Nitro TC3, project thumper

[Sharkey]

since i have my sportsline mostly built and running like a champ, its time for another project. ive had my nitro tc3 now since 2004, its been upgraded with a version 2 rear suspension and a few choice suspension upgrades, but aside from that, the rolling chassis remains pretty much stock. over the years its had quite a few engines. it started life with the hpi/novarossi 12 from my old nitro rs4. i ran the car for a couple months then in went a rossi pixi black .12, and i raced it that way till 2007, and bashed till 2009. with the motor tired, i tossed in an old os .15cvr, when that died i ran a traxxas motor for a bit, then rebuilt the pixi after finally finding parts. just after break in the piston cracked, unable to find another piston and sleeve i retired the motor for good, and moved on. not racing anymore, knowing i wouldnt be satisfied with the power of a cheap smallblock, i decided bigblock was the way to go. i purchased a rossi t6 .21 for $40 brand new, fabbed some mounts, and in it went. diffs didnt last long, i ended up with a set of dynotech racing aluminum ring and pinions, and played around with the gearing, it all worked quite well. unfortunately the first large scale outing of the year was the last for this combo, the connecting rod finally had enough of the extreme rpm the motor was pulling on the large track, the bottom of the rod stretched and the rod bushing fell out. i thought about another .21, however as fun as 80mph with a touring car was, doing it again seems pointless. i tossed around the thought of retiring the car, however its sort of my "project x" (any car guy will know what project x is), it'll keep going till i find the perfect combo.

a couple pics of it with the .21

this brings me to the beginning of the next phase. years ago i always like the os 4 stroke car motor. something different. however the low advertised power, amount of custom work, and the price kept me away, like many people. well, years later ive got bit by the bug again. however the fs 26s-c has been discontinued since 2009, there are none around anymore. now you can convert an fs30s airplane motor by changing the camshaft and valve springs, however the camshaft isnt available. this led me in the direction im taking. ive purchased a used fs 40 surpass 4 stroke, and have tracked down the crank, cam and head from the fs 40s-c car motor to convert it to the car spec motor. i figured the .40 4 stroke was a replacement for a .21, and the tc3 has a .21, so it'll work out. this project isnt about being the fastest, or best handing, since i quit racing its been all about fun, and the 4 stroke seems fun.

so far ive mocked the motor up in the car and figured out gearing. the 4 stroke has a max rpm of 22000, however modded they have been dynoed at over 26000rpm. being the torque of a 4 stroke and low rpm, gearing is key. with the .21 i had machined the 2 speed clutch hub and one way bearing for hpi 37 and 41 tooth spur gears, and ran 19/23 tooth pinions on an hpi clutch bell, so gearing is quite tall already, but would limit the 4 stroke to around 42mph. scared of valve float i dug around and found a 29 tooth savage metal tranny gear that with some machining will thread onto the clutch bell. couple that with a revo 36 tooth 2nd gear spur, and it comes out with a 3.10 final drive ratio, should be enough for 60mph.

im waiting for a bunch of parts for the motor, both for the conversion and just general rebuild stuff. its getting the car crank, cam, head and intake, along with a set of crank bearings, cam followers and pushrod tube seals. im planning on running a 10e rotary carb to start with and eventually move up to an hpi composite k4.6 carb. ill be building my own header, ive been reading about how well these motors respond to a stepped header with a megaphone end (read: almost double the power output, dyno confirmed). ill start with that, ive read about some more tricks with these motors, ill wait till i get it all figured out before screwing with it more.

ill leave you with a couple of pics of it thus far

 

[atom3624]

Pardon my ignorance, but are the gears the wrong way around on the clutch bell?

Al.

 

[lordraptor1]

Pardon my ignorance, but are the gears the wrong way around on the clutch bell?

Al.

looks like it to me also. anyway the 4 strokers have more toruque than a 2 stroker, so gear it accordingly, in an aircraft a 4 stroke engine is capable of spinning a larger prop than a similar sized 2 stroker.

also besides your clutch bell gears look rather chewed up, were you running it as a rally car i teh gravel

 

[Sharkey]

yes the gears are backwards, the larger pinion was 2nd gear, its now going to be used for 1st gear. i had them that way for fitting. and no, not running it as a rally car, that my biggest gripe about this car. it seems to vacuum up every last pebble in a parking lot, i go through a lot of gears on this car, always have. the pinions arent actually that bad, the top of the teeth are pitted, however ive cleaned the face of the teeth and they will be good for a while longer.

