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 Dune buggy build 
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Second post on here! 2 summers ago I started this build, and my goal is to finish by mid-winter. Life got a little busy, but ill get her done:

Initial plan was essentially to build a mini dune buggy. I bought Go Kart plans, began to understand the basic components, then skewed off the plans. Im a really big guy (6-8" 340) so I just dont fit things well. But I can MAKE things fit me well. This definitely influenced my build.

Specs:
-6 wheels. Essentially they are the largest size 3-wheeler wheels I could find. High surface area, and lots of float.
-2 axles in the back (maybe), both will have a mini differential pulled from a Miata if so. Both rear axles will have power. I currently debating just running 1 axle.
-Predator 670cc 4-stroke V-twin engine
-Comet 780 CV transmission w/comet driven.
-Ill run a jackshaft that will split the power between the two rear axles.
-chain and sprocket driven after the CVT.
-Suspension is 4 shocks and A-arms up front. Rear will essentially be one big swingarm that has 2 or 4 shocks.
- I have a set of skis for the front
-If I get this done fast enough, ill make snow tracks for the rear.
-I'll likely mount a third seat in the rear, just like a "gunner" seat on the Chenworth military buggy.
-Im planning on doing a tow bar up front, that way I can just disconnect the chain off the CVT to essentially put it in neutral and tow it where I need to go.
-Winch up front because all the cool kids have them.
-Im considering mounting an adjustable rifle rest for the roof or passenger for long dustance shooting in the rural environment. Beats laying down on the hot ground.


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Last edited by TNThomas on Wed Nov 09, 2022 8:01 am, edited 2 times in total.



Thu Nov 03, 2022 10:36 pm
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keep up the good work and keep this post alive

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Thu Nov 03, 2022 10:50 pm
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Cool project. This brings back a lot of memories of working on SAE Mini Baja back in college; what you're doing is very similar.

Some constructive criticism though - you've got a fair amount of weight in that thing, and you'll need a LOT more motor than that Predator engine. The dual rear axles won't help; you won't have the power to even come close to spinning the tires, and if you've spent much time playing with off road vehicles you'll agree that wheel spin is an important part of maneuverability and fun factor too. Some sort of liquid cooled snowmobile engine making 50+ hp would work a lot better, and fortunately those are really easy to find around here. And, a lot of those are lighter than that Predator engine too.

Keep in mind that two rear axles will drastically increase your turning radius. Often with buggies like this that only have a single rear axle, the vehicle will tend to understeer (i.e. pushing the front tires when trying to turn); dual rear axles makes this a lot worse. If you go ahead with this design, I'd suggest moving as much weight forward as possible to get traction on the front wheels.


Thu Nov 03, 2022 11:19 pm
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Yondering wrote:
Cool project. This brings back a lot of memories of working on SAE Mini Baja back in college; what you're doing is very similar.

Some constructive criticism though - you've got a fair amount of weight in that thing, and you'll need a LOT more motor than that Predator engine. The dual rear axles won't help; you won't have the power to even come close to spinning the tires, and if you've spent much time playing with off road vehicles you'll agree that wheel spin is an important part of maneuverability and fun factor too. Some sort of liquid cooled snowmobile engine making 50+ hp would work a lot better, and fortunately those are really easy to find around here. And, a lot of those are lighter than that Predator engine too.

Keep in mind that two rear axles will drastically increase your turning radius. Often with buggies like this that only have a single rear axle, the vehicle will tend to understeer (i.e. pushing the front tires when trying to turn); dual rear axles makes this a lot worse. If you go ahead with this design, I'd suggest moving as much weight forward as possible to get traction on the front wheels.


I appreciate the input! Thanks. I have had some helpful comments from more experienced builders, and I welcome them! I have had a little devil in the back of my head telling me that the 670 wouldnt be big enough. I love the look of the 6 wheels, but you are definitely right with the big turning radius. Sucker will be long too, just a little annoying to store. And I actually am not that familier with atvs or utvs or buggies for that matter. I have just worked on and rode alot of motorcycles, worked on alot of cars, and probably ridden just shy of 1,000 miles on snowmobiles (rented, not my own). I actually was entertaining the snowmobile engine idea the other day. WAY more hp and torque. Lots of used sleds for cheap too. Do you think liquid cooled would do fine in 90ish temps? From my understanding they partially rely on snow hitting the engine to stay cool.

