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  1. #1
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    Revo 2.5/3.3 modifications

    what are some of the best Revo 2.5 modifications? I have already upgraded to a 3.3 engine and I have ported the engine. Other than that it is stock. I have a list of some mods I would like to do at some point but I wasn't sure if some are worth it and if there are any others I should consider. I do want to keep this as a basher but I want it to be ok around a track. Finally I'm not currently interested in getting a new engine as the current engine I have can wheelie and flip over the truck after it has shifted into second.(I have only seen videos of .28 engines do that with a revo)(The short chassis does help)

    150cc fuel tank

    GTR shocks w/ variable dampening

    Tires- my current tires are falling apart...upgrade to some other brand, stick with traxxas talon?

    wheelie bar

    resonator muffler/exost

    TQi+tsm transmitter/receiver

    remote starting- I can't find the losi ross anywhere so it may not happen

    li-ion Rx battery- 2 Samsung 30q cells with a 20a bms could be made to fit in the battery box, it could power a remote starter and it would last twice as long as the stock battery with no additional weight

    wide ratio transmission gears- not positive it's what I want, but I think it is

    single servo- brushless?

    losi or OS carb- possibly the losi 3.4 carb, I did read somewhere that OS makes a better compatible carb

    RPM or aluminum arms

    extended chassis?- I don't know if I want a longer chassis yet...

    I'm considering modifying my Revo over the next year if time permits and I just wanted to know if these are good modifications and if there is anything else I should consider.

  2. #2
    RC Qualifier chops1sc's Avatar
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    One of my favorite is the RPM Tru-trac arms for the rear. I know you have RPM already listed but I just wanted to add my praise for not having to deal with rear toe links.

    Another one of my favorites is Tekno sway bars. While they do not sell the full kit you can order the parts needed to make it work.

    17mm adapters is also a good mod.
    Revo .18TM BL Rustler Stampede MERV HPI Sprint 2

  3. #3
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    Nitro is not dead but definitely not popular anymore. Most companies seem to simply let their supply run dry and discontinue the items so either you won't find what you want or it will come at a price.

    My opinion(s):

    No wheelie bar. I had one on my T-Maxx and didn't like how the truck would bounce off it when I rolled or flipped it. I installed a wing on my Revo and that makes for a great carrying handle and "wheelie" bar.

    If sticking with the 3.3, consider a THS pipe and a Losi 3.4 carb - the OS will go for nearly double the cost. If you like the cool factor of remote start then go for it but that just adds weight. A proper tune will get the engine to start after a couple pulls from a pull start and it'll run all day.

    Gearing is what you want. All three gear sets have the same first gear ratio but the second gear is different. I personally run 16t/38t clutch bell/spur and standard gears.

    Shocks: if you have the standard aluminum body then go with the GTR and TiN shock shafts. Figure out the shock fluid and springs that fit your style.

    Single servo will lengthen your battery times. Don't look at only the speed and torque but also the power it draws. Savox is oft-recommended but many report brown-outs. I personally like Promodeler as they are high quality.
    The Super Derecho

  4. #4
    RC Champion grizzly03's Avatar
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    On mine I had the GTR shocks, a Picco 26 carb , drilled out the resonator pipe, wide ratio, pull start, riding on original Badlands also with the short chassis. I have switched to the long chassis and can tell it doesn't wheelie like it used too.

  5. #5
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    OK, As for the wing I don't really like the look of a wing on a truck body but I will look into it.

    Is the THS pipe better than the traxxas resonator? based on how it is recommended I would think it is.

    What of the three gear sets comes with the 2.5? I thought I heard it was close ratio but I'm not positive.

    How does the picco 26 carb compare to losi 3.4?

    Finally grizzly03- Would you upgrade to long chassis again? I have heard that the shorter chassis is better for "agility" and the long chassis can put the power down better. And what do you mean by drilled out the resonator pipe? Did you drill out the part that the exhaust reflector connects to for more top end?

  6. #6
    RC Champion olds97_lss's Avatar
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    THS used to offer 2 pipes, one for bottom end and one for mid-top end. The bottom end one was nice, it's what I run on one of mine. Still wasn't enough and ended up with a 21TM engine in it.

