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 Post subject: Rotax 399cc
PostPosted: Tue Nov 07, 2006 7:43 pm 
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Howdy,
got a few questions about my Rotax model 401 399cc sled engine which is going on my kart.

1. Anyone know the rpms this will put out?

2. Is it true that two strokes do not perform well with a straight pipe exhaust due to lack of back pressure?

3. Since this is only fanned cooled any ideas how to keep it a bit cooler during the warmer weather?

Thanks


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 Post subject: Rotax
PostPosted: Tue Nov 07, 2006 9:24 pm 
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12000 is not hard to hit on a two stroke.The pipe is what makes a lot of the power,it has to have the bid chambered pipe to run right.Run it a little fat in hot weather.


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 Post subject:
PostPosted: Tue Nov 07, 2006 9:32 pm 
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If you strait pipe your two stroke it will rob it of power and seize up in a matter of time, you need to have a engineered pipe for it with a expansion chamber,for the cooling just run a 20/80 mix of coolant and try and make air ducts to the motor,2 strokes generally put out more power due to only havening to make 2 strokes in stead of 4 that motor will put out plenty of power for a buggy, my guess is around 10,000


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 Post subject:
PostPosted: Tue Nov 07, 2006 11:57 pm 
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It's not backpressure per se that you need. A 2-stroke needs a 'tuned' exhaust to make best power. The exhaust as it flows out drags along with it some of the incoming fuel charge. A correctly tuned exhaust will have a backwave that will actually stuff this fuel back into the cylinder and create more pressure for more power. Without this backwave (I don't know if that's the proper term for it), the fuel will just flow into the exhaust and be wasted. An incorrectly sized pipe can also reflect too much exhaust and stuff burned gasses into the cylinder.

When I learned all this I abandoned my plans to put a Rotax 462 into my Dune. The chamber would have taken up nearly as much space as the engine itself.
http://www.buggynews.com/viewtopic.php?t=5355

If anyone knows some trick that will allow a much smaller chamber, I'd sure like to know it.

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 Post subject:
PostPosted: Wed Nov 08, 2006 12:47 am 
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They look somewhat the same as a 582 or 532 which is used in ultralights. For a muffler and exhaust pipe look on ebay for one from a ultralight. Rotax uses the same muffler on the 277, 377, 477, 503, 532 and 582. And all the of there motors work great and reliable with these mufflers.


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 Post subject: new air intake
PostPosted: Fri Mar 02, 2007 6:08 pm 
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Just fabbed a new intake, looks pretty nice.


Attachments:
File comment: New Intake
DSCF0245.JPG
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 Post subject:
PostPosted: Thu Mar 15, 2007 8:39 pm 
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Its been some time since I've messed with a 400cc Skidoo sled but if memory serves me correctly I think the "sweet spot" rpm of that engine is either 6200-6600 or 6800-7200 rpm, but no more than that.

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Last edited by firstatv_700efi on Thu Mar 15, 2007 8:58 pm, edited 1 time in total.

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 Post subject:
PostPosted: Thu Mar 15, 2007 8:51 pm 
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I agree, a 2 stroke will see high rpms, but not sled motors in general, most cvt clutches would explode that high in the range, Like first said 6800-7200 or so...Actually most 2 smokes that see 12 k are like weedeaters and such....Talk to rman he is pretty good at building them pipes and i bet the price is really reasonable...keep it cooler by running it a bit rich as well....

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 Post subject:
PostPosted: Thu Mar 15, 2007 8:52 pm 
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Location: Dewitt Michigan
guy48065 wrote:
It's not backpressure per se that you need. A 2-stroke needs a 'tuned' exhaust to make best power. The exhaust as it flows out drags along with it some of the incoming fuel charge. A correctly tuned exhaust will have a backwave that will actually stuff this fuel back into the cylinder and create more pressure for more power. Without this backwave (I don't know if that's the proper term for it), the fuel will just flow into the exhaust and be wasted. An incorrectly sized pipe can also reflect too much exhaust and stuff burned gasses into the cylinder.

When I learned all this I abandoned my plans to put a Rotax 462 into my Dune. The chamber would have taken up nearly as much space as the engine itself.
http://www.buggynews.com/viewtopic.php?t=5355

If anyone knows some trick that will allow a much smaller chamber, I'd sure like to know it.



i got a trick, add an engine with valves.... :D

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 Post subject:
PostPosted: Fri Mar 16, 2007 7:37 am 
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Depending on how much room you have to work with, and how the motor is to be mounted will generally determine how the pipe should be built, if you check out hello frome a newbie thread you'll see how I build and mount my pipes, the 377 rotax relly responds well to a single pipe... I'll look to see if I have some pix somewhere... :shock: here's 2 of 377 pipe that was pretty quiet and torquey as heck...


Attachments:
File comment: 377 pipe/muffler after testing and tuning
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File comment: paint breakdown of pipe components
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 Post subject:
PostPosted: Fri Mar 16, 2007 7:46 am 
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Or If you feel the need for twin pipes they would look more like this...These are on a ported,cut piston 500 cc Polaris motor, they will be flowing into a 2 in 2 out muffler, I'll post more pix as they come :shock:


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File comment: pipes in buggy
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 Post subject:
PostPosted: Fri Mar 16, 2007 11:06 am 
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Location: wilton, IA
Rman (spec) When i come to dog days maybe u can give me some ideas on exhaust setup for mine.Likew your work =D>


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