 

[lordraptor1]

yes the gears are backwards, the larger pinion was 2nd gear, its now going to be used for 1st gear. i had them that way for fitting. and no, not running it as a rally car, that my biggest gripe about this car. it seems to vacuum up every last pebble in a parking lot, i go through a lot of gears on this car, always have. the pinions arent actually that bad, the top of the teeth are pitted, however ive cleaned the face of the teeth and they will be good for a while longer.

oh ok, when i was in co springs they set up a track in a parking lot every summer for racing and what they did was went through the parking lot the day before sweeping it, adn the next mornign before they set up the track they went in with a vacumn thing to do a second clean up and then hosed teh area with some sugar water for traction before setting up the track . they ran 1/10 and 1/8th scale nitro (nitro rs-4's and 1/8 onroad such as picco, serpent, hpi proceeds, etc), i left in 02 or 03 so don't know if they still run or not but i am sure they do

 

[Sharkey]

when i used to run 1/10 scale nitro touring we used to blaw the parking lot off real good and spray expired soda fountain drink syrup in the corners (hobby shop owner owned 2 gas stations, thats where we got that stuff). even just a clean track is fine, however with the large scales we don't clean the lot. we set up an open track, we have no timing system, and we have plenty of fun just on an open track.

 

[Sharkey]

still impatiently waiting for parts for this. in the mean time i fabbed some engine mounts and figured out an intake manifold for the big block carb. the carb is off an hpi k4.6, i decided on that because of the composite body. im not planning to use this setup right away, i do have the fs40sc intake manifold coming and a 10er (15 cvr) carb that im going to try out first, its a known combo thats proven to work. once i get the car sorted a bit ill put this setup on.

the motor isnt yet bolted in, i need the flywheel and clutch bell on the motor before i can drill the bottom holes, and to get that stuff on i need my parts to get here.

 

[lordraptor1]

i'd run take a piece of tubing from the carb to the front of the car and pit the air filter as close to teh front as possible essentially making a cold air intake

 

[Sharkey]

i got part of my order last week, unfortunately it was only 3 things. one of those things was the crankshaft, so i have made some progress. i now see what everyone talks about with the crankshaft, its designed for a keyed flywheel and is a large size, needing a collet thats almost 8mm. instead of tracking down a flywheel for it i managed to machine a collect to fit and made a ntc3 3 shoe pullstart flywheel fit. the tap i ordered also showed up so i got the 29 tooth pinion gear threaded and on. the motor mounts are now finished as well. i did have a glitch with gearing, so i have the option of *43/23 1st, 37/29 2nd, or 43/22 and 36/29. im starting with slightly less top speed and a 6 tooth gear split, and i can change so i get more top end, more acceleration, however its a larger 7 tooth split on the gear change, and it might be too much. gearing is something im going to have to play with, however with using hpi 1m gears, i have lots of options.

at this point im just waiting for the rest of my parts to show now. once they do ill be able to build the motor, build the header and it'll be ready to go.

not much has changed that you can really see, however i did snap a pic to show how tall the gearing actually is

 

[CSR260]

looking good.. looks very tiny :lol: what size is it?

 

[Sharkey]

the nitro tc3 is a 1/10 scale 4wd touring car designed for a small block nitro engine, .12 to .18. i ran a big block .21 in it, im now the 4 stroke is a .40.

 

[lordraptor1]

should try a magnum fs70 four stroke .70 . i picked one up locally for 190.00 out the door brand new for my piper cub

 

[Sharkey]

the biggest thing with an airplane motor is the lack of rpm. airplane motors typically see a max rpm of 13000. the os fs26s-c and fs40s-c were converted airplane engines, the biggest difference in the car versions are the valve springs and camshaft, and push the max rpm up to 22000. 13000rpm in a car just isnt usable.

