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Old 08-25-2019, 06:13 AM
Slowpoker Slowpoker is offline
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Default Need advice on motor swap

I would like some comments from the forum on the possibility of using a Predator 420 on my World Extreme kart.

I was given a free, brand new HF Predator 420 motor.

First and main question is, due to limited space, can I remove the fan shroud and plastic fan from the motor to reduce the width? I know it's part of the cooling system, but on this kart, the motor is out in the airflow, not blocked by the seat or frame.

I would put an ARC billet rod and flywheel in it which would allow me to keep the electric start which would be nice. Getting rid of stock exhaust and air filter of course, and I have a remote fuel tank and pump already, so that would also slim things down. I would move the keystart box up front.

I want to take in consideration practicality, cost effectiveness, and ease of fit without going overboard - this is all about having fun, right?

I have a budget of about 700 bucks, so maybe a 34 Mikuni kit and a Hilliard Extreme clutch to round it out.

This is purely a fun kart driven on pavement. No formal racing, no offroad.

Comments, suggestions, alternatives???

Thanks

Doug
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Old 08-25-2019, 06:33 AM
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For a $700 budget, you'd be better off building a predator 212 or even a genuine Honda GX200 IMO.

With that kind of money, you can get 16+ hp out of a small block, and it'll rev higher than you'll probably ever get a 420 to go, which means a higher top speed.

Plus no modification to the frame.

My 2
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Old 08-25-2019, 07:02 AM
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I doubt you'd get a gx200 to 16 horses with 700 bucks if you do not already own the gx200
and frankly I doubt you get a clone to 16 hp reliably

but the idea is sound otherwise.. I wouldn't install a 420 either..
a modded small block is the way to go indeed IYAM.
Since even if you just get the 200cc clone to say 13horses..
it'll rev much higher than the 420 and thus would make the faster kart in the end
while being lighter and thus quicker too.

And if you want a modded big block, there's only ONE to use IMHO.. the GX390
(fully modded reaches 40-45 horses while still being reliable-esque)
I bet any chinese engine (that does include the predators!)
would fly apart at this kind of modification.

OH that brings me back.. get the Tillotson block.. not only is it made to be raced, it's also proper eye candy.. much nicer than your ordinary clone
maybe it is sound enough to handle 16 horses reliably.

So yeah a free 420 is awesome.. and I do understand that you would like to make use of it.
but that'S not the project for such IMHO.
A small buggy, yes.. an AWD six wheeler, of course... a two seater yard kart, perhaps..
a true race kart that just neds to be fast .. NOPE!


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Old 08-25-2019, 07:14 AM
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'course, what's on there already looks to be a great start on a 212 build. What's it got done to it already?

$700 would turn THAT into a monster.
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Old 08-25-2019, 07:27 AM
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good catch!

.. I cannot tell if it's a predator or some other clone
but chances are it's a fresh predator 212 (cheapest engine in america)
it looks new to me
(no grime or dirt on the crankcase to be seen, all the plastic parts are not yet discoloured, low oil still present)
stock carb.. maybe rejetted maybe not ...
So maybe a box stock project.. maybe a cheap engine placeholder installed to sell the kart.. *shrugs*

but since you need to crack it open anyways (if you intend to run it)
that may be a very nice starting point.
maybe it's not a BSP or enigne blank..
and thus it already has the flywheel and con rod you are looking for...
so carb upgrade maybe flat top piston, a cam some vavle&spring upgrades and you are already at a more or less reliable 12-13 horses for less than 300 bucks.
And if it is an untouched engine.. it's as nice of a starting point but you need two more billet parts

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Old 08-25-2019, 07:41 AM
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Yep, Predator.
Either that or someone salvaged the blower housing. I can just barely make out the red/black sticker.
OP, for the work and money it'd take to smack a 420 on there, you're far better off fully building that small block. You'd have to hack the frame up(NOT GOOD ON A RACE KART), and even if you managed to fit it, the sheer torque from that engine might turn the chassis into a steel pretzel.
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Old 08-25-2019, 07:53 AM
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Yes, the motor that's on there is Predator 212. It has a billet rod and flywheel, governor removed.

I definitely don't want to do any modding to the frame.

I'll stick a flat slide Mikuni on it, maybe a mild cam and call it a day.

Thanks for all the great suggestions.
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Old 08-25-2019, 08:28 AM
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If that 420cc (or even the present engine) were a vertical 90 engine combined with that forward raked 15+/- mount, only then would I consider deleting the blower shroud as something viable.

As it is, the critical parts of those engines are not in the slipstream proper—their cylinders are actually pointed away from it, facing the opposite direction, not to mention the design of the cooling fins and their orientation are just not optimized for non-forced (no blower) cooling from the ambient air. That’s just a non starter from the word go.

I see JT is still gifted with hilarious hyperbole. While substantial, the 420’s torque spec isn’t overly mind blowing. I think the chassis would handle it with aplomb.