You may have noticed my back end doesnt exist, and thats because I dont feel 100% confident with my plans, so I have been thinking while buttoning up the front. I could do A arms in the rear too. If I killed one axle, that would probably be the route I would go.

Another huge pro of a snowmobile engine is that I havnt bought my CVT or driven yet. Thats going to set me back about $500, and I could find a sled for a close-ish price point that already has the engine and CVT attached to it! Probably save money this way. My 670 is brand new too, so should sell easy.

Do you have any input on snowmobile engines/sleds that could work well? I would prefer 4 stroke, but I know two strokes are the way to go for power. I basically am aiming for big and reliable.

Thanks for any extra info!


Thu Nov 03, 2022 11:57 pm
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As far as snowmobile engines are concerned, I would lean towards 2 stroke. It's going to be lighter, more available, and have more power. The 4 stroke sleds I have ridden that aren't turbocharged have all felt pretty anemic. Cooling won't be a problem with a properly sized radiator. Most snowmobile cooling systems use a heat exchanger in the tunnel that is cooled by snow thrown at it by the track, this is done because a traditional radiator would pack with snow and become useless. You would however probably see a reduction in performance unless you could keep Temps below around 125°f as most engines start pulling timing around there.


Fri Nov 04, 2022 5:58 am
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Cool project! Looking forward to the next installment!


Fri Nov 04, 2022 8:28 am
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That shop is so tidy it looks more like a medical laboratory than a metal fabrication shop!
Do you do all the welding and grinding outside?

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Fri Nov 04, 2022 8:44 am
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TNThomas wrote:
Yondering wrote:
Cool project. This brings back a lot of memories of working on SAE Mini Baja back in college; what you're doing is very similar.

Some constructive criticism though - you've got a fair amount of weight in that thing, and you'll need a LOT more motor than that Predator engine. The dual rear axles won't help; you won't have the power to even come close to spinning the tires, and if you've spent much time playing with off road vehicles you'll agree that wheel spin is an important part of maneuverability and fun factor too. Some sort of liquid cooled snowmobile engine making 50+ hp would work a lot better, and fortunately those are really easy to find around here. And, a lot of those are lighter than that Predator engine too.

Keep in mind that two rear axles will drastically increase your turning radius. Often with buggies like this that only have a single rear axle, the vehicle will tend to understeer (i.e. pushing the front tires when trying to turn); dual rear axles makes this a lot worse. If you go ahead with this design, I'd suggest moving as much weight forward as possible to get traction on the front wheels.


I appreciate the input! Thanks. I have had some helpful comments from more experienced builders, and I welcome them! I have had a little devil in the back of my head telling me that the 670 wouldnt be big enough. I love the look of the 6 wheels, but you are definitely right with the big turning radius. Sucker will be long too, just a little annoying to store. And I actually am not that familier with atvs or utvs or buggies for that matter. I have just worked on and rode alot of motorcycles, worked on alot of cars, and probably ridden just shy of 1,000 miles on snowmobiles (rented, not my own). I actually was entertaining the snowmobile engine idea the other day. WAY more hp and torque. Lots of used sleds for cheap too. Do you think liquid cooled would do fine in 90ish temps? From my understanding they partially rely on snow hitting the engine to stay cool.

You may have noticed my back end doesnt exist, and thats because I dont feel 100% confident with my plans, so I have been thinking while buttoning up the front. I could do A arms in the rear too. If I killed one axle, that would probably be the route I would go.

Another huge pro of a snowmobile engine is that I havnt bought my CVT or driven yet. Thats going to set me back about $500, and I could find a sled for a close-ish price point that already has the engine and CVT attached to it! Probably save money this way. My 670 is brand new too, so should sell easy.

Do you have any input on snowmobile engines/sleds that could work well? I would prefer 4 stroke, but I know two strokes are the way to go for power. I basically am aiming for big and reliable.

Thanks for any extra info!


I'm not a snowmobile expert so I'll let somebody else chime in there, but I'd be pretty confident in using a decent size radiator mounted up on the roll cage so it gets lots of air flow. I definitely would not go with an air cooled motor; that was the problem with the old Honda Oddysey buggies. If you haven't driven one of those, I'd make a point of doing so before finalizing any plans on your buggy. They didn't have much suspension, and motors tended to overheat (especially the 350 model), but understanding the handling characteristics will have a huge impact on getting your buggy set up right.

