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View Full Version : O.s. .18 Tm Vs. Trx 3.3



AKASHA
10-30-2007, 02:47 AM
I have heard a lot of very mixed reviews on both motors and am now at the point where I need to decide on what to do with my revo's motor, as the compression has gone seriously downhill the past few times out. I can completely rebuild the TRX for just over $80 shipped or spend almost double that and get into the O.S. TM. My main concerns at this point are pretty much what everyone elseís would be; longevity, tune ability, power, compatibility, and replacement costs for future parts, aka piston/sleeve, con rods, carb parts, seals, bearings and the likes. I bring up compatibility in terms of the headers needed to adapt my now three different exhaust pipes, and roto start system. Will the TRX back plate fit on the os motor? I mean if the easy start systems back plate will why wont the roto starts? Will the TRX header fit on the o.s. exhaust outlet? Little things that say to me more money than itís really worth ya know.

I have been toying with the idea of going with a big block but know that when racing it is going to be a lot harder to control and is also going to put me in a totally different class of vehicles as it would then be a big block, possibly limiting my chances of getting back out there again. Around here there isnít too many people that race in the MT classes and most of what they have is well close to stock ;) Most play with the revoís, tmaxxes, and an occasional BB hellfire.

I was, I guess, one of the lucky few to have such great luck with my TRX motor as it has had more than 5 gallons of fuel ran through it and is still going. I can send it in for a re pinch for $20 and be good to go for a while still, but would prefer to just get a new piston/sleeve as this one does have a few small nicks on the top sides of the piston. ( caution, even though they look like they are spinning slowly, dremel buffing tips can still send items not held securely flying across a room with high velocities :o) I could probably just use it for a back up if that ever becomes a problem.

I am looking for first hand experiences here and not the fan boys point of view. I don't want this to turn into any kind of flame war, I am just looking for rational explanations of why one is better than the other and if you were to go this route why? THX

IMADMAN
10-30-2007, 04:33 AM
I have a OS 18TM in my revo, all my friends run 3.3's. Both are very capable engines. In your case would'nt you be able to swap your worn 3.3 for a new one for less than $80.00 under the Traxxas warranty? If money is the issue you're probably better off going that route. My revo is fast than theirs but I get a lot of unwanted wheel spin and wheelies, to control that I can't go past 3/4 on the throttle. I do notice the temps run pretty high in the 3.3's though as long as you don't run continuously back to back to back....ect. you should get good life out of it. I got my revo 2nd hand with the 18tm in it already and I was really surprised at the amount of power it put's out. Again if you're on a limited budget the 3.3 is probably your best bet as majority of the parts are cheaper and easier to come by. Being a good consistent driver always beats a driver with a heavy tigger finger. Hope this helps

ironoutlaw
10-30-2007, 09:35 AM
thats true the traxxas engine parts are alot cheaper and the o.s. is not a whole lot faster than the stock 3.3 , and the header is different so i would say stick with the stock one

Adanmtxt1
10-30-2007, 11:09 AM
Luke, use the search... I mean, force.... use the force... :D

http://www.radiocontrolzone.com/showthread.php?t=222302&highlight=trx+3.3+os+.18tm

The thread I started: http://www.radiocontrolzone.com/showthread.php?t=221215


IMHO, you cannot go wrong with the .18TM. Virtually no one has an issue with it, which cannot be said of the TRX2.5R. I do not know about the 3.3, but it might be more reliable than the 2.5R. The real issue is that some carbs are fantastically easy to tune and are just as good as the OS, but many others are not as reliable, and some (like mine) are impossible. I would spend an entire tank trying to get it right; first it would be too rich and bog down (sometimes stall), so I would lean it out 1/8 turn, but then it would be irratically lean. I just couldn't do it.
Conversely, the .18TM (like my .12 CV-R) is incredibly easy. Even if you don't tune it, it will run very well with good fuel economy and great power. Tuning is easy and it has a big 'sweet spot'.


But, I respect other's opinions and experiences, as well as their budgets. If you can swing the .18TM (I paid $199, last I saw was $169, Tower says 'discontinued'), I would go for it. If not, I am sure the TRX3.3 will serve you well, and if not, they have great customer service, as well all know.
I know I have a thread

AKASHA
10-30-2007, 07:53 PM
I have a OS 18TM in my revo, all my friends run 3.3's. Both are very capable engines. In your case would'nt you be able to swap your worn 3.3 for a new one for less than $80.00 under the Traxxas warranty?
Not sure if that is a viable option as I bought this used so I have no recipt for it.

