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Noob with an old 2.5 revo

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sounds like u have it all sorted. and if u have the trx3.3 motor u should defo get it in there once uv mucked around with the 2.5. from what iv heard there is a big difference. I'm going from a 3.3cc to a 4.3cc. a fair bit more power and should make it a big handful
 
Yeah, I'd love something bigger than 3.3, but I gather that'll require upgrades in the drivetrain to handle it + the substantial cost of the motor, mount, pipe etc.

I reckon the 3.3 with THS pipe running on 25% will keep me happy for quite a while, for a total outlay of about $110 - bang for buck that's hard to beat.

Next on the wish list after the 3.3 goes is an rpm true track conversion for the rear, rpm front arms, those red alloy suspension pushrods (I've bent a stocker already, straightened out with a pair of pliers & a vice no probs tho) & a rear wing.
 
rear wing is a good buy, and i was pretty happy with the 3.3. I'm putting another one back in till i get the new picco. so I'm looking forward to running that in and getting it going hard again.
 
I'm gonna get out the needle files & do some work on the breathing of the 3.3 before I put it back together (I port cylinder heads for racing engines as a big part of my job, got a fair bit of experience with improving airflow & I've ported a few 2 stroke bike engines in the past - a little nitro engine is not much different, just need smaller metal removal tools).
Should be able to crank it up a bit more than a stock 3.3.
Best bit is I won't end up covered head to toe in metal fillings & I can port it sitting in front of the telly.
 
lol, u gonna test it out on the old sleeve and then do a final job on the new one?
 
Mostly it'll be cleaning up the flow path through the crank & block, as well as into the sleeve ports, I won't change the port timing much, just concentrate on getting more air in & out in the existing rpm range.

PS - I'm an Aussie too, in Adelaide - where are you?
 
I'm in brissy. if you mod the sleeve you should do some before and after vids. stop start running type stuff. make sure you do it in the same place with the same camera. do a before and after tune once uv ported it too. would be great to see the difference.
 
Well this got it's first real mod this morning, had it out last night at a skate park with some mates (highly recommended!! - big air, lotsa jumps & the bowl is just wild fun).
Spent some time stirring up dust in the dirt nearby, came WOT with wheels spinning off the dirt onto a concrete path & rounded both rear wheel hexes, stripped them out completely & took the wheel centres with them.
So this morning it got a fresh set of wheels to take 17mm hexes & a 17mm alloy hex conversion, that should sort it.
Hoping my THS pipe & new air cleaner will arrive today, but it's not looking good (bummer).
 
I can't reccomend modding the engine, because most people ruin them that way. I can reccomend the Extreme rc mods or THS pipes though....those will really wake up your 3.3.
 
This was playing up last night, stalled out of the blue under brakes, fired up again no probs, drove out about 10m & cut out again, kept doing it.
Started & idled fine but would cut out both under brakes & under power.
Was getting pretty hot idling as well.
Messed with the tune - didn't help.
Replace the glow plug - same.
Hosed out the carb - same
Check the lines were clear - same
removed failsafe - same

Cracked the shits & went home.
Pulled it down this morning, pulled the motor apart - all good, resealed it real well.
Stripped the carb, resealed that including some grease on all the O-rings
Cleaned up the pipe & header, checked for cracks/leaks, refitted & resealed.
Cleaned out the fuel tank, blew compressed air through everything.
Put it all back together & fitted the new motor save filter that arrived yesterday arvo.
Fresh tank of juice, needles reset to factory.

Problem solvered, all good, retuned it & running well.

Still dunno what was causing it, had to have been a fuel supply issue, but I dunno why - nothing stood out as being the cause, but whatever it was cleaning & resealing everything seems to have fixed it.

I hate not knowing what the problem was - if it happens again I'm none the wiser as to where to look first.

---------- Post added at 10:10 PM ---------- Previous post was at 10:01 PM ----------

Pics (minus the motor saver filter I fitted this morning):

P4030621.webp


P4030620.webp


P4030619.webp
 
I can't reccomend modding the engine, because most people ruin them that way. I can reccomend the Extreme rc mods or THS pipes though....those will really wake up your 3.3.
Click to expand...

I've got 18 years experience porting heads, I'm not gonna ruin it!
But I reckon I'll get it up & running stock to start with - otherwise I'd have no idea what difference I'd made.
I'll run it stock for a bit, then pull it down again, fit an upgraded rod & port it at the same time, then I can get a back to back comparison of performance.