Hey! Gear it down, add some meaty 15” ATV knobbie tires and that kart could be a viable creeping, crawling off roader with that fat, lumbering 420cc! Nice and slow revving.
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Old 08-25-2019, 08:54 AM
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I concur my good man... With aplomb......
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Old 08-25-2019, 10:57 AM
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me three

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Old 08-25-2019, 11:42 AM
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Quote:
Originally Posted by Slowpoker View Post
I definitely don't want to do any modding to the frame.
A wise decision. Race kart frames are often (usually) made from chromoly steel. Higher strength material allows for a thinner wall, and thus lighter weight. Cutting and welding, unless precisely done (preheat, TIG welded, post heat and controlled cool) can cause cracking issues at the welds. Not to mention the risk of warping the frame, which was undoubtedly welded in a jig to keep it true.
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Old 08-25-2019, 12:24 PM
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stage 4 kit on a 212 would be the best bet
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Old 08-26-2019, 05:36 PM
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I ordered a flat slide Mikuni kit, mild cam, valve springs and rocker arms for the 212 to start with today.

One more question, just for my curiosity, several people mentioned that the 212 would rev a lot higher than the 420, giving a better top end. I understand that, but wouldn't the extra torque of the 420 allow me to pull a higher gear, making up the rpm difference?

I appreciate of the great comments and suggestions.

Doug
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Old 08-27-2019, 04:09 AM
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Quote:
Originally Posted by Slowpoker View Post
I ordered a flat slide Mikuni kit, mild cam, valve springs and rocker arms for the 212 to start with today.

One more question, just for my curiosity, several people mentioned that the 212 would rev a lot higher than the 420, giving a better top end. I understand that, but wouldn't the extra torque of the 420 allow me to pull a higher gear, making up the rpm difference?

I appreciate of the great comments and suggestions.

Doug
In theory, yes, but in reality, clutches and torque converters just can't handle those high ratios. They end up slipping and burning up.

IF you were to use a grossly oversized torque converter, as in one that's intended for 25+ hp engines (snowmobile, utv, etc) then it might hold up, but then you'd be dealing with engagement speed and transition rate issues. Many of those torque converters wouldn't even engage till you were in the 3000+ rpm range, and you'd redline your engine before they hit peak ratio.
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Old 08-27-2019, 05:29 AM
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what he said..
it's the clutch(TC) engagement speed limiting your possibilities..

the engines both idle at about the same speed and lowest clutch engagement speed
for our clutches is 1800 rpm (clutch starts grabbing) to 2200 rpm (clutch fully locked)
So at 1799rpm your road speed is still zero;
and at 2200rpm your road speed must match the calculated speed
for the clutch to be able to fully lock
(otherwise it's still slipping and eventually burning out)

and 2200 rpm means
@ 6:1 ratio -> 12 mph
@ 5:1 ratio -> 14.4 mph
@ 4:1 ratio -> 18 mph
@ 3:1 ratio -> 24 mph

And while it's certainly doable to hit 12mph in a very short amount of time,
it's highly unlikely to reach 24mph in the same amount of time;
so although the 420 has more than twice the torque of a 212 ..
you cannot just cut the gear ratio in half.
Especially since as long as the clutch is slipping (anywhere from 1800 to 2200 rpm)
some of the motor power is converted to heat and doesn't even reach the wheels

there are racing clutches that are able to withstand such abuse for a while
if they're allowed to cool down again,
but they'll set you back 100-150 bucks easily even 300 and more if you pick a disc clutch.

And that's why 'high' power industrial engines like the 420 don't make much sense
if you want them to go fast,
they're great if you want to have some offroading grunt however.
but on a chassis like yours pretty much pointless,
since no matter what, you need to be able to go slow without destroying aynthing.

Single exception:
it's a proper race mod.

You can live with the high abuse on the clutch on a race...
since ideally you do not slow down until the race is over allowing the clutch to cool down again.
So insane ratios aren't too much of an issue.
And you don't care much if your 300 dollar clutch needs a 100 dollar overhaul
every 10 races if it wins you some of those.
Much different if you have to pour another hundred bucks in your clutch
every other week just for cruising down the alley I guess

'sid
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Old 08-27-2019, 05:45 AM
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And power requirements go up approximately by the square. To go twice as fast requires 4 times the power. Roughly. And that's assuming your kart is geared to make the most of your engine's horsepower (basically the engine hits Max RPM at exactly the same moment it hasn't got enough HP to propel the kart any faster)
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Old 08-27-2019, 05:42 PM
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Sounds reasonable - great explanations, thanks!
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Old 08-27-2019, 10:43 PM
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Your cylinder head will be the limiting factor on power with current powerplant. If you get one with bigger valves and any kind of port work at all I bet you’ll be at your power that you want. And still under your $700 budget.
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Old 08-28-2019, 07:23 AM
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Weight is a big factor in the 420 vs 212 debate also. Those predator blocks will surprise you with what they will take before they break. Id recommend contacting Gary Costanza for a head, he has done the last two Ive had and my predator will and has run with and outran any big name builders motors.
What cam did you order? I know you said mild, but Im curious about the specs.
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Old 08-28-2019, 08:45 PM
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I ordered the Mod2 cam from GoPowerSports
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