing what these changes do in person so when you ask what people's favorite pinion/spur gear combo is, I would throw in the "why" and "what for's" as well. When gearing an RC you can always expect a pretty even trade-off. You can go for quick, or you can go for fast but you can't have both.

When you say you are after more low-end "umph", are we talking more wheelie action? If it's simply more bottem end grunt, I would suggest looking into a different powerplant such as a big-block or this Picco P2 mid-block everyone's talking about. The 2.5 is intended to be a real racing engine with power to boot whenever you need it. It's quite tuff to design an engine that has good consistant power throughout it's entire powerband and then expect it to pull tree stumps on the weekends. But maybe this new Picco P2 mid-block has just that?

(in reply to Dlock)
       Post #: 4

RE: T-maxx 2.5 techie questions - 12/17/2003 4:29:49 PM   
supraown4ge


 

Posts: 27
Joined: 11/22/2003
From: McKinney, TX,
Status: offline 		im new to nitro engines so i dont really know about tuning them, but i will be gettin a t-maxx soon with a .18 xtm racing engine and i was wondering if it would be ok if i used that setup too. ive found a 72t spur gear made by kimbrough but i wasnt sure if it was a good product. also would the clutch bell from traxxas fit into that engine.
thx

(in reply to godlyone)
       Post #: 5

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