If money is the issue you're probably better off going that route. My revo is fast than theirs but I get a lot of unwanted wheel spin and wheelies, to control that I can't go past 3/4 on the throttle. I do notice the temps run pretty high in the 3.3's though as long as you don't run continuously back to back to back....ect. you should get good life out of it.
Then really whats the point of having them? go out for one or two runs? I don't think so. I would consider myself a racer by choice but a basher by nature haha. Kinda like whats the point of having a car with 700+HP and not getting on it once in a while?


I got my revo 2nd hand with the 18tm in it already and I was really surprised at the amount of power it put's out. Again if you're on a limited budget the 3.3 is probably your best bet as majority of the parts are cheaper and easier to come by. Being a good consistent driver always beats a driver with a heavy tigger finger. Hope this helps

I am one of the ones that does have a lead foot/finger, I fully understand the statement of slower is faster on a track, but when I am out playing around it's ballz to the wall. I live my life a 1/4 mile at a time, blah blah blah lol.

Adanmtxt1 I do appreciate your input on the matter, it has lead me to believe that I am now left with a simple decision, a little less low end with the TM vs. a smoother more powerful mid top end. I guess if push comes to shove I can compensate for the tm's little less low end by gearing the bell a bit lower. God knows I have to use a 13T now with this worn out motor to get off the line like it used to, and I imagine from what I have heard thus far a 13T on either motor s going to put it on its lid.

One thing I do like hearing is that the TM has a wider "sweet spot" for tunning. Right now with my back problems it makes it difficult to continuously tweak the TRX hour after hour, but I think that has more to do with the loss of compression and not so much the weather as in the summers here it stays pretty consistent. Desert dry, hot, no humidity, and high elevation. I am not sure on the EXACT elev. but I know we are over the 5700' mark.

Well so far I guess it is leaning towards the TM. Just wish I could afford something like the RB Concept TM523 or a .21TM

Duster_360
10-30-2007, 09:15 PM
I started back into rc with a 2.5 tmaxx after a long time away (was into planes then) and ran it hard. It's a somewhat challenging engine to make run and run well, it has a small tuning sweet spot and does require fiddling at least every time out. I scratch built a 2nd Tmaxx - a light weight version like Slayden was racing and stayed with a 2.5 - same experience with this engine. They are powerful and wheelies can be a prob if they are tuned well. I am a basher with a big grassed back yard and pretty much only two speeds - idle and WOT.

I bought an early version of the 18Tm when they 1st came out and were well over $200. I put it in my light Tmaxx and the diff was daylight and dark. I can go for weeks and not touch a needle - just gas, start and rip. the TM runs cooler than the 2.5, even with a Nova cooling head. As pointed out, TM power band is a little diff, more mid and top, but it has plenty of bottom end too, just not so much that its always on its lid - I don't see any need to re-gear, but I'm not racing either. These small engines are a sensitive to unsprung weight and it takes a lot away from one to run a heavy set of tires and wheels.

I have another 18TM NIB and bought a used one that was too good a deal to pass up. I'm looking forward to a lot more gallons thru mine - I'm not sure I've seen a better combo in this size truck than 18TM, BBs are too much power and they're constantly tearing stuff up in the drive train and need more wheelbase when they are running to be stable. Surprisingly, I have a NIB 3.3 too - my orig, stock Tmaxx is getting that one after I upgrade diffs and shafts so I won't be having probs. It will be interesting to compare the two directly.

I find it interesting I've not seen a head to head dyno on both the TM and 3.3. Going to OS's website there is no mention TMs been discontinued - ? TH invested heavily in EB 18TMs (and other OS engines) and may just be selling them off. One other comment - TRX never used to care if you had a receipt or were orig owner to do the engine replacement program - as long as you've got a 3.3 to swap, that used to be enough to do the ERP. I fully understand budgets, but you will not regret running an 18TM if you can swing it!!

PocketAce
10-31-2007, 12:41 AM
I would go with the .18. You can't beat the O.S. reliability and bang for the buck, it's a great engine.