I was also going to say that if it were me, I would not use a Miata differential. For one thing, a differential is not needed or helpful, unless you plan to drive this mostly on pavement. Solid axle is the way to go for traction and controllability when you slide it around, and that's easily done with a chain/sprocket setup driving power from your CVT to the axle. The axle itself can be a full solid axle, or better, a short center section on bearings with independent suspension.

Also, looong A-arms are the way to go. Get those pivot points as close to the center as you can go, and engineer the shocks and springs to maximize travel and control damping. Tons of wheel travel is important for good off road performance, as is correctly valved damping and spring rates. A good example of that was our old Mini Baja car in college; you could drive it over curbs and up/down stairs and not feel the bump, just a smooth ride.


Fri Nov 04, 2022 2:33 pm
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laneends wrote:
As far as snowmobile engines are concerned, I would lean towards 2 stroke. It's going to be lighter, more available, and have more power. The 4 stroke sleds I have ridden that aren't turbocharged have all felt pretty anemic. Cooling won't be a problem with a properly sized radiator. Most snowmobile cooling systems use a heat exchanger in the tunnel that is cooled by snow thrown at it by the track, this is done because a traditional radiator would pack with snow and become useless. You would however probably see a reduction in performance unless you could keep Temps below around 125°f as most engines start pulling timing around there.



Thanks for the info! I hadnt thought about the snow clogging up a radiator, that makes sense. Yea, 2-stroke is the way to go. I dont like mixing gas, or the noise, but I also like the power. I would probably get a big radiator and mount it just above the seats, lots of airflow.


Sat Nov 05, 2022 8:55 am
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jukk0u wrote:
That shop is so tidy it looks more like a medical laboratory than a metal fabrication shop!
Do you do all the welding and grinding outside?


Thanks! I do all my cutting inside, and about 80% of my welding inside as well. Yea, I have found that my brain can think better, visualize better, and get less stressed out if my working environment is super tidy. Helps to not loose tools too. I can work in messy environments, but reducing subtle distractions is important when I am winging it!


Sat Nov 05, 2022 8:59 am
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TNThomas wrote:

Thanks for the info! I hadnt thought about the snow clogging up a radiator, that makes sense. Yea, 2-stroke is the way to go. I dont like mixing gas, or the noise, but I also like the power. I would probably get a big radiator and mount it just above the seats, lots of airflow.

If the engine you get still has the oil injection intact, this is a non issue! Just would have a separate tank for oil.
Also make sure you get the exhaust pipe with the engine.


Sat Nov 05, 2022 9:07 am
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Yondering wrote:
TNThomas wrote:
Yondering wrote:
Cool project. This brings back a lot of memories of working on SAE Mini Baja back in college; what you're doing is very similar.

Some constructive criticism though - you've got a fair amount of weight in that thing, and you'll need a LOT more motor than that Predator engine. The dual rear axles won't help; you won't have the power to even come close to spinning the tires, and if you've spent much time playing with off road vehicles you'll agree that wheel spin is an important part of maneuverability and fun factor too. Some sort of liquid cooled snowmobile engine making 50+ hp would work a lot better, and fortunately those are really easy to find around here. And, a lot of those are lighter than that Predator engine too.

Keep in mind that two rear axles will drastically increase your turning radius. Often with buggies like this that only have a single rear axle, the vehicle will tend to understeer (i.e. pushing the front tires when trying to turn); dual rear axles makes this a lot worse. If you go ahead with this design, I'd suggest moving as much weight forward as possible to get traction on the front wheels.


I appreciate the input! Thanks. I have had some helpful comments from more experienced builders, and I welcome them! I have had a little devil in the back of my head telling me that the 670 wouldnt be big enough. I love the look of the 6 wheels, but you are definitely right with the big turning radius. Sucker will be long too, just a little annoying to store. And I actually am not that familier with atvs or utvs or buggies for that matter. I have just worked on and rode alot of motorcycles, worked on alot of cars, and probably ridden just shy of 1,000 miles on snowmobiles (rented, not my own). I actually was entertaining the snowmobile engine idea the other day. WAY more hp and torque. Lots of used sleds for cheap too. Do you think liquid cooled would do fine in 90ish temps? From my understanding they partially rely on snow hitting the engine to stay cool.