    I tried a losi 3.4 carb on my 3.3 before getting the 21TM. It did improve bottom end quite a bit, but it would bind on me constantly after about the 5th tank, so I ditched it in favor of the OS carb from the 18TM (I had one on hand). It helped the 3.3 hold a tune way better, but didn't really do much in regards to performance.

    +1 on the true track. I've run that on all my revos for many years and prefer it over having turnbuckles on the rear. Well, until I converted my v1 brushless to the 2.0. RPM doesn't make a true-track for that.

    The engine bay chassis brace is also a decent upgrade. Helps keep the chassis from flexing. M2C makes a better one. I run the M2C on my BB revo and traxxas one on my 21TM revo.

    If you want to stick with traxxas tires, I prefer the ones that come on 3.3 t-maxx. They seem to grip a bit better and don't get the sidewalls cut up as easy when running at skate parks.
    https://www.rcplanet.com/traxxas-3-8...3-3-2-tra4973/
    https://www.youtube.com/c/olds97lss

  7. #7
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    that engine brace may be a good idea. I figure that with the larger engine, porting, resonator pipe, and an upgraded carb this Revo may make more than twice the stock power of the 2.5. I don't necessarily want to stick with traxxas tires. I just want to find the best for the money.

  8. #8
    RC Champion grizzly03's Avatar
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    Quote Originally Posted by Bob2.0 View Post
    ...How does the picco 26 carb compare to losi 3.4?

    Finally grizzly03- Would you upgrade to long chassis again? I have heard that the shorter chassis is better for "agility" and the long chassis can put the power down better. And what do you mean by drilled out the resonator pipe? Did you drill out the part that the exhaust reflector connects to for more top end?
    Picco carb is a 7.5mm, the Losi is 7mm, and the stock Traxxas is 5.5mm throat diameter. The Picco needed to be modified to fit and the Losi carb is a drop in upgrade. No difference between the two. They both made tuning easier than stock carb, (the same was said about the OS carb). If the short chassis bodies were easy to find I would have stayed short chassis. But the longer chassis is more stable and jumps better. I drilled out the stinger (exhaust outlet), I forgot to what size but it wasn't much. The carb and drilling stinger gave it more low end.


    Quote Originally Posted by Bob2.0 View Post
    ...I figure that with the larger engine, porting, resonator pipe, and an upgraded carb this Revo may make more than twice the stock power of the 2.5...
    You can have the biggest engine in the world and have a stock Traxxas 2.5 put out more power. Learn how to tune first. Without a good tune no amount of mods is going to help.

  9. #9
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    I think I know how to tune... I'm no expert but I'm not bad at it. I was just pointing out I think an engine brace would be a good idea where the 3.3 is giving more power than a 2.5. Also I think the wärtsilä RT-flex96C puts out hundreds of times the power of a 2.5 even at an idle. Lol

    I know from my gasoline thread it may sound like I'm bad at tuning ... If you want to know how hard it is, put gasoline in your RC cars tank, drop an lc3 plug in there and try tuning it.

  10. #10
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    How do you need to modify the picco carb to fit the engine? I should try drilling out my exhaust. I'll be replacing the one I currently have soon so I might as well practice on it.

    Has anyone tried the high performance disk brake? If so how do you like it and is it worth it? Also where I'm not racing would it make a difference?

  11. #11
    RC Champion olds97_lss's Avatar
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    The engine brace is more for supporting the heavier engine. Even with a 2.5R, it's not a bad idea as the engine area flexes quite a bit if you push on the engine with your hand. Over time, the chassis eventually cracks.

    It still flexes with the plate on there, but it's spread out a bit more. I wish I could find CNC'd cradle supports, but never did. I crack the stock cast ones periodically, then the engine bay really flexes.

    With nitro, light tires are best for good throttle response. I stuck with zero offset on my revo's usually to avoid having the pivot balls pop through the RPM carriers. With .5" offset (geode wheels, revo 2.0 wheels), the extra leverage would cause the pivot balls to pop through on off kilter landings. Especially on the front. With truetrack on the rear, it was less of an issue there.

