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-   -   Engine selection help (http://www.diygokarts.com/vb/showthread.php?t=42381)

Rhill 11-13-2019 05:05 PM

4 Attachment(s)
Heres a few

Kartorbust 11-13-2019 05:21 PM

Hmmm with that, I can see why the GX390 may be struggling with that. For reference a 4x2 utility John Deere Gator has between a 18.5 and 20hp gas engine and weighs probably close to what this does. However those have a stupid low gear ratio in a transaxle with in the case of older Gators a Comet 780 CVT. In your case you have what looks like a Comet 40 series CVT.

karl 11-13-2019 05:32 PM

Quote:

Originally Posted by Rhill (Post 536711)
Heres a few

That needs a sled engine or motorcycle/quad ect.

I mean buggy's that size usually have a 1600cc flat 4 hanging off the back.

Definitely underpowered, and the clutch not being able to align properly is affecting top end speed. Belt misaligned in high gear.

But man Im jealous, nice rig.

Randy H 11-13-2019 05:48 PM

4 Attachment(s)
A better clutch would help some, wider gear ratio. Gearing change and seriously modified GX390, you could have fun with it.

But that machine deserves some serious horsepower.

Rhill 11-13-2019 06:47 PM

So would I be better off trying to modify what I already have or try a whole new set up?

Kartorbust 11-13-2019 06:51 PM

You have room for a lot of engine choices. Like already mentioned a 1.6L air cooled VW Bug engine with transaxle will boogie along just fine. Other options, I'd probably say a minimum of a 600cc motorcycle engine. A 2 stroke or 4 stroke sled engine in the 500cc range and up. If you are wanting to stay industrial engine types I'd look at larger single cylinder to the V-twins such as the GX688 Honda, Predator 670, Briggs 18hp V-twin.

If you want to keep what you have, I'd suggest putting a jackshaft in and deepen your ratio. It looks like you are around the 6:1. With that size buggy, you want to be closer to the 9:1 or lower (10:1). You'll lose a lot of top end speed, but you'll gain acceleration and have the torque to move it around.

625cc Single cylinder engine https://vegascarts.com/collections/e...lf-cart-engine

The obligatory Predator 670 https://www.harborfreight.com/engine...epa-61614.html

627cc Vanguard V-Twin 21hp https://www.northerntool.com/shop/to...1674_200161674


Couple things, if you go down the 4 stroke snowmobile engine route, the Yamaha Phazer 500cc engine is hard to beat. 80hp out of the box, the engines are good to around 10,000 miles (need to verify for sure), they have around a 2:1 gearbox which will double the gear ratio for you and comes with electronic/mechanical reverse. It's a watercooled engine and the radiator to run with it would be one for a 4 cylinder Honda Civic. It has electronic fuel injection already on the engine.

Keep in mind the radiator needed for a motorcycle engine powered buggy is generally a Honda Civic one. They are cheap to get a hold of and give plenty of cooling. You are using an engine that's moving something that weighs more than a sled or motorcycle and it needs to be kept cool. 4 stroke engines are not cheap to rebuild in most cases.

One thing I've noticed with people who have used motorcycle engines is that they do not gear it low enough, or shift the engine in their power range.

Buggy build with a Phazer sled engine. http://www.minibuggy.net/forum/proje...ghlight=Phazer

itsid 11-13-2019 09:10 PM

Quote:

Originally Posted by Rhill (Post 536692)
Ok so it has a torque converter and the sprockets the small one has 8 points the back has 62 and it has 12 inch tires

12" you sure?

with that info it'll move the heavy beast just fine..
not fast.. but fine
in fact it'd do so with way more than 2000 lbs !!

KartInfo by kartcalc.net:
Code:


KART
RW diameter: 12 in | 30.48 cm
Total weight: 2204.62 lbs | 1000 kg
ENGINE
Original HP: 13
Asummed HP: ~13
Torque: 18.97 ft lbf | 25.71 Nm
RPM: 3600
TRANSMISSION
Final ratio: 7.75:1
TC type:   series 40
Lowest ratio: 18.83:1
Highest ratio: 7.75:1
PERFORMANCE
Max Wheel Torque: 357.07 ft lbf | 484.12 Nm
Min Wheel Torque: 146.96 ft lbf | 199.25 Nm
Acceleration: 6.33 ft/s | 1.93 m/s
Top Speed: 16.58 mph | 26.69 km/h

So excuse me, but I think you mistook wheel diameter for rim diameter ;)
those look like 22" on 12" rims to me
[EDIT]
shoot 12" rim bearclaws are 25" in diameter...
let's fix that...

and with that gear ratio is off :D

you'll need more teeth on the axle...
KartInfo by kartcalc.net:
Code:


KART
RW diameter: 63.5 cm | 25 in
Total weight: 450 kg | 992.08 lbs
ENGINE
Original HP: 13
Asummed HP: ~13
Torque: 25.71 Nm | 18.97 ft lbf
RPM: 3600
TRANSMISSION
Final ratio: 9.5:1
TC type:   series 40
Lowest ratio: 23.09:1
Highest ratio: 9.5:1
PERFORMANCE
Max Wheel Torque: 593.64 Nm | 437.85 ft lbf
Min Wheel Torque: 244.25 Nm | 180.15 ft lbf
Acceleration: 2.52 m/s | 8.27 ft/s
Top Speed: 45.36 km/h | 28.18 mph
PROBLEMS
You might burn your clutch/belt!
Gear ratio too high!
Suggested final ratio: at least 9.7:1

something like 77-80 teeth should work fine on the axle if you keep the 8T TC sprocket

if you want to keep the ratio fixed..
you need a 21hp engine to move the 992 total weight I assumed above.
the more the better ;)

