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Old 03-28-2020, 12:18 AM
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Default Predator 420 vs Duromax 440 for Stage 2 Parts

Doing some plans for a mini buggy, and I'm trying to decide between the Predator 420 and Duromax 440. As mentioned in a previous thread, I was originally going to run a Predator 670 but I've decided against it due to weight, cost, and the added complexity of a v-twin. I'm tempted to buy the Duromax 440 simply because of the extra 20cc advantage. It produces significantly more power and torque over the Predator; 18HP/26FTLBS for the Duromax vs 13HP/18FTLBS for the Predator. This is all well and good but my main concern is the compatibility of Stage 2 parts. I plan to use billet rods/flywheel, cam, springs, the whole shebang, but I'm worried that the parts may not interchange (the Stage 2 kit was built with GX390s/420s in mind). Being a GX390 clone, I would imagine the 440 would be able to work with these parts without issue, but has anyone here built one of these engines? Thanks in advance.
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Old 03-28-2020, 01:58 AM
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The predator is going to have more aftermarket options available I'm sure.

I'm also still not convinced the duromax 440 makes 18hp. There is absolutely nothing special or unique about its design that would allow it to produce 5hp out of 20ccs. Reviews on Home Depot and Amazon both seem to support this.

I read somewhere about somebody dyno'd one and it made 13.5hp stock after break in. The 18hp is "calculated" based off the peak torque at peak RPM, but the problem is it (not any engine) does not produce peak torque at peak rpm.
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Old 03-28-2020, 08:37 AM
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That sounds reasonable anickode. 1/2 a HP from 20 cc instead of FIVE!

I'm pretty sure that RBG has confirmed that the Stage 2 Predator 420 kit will fit the DuroMax 440. I'd go 440 just so I could say I've got a 440 on my kart!
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Old 03-28-2020, 10:03 AM
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What fits the Predator 420 will fit the 440. RBG did like a stage 4 on a 440 with 420 parts. Though he had to add a Honda starter because it would reach the ring gear on the flywheel.

https://www.youtube.com/watchfeature...&v=pVzgw9I45XQ
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Old 03-28-2020, 12:39 PM
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Cool, thanks. I won't need electric start anyway so that's not a big deal to me. And maybe they don't actually produce 18 horsepower, but they're about the same price so the extra 20cc is a bonus as far as I'm concerned. I looked up that Red Beard video (dead link) - very helpful! Can't believe I haven't seen it before. I'm not going quite as far as he did though. Keeping the balance shaft, using a jetted carb rather than a brand new one, stock pushrods, stock rockers, etc. He's used these 440s on multiple projects by the looks of it, and he recommends them. Glad to know all the parts interchange.
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Old 03-28-2020, 02:07 PM
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You know what makes 18 hp? The Honda GX610, a v-twin industrial engine with 618CC’s of displacement.

I’ve never seen a unicorn before, nor have I seen a duromax make the HP they advertise on any of their engines.
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Old 03-28-2020, 02:10 PM
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Seems like false advertising then. I wonder how they "got to" 18 horsepower with their tests.
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Old 03-28-2020, 03:57 PM
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What I've read from Vegas Carts is, engines rarely make advertised power ratings. That's why Honda, Briggs and Stratton, and Tecumseh were sued years ago and why engine makers rarely if ever advertise HP ratings, unless its Gross HP. So it's been displacement ever since.

For example, the Briggs and Stratton 479cc Vanguard V-twin has 2 hp ratings, 14hp and 16hp. Know what the difference is? The 14hp has a more restrictive carburetor than the 16hp. So take HP ratings with a heaping grain of salt. Same with electric motors, usually AMP ratings on those are more reliable for a baseline than hp.
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Old 03-28-2020, 04:02 PM
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Quote:
Originally Posted by Kartorbust View Post
What I've read from Vegas Carts is, engines rarely make advertised power ratings. That's why Honda, Briggs and Stratton, and Tecumseh were sued years ago and why engine makers rarely if ever advertise HP ratings, unless its Gross HP. So it's been displacement ever since.