    If your looking for take off's, arrma outcast tires are well liked. I have a set of kraton wheels/tires on one of my nitro revos at the moment. They are very light. Not a ton of grip though, at least in grass. Allows for a bit of sliding when landing bad vs grabbing and flipping/ripping parts out, but they are offset.
    https://www.youtube.com/c/olds97lss

  12. #12
    RC Champion grizzly03's Avatar
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    Quote Originally Posted by Bob2.0 View Post
    How do you need to modify the picco carb to fit the engine? I should try drilling out my exhaust. I'll be replacing the one I currently have soon so I might as well practice on it...
    It had to be turned down to fit the 13mm opening in the block and throttle linkage to be able to open the slide all the way without binding. IMO go with the Losi carb, as it's not worth the hassle. Be careful if you decide to try drilling out the stinger. If you go too big, the exhaust is no good and will ruin an engine.

    Quote Originally Posted by olds97_lss View Post
    With nitro, light tires are best for good throttle response.
    +1. That's why I liked the original badlands, light tire w/lots of traction.

  13. #13
    RC Champion olds97_lss's Avatar
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    Quote Originally Posted by grizzly03 View Post
    It had to be turned down to fit the 13mm opening in the block and throttle linkage to be able to open the slide all the way without binding. IMO go with the Losi carb, as it's not worth the hassle. Be careful if you decide to try drilling out the stinger. If you go too big, the exhaust is no good and will ruin an engine.


    +1. That's why I liked the original badlands, light tire w/lots of traction.
    You would probably like the outcast backflip or backflip LP's. The LP's are smaller OD, so less cushion, but a pretty aggressive tread pattern. Both are pretty light.

    Backflips are 12.5oz, backflip LP's are 9.875oz. Proline mounted badlands are 8.5oz. The trencher 3.8's I run on my 6S trucks are 13.4oz.

    A list that I add weights too when I get new tires or see something someone posts. The column on the right with Y are ones I have weighed myself on a USPS scale:
    Last edited by olds97_lss; 02-12-2020 at 02:04 PM.
    https://www.youtube.com/c/olds97lss

  14. #14
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    I found a nearby hobby shop that's has proline Badlands on sale for under $40 a pair so I may go that route when I get around to getting tires. I also have an engine brace in my eBay shopping cart right now so I will order them later.

  15. #15
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    has anyone tried the high performance disc breaks? Are they worth the money if I'm only bashing?

    Also I have seen a lot clutch upgrades. Are any of them good?
    Last edited by Bob2.0; 02-12-2020 at 04:38 PM.

  16. #16
    RC Champion grizzly03's Avatar
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    Olds: Thanks for the list, going to make a copy and put it in my RC notes.

    Bob: The stock brake disc works fine for me. When I put the brakes on it stops. I did install a stronger 2075 servo(125oz) in place of the weaker stock 2055 servo. Clutches?? I never had any luck with aluminum shoes. Can't comment on others, switched back to stock and have no problems (I install in leading edge direction). The only other upgrade I would look into would be a Forward Only Kit if you have reverse.

  17. #17
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    Ok, doing what I do I have found the reverse to be very handy so I think I will keep it. Why do people remove it in the first place? I know you don't need it for racing but for bashing its one of the reasons I originally wanted the revo.

  18. #18
    RC Champion grizzly03's Avatar
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    It's a personal preference, if you use it then keep it. Removing reverse frees up some power, as there are less parts inside the transmission that need to turn (less rotating mass). For me, I never really used reverse and by going with a FOC kit it made a noticeable difference on take off.

    You asked for performance mods and that's why I suggested it. An engine will accelerate faster if there is less weight it needs to turn.

  19. #19
    RC Champion olds97_lss's Avatar
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    Quote Originally Posted by Bob2.0 View Post
    has anyone tried the high performance disc breaks? Are they worth the money if I'm only bashing?

    Also I have seen a lot clutch upgrades. Are any of them good?
    Got a link to the "high performance brake"?

