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BAJA SRT4 100cc gasoline twin cylinder 2-stroke 1/4 scale

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Old 01-18-2012, 03:06 AM
  #1  
JariV
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Default BAJA SRT4 100cc gasoline twin cylinder 2-stroke 1/4 scale

Hello guys,

I have been building a new large scale project.

BAJA SRT4 100cc gasoline twin cylinder 2-stroke 1/4 scale


Basics:
- Wheelbase currently 600mm (23.62 inches)
- Overall length with Ford Escort body 960mm (37.8 inches)
- Track width (adjustable between 480 - 550mm (18.9 - 21.65 inches)
- Weight 19,9kg in full driving condition with body on and full tank of gasoline
- Four wheel drive
- 3 silicon filled differentials, rear, center, front, aluminum diff housings (Limited slip diffs available)
- front and rear sway bars with metal Uniball link ends
- front and rear disc brakes with longitudinal adjustable brake arm
- independent suspension on all corners
- layout with much resemblence to 1/8 offroad cars
- 5mm thick aluminum chassis plate
- Weight balance 49% on front axle, 51% on rear axle

- Engine 100cc aviation twin cylinder flat two stroke engine modified for car use, selfmade twin exhaust, 22mm Walbro carburator, adjustable CDI ignition, stock power 10,2hp
- engine is now ported and piped, new power target is estimated to be around 15-20hp
- Arkansas 3-shoe clutch made for BZM 50cc engine, adjustable
- Self-made starter "system" (same style as old English outboard marine motors)
- Carburator and air cleaner are the only parts above the top level of the tires, very low center of gravity
- Targeted max speed 100 km/h @ 10.000 rpms

- Modified primary gears to have direct drive from clutch gear to center differential (90 degree center diff gears eliminated = less power loss)
- Fully adjustable silicon shocks with ajustable shock mounts, vertical wheel travel 100mm with current track width, 140mm with widest adjustable track width
- 750ml fuel tank, 4% premium gasoline with Elf Competition 2-stroke oil
- Jumbo (Hitec, Rhino) servos on both steering and throttle/brake
- 4600 Mah battery
- Extra large 4-stage airfilter
- Aluminum wheels, Baja 5T
- Hostile MXTs, ice spikes (64 pcs / one tire)
- Futaba 4PK transmitter

I still have the paintjob to think about. Otherwize fully ready for testing. This car would be VERY easy for mass production. Wink wink if someone is interested :lol:

Pictures:








































What do you guys think?
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Old 01-18-2012, 04:15 AM
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Default RE: BAJA SRT4 100cc gasoline twin cylinder 2-stroke 1/4 scale

What do you guys think?
That is one of the coolest looking RC's I have ever seen. Love the dual exhaust setup. Absolutely beautiful. The way the body fits as well, looks incredible. I cannot believe that beast of a mill and its brethren fit under the bod. Very scale, very clean. Great job man, looks great.
Can't wait to see vids of it running!! Great work
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Old 01-18-2012, 05:18 AM
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Default RE: BAJA SRT4 100cc gasoline twin cylinder 2-stroke 1/4 scale

looks a beast but,No Shrouded Fan cooling?maby use computer fans to cool this beast
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Old 01-18-2012, 05:59 AM
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Default RE: BAJA SRT4 100cc gasoline twin cylinder 2-stroke 1/4 scale

I don't think it will need any fan. The fins on the cylinders are big enough and I can always adjust a bit too much fuel to cool it down. Additional to that I will cut holes in the front body grille section between the headlights and direct airflow towards the cylinders. The cylinders are also inline with the airstream coming from the nose section and I'm confident I will get it to work. The only thing that this car will not like is idling in hot weather for longer periods. But that's easy, either you drive it or you shut it down.

About the cooling:
Just turn the rpms in your own car a little above idle like 2500 rpms and observe by hand how big a volume of air you feel coming out from the engine fan exit. It's not much. With cruising speeds and above you will get sufficient airflow to the cylinders, no problem but the airflow in all of the commercial models is 90 degrees from driving direction. Mine has the fins in driving direction like old motocross bikes. I'm talking about late Seventies - early Eighties motocross bikes engines which mostly were aircooled ones. Not much relatively bigger fins or so much more in number on the cylinders and always lots of obstructions in front of the engine, for instance practically always a hot exhaust header, front fender, frame to mention few. And a lot more weight to carry around. But of course these engines have a gearbox to help acceleration but they have to work A LOT harder than the engine in my application.