A home made inertia dyno would be a handy thing for evaluating changes as well as tuning, wouldn't be a hard thing to make either, just wieghted drums driven by the wheels & hooked up to a timer to time how long it takes to accelerate the weight to XXrpm. A reduction in time to accelerate a the mass of the drums indicates an increase in power.
If it was easily portable tuning to conditions would be easy as you could have the thing stationary & tune for max power whilst keeping an eye on temp etc.

Meh, I think to much.
 
Yeah, you do. These engines are unlike anything else you've ever dealt with. Do your research on modding rc nitro engines, or else you will ruin it.
 
Me & a mate are about 1/2 way through building an engine dyno for RC nitro engines.
It's an inertia dyno, flywheel & shaft, flywheel bearings & cages, flywheel mounting frame & engine mounting frame are all done - handy to have 24/7 access to a full machine shop. Flywheel is billet steel, bearings are ex high speed die grinder bearings (good for 30,000+rpm & lotsa load), bearing cages are billet alloy & all framework is TIG welded fabricated alloy. It's be mounted in a checkerplate alloy box for easy transportation. Got an old laptop laying around to use with it.
Got some software to run it & log & graph results, probably won't produce 'real' power figures but should be very repeatable.
Will be real handy for bedding in engines, tuning & evaluating modifications. Engine bed in will be able to be done in the shed with bourbon in hand & under controlled conditions.
We'll be able to find the best setup from pipes & glow plugs, engine temp ranges & through to porting, quench modifications etc etc.
Get an engine all tuned for max performance on the dyno, note everything including engine temp & then we'll have a target engine temp to aim for for peak performance as well as knowing what setup suits that particular engine.

Down the track we'll grab a 'dyno mule' 3.3 motor to mess with & find out what does & doesn't work.

To set up the dyno & get it functional we'll use my 2.5, when she's up & running it's first real task will be bedding in a mates new 3.3 & tuning it, then I'll tune my 2.5 with the new pipe & can start looking at my 3.3.
 
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Took the Revo out again on sat night, was running great for 3 hours, switched to 25% nitro even tho the pipe hasn't arrived yet - made a big difference.
Then it leaned out out of the blue & stalled, couldn't get it restarted & it was late so called it a night.
Pulled it down, pipe is busted clean off at the flange - guess I really need the new pipe now!
Shifted the trans forward 1.5mm, it was too close to the air cleaner, spur gear wasn't sitting right on the bell gear & I popped the front driveshaft out a couple of times as it wasn't engaging deep enough on the splines. I just elongated the trans mount holes & filed a little out for clearance, heaps more air cleaner clearance, more spline engagement on the front shaft & gear mesh is much better, calling that a worthwile mod.
New pipe should be here any day now, can't wait to try it out with the 25% fuel.
Piston & sleeve for the 3.3 may get here by the end of the week, if so I'll rebuild the 3.3 over the weekend & get it all run in, that should be fun, the mate with the 3.3 rustler got his new motor bedded sat night & fitted his new THS pipe, running on 25% it's almost uncontrollable, can't wait for that sort of power in the revo.

Engine dyno is progressing, redesigned a few things, maybe done this week, maybe next week.

---------- Post added at 9:27 PM ---------- Previous post was at 9:15 PM ----------

Sweet - piston & sleeve just showed up for the 3.3.

Still no pipe tho :(
 
New 3.3 motor all finished & fitted, new wing & mount will be here tomorow along with a new 38t spur gear (old one is looking a little sad).
Pipe still hasn't showed up, but I'm hopefull it'll get here today or tomorow.

Had to get the wing as the 3.3 sticks up a lot higher than the old 2.5, the head would get beat to sh|t real quick without a wing to protect it.

Can't wait to get the new pipe & wing on & get it all fired up & broken in - should be a major transformation going from a stock 2.5 on 16% fuel to a 3.3 with a THS pipe running on 25%. Probably close on double the power.
 
Sounds about right. If you added a Picco .26 you could double that figure again. lol. No such thing as too much power.......
 
Yeah, that was my first thought, but it's not.
I didn't 'have' to move it forward, it was ok where it was, it just solved a few minor niggles - mostly it being a PITA getting the air cleaner on & off. I'm putting it down to manufacturing tolerances & tolerance stack resulting in the motor sitting a little further forward & the trans a little further back than usual.
 
Yeh mines pretty tight but if something is bent then I'll know cuz I'll start breaking stuff I normally wouldn't. Eg spur gears, if u break one then fe, if u replace and adjust correctly and it breaks again then yeh... Hard to tell on revo tho cuz there not straight.... Unless there are points in which line up and measure up edge to edge etc
 

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