Gear Ratio Pickle on EZGO Conversion

[Danger Nooney]

I am looking for some assistance in figuring out my gearing on my EZGO electric to gas conversion. I finally got it running and staying together, but I top out at 21 mph regardless of uphill or down. Plenty of low end.l, but the gearing is holding me back. I will start at the diff and work my way forward. It’s a stock electric rear end that I swapped 8:1 gears into. It is run off a shaft with a 10 tooth sprocket with a really short 50 chain. That runs to a sprocket on my blast LED FNR gear box which has a 12 tooth sprocket on the same shaft as the driven pulley on my 40 series TAV. Driver pulley is on a HF 459cc motor, ungoverned. It climbs hills like a Billy goat, but I want more speed. I have little to no room for a larger sprocket on the gear box due to the proximity of the output shaft. It also has a weird splined shaft with a locking collar that I can’t seem to find a larger sprocket for. It looks like it’s from a motorcycle with a two bolt collar that holds it on the shaft. It doesn’t look like I can do a smaller sprocket than the 10 tooth on the diff shaft so I feel a little stuck. What ratio I am at now with the setup below. I know how to figure driver to driven but when you throw the FNR and the 8:1 diff in I am lost.

• Blast LED FNR gear box 12 tooth sprocket, forward ratio of 1:2
• Blackhorse Racing (comet clone) 40 series TAV with medium weights in the driver pulley for 2,200 rpm engagement
• 23” tires
• Stock electric EZGO ST 36v rear differential with ¾” jackshaft coupled to the rear end with a 10 tooth sprocket, spinning CCW and 8:1 gears

 

[BSR#2]

I am looking for some assistance in figuring out my gearing on my EZGO electric to gas conversion. I finally got it running and staying together, but I top out at 21 mph regardless of uphill or down. Plenty of low end.l, but the gearing is holding me back. I will start at the diff and work my way forward. It’s a stock electric rear end that I swapped 8:1 gears into. It is run off a shaft with a 10 tooth sprocket with a really short 50 chain. That runs to a sprocket on my blast LED FNR gear box which has a 12 tooth sprocket on the same shaft as the driven pulley on my 40 series TAV. Driver pulley is on a HF 459cc motor, ungoverned. It climbs hills like a Billy goat, but I want more speed. I have little to no room for a larger sprocket on the gear box due to the proximity of the output shaft. It also has a weird splined shaft with a locking collar that I can’t seem to find a larger sprocket for. It looks like it’s from a motorcycle with a two bolt collar that holds it on the shaft. It doesn’t look like I can do a smaller sprocket than the 10 tooth on the diff shaft so I feel a little stuck. What ratio I am at now with the setup below. I know how to figure driver to driven but when you throw the FNR and the 8:1 diff in I am lost.

• Blast LED FNR gear box 12 tooth sprocket, forward ratio of 1:2
• Blackhorse Racing (comet clone) 40 series TAV with medium weights in the driver pulley for 2,200 rpm engagement
• 23” tires
• Stock electric EZGO ST 36v rear differential with ¾” jackshaft coupled to the rear end with a 10 tooth sprocket, spinning CCW and 8:1 gears

That's a fast way to learn those torquey big blocks dont need a bunch of gear.

You are in a pickle.
Thats 4 gear reductions. And no room to change sprockets.

that fnr box MIGHT be 2:1 forward and 2.6:1 reverse. Maybe worded wrong on website.

You gotta tach on there??? I know it has nothing to do with the over geared problem, just wondering what kinda rpm it was turning w/o governor.

40-SERIES-GO-KART-FORWARD-REVERSE-GEAR-BOX

40 Series GO KART FORWARD REVERSE GEAR BOX, GO KART FORWARD NEUTRAL REVERSE GEAR BOX Replaces COMET PART.

blastled.com

 

[Denny]

With that heavy bugger I would call it good. Right now you will get good belt life. If you go higher kiss that goodbye and forget climbing hills. Not to mention sketchy steering and handling.