    I run dynamite max life 2 shoe in my 21TM revo. Slips less than the stock clutch or MIP clutch. I moved the transmission in my BB revo so I could fit a 1/8th clutch/bell on it and I think I run HPI Savage XL alloy 3 shoe in it.

    The stock clutch was fine when it was a 2.5R or 3.3, but it slipped a lot when you add a stronger engine, then it melts/dies/glazes up pretty quick.
    https://www.youtube.com/c/olds97lss

  20. #20
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    High performance brake- https://m.traxxas.com/products/parts/5364X

    Is there any specific clutch you would recommend?

  21. #21
    Marshal Double G's Avatar
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    I have a .21TM and run either stock or MIP clutch; leading edge direction vs trailing edge.
    The Super Derecho

  22. #22
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    Would it help to make any changes to a nitro engine for high altitude? I never really though about it until I started working on designing and building a paramotor. At my altitude (5000') the air density is roughly 2/3 of what is at sea level.(.75kg/m³ vs 1.2 kg/m³) Because of that at 5000' the effective compression ratio is about 2/3 of the engines average effective sea level compression ratio. Also the engine losses about 25% power. Would it help to increase compression ratio? Also would I want to run a hotter glow plug or a higher nitro percentage or should I just keep everything stock? I have only run my engine on 30% nitro and on gasoline and it ran fine, but if it would benefit from a higher compression I would like to modify it.

  23. #23
    RC Champion grizzly03's Avatar
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    Here is a good Thread. Even a Traxxas employee (Nitro Chicken) weighs in. forums.traxxas.com/showthread-high-elevations

    Your making it more complicated than it is, trying to do modifications isn't going to lead you to having reliable fun. Which is why you abandoned your other project. Do the simple ones and enjoy running it with your Uncle.

  24. #24
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    Sorry, modify wasn't the right word. I was referring to running a hotter plug or a thinner head gasket to try and give the fuel mixture a combustion closer to what it would have at sea level.

  25. #25
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    Here are some pics of my the engine porting job.

    Sent from my KFKAWI using Tapatalk

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    **Support for non-Traxxas products need to be provided by the company that manufacturered it. Traxxas does not pay for this forum to provide a means of Support for products that don't have their name on it. Last warning.**
    Last edited by Double G; 03-03-2020 at 09:09 AM.

  27. #27
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    New update... I was driving around my Revo the other day and I didn't know that the battery was as dead as it was. Half way through the tank the reverse servo started twitching and at 25mph it shifted into reverse... The transmission will need rebuilt but I haven't opened it up yet.

    Also I think the gasoline took a bigger toll on the engine than I previously thought. It has almost no compression and only about a quart and a half through it. The engine runs ok besides a little bit rough of an idle and a hard time starting when cold. The only other noticable difference is I can't do second gear wheelies. Will it damage the engine if I don't replace the piston/sleeve soon? Or would it be ok if I just run until it won't run at all?

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    Apologies Double G, i think you miss understand me...I have an old Revo and thought others on this forum with similar after market mods may have experience that would be valuable to me and help me solve my problem. this is a Traxxas brand community site talking all things Revo etc.. i am fully aware the Sirio brand is now non existent and so there is no product support - I am not looking for support as such.
    anyway good intentions shot down...thanks anyway.

  29. #29
    Marshal Double G's Avatar
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    Quote Originally Posted by Bob2.0 View Post
    New update... I was driving around my Revo the other day and I didn't know that the battery was as dead as it was. Half way through the tank the reverse servo started twitching and at 25mph it shifted into reverse... The transmission will need rebuilt but I haven't opened it up yet.

    Also I think the gasoline took a bigger toll on the engine than I previously thought. It has almost no compression and only about a quart and a half through it. The engine runs ok besides a little bit rough of an idle and a hard time starting when cold. The only other noticable difference is I can't do second gear wheelies. Will it damage the engine if I don't replace the piston/sleeve soon? Or would it be ok if I just run until it won't run at all?
    As you know there really isn't a whole lot of parts with a nitro engine. A rebuild consists of the piston, sleeve, rod and bearings. Those alone would cost more than a new engine that is being sold by someone who parts out RC's. You could go that route and have a spare block and crank (I don't remember if you modded it) should you need it. Or scrap them and go with a new engine. Run it till it blows, 'cause in the end, it will cost about $100 to get you back up and running.

