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Hot Traxxas 3.3 engine build.

Old 02-17-2019, 01:59 PM
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Default Hot Traxxas 3.3 engine build.







This is a mini build log of a lowly Traxxas 3.3 engine in building for my Jato. I’m pretty much doing anything and everything to this engine to get it to spool as quickly as it can and make a bit more power/rpm than it would bone stock.

Things staying stock:
cylinder head
bearings
standard type glow plug

Modified goodies:
Modified crankcase
Modified crankshaft
Modified crankshaft timing
Modified/lightened piston
OEM conrod swapped for Sirio 2.5/3.3 conrod
Modified liner timing
Boost port unshrouding at BDC
Smoothed exhaust port flow
Modified big block carburetor with 8mm choke

This engine was new and unrun, built from spare parts. I do not believe in using an EBIS system nor do I believe in lapping the piston. This engine will get broken in the traditional way using my own fuel blends proven to make superb running engines last a long time. If I could get a barstock piston made for it, I would have. Cast pistons are
not known for lasting a real long time, but I’ve yet to wear a 3.3 piston out...

When I have all of the timing changes made and degreed, I’ll post them for all to see.

Last edited by 1QwkSport2.5r; 02-17-2019 at 02:04 PM.
Old 03-27-2019, 03:51 PM
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My TRX 3.3 drag build is done. Hereís some pics of the rest of the engine. Nothing crazy, but far more extreme than Iíve done thus far. The 8th scale .26 carb is pretty monstrous compared to
the TRX carb. I might need to modify the brake linkage a little bit.
Old 03-31-2019, 04:38 AM
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I have found that depending on whether the engine was assembled at the factory or assembled from parts usually gives different timing figures. I think there have been some running changes over the years with regard to timing profiles and such.

This engine was assembled from parts from several engines. The piston/liner was a retail packaged matched set, and the rest came from chop shops or my spare parts box.

Box stock canvas:

Crank bore: 7.6mm
Crank inlet timing: 34/63
Carb choke: 6.15mm (Traxxas carb)
Exhaust timing: 84/84
Transfer timing: 65/65 (a bit advanced for an RTR engine)
Boost timing: 57/57

Modified canvas:

Sirio conrod swapped in place of OEM conrod.
Crank bore increased to: 8.5mm
Crank inlet increased to: 32/64
Crankweb and counterweight re-profiled and lightened
Carb swapped for a big block .26 engine: 7mm choke
Exhaust port widened and timing increased: 88/88
Transfer ports increased to: 67/67
Boost port unshrouded and timing increased to: 60/60
Piston lightened and modified to unshroud boost port
Crankcase modified to flow better between transfer and boost ports
Starter backplate modified - phosphor bronze gushing removed and replaced with three ball bearings.

Thats about it. I am going to try getting this engine broken in and thoroughly tested very soon.
Old 04-02-2019, 01:34 PM
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very interesting! would love to hear/see your results!
Old 04-03-2019, 05:41 AM
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Originally Posted by D3MON View Post
very interesting! would love to hear/see your results!
The idea behind this engine was to make the 3.3 better than it already is. This engine has known faults, and I addressed those faults while at the same time getting the engine to make a little better lower. It probably wonít have the insane low end itís known for, but it should spool damn fast and rev well. Better breathing and a rocksteady conrod should have it run really well. This engine is actually timed really well out of the box, it just needed to breathe better and have a rod that can survive. Iíve never broken a rod in a 3.3, and Iíve had 6 of them, so with the right fuel and engine care, it works fine in stock trim. I didnít have as much faith in it holding up in modified trim.
Old 04-11-2019, 05:20 AM
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I have run about a dozen tanks of fuel through the new 3.3. So far Iím pretty impressed with it. It spins the Road Rage tides with ease. I wore out the rear set in 7 tanks. Even though itís still pretty rich, the idle is stupid low and stable, it revs nicely, and I can easily tell itís got a lot of power. It runs real consistently at 220-240F on 10% Nitro 14% oil fuel. Looking forward to adding some nitro and running it a bit leaner. Iíll get GPS readings each quart for a little extra stuff to have in my
notes about this engine.

Current setup: stock manifold slightly polished/modified & Resonator 2 chamber pipe with drilled stinger.

22/58 gearing, 10k diff oil. Running off-road gearing for breaking the engine in. Will go to 24/54 or 24/52 for speed runs. All Iím trying to do is do better than what Traxxas says the Jato can do bone stock (65.1mph on 33% nitro fuel). I am confident it will.

1100MaH 2S LiFE receiver pack, Spektrum radio.
Old 04-16-2019, 06:36 AM
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Since Iíve pretty much turned my road rages into drag slicks over the course of one quart of fuel, I opted to get a set of Jaco foam tires for my Jato. I painted the wheels and did a precision balance on them. This should give smooth high speed traction and help the squirrely Jato more planted. I need to make some suspension adjustments and I think adding sway bars will help quite a bit.

