Multiple questions on Super Mario Kart Build

[Slinky]

Okay so I have taken on the task of using a jakks super Mario toddler ride on toy and converting it into a life-size asphalt go kart with a 140cc piranha 4-speed semi-auto electric start engine.

I am a machinist and a backyard mechanic so I have a decent amount of fabrication skills, but there are still many things that I am learning about go karts. Over the past few weeks I have got most of the frame together but I am continuing to learn every day to continue making progress, the following or the questions I have currently.

1. I am currently attempting to implement caster into my spindles to aid in Kart jacking and also implementing the Ackerman angle (trailing arms angled to meet over center or rear axle), from what I read I believe I want about 20* of caster toward the rear is this true?

2. My overall Kart dimensions are around 66" x 36" with around 48" front to rear axle spacing (32" wide axle with 11"x6" rear tire and 10.5"x4.5" front), do the front and rear wheel width spacing have to be the same? If not how much does it affect steering?

3. Does the pitman arm off of the steering shaft have to be at a 90* angle off of the shaft? And does the angle of the Pitman arms have to match the angle of the spindle trailing arms?

4. Does the angle of the steering shaft affect the steering? If so how greatly?

5. How does having a leading Link vs a trailing arm affect the steering?

6. Do I want there to be one hole in the pitman arm off of the steering shaft to attach both tie rods to? Or do I want them spaced on sort of a triangle bracket off of the steering shaft?

7. With my 11" rear tire size and the 140cc piranha with a 15T stock engine sprocket I am looking for a top speed of a round 50-55mph (kart will weigh around 300lbs total including rider/engine when done) but still have a decent amount of torque, what size sprocket combo or at least just axle sprocket will accomplish this?

8. With my current axle spacing of 48", axle width of 32" and 3.5" ground clearance on my maxxis slicks will my cart be somewhat stable on pavement above 50mph?

Thank you in advance for the answers to my questions.

 

[bob58o]

7.) Do you know what the ratio is for each gear?

 

[Slinky]

7.) Do you know what the ratio is for each gear?

From what I have read online I believe they are as follows..

First Gear: 3.272 (11/36)

Second Gear: 1.937(16/31)

Third Gear: 1.35(20/27)

Fourth Gear: 1.043(23/24)

 

[Slinky]

Bump for some help!

 

[bob58o]

Sorry.
I'm really not familiar with these engines.

If you gear so forth gear @ 7500 RPM is 50 mph that would need a 4.9 : 1 Total Gear Ratio and that would give you 57mph at 8500 rpm.
I'm trying to look and see if there are primary or secondary reductions in the gearbox.
And trying to find a torque/hp vs rpm curve for a 140cc. Guessing it will be similar to a 125cc?

The rest of the stuff I don't really know about.
I guess I don't really know about any of this. LOL

 

[OzFab]

1. No, you don't need that much; 10 is excessive...

2. A wider front axle will aid steering, a wider rear axle will hinder steering.

3a. The reason for the pitman arm being at 90* is so you can turn left & right the same amount; if the pitman arm was at 45* to the left (for example) that would limit the amount of travel. Now, if you mean "does it matter if it's 5* off?" No...

3b. Not if you want to implement Ackermann...

4. No

5. It doesn't, trailing arm simply makes it easier to implement Ackermann but, the tierods can get in the way of your feet...

6. That depends on how the steering arms on the spindles are set; a triangle pitman arm is used to add Ackermann...

7. Good luck with that... & that's all I'm saying on that...

8. There's much more to it than that, a lot to consider...

 

[Slinky]

Sorry.
I'm really not familiar with these engines.

If you gear so forth gear @ 7500 RPM is 50 mph that would need a 4.9 : 1 Total Gear Ratio and that would give you 57mph at 8500 rpm.
I'm trying to look and see if there are primary or secondary reductions in the gearbox.
And trying to find a torque/hp vs rpm curve for a 140cc. Guessing it will be similar to a 125cc?

The rest of the stuff I don't really know about.
I guess I don't really know about any of this. LOL

I agree there is not much info on these engines out there (due to being Chinese imports).
What I know is that the piranha 140cc is basically the same as the YX140, and it's also very similar to the Lifan 140cc and somewhat similar to the common Lifan 125cc.

From what I could find it's power and TQ output is around 10-11hp@7500 rpm and makes around 8-9lbft of TQ.

I am skeptical to buy/try random sprocket sizes due to having to spend the money multiple times on sprockets and chain modifications. I was thinking between a 42T to a 46T would be what I would want to achieve 50MPH, but I have no idea what primary or secondary reductions the transmission has..

 

[bob58o]

I'd guess something like a 24T would be your best bet if the engine has the power to get you there....

I hope somebody else jumps in. Like I said, I'm not familiar with these engines.

Most 140cc engines I found info for had a 3.7:1 Primary Reduction. And 4th gear was around 1:1

So if you have 3.7:1 in fourth gear and enough power to push the 300lbs to 50mph at 9000 RPM, the numbers tell me a 24T sprocket, but that doesn't seem right.

24:15 = 1.6:1
So 4th Gear would be 5.92:1 (3.7 x 1.6)

11" Tires have a 2.88' Radius

9000 RPM
2.88' per Axle Revolution
5.92:1 Gear Ratio
60 minutes per hour
5280 ft / mile

(9000/5.92*2.88*60)/5280 = 49.5 MPH

So if the engine has the power to push you to 9000 RPM in 4th Gear, then a 24T sprocket (with the 15T) seems to get you to ~50mph.