 

[Danger Nooney]

I have a tach and it can easily get to 4,500 rpm’s which I know is dicey. The engine braking going down hills feels like I am about to tear something up as well. I wish I had gotten 6:1 gears but I bought the 8:1’s used for cheap on eBay. This thing needs overdrive, haha

When I started this project I looked for a gas cart rear end with reverse built in but couldn’t find one. Maybe I should start looking again.

 

[Danger Nooney]

What is my current ratio after all the reductions?

 

[BSR#2]

I have a tach and it can easily get to 4,500 rpm’s which I know is dicey. The engine braking going down hills feels like I am about to tear something up as well. I wish I had gotten 6:1 gears but I bought the 8:1’s used for cheap on eBay. This thing needs overdrive, haha

When I started this project I looked for a gas cart rear end with reverse built in but couldn’t find one. Maybe I should start looking again.

4500 rpm is about all I'm seeing big blocks around here get up to. They got that big power coming in at 2500-4000. Most are running 4-8:1 rear gear, depends on 1 or 2 seater, gear boxes and tire height. They got that big hill climbing, low rpm thumping power and still run 40+ mph on the flat level, hard pack surfaces.

What is my current ratio after all the reductions?

As far as I can tell, with your info and that fnr at 2:1 forward, it should be close to this. I'm not familiar with the 40 series ratios, so I subed the 30 series with a 7" driven. 3.15:1 low, and 1.12:1 high.

42:1 on the low side of the t/c

14:1 on the high side, final drive.

That's comes out to around 20-21 mph with 23" tires, at 4500 rpm.

That 12t to 10t is an overdrive, .83:1, but thats just not enough. You would need another .5:1 overdrive somewhere. That's another jackshaft, 2 more sprockets 20t to a 10t, and a small chain. I'm sure you are limited to space now.

Even with a 6:1 diff gear, would only drop to 11:1 on the high side, at around 27 mph. That small gain is probly not worth the cost.

A live axle kit, but thats probably gonna need different wheels, brake set up, brackets, braces for suspension, . . again more cost.

You are in a tough spot.

 

[Danger Nooney]

Thanks for your advice. Based on your calculations, it doesn't sound like I would be happy with the 6:1 conversion. The 8:1's gave me a lot of trouble on install since I had to find a press. I have considered a live axle. I like the simplicity of them and having no differential to contend with. I don't think it would be that hard to fab some perches for bearings on my current leaf spring attachments. Not sure what I would do about the brakes. My brakes suck anyway so maybe I could just run the single caliper on the shaft. I don't know if that would be enough to stop a 4 seater cart. I am working through a lot of bugs right now trying to get existing parts to work so that might be my best option.

How are the gas golf cart rear ends geared? Like an ME29 or a fuji for instance. I would think they would be geared higher than electric rear ends to keep the RPM's down. Never seen one in person.

 

[BSR#2]

Thanks for your advice. Based on your calculations, it doesn't sound like I would be happy with the 6:1 conversion. The 8:1's gave me a lot of trouble on install since I had to find a press. I have considered a live axle. I like the simplicity of them and having no differential to contend with. I don't think it would be that hard to fab some perches for bearings on my current leaf spring attachments. Not sure what I would do about the brakes. My brakes suck anyway so maybe I could just run the single caliper on the shaft. I don't know if that would be enough to stop a 4 seater cart. I am working through a lot of bugs right now trying to get existing parts to work so that might be my best option.

How are the gas golf cart rear ends geared? Like an ME29 or a fuji for instance. I would think they would be geared higher than electric rear ends to keep the RPM's down. Never seen one in person.

Gas golf carts are really low geared. I haven't worked on many. Some had the governor in the transmission, that was definitely new to me, and some had governor in the engine. They all have really big t/c drivers, drivens and belts. Like you see on Polaris, or snowmobiles.

I'd say they are around a 12:1 diff gear, not counting the t/c ratio.

They are not as low geared as yours, but kinda same situation. Seems like any more then 3000 rpm, there was no more mph. They go up hill just as fast as they go down hill.