    Quote Originally Posted by Robert JP View Post
    Apologies Double G, i think you miss understand me...I have an old Revo and thought others on this forum with similar after market mods may have experience that would be valuable to me and help me solve my problem. this is a Traxxas brand community site talking all things Revo etc.. i am fully aware the Sirio brand is now non existent and so there is no product support - I am not looking for support as such.
    anyway good intentions shot down...thanks anyway.
    You were asking questions specific to the engine. Traxxas will allow how you got the engine to fit in a Traxxas vehicle but not requesting resources on how to fix it.
    The Super Derecho

  30. #30
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    Where it only has about 2 quarts through it and the compression loss came from overheating and it never overheated for over a minute at a time, would the bearings, crankshaft, and piston rod be fine if I just replaced the piston and sleeve?

  31. #31
    RC Champion olds97_lss's Avatar
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    Overheating means lack of oil usually as it was too lean, which caused it to heat up. So that means all the moving parts have been stressed/worn as well. The con-rod should always be replaced whenever the piston/sleeve is replaced as the bushing wear out similar to the piston/sleeve.

    You could also pull the engine apart and check for pinch just to be sure it's actually worn and see if the piston/cylinder wall is scored.

    With it apart in your hands, if you can easily push the piston to the top or out of the sleeve through the top, it's worn a lot.

    Examples:






    Where it should go if there's a lot of pinch left:


    Those are some I had repinched many years ago. These days though, usually, when an engine wears out, I just replace it and keep the old one for spares. Back then, I was a bit more frugal.
    https://www.youtube.com/c/olds97lss

  32. #32
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    I know it wasn't lean. It was just the gasoline that just burns a ton hotter. Now that I think about it when I took it apart to get pics of the porting job and to replace the back plate it had as much pinch as the top xtm in your pictures. I should probably check the glow plug and the cylinder head to make sure everything is sealed well. Also I don't remember it lacking that much compression before I replaced the cylinder head. Hmmm

  33. #33
    RC Champion olds97_lss's Avatar
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    The XTM in the first photo didn't really "need" a pinch, but I had it done as well since I got a discount when sending multiple. I think I had rayaracing do it. It helped get a few more gallons out of each engine.
    https://www.youtube.com/c/olds97lss

  34. #34
    RC Champion grizzly03's Avatar
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    Quote Originally Posted by Bob2.0 View Post
    Where it only has about 2 quarts through it and the compression loss came from overheating and it never overheated for over a minute at a time, would the bearings, crankshaft, and piston rod be fine if I just replaced the piston and sleeve?
    That's all it takes. I would pull it apart and check each part if you're unsure. Heat causes things to stretch and warp.

    Also the fangs you put on the cylinder sleeve will affect fuel flow. Should try to point fangs so that they converge.

  35. #35
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    Ok, I have had everything apart, it honestly looks like it only has only 2 quarts through it... It has good pinch, the cylinder walls don't have much scoring, and all the other parts look like they have only a few hours on them. I'm honestly starting to think that the glow plug or the cylinder head is leaking. I'm just wondering how it could be leaking... All the screws are very tight and so is the glow plug. I may need to use soapy water.

    Thanks for the info grizzly03. If you think about it, that last fang shouldn't have much angle so the fuel/ air don't intersect as soon with the port that shoots upwards.

  36. #36
    RC Champion grizzly03's Avatar
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    Quote Originally Posted by Bob2.0 View Post
    ...the cylinder walls don't have much scoring...
    There shouldn't be any, only a polished surface.

  37. #37
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    There are like 3 lines... I don't think that could completely kill all compression. I think even if the sleeve is partly to blame I think there must be something else leaking.

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    I was wondering if anyone knows of a "big bore" kit for the 3.3

  39. #39
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    Try ABmods or RBmods.
    The Super Derecho

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