For example, the Briggs and Stratton 479cc Vanguard V-twin has 2 hp ratings, 14hp and 16hp. Know what the difference is? The 14hp has a more restrictive carburetor than the 16hp. So take HP ratings with a heaping grain of salt. Same with electric motors, usually AMP ratings on those are more reliable for a baseline than hp.

The Honda GX340 and 390 are the same way now. Both 389cc engines, different carbs.
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Old 03-29-2020, 12:37 PM
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Quote:
Originally Posted by SquidBonez View Post
Seems like false advertising then. I wonder how they "got to" 18 horsepower with their tests.
From what i can tell is that took the peak torque rating that typically happens at 21-2500 rpm, and then multiplied it by the peak rpm the engine produces (3600-3800 rpm). The problem is that peak torque doesn't happen at peak rpm.

Duromax is a small enough company (not like honda/briggs/tecumseh) to where they can get away with it right now.

They will have a class action lawsuit against them in the future for false HP ratings if they keep this up.

You can get legitimate horsepower ratings through the SAE test methods. The same SAE organization that has test methods for the oil you put in your car has test methods for rating horsepower and torque in small engines.

I spoke with a SAE representative that performs oversight to honda/briggs/etc and he said that engines must be held under static conditions in order for them to be SAE certified.

some of the static conditions include:

temperature
rpm
load

The dynamometer must be capable of being certified via a known laboratory standard to a very precise tolerance.

So what happens is that you run an engine that must be held at a the same load, rpm, and temperature (intake shroud and head) for minutes and minutes until ALL variables are static. The head must come up to temp, the intake shroud must come up to temp, load must be stable, rpm must be stable, THEN a measurement is taken at that specific RPM. This is often done in steps, liek 1500 rpm, 2000 rpm, 2500 rpm, with the peak hp and peak tq steps being taken wherever they occur.

So in other words, a load bearing dyno is the only dynamometer that can produce SAE horsepower numbers.

From what I am aware of, BRIGGS, KOHLER, and HONDA all follow these methods because they ADVERTIZE or list in their footnotes for their torque curves the test methods that they used. Briggs is a little sneaky about it and will report GROSS HP instead of NET HP. Briggs will remove the intake and the exhaust and report gross hp, whereas the NET hp is with the intake(air filter)/ and exhaust (muffler) attached.
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  #11  
Old 03-29-2020, 02:05 PM
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Kartfab, that's exactly what they do. Purely calculated based off peak torque.

Duromax sells a generator with a 713cc V twin... I wish they'd sell that as a crate motor.

Although I suspect that unless they MASSIVELY overinflated the HP ratings (like claiming 35 hp), it would expose their overratings in their smaller engines.
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Old 03-29-2020, 03:03 PM
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I'd love to try this beast of a thumper https://vegascarts.com/collections/e...lf-cart-engine or even their smaller 460 https://vegascarts.com/collections/e...e-diy-assembly but only as a crate and not an assembled engine.
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Old 03-29-2020, 04:06 PM
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Quote:
Originally Posted by Kartorbust View Post
I'd love to try this beast of a thumper https://vegascarts.com/collections/e...lf-cart-engine or even their smaller 460 https://vegascarts.com/collections/e...e-diy-assembly but only as a crate and not an assembled engine.
Man that great honking one-lunger would be perfect in my Gator build... No need to move the axle back to accommodate the fat twin that I'm using.