My first quart of break-in fuel is only 10% Nitro and 14% oil and after one quart of fuel so far, Iím really happy with how the engine turned out and is running. It spools up incredibly quickly and it idles down so low and stable, youíd think it was a Novarossi. Hereís a video I took the other day and a couple pics.
Old 05-09-2019, 01:13 PM
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that thing is quick! did have a question, why run 10% nitro? for the most part 20%+ is what i have seen as recommended, just curious.
what ever works, works, im not trying to say anybody is doing anything wrong.
Old 05-10-2019, 03:15 AM
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Originally Posted by D3MON View Post
that thing is quick! did have a question, why run 10% nitro? for the most part 20%+ is what i have seen as recommended, just curious.
what ever works, works, im not trying to say anybody is doing anything wrong.
Its my break-in fuel. 1st quart is 10/14, 2nd is 15/13, 3rd is 20/12, and 4th and on is 20/11. Nitro/oil respectively. I do this on all of my engines now and it works really well.
Old 05-10-2019, 07:04 AM
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Originally Posted by 1QwkSport2.5r View Post

Its my break-in fuel. 1st quart is 10/14, 2nd is 15/13, 3rd is 20/12, and 4th and on is 20/11. Nitro/oil respectively. I do this on all of my engines now and it works really well.
that makes sense! thanks for the clarification!
Old 05-11-2019, 04:26 AM
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Originally Posted by D3MON View Post
that makes sense! thanks for the clarification!
The truth is, they donít need much nitro to run fast, either. One of my next videos will be my modified Jato running on Zero nitromethane. This will be after I make more changes to the 3.3. It needs some tweaking.
Old 05-14-2019, 01:16 PM
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saw a video on one of my nitro rc groups on FB, was a guy running 0% on his RC10GT, thing was fast and seemed to have ran great!
looking forward to seeing your Jato on 0%!
Old 05-14-2019, 04:29 PM
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Anything will run fine without any nitro. You adjust the head spacing and glow plug to suit the fuel and likely will have little issue with it. Non-nitro laden fuel does requires skilled tuning hands though. Your sweet spot range is pretty narrow without nitro.
Old 05-25-2019, 12:07 PM
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Hereís the head button a friend from Australia made for me fitted for Nelson glow plugs. Nelson plugs are cheap
and make the same power that Turbo plugs do. From left to right, standard plug 3.5cc Nova head, turbo plug 4.6cc Nova, and Nelson plug 3.3cc Traxxas head. The heatsink for the 3.3 needs to be cut and modified to fit the Nelson head button and then I can get it installed and tested. Should be interesting.
Old 08-19-2019, 02:58 PM
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More progress. I goofed off at work and fitted the Nelson head button to a custom cut Traxxas heatsink. I needed to cut a 3.3 head/heatsink to fit a head button. Traxxas heads are one-piece. Next I had to cut the bottom of the heatsink to have a flat surface for the button to mate to. Then I needed to fit the button to the liner. I also needed to machine the glow plug hole in the heatsink to fit a 3/8” nut driver. The Nelson plugs have a 3/8” hex head. My friend who made the button machined the button 0.2mm larger in diameter than he was supposed to. So with a little work, that was machined down to fit and all is ready to bolt-on. This plug should allow for better power and smoother delivery up to 40% Nitro.
Old 09-07-2019, 04:32 AM
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I forgot to add this photo. Apparently itís the only photo I took showing what I did. The backplate has a bronze bushing installed for the starter shaft to ride in. Bronze is a long lasting material that needs very little
lubrication to hold a seal. I decided to see if ball bearings would make any difference in how the engine performed, so I ordered some bearings from Avid. Due to the thickness of the backplate web and the bearings only coming in a 2.5mm width, I had to install 3 bearings together so the same space would be occupied within the backplate. If I did this again, Iíd get the flanged bearings for the inside of the backplate (Avid has them on backorder when I placed my order) and use the regular bearings for the middle and outside.

The engine runs runs really nicely and there are no leaks from the bearings, so Iíll have to see how this works long term. I have several more backplates, so I may do some more experiments.
Old 10-13-2019, 11:19 AM
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Hereís my next addition to this project. The Traxxas manifold is no good. Too long. Opted for a short on-road header - Novarossi 41613-S. This is a short conical onroad manifold for 1/10th scale engines. This should give more midrange and top end. I will need to make some different manifold seals since Traxxas engines have odd size exhaust ports. Iíll also need to modify the backplate a little to clear the manifold. Not a big deal.
Old 10-27-2019, 05:34 PM
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Nelson HD glow plug lit for the first time in a modern RC Car engine.
I still need to get the exhaust sorted, but I’m comfortable in putting the new head and button assembly onto the mod engine in the Jato. Just for giggles, I used my spare engine to fit everything and test the glow plug operation. It should light some hot fuel!!
Old 01-31-2020, 02:42 PM
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I spent a little time to adapt the new Novarossi 41613S manifold for the Traxxas crankcase. I need to get more tubing to make more manifold seals. Iíll need to make sure it seals well. I checked my customized backplate with bearings installed in place of the bronze bushing and it looks perfect inside and the bearings are butter smooth. Now the snow needs to melt so I can run it.


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