 

[atom3624]

Different sound as well.
If they've got the revs up, does that mean they keep the 4-stroke torque advantage or they lose on the torque relative to stock 4-stroke?

Al.

 

[Sharkey]

they still have a huge advantage in torque over a 2 stroke, however like any engine, power is a balancing act. a plane motor is designed for the most torque at a specific rpm, where a car motor needs a broad powerband. with the car cam profile it does lose some torque compared to the plane version. power goes from .65hp at 12000rpm to .9hp at 18000rpm. os did drop the ball on these motors, there is tons more power to be had. on the smaller .26 just a carb swap and a stepped header doubles the power output. shimming the valve springs and the max rpm can be pushed up over 25000.

the few people that have raced with a 4 stroke say that with a properly set up car and geared correctly, a 4 stroke will out accelerate a 2 stroke any time.

 

[Sharkey]

my parts showed up yesterday, the motor is now all assembled and bolted in the car. i just have some details left, like bending up a header and building throttle linkage. being i need to pick up some linkage rod and i forgot my tubing bender at work, i said screw it and fired it up. this motor sounds so cool, i cant wipe the smile off my face. its got a real nice crackle to it, something i cant get on video. everything in the car seems to be fine now, so just gotta work out a couple small things and i can start working the bugs out.

 

[atom3624]

Looks a doddle to work on, just so much room!!
Which shell is going on top of that lot?
Will cooling be a problem?

Al.

 

[Sharkey]

ive got a mk 4 supra body for it, nothing special. cooling might be an issue, most people run fans with 4 strokes because of the lack of cooling fins. i have found one other person to do a 4 stroke in a nitro tc3, he didnt use a fan and temps wernt out of control. the biggest issue is finding a fan small enough that blows enough air, a typical computer fan isnt up to the task.

 

[Sharkey]

first run didnt go so well, although its pretty much what i expected. at first it was way too rich, sucked back 1/4 of a tank just at idle. once i leaned it out a bit it started running better, got a little driving out of it then it started acting lean. the end result was the high end needle almost falling out of the carb and it was still lean, fuel was boiling in the carb (i was warned that its best to use a composite carb or a plastic spacer on the manifold, and im not), and a broken header.

i gotta say though, the couple times i was able to get on it, this thing is insane. even with the tall gearing at 1/2 throttle i could easily out accelerate the old .21 i had in it. i bet i could run a single speed with as tall a gearing as i have for 2nd and it would pull it with ease. i cant wait to see how this thing works once i get the glitches figured out. that being said, i already have a new header bent up and some ideas on fixing the fuel delivery issues. there is great debate with the 4 stroke of how to run the fuel system. most agree that with a muffler the exhaust pulse is too strong and you end up with the needles barely open. some people run with no tank pressure, others run a perry pulse pump. when i initially ran it i ran with no tank pressure, however the crankcase pulse seemed pretty strong so i tried hooking that to the tank, but its obviously not enough. next im going to try a pulse straight off the header without a muffler of any sort. i don't want to run a fuel pump, mainly because i lack the room for it, and initial tests show ill need to figure out a fan for the motor, something else i really don't have room for.

 

[Sharkey]

a little update for anyone still reading this

ive run it a little bit more and sorted my fuel delivery problems, at least as a temp fix. bent up another simple header and hooked it to a savage 28 tuned pipe (the polished metal one with large stinger), i now have plenty of fuel to the carb. being a dual chamber pipe it did create a lot of backpressure and did kill a lot of the low end torque i had with the open header, however i was able to get the thing wound out a bit. id say it still pulls as hard as the old .21 did, it just tops out sooner. im trying something else, i modded a traxxas plastic pipe with a large stinger (over 3/8" ID), took the guts out and glued it all together. next chance i get ill give it a try, with less backpressure it should have a little more power. i did play around with the large carb i had, it didnt work out so well, to make it work properly i need to make a billet manifold, so for the time being im keeping the small rotary carb on it.

next thing is a fan, this motor gets hot quick. ideally you keep the motors under 220 degrees, right now im hitting 250 if i run it for more than 1/2 a tank. however the restrictive pipe may be causing some of this.