I made my exhaust so that it does not heat the cooling air charge in front of the cylinders. That is why I had to make heavy bends to my exhaust headers to I could fit everything inside the body. Otherwize the would have been sticking out a lot and would have looked stupid.

So I'm relying in the cooling airstream coming from front fenders and the grille once I have it cut.
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Old 01-18-2012, 06:38 AM
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Default RE: BAJA SRT4 100cc gasoline twin cylinder 2-stroke 1/4 scale

And one other thing if the 100cc would not offer "enough" power... you can always install for instance 120-170cc flat twin and it would only require very minimal mods
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Old 01-18-2012, 06:39 AM
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Default RE: BAJA SRT4 100cc gasoline twin cylinder 2-stroke 1/4 scale

You need some sort of cooling, these engines run hot even with a prop blowing on them. Even with holes in the body, I seriously doubt there will be enough air flow to even remotely keep that engine cool. You will burn it up.

Nice car though, I always wanted to throw some water cooled cylinders on one of these engines and do something with it.
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Old 01-18-2012, 07:13 AM
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Default RE: BAJA SRT4 100cc gasoline twin cylinder 2-stroke 1/4 scale

Well I have airplanes too myself and I also have experience of these gas twins. And the cowling and 3D props. I don't agree with you on burning it up but of course it is always possible with a 2-stroke. I'm only more optimistic than you in the matter of cooling this engine.
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Old 01-18-2012, 09:16 AM
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Default RE: BAJA SRT4 100cc gasoline twin cylinder 2-stroke 1/4 scale

I will be curios to see if the Smartech/nutech drivetrain holds up,i know it didnt hold up well on mine with a 30.5 and come added weight,anyways cool project.
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Old 01-18-2012, 11:44 AM
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Default RE: BAJA SRT4 100cc gasoline twin cylinder 2-stroke 1/4 scale

Awesome man
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Old 01-18-2012, 12:29 PM
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Default RE: BAJA SRT4 100cc gasoline twin cylinder 2-stroke 1/4 scale

Thank you.

The parts are not Smartech/Nutech. But if they break easily then I already have a solution for that.
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Old 01-18-2012, 02:52 PM
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Default RE: BAJA SRT4 100cc gasoline twin cylinder 2-stroke 1/4 scale

Escort mk1? You must be God!! Oh, Lars want!
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Old 01-18-2012, 03:30 PM
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Default RE: BAJA SRT4 100cc gasoline twin cylinder 2-stroke 1/4 scale

My good friend makes these bodies, not me. We have sold these bodies worldwide. For instance there is already one in Norway also

Currently the mold is under some detail updates and we are out of stock. Once the mold is updated we will continue with next batch of bodies.
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Old 01-18-2012, 04:06 PM
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Default RE: BAJA SRT4 100cc gasoline twin cylinder 2-stroke 1/4 scale

Are these meant to fit the Baja's wheelbase and width? I think i have to wait a bit anyway to buy anything, money and space is a bit tight for now. And i even have to buy a whole new chassi aswell, hehe! I know of one that have made some very nice bodies for Opel Kadett and Escort mk1 and 2, he posted some pics on another forum. These are meant to fit FG wheelbase/width.
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Old 01-18-2012, 05:11 PM
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Default RE: BAJA SRT4 100cc gasoline twin cylinder 2-stroke 1/4 scale

This body is intendedto be used with a +30mm stretched Baja chassis but you can do it with a stock chassis too. That is what I did.But afterwards I got a stretched chassis and it looks better with that. My friend makes those too.

Here's the body on a stock chassis Baja 5b and with wheel extenders. All stock or near stock offset Baja 5b wheels fit.

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Old 01-18-2012, 05:24 PM
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Default RE: BAJA SRT4 100cc gasoline twin cylinder 2-stroke 1/4 scale

Awesome work Jari.
Looking forward to seeing this run.
Love the body too by the way.



Couldn't help but noticing that red V8 in the background...... what's going on there?




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Old 01-18-2012, 06:47 PM
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Default RE: BAJA SRT4 100cc gasoline twin cylinder 2-stroke 1/4 scale

That center diff assembly is the exact same as the nutech,same with the front and rear gear boxes,anyways cool project and we will see how she holds up.
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Old 01-19-2012, 12:20 AM
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Default RE: BAJA SRT4 100cc gasoline twin cylinder 2-stroke 1/4 scale

Whittron, they are not Nutech parts. Only Nutech parts are aluminum diff cases, shock plates and shocks. The similarity with Nutech is very clear.

