Build planning

[Angelk]

Hi all, its probably about time I joined. I have spent way too many hours reading forums on here over the years. I just purchased a mini sprint chassis for 50 bucks that I have intentions of making a kart out of.
I would like this cart to be able to do 50mph with ease. So that leads me to my drive train dilemma. The two engines I am looking at are either the predator 212(6.5 hp) or 420(13hp). I will be using a torque converter, probably a comet 40 series or similar knockoff. From what I have read I should probably use number 40 chain as well. So that means I am stuck with a 10t sprocket coming off of the converter. Because I have yet to see a converter that comes with a #40 chain 12 tooth sprocket. I am thinking of using a sprocket with 50 teeth on the axle(it is a solid axle). Assuming 18 inch tires this should get me to around a top speed of around 60 once I get that pesky governor out of the engine. So with all this in mind, my question is will the 212 engine with basic upgrades(exhaust, intake, jetted carb) have enough power/torque to get me going pretty quickly without risk of damaging parts? Or should I go with the beefy 420 with the same upgrades? The chassis is more or less complete and will weigh probably 200lbs without the engine. Also if any of you have better suggestions for gear ratios or anything else that achieves the same goal let me know.
Thanks

 

[bob58o]

Because you mentioned 60mph and 50mph with ease...

Use the 420cc, No Gov, 40 Series TC, 18" Tires, 11T on JS, 48T on Rear, #420 Chain.
Should give you 60mph at 5000 RPM, 44mph at 3600 RPM

 

[OzFab]

... But, using the above setup, the question is will it move at all?

High top speed or quick acceleration: pick ONE; it's a trade off...

If you want a high top speed, you'll have lousy acceleration (or none at all); if you want good acceleration, you'll end up with a lower top speed...

 

[bob58o]

... But, using the above setup, the question is will it move at all?

It'll be fine.
I was trying to be concise and not bore people with math they won't follow.
But since you asked. LOL
Remember it's a big block. Double the Torque vs a 6.5HP. Plus 40 series TC (Double the Torque of a CC).
So basically 4X the Torque compared to a 6.5HP engine with CC.

40 series TC is 2.43 : 1 in Low Gear.
With 48T : 11T (4.4 : 1 Sprocket Ratio)
That makes 10.6 : 1 Final Drive Ratio (Lowest Gear Ratio)
18.4 Lb-Ft Torque

18.4 Lb-Ft x 10.6 Gear Ratio = 195 Lb-Ft
20% loss from the belt drive set up
156 Lb-Ft at the axle

~156 Lb-Ft / 0.75 Ft Tire Radius = 208 Force Lbs

Roughly 208 Force Lbs Pushing the kart at TC engagement.

We know similar kart sized kart with 12" Tires, using a CC and 6.5 HP engine will move with 6:1 Gear Ratio.
8.1 Lb-Ft * 6:1 Gear Ratio = 48 Lb-Ft
48.6 Lb-Ft / 0.50 Ft Tire Radius = 97.2 Force Lbs

Roughly 97 Force Lbs Pushing the kart at CC engagement

If a 6.5HP engine with CC can move a kart with 97 Force Pounds at clutch engagement,
Then surely a 13HP engine with TC can move the kart with 208 Force Pounds at TC engagement.

The engine and gearing I suggested would be similar to take off if using a 6.5HP engine, a CC, and 19:1 Gear Ratio. No doubt it should move, no problem.

 

[Angelk]

Ok so being a freshman in mechanical engineering I like the math. So if it has roughly 208 force pounds how much acceleration does that equate too? Or I guess I am asking how do I visualize a force pound? I know weight has to be factored in so the kart will probably weigh about 375 without a driver so 550lbs with me in it.

 

[bob58o]

Come on, a ME student surely knows F=ma
Convert Force Pound to Newtons.

208 lbs = 925 Newtons

925 Newtons = (mass in kg)*(acceleration in m/s^2)

550 lbs = 250 kg

925 = 250*acceleration
a = 3.7 m/s^s

~0.38 g's

 

[Nosandwich]

Come on, a ME student surely knows F=ma
Convert Force Pound to Newtons.

208 lbs = 925 Newtons

925 Newtons = (mass in kg)*(acceleration in m/s^2)

550 lbs = 250 kg

925 = 250*acceleration
a = 3.7 m/s^s

~0.38 g's

IDK...doesn't seem like he understands paragraphs?

 

[Angelk]

Hey, cut me some slack, my brain is fried from finals! Thanks though

 

[Nosandwich]

Let us know how you do...( you must maintain a certain GPA to be a member here.)

 

[ezcome-ezgo]

I was a freshman in ME once, and I didn't know a newton meter from a fig newton.

 

[Nosandwich]

I was a freshman in ME once, and I didn't know a newton meter from a fig newton.

FYI: A Newton yard is equivalent to 1.0936 of a Newton meter, and a fig Newton tastes better.

 

[bob58o]

Well they don’t use the imperial system to teach Science, so I find that hard to believe. Unless you were dunking those Fig Newtons in your Irish coffee.
Everybody who took Physics in HS has done a problem like,

“Ignoring Friction, what is the magnitude of acceleration when a 10 Newton Force acts on a 10 kg box?”

 

[ezcome-ezgo]

My brain as a freshman:

 

[Nosandwich]

Well they don’t use the imperial system to teach Science, so I find that hard to believe. Unless you were dunking those Fig Newtons in your Irish coffee.
Everybody who took Physics in HS has done a problem like,

“Ignoring Friction, what is the magnitude of acceleration when a 10 Newton Force acts on a 10 kg box?”

Well, if it's ex Dallas Cowboy Nate Newton, and it's 10 kg of fig Newtons, the answer is PDQ!

Sorry Angelk, you see how we roll, (easily distracted)....oh LOOK!!!! A squirrel!

 

[bob58o]

My brain as a freshman:

That is what college is for. Experimentation.

 

[Nosandwich]

That is what college is for. Experimentation.

Must be why I skipped College...after High School, I was already an expert!

....did I saw "High" school out loud?