But that doesn't really seem right to me. I dunno?
Hope somebody else jumps in. Maybe somebody with more experience with these types of engines.

 

[Slinky]

1. No, you don't need that much; 10 is excessive...

2. A wider front axle will aid steering, a wider rear axle will hinder steering.

3a. The reason for the pitman arm being at 90* is so you can turn left & right the same amount; if the pitman arm was at 45* to the left (for example) that would limit the amount of travel. Now, if you mean "does it matter if it's 5* off?" No...

3b. Not if you want to implement Ackermann...

4. No

5. It doesn't, trailing arm simply makes it easier to implement Ackermann but, the tierods can get in the way of your feet...

6. That depends on how the steering arms on the spindles are set; a triangle pitman arm is used to add Ackermann...

7. Good luck with that... & that's all I'm saying on that...

8. There's much more to it than that, a lot to consider...

Thank you for the info.

3. The main question I have after those answers is if I build the ackerman angle into the tire spindles, do I just just basically align or pretty much stack the interview tie rod holes over the center of the steering wheel?
And does the height of where the inner tie rods meet the steering shaft have to match the height of the spindles?

7. And as for the speed and gearing, theoretically on a closed course with all safety precautions in place what would be the appropriate axle sprocket tooth count to attain the theoretical 50mph speed?
(is the post above this by bob58o correct)

 

[ezcome-ezgo]

Bob's math is principally correct. There is virtue in GAB.

 

[Slinky]

Bob's math is principally correct. There is virtue in GAB.

What exactly does that mean "Virtue in GAB"

 

[bob58o]

What exactly does that mean "Virtue in GAB"

Not sure, but it sure is flattering.
Think it means math is math.

---------- Post added at 01:23 PM ---------- Previous post was at 01:19 PM ----------

If you were to try a 46T:15T and it does have a 3.72 primary, then 4th gear is around 11.3:1 overall ratio.

With 11" Tires, 9000 RPM in 4th would be 26mph.

 

[ezcome-ezgo]

GAB is "going all Bob", a term coined here largely because we are blessed with a member named Bob58o who has a propensity to analyze virtually anything down to a molecular level.

 

[bob58o]

BTW did you buy this book? LOL
https://www.amazon.com/How-Build-Go-Kart-Beginner-ebook/dp/B0078Q2JNA
You can get hit with the blue shell and still stay in first place...to avoid getting hit with green shells..."
I am pretty sure that is a mario cart reference, which is fine in a book about playing a video game, but this book isnt advertised as a video game guide.

 

[Slinky]

Haha that's funny.
Thanks guys, turns out my engine has a 14t sprocket on it, I'm going to give a 25t axle sprocket a try when I get it running.

 

[Slinky]

My next question which is somewhat controversial from what I've seen in some threads is do I need an oil cooler?
Pretty much every company that sells the YX/Lifan engines recommend them above 125CC, but I would too if I was trying to sell more product. I have read tons of mixed reviews saying that will coolers are not necessary/are necessary to keep your engine from overheating at high RPMs during long periods of time.
I see many people also saying that with an oil cooler A lot of the time you don't have enough pump pressure in the engine to circulate the oil and you can damage the engine and/or the oil becomes too cold running through the cooler and does not become hot enough to boil off enough of the moisture and causes your engine oil to become acidic and do more harm than good.
But I also saw a lot of people using thermostatic fluid control valves inline to basically bypass the cooler until the oil is at a certain temperature in which the valve allows the oil to then flow through the cooler.
Everyone's thoughts?

 

[Ebrownie]

I would say you are fine. At some point it becomes too complex for a go kart. Karts are meant to be simple and fun, and worrying about your oil running too cool all the time or wiring in a thermostat doesn't seem worth it. Just put it on and ride it till it doesn't go anymore.

 

[OzFab]

if I build the ackerman angle into the tire spindles, do I just just basically align or pretty much stack the tie rod holes over the center of the steering wheel?

Correct.

However, if you have forward facing steering arms, building Ackermann into them can prove difficult as the arms may interfere with the tyres; with forward facing arms, it's best to build the Ackermann into the pitman arm...

And does the height of where the inner tie rods meet the steering shaft have to match the height of the spindles?

For best results, the tierods should run as parallel (on both axes) to the front axle as possible...

 

[Slinky]

I would say you are fine. At some point it becomes too complex for a go kart. Karts are meant to be simple and fun, and worrying about your oil running too cool all the time or wiring in a thermostat doesn't seem worth it. Just put it on and ride it till it doesn't go anymore.

But what if they oil cooler helps me mentally relax and enjoy the kart more?
Haha
The extra cost/effort is worth it to me if it will prolonged the life of the engine, that's why I was asking, I tend to try to make things bulletproof.

 

[Slinky]

I will be welding up the steering today, just to be 100% clear I want around 10* of KPI (king pin inclination) and around 5- 10* positive caster, and around 0* of camber, while implementing ackerman angle for proper steering with my live axle?
And also while having these angles end up with my actual wheel stud at 0* camber + 0* toe?

I should be able to draw a straight line through the kingpin, and that line should extend to the center of the tire's contact patch correct?