Dirty, that V8 is a big block Mopar with a turbo and intercooler and 4-speed manual trans that I will install into my 1969 Dodge A-108 panel van once I get it back. My friend is painting it now. There was a lot of rust but luckily no more...
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Old 01-19-2012, 09:20 AM
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Default RE: BAJA SRT4 100cc gasoline twin cylinder 2-stroke 1/4 scale

totally awesome build...should be a beast,i like that motor and them pipes[8D]. i look forward to the vids of it running. can't see cooling being an issue when you're ice racing

i assume they are carson diffs,shocks etc that you used...carson are in fact made by smartech and are built to the old titan/hurricane C5 spec models that had a few upgrades from the regular titan...both used splined diff cups and fg style cases, so stronger than the nutech spring loaded set up(the C5 came with the alloy diff cage set up and were sealed i believe unlike the stock titan)...with the outer cnc cases they should stop these models achilles heel of diff box flex/ring &pinion stripping, only possible problem i see would be snapping dog bone pins or twisting them.
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Old 01-19-2012, 10:25 AM
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Default RE: BAJA SRT4 100cc gasoline twin cylinder 2-stroke 1/4 scale

Moo,

I'm glad you replied. I know that you had knowledge about these parts and you are absolutely right. I also think the dogbones are the weakest links. Well other than that these diffs only have 2 bevel gears per unit so that might be another thing. But the MCD aluminum limited slip diffs with either custom made dogbones or possibly Baja drive cups and reinforced dogbones should handle the problem. Or the new big Losi parts. There are a lot of options but first I want to see what the current parts are capable of.
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Old 01-19-2012, 10:33 AM
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Default RE: BAJA SRT4 100cc gasoline twin cylinder 2-stroke 1/4 scale

Cool build.... I want to see it run.....
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Old 01-19-2012, 11:43 AM
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Default RE: BAJA SRT4 100cc gasoline twin cylinder 2-stroke 1/4 scale


ORIGINAL: mooman007uk

totally awesome build...should be a beast,i like that motor and them pipes[8D]. i look forward to the vids of it running. can't see cooling being an issue when you're ice racing

i assume they are carson diffs,shocks etc that you used...carson are in fact made by smartech and are built to the old titan/hurricane C5 spec models that had a few upgrades from the regular titan...both used splined diff cups and fg style cases, so stronger than the nutech spring loaded set up(the C5 came with the alloy diff cage set up and were sealed i believe unlike the stock titan)...with the outer cnc cases they should stop these models achilles heel of diff box flex/ring &pinion stripping, only possible problem i see would be snapping dog bone pins or twisting them.
So i was right,they are smartech parts,i thought they looked idenitcal to the smartech/nutech parts.
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Old 01-19-2012, 12:34 PM
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Default RE: BAJA SRT4 100cc gasoline twin cylinder 2-stroke 1/4 scale

We don't have Smartech here so I don't know to the exact detail if they are the same parts. But Nutech parts are different on the inside. Not even one interchangeable part for instance in differentials. Totally different.
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Old 01-19-2012, 02:57 PM
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Default RE: BAJA SRT4 100cc gasoline twin cylinder 2-stroke 1/4 scale

Two project photos. First one is about grille cutouts to supply cleaner and cooler airstream to carburetor and cylinders. Second one is for show; bigger brushed aluminum exhaust tips



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Old 01-19-2012, 05:01 PM
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Default RE: BAJA SRT4 100cc gasoline twin cylinder 2-stroke 1/4 scale



First off, your gonna cook that engine with no cooling system. Secondly, that engine's max rpm is like what...8800?   I guess you don't want it to be fast.

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Old 01-19-2012, 11:38 PM
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Default RE: BAJA SRT4 100cc gasoline twin cylinder 2-stroke 1/4 scale

Johnny, please tell me how you know that? Are you ABSOLUTELY sure?

I think you are wrong. I don't see a problem with cooling when all the details are taken into account.

Yes, the STOCK engine rpm is around 8800 but this engine is not stock anymore. Ever heard about tuning? Tuning allows the engine to have more power over a wider band and with a tuned pipe you can extend the rpm band A LOT. Does the exhaust system look like it's a stock system for an aviation 2-stroke engine?

Secondly, the primary gears have been selected so that 10.000 rpms from the engine yield 60 mph speed for the car. That is only a starting point. And the torque coming from 100cc engine... well it's not lower that from a 23-30.5cc normal gas engines. Or 50 - 60cc engines.

Try to think outside the box and see the technical side. Not only catalogs or basic applications.
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