You may have noticed my back end doesnt exist, and thats because I dont feel 100% confident with my plans, so I have been thinking while buttoning up the front. I could do A arms in the rear too. If I killed one axle, that would probably be the route I would go.

Another huge pro of a snowmobile engine is that I havnt bought my CVT or driven yet. Thats going to set me back about $500, and I could find a sled for a close-ish price point that already has the engine and CVT attached to it! Probably save money this way. My 670 is brand new too, so should sell easy.

Do you have any input on snowmobile engines/sleds that could work well? I would prefer 4 stroke, but I know two strokes are the way to go for power. I basically am aiming for big and reliable.

Thanks for any extra info!


I'm not a snowmobile expert so I'll let somebody else chime in there, but I'd be pretty confident in using a decent size radiator mounted up on the roll cage so it gets lots of air flow. I definitely would not go with an air cooled motor; that was the problem with the old Honda Oddysey buggies. If you haven't driven one of those, I'd make a point of doing so before finalizing any plans on your buggy. They didn't have much suspension, and motors tended to overheat (especially the 350 model), but understanding the handling characteristics will have a huge impact on getting your buggy set up right.

I was also going to say that if it were me, I would not use a Miata differential. For one thing, a differential is not needed or helpful, unless you plan to drive this mostly on pavement. Solid axle is the way to go for traction and controllability when you slide it around, and that's easily done with a chain/sprocket setup driving power from your CVT to the axle. The axle itself can be a full solid axle, or better, a short center section on bearings with independent suspension.

Also, looong A-arms are the way to go. Get those pivot points as close to the center as you can go, and engineer the shocks and springs to maximize travel and control damping. Tons of wheel travel is important for good off road performance, as is correctly valved damping and spring rates. A good example of that was our old Mini Baja car in college; you could drive it over curbs and up/down stairs and not feel the bump, just a smooth ride.


Very good info, much appreciated! The 670 is air coold, so thats another reason to ditch it. Also the Predator 670 isnt as reliable as their smaller engines. My biggest issue on this build is my lack of time, and slightly limited budget. Single income, I have a 4yo, a 2yo, and another on the way in May. Ideally I would do exactly what you said. A-arms in the back, with a tuned suspebsion.

Ill do some thinking, but the snowmobile engine is definitely a go. Realistically ill probably stick to the big rear swing arm in the back. Not going to be as good, but simple, cheap, and faster to build. I already have the plan in my head as well. Im a teacher, so ill have a few weeks off in December to build. I already have the shocks (24"tall). The main reason why I want duel axles is for additional float and weight dustribution. Im running 1" solid gokart axles, but I think Ill bend one if its a solo axle. A-arms would fix that, but there is the time issue as mentioned. Ill mainly be riding in sand and Idaho dirt roads. The Diffs are primarily with the duel axles in mind, I feel that the rear axles will fight each other on turns otherwise. But I agree, a solo axle would better be suited for solid.


Sat Nov 05, 2022 10:44 am
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Cool, but you need a tube bender!


Sat Nov 05, 2022 12:42 pm
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laneends wrote:
TNThomas wrote:

Thanks for the info! I hadnt thought about the snow clogging up a radiator, that makes sense. Yea, 2-stroke is the way to go. I dont like mixing gas, or the noise, but I also like the power. I would probably get a big radiator and mount it just above the seats, lots of airflow.

If the engine you get still has the oil injection intact, this is a non issue! Just would have a separate tank for oil.
Also make sure you get the exhaust pipe with the engine.


Ah, that would be nice! I am going to start looking at engines/donor sleds. Good thinking on the exhaust too. Another pro of a sled is the reverse. Not 100% sure how it works, but I think its some fairly simple gear on the snowmobile jack shaft.


Sun Nov 06, 2022 11:39 am
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On 2 stroke sleds for about the last 20 years, reverse actually starts the engine backwards. No gear box. 4 stroke sleds can't do that so reverse is a gear box. If interested I have a 2009 ski doo 800 that is torn apart but otherwise a serviceable sled, would have all wiring, clutches, engine, carbs, the whole nine. I'm never going to get around to putting it back together. This engine would put out around 160hp.


Sun Nov 06, 2022 12:04 pm
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