'sid

Rhill 11-14-2019 06:46 AM

I prolly did read the tires wrong. And it does move it pretty good as long as I’m not on a incline idc so much about going fast as I do being able to pull myself up the hills or through a little bit of mud. So should I just do more teeth on the rear sprocket or change both front and rear

JTSpeedDemon 11-14-2019 07:37 AM

I'd try more teeth on the axle sprocket. With those massive tires, I don't think you'll have clearance issues.
Try playing with the gearing before you commit to a huge engine swap. Those can get complicated REAL fast.

itsid 11-14-2019 10:33 AM

I don't like miniscule sprockets
(10T is the minimum in my book.. less and you must run into lifetime issues rather quickly)
especially when it comes to bigger loads (high weight and/or high power engine)

an 8T sprocket wears 20% faster than a 10T sprocket.. thus wears out the chain earlier and in turn the driven sprocket...

You need 9.7:1 (9.68 I think it was),
I'd pick 10->22 and 10->44 for the sprockets (4.4 *2.2 = 9.68)
[EDIT]
Oh right sorry... no additional jackshaft :oops:
well then 10->97 I'm afraid
or 8->78 (still not a fan of the 8T sprocket!)

'sid

Rhill 11-14-2019 11:24 AM

Quote:

Originally Posted by itsid (Post 536763)
I don't like miniscule sprockets
(10T is the minimum in my book.. less and you must run into lifetime issues rather quickly)
especially when it comes to bigger loads (high weight and/or high power engine)

an 8T sprocket wears 20% faster than a 10T sprocket.. thus wears out the chain earlier and in turn the driven sprocket...

You need 9.7:1 (9.68 I think it was),
I'd pick 10->22 and 10->44 for the sprockets (4.4 *2.2 = 9.68)
[EDIT]
Oh right sorry... no additional jackshaft :oops:
well then 10->97 I'm afraid
or 8->78 (still not a fan of the 8T sprocket!)

'sid

So if I get a front sprocket that has 10 teeth how many does the back one need to have for me to get as much pull I can out of it

Kartorbust 11-14-2019 11:32 AM

Quote:

Originally Posted by Rhill (Post 536766)
So if I get a front sprocket that has 10 teeth how many does the back one need to have for me to get as much pull I can out of it

97 teeth on the axle. That's a huge sprocket, 15.732" outside diameter.

Randy H 11-14-2019 07:26 PM

2 Attachment(s)
I think your going to want to boost your engine power, even a so called stage 1 kit would help. Like this.

http://www.nrracing.com/category-s/2156.htm

Depending on the model you have (UT1 or UT2) governor removal won't do much. UT2 have a rev limiter built in. NR does sell a non rev limited coil.

IMO a modified big block needs a better torque converter than a 40 series, especially with the funky back plate style.

With those tires and the weight of the machine you, as mentioned, have to make some gearing changes. Likely another jackshaft will be needed. Even with a better unit like a 780.

It's a financial decision, upgrades here aren't cheap. But on a buggy that size if you can afford it, I think it would be a good plan. Depending on engine upgrades or replacement, it might necessary.

Here's some info that might help.

Kartorbust 11-14-2019 08:03 PM

Quote:

Originally Posted by Randy H (Post 536789)
I think your going to want to boost your engine power, even a so called stage 1 kit would help. Like this.



http://www.nrracing.com/category-s/2156.htm



Depending on the model you have (UT1 or UT2) governor removal won't do much. UT2 have a rev limiter built in. NR does sell a non rev limited coil.



IMO a modified big block needs a better torque converter than a 40 series, especially with the funky back plate style.



With those tires and the weight of the machine you, as mentioned, have to make some gearing changes. Likely another jackshaft will be needed. Even with a better unit like a 780.



It's a financial decision, upgrades here aren't cheap. But on a buggy that size if you can afford it, I think it would be a good plan. Depending on engine upgrades or replacement, it might necessary.



Here's some info that might help.

Fortunately the UT2 can be swapped for a UT1 and it should just be a CDI change, correct me if I'm wrong, but that is what I believe NRracing states as does ARC. Not to hijack, but thanks for the 780 specs sheet, been looking for that for the last couple weeks, you just saved me a ton of time.

Also I do agree, another jackshaft will be way better in the long run to get the gear ratio you need. It appears that the swingarm has plenty of room for one and all you would really need are 2 extra sprockets (input from the CVT sprocket) and the output sprocket, then a second chain, and two pillow block bearings.

Randy H 11-14-2019 08:41 PM

1 Attachment(s)
^
I believe the keyway is in a different location, so maybe the flywheel can used, without a key. Timed correctly.

I like the idea of having timing advance with the UT2. If I get a chance I'll take a look this weekend. Supposed to be a balmy 40 in west Michigan. I'll do a coil swap and see if it has sparkage.

http://www.nrracing.com/product-p/30500-z5k-801.htm


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