Red beard on you tube does some really good work with different rear end set ups, different gear boxes, cv axle boxes, irs, trailing arms, a bunch of different stuff. Check em out, you might see a better set up for you with what you have.

 

[Danger Nooney]

I am very familiar with Red Beard, haha. I use his videos quite a bit

 

[BSR#2]

He just lives in the next town from me. Never met him, seems like a nice enough fella.

 

[Danger Nooney]

Would I gain anything by going to a larger diameter TC, like one from a Polaris? I have room for larger pulleys

 

[BSR#2]

Would I gain anything by going to a larger diameter TC, like one from a Polaris? I have room for larger pulleys

I doubt it. The larger diameter driven will be more low geared.

A smaller driven and /or larger driver would drop gear ratio for you. But I wouldn't even know where to start looking for that.

 

[Danger Nooney]

I might be able to squeeze a 13 or 14 tooth on the driver and possibly a 9 tooth on the driven. This is a picture of my gearbox I pulled off the internet.

 

[BSR#2]

I might be able to squeeze a 13 or 14 tooth on the driver and possibly a 9 tooth on the driven. This is a picture of my gearbox I pulled off the internet.

That's definitely worth a try. If that jackshaft is 3/4", I think a 10t is the smallest.

5/8" jackshafts can go to a 8t. But thats a lot of power being applied to a 5/8" shaft. But, I would try it anyway, .
It wouldn't be the 1st time I broke something. And thats how we learn.

 

[Danger Nooney]

Let’s say I ditch the EZGO rear end and go with a live axle and I keep the 12 tooth on the gear box. What would be a good starting point sprocket for a live axle?

I have seen some of these gear reduction boxes that bolt to the motor. Any way to reverse one of those to get the opposite effect?

 

[BrownStainRacing]

Let’s say I ditch the EZGO rear end and go with a live axle and I keep the 12 tooth on the gear box. What would be a good starting point sprocket for a live axle?

I have seen some of these gear reduction boxes that bolt to the motor. Any way to reverse one of those to get the opposite effect?

If you could keep the jackshaft set up you have now, it would be so much easier to dial in the correct gear ratio for the weight.

Pick a axle sprocket that would give you plenty of ground clearance and change the jackshaft sprockets for the gear change. It would be cheaper buying jaskshaft sprockets then axle sprockets.

I've never had to take apart a bolt on gear box. It may take a different crank??????

 

[Danger Nooney]

BrownStainRacing,
Thanks for your reply. I don’t understand how I could keep my current jackshaft setup with a live axle since the support is welded to the axle tube. I will have to get rid of that unless you have something in mind. I have attached a better picture. I am also wondering if I can attach my current cradle to a live axle. I am depending on the axle housing for a lot of attachment points

 

[BrownStainRacing]

BrownStainRacing,
Thanks for your reply. I don’t understand how I could keep my current jackshaft setup with a live axle since the support is welded to the axle tube. I will have to get rid of that unless you have something in mind. I have attached a better picture. I am also wondering if I can attach my current cradle to a live axle. I am depending on the axle housing for a lot of attachment points

I didn't know if you was gonna fab something different up with swing arm, and different brackets or which way you was going, .

A 60t/12t with t/c in high, is only gonna be around a 5.6:1. I don't know if that'll be enough to pull 23" tires and 4 people.

If you could change that gear box sprocket
60t/10t = 6.72:1
60t/9t = 7.46:1 , if a 9t is made to fit that output shaft.

A 72t for a #40 chain is a big sprocket, those 23" tires will help with ground clearance.

 

[Denny]

You’re moving 1200 lbs gross weight with 23” tall tires. In my opinion right now you say it pulls hills good with all that weight. Why mess with perfection? Anything you do to make it faster is just going to make it eat belts, ride worse and be less reliable. Just curious on what you’re trying to accomplish and what your goals are for the machine?

 

[Danger Nooney]

I guess my goal would be to top 25 mph and have it not feel like it is revved to the moon. 25 mph at 3,500 rpm would be nice. To not have such harsh engine braking going downhill would be nice as well.

If everything stayed the same and I went to 28” tall tires, how fast could I go?