4 stroke

Not your average Savage Hop ups. These are highly modified, with some home-made parts.

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Roost
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4 stroke

Post by Roost » Sun Apr 06, 2014 9:30 am

here's what i got going on
after converting to bl then getting bored of that I sold off the motor and controller. that was a while ago and now i'm missing my savage, So I realized i have almost enough parts laying around i might be able to come up with something

might be a little under powered being a fs40, its just what i had laying around


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Post by Roost » Sun Apr 06, 2014 9:32 pm

I liked Sharkey's starter setup

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Sharkey_t
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Post by Sharkey_t » Mon Apr 07, 2014 12:37 am

looks good. hard to say how the saito will react to car use. the my os fs40 car 4 strokes will rev to 26000rpm, however thats due to the stiff valve springs and camshaft profile, generally an airplane 4 stroke wont rev nearly that high.

i honestly dont have cooling issues on my 4 strokes. once i got the tuning down they seem to run around 260*f, however thats in an onroad car.

if you want to make power with the 4 stroke, the 2 biggest things would be the carb and exhaust. i run traxxas 3.3 carbs on mine. the 6.5mm bore works well, big block carbs tend to be too big, a typical smallblock carb (12-15) works, however i found the 3.3 carb to be the sweet spot for me. you need some freeflowing exhaust, i bend my own using 5/16" brake tubing (or you can use aluminum tubing) and use a much larger muffler than specified for the motor. a 120 sized muffler is typical for 4 strokes in cars.

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Post by Roost » Mon Apr 07, 2014 9:06 am

Some good advice

It wont be winning any speed records thats for sure but if i like the whole 4 stroke thing ill put a fs40s-c cam and springs in a fs52 along with the mods you mentioned, then i might have something

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Post by Roost » Sat Apr 12, 2014 2:32 pm

how she sits now

nothing really is fastened down, still lots of work to do


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Post by johny723 » Sun Apr 13, 2014 4:49 pm

the motor will not have the torque to move the MT tires, but it could be interesting to see how it performs out of a " MT class "
I mean putting smaller wheels( = lighter) and lower shock towers ( hellfire shocktowers). Making it kinda "rally" or even "onroad".
just a suggestion!
Otherwise a cool project!
BTW, the badlands in the first picture are MT size and some buggy size in the last one right?

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Post by Roost » Tue Apr 15, 2014 6:08 pm

thats my thoughts on the tires exactly, plus i really just wanted to see how it will handle with buggy tires. the servo should have to work less against gyroscopic force making it more responsive? should be interesting

correct mt tires in the first pics buggy in the lower

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Post by Sharkey_t » Tue Apr 15, 2014 8:55 pm

its actually quite the opposite, a 4 stroke will make far more low end torque, however they top out around 20,000rpm depending on the motor (ive had my fs40 car motors above 26000rpm). as a result you need to change the gearing to suit the narrower powerband, and most gear it to see the same top speeds as a 2 stroke, resulting in a loss of off the line power.

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Post by Roost » Sat Apr 26, 2014 12:23 pm

Just couldn't help myself

Magnum 52XL (with os valve cover :P) and OS 40s-c Cam and valve springs, should make for a high reving big bore! and also got a 40s-c intake manifold on its way. Going to break it in with a prop and tach.

what im excited about as to see what kind of rpm increase the cam and springs will offer

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Post by Roost » Sat Apr 26, 2014 2:02 pm

Hard to make out but you can notice the difference in duration, noticeably more duration on the "car" cam,

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Post by Roost » Sun May 04, 2014 6:47 pm

seeing how the 4 stroke is a little on the heavy side im trying to get it low as possible

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Last edited by Roost on Mon May 05, 2014 8:10 am, edited 1 time in total.

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Post by Sharkey_t » Mon May 05, 2014 12:36 am

its looking good. one thing though, i know its tempting to mount the carb facing down as its less likely to break off if you flip the truck, however it doesnt work very well. iirc it blocks half the port off, and our carbs dont really like pointing downhill. the airplane carb was designed to be an updraft, the car engine carbs arent designed like that.

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Post by Arafebut94 » Thu Aug 04, 2016 1:06 am

Nice Tom.. hope you build something super cool out of it..

body off.. ummm.. I fear you may uncover a tad more rust..

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