It ain't $900 perfect though, that's for sure.
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Old 03-29-2020, 04:09 PM
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It's a modified ZongShen (or some Chinese company) from the little bit I've found. They did some internal tinkering with it and made it better. It's a better alternative for those who want more power, without needing to modify for a V-Twin. I'm waiting to see if more people use it before I decide if it's worth getting into for the money.
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Old 03-29-2020, 05:22 PM
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Quote:
Originally Posted by Kartorbust View Post
I'd love to try this beast of a thumper https://vegascarts.com/collections/e...lf-cart-engine or even their smaller 460 https://vegascarts.com/collections/e...e-diy-assembly but only as a crate and not an assembled engine.
Hm, never visited Vegas Karts before. "No Internal Mechanical Governor" huh? Wonder what they rev to. Still, I'm probably just going with a built 420/440 because there's more aftermarket support. The 460 looks appealing though.
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Old 03-29-2020, 07:29 PM
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So it looks like Vegas Carts have their own stuff to build the 460 with billet parts. Seems to be a bored and stroke 390? But I agree, the 420 and 440 have a much wider selection that is known to work well. Just take power ratings with a nice helping of salt and don't set your expectations too high so you can be surprised.
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Old 03-29-2020, 07:36 PM
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Quote:
Originally Posted by Kartorbust View Post
It's a modified ZongShen (or some Chinese company) from the little bit I've found. They did some internal tinkering with it and made it better. It's a better alternative for those who want more power, without needing to modify for a V-Twin. I'm waiting to see if more people use it before I decide if it's worth getting into for the money.
Must have done some tweaking... ZongShen rates the stock engine at 18.8hp (believable for 625cc). I'm curious whether Vegas actually dyno'd one or it's just a guesstimate.
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Old 03-29-2020, 09:35 PM
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Quote:
Originally Posted by anickode View Post
Must have done some tweaking... ZongShen rates the stock engine at 18.8hp (believable for 625cc). I'm curious whether Vegas actually dyno'd one or it's just a guesstimate.
vegaskarts had russel at nr racing dyno their engine. he didnt publish the numbers but i want to say that it couldnt rev very high with performance mods going on. Geoff whited out the NR racing letterhead on the dyno sheet, then deleted the post a few months later. IIRC the torque was impressive, but the rpm was not.

The small block engines like predator 212 will always be able to rev about 1k higher with the exact same mods. The bigger the bore, the more torque it will produce though.

My 2 cents is that if you are wanting to keep an engine stock or maybe stage 1, it doesnt really matter which size engine, as you will only see maybe a 1-3 hp gain with stage 1.

If you are sticking it on a mini bike, a small block will be better as it is less expensive.

If you are going to put an engine on a 2 seater go kart, or something heavy, it should be a big block, even if it costs more to upgrade.

Consider the cost of a bone stock v-twin that makes 16-18 hp vs a modified 390-460 vs a modified small block.

Ive had all three, and i can say that small blocks are best for mini bikes, big blocks are best for go karts, and v-twins are great for mini buggies (as a general guideline).

With the coronavirus looming, dont be afraid to look on some classified ads for the following keywords:

power washer
wood chipper
trash pump
pressure washer
heated power washer


you just might end up with a $50-$100 big block before you know it. I ended up paying $20 a pop for honda v-twins, $50 for a gx390, and $40 for another gx390. Only one was a dud, and i turned that one into the stroker build on my youtube channel. Still have the v-twins wanting to put them on mini buggies.
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Old 03-29-2020, 09:58 PM
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Quote:
Originally Posted by anickode View Post
Must have done some tweaking... ZongShen rates the stock engine at 18.8hp (believable for 625cc). I'm curious whether Vegas actually dyno'd one or it's just a guesstimate.
According to their description 2 years of R&D went into it. Flat top piston with 9:1 compression vs the 8.6:1 for a stock ZongShen. According to this https://www.engine-specs.net/zongshen/gb620.html they claim it's a splash lube, but Vegas claims it's a pressured lube (does have an oil filter). So probably some light porting was done.
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Old 03-30-2020, 06:02 PM
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Food for thought https://vegascarts.com/blogs/faq/sho...o-my-golf-cart
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