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Not sure on the KTM engines yet. I am working on the smaller brother 450ex version now. It's a freebie job for in-laws, trying to keep the paying cutomers happy during normal bussiness hours and playing around with the KTM in my spare time. After I get the build complete I will be testing some different size carbs on it.

I can tell you, on my TRX450r (stock bore/stroke, to keep 450cc) motors that have all the goodies. I see gains of 3- 3.5 hp on the top-end, with no loss of hp/tq anywhere in the rpm range. This is testing the stock 40mm carb against a 43.5mm bored carb. Nothing else changed, just swapping the carbs out. Most of these motors are designed to be biased towards the mid-topend power

From the bore/stroke ratio of the "ex" version, leaning more towards a strong mid rpm motor then a screamer. I am not sure of the exact size of the carb needed, where you start trading peak hp/tq for losses in the lower rpm's.

It's winter time here, and I have alittle time to complete the build I am working on. I will posting the details of the build on this site. The good and the bad of what I have found in my experience with this type of engine. Maybe it will point others in a direction in which they want to take their build towards.

Sorry, I can't give you actual results just yet. Maybe someone with more experience will chime in.
 

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check out KTM talk, would appear to be good gains on the 525's with a 41mm setup over the 39 and easy tuning.

my experince has been the really big bore carbs tend to be more finicky in the tuning due to the lower air speeds.
 

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Driver 311 and I dyno'd my bike w/stock 39mm, again at 40mm and again at 41 x 41.5 Ovalized, driver has the graphs, the carb measured 38.8mm stock, I bored and polished to 40mm if I remember right gained about 3/4hp with no loss anywhere, I then ovalized the carb to 41 x 41.5 and dyno'd the quad again, with a gain of about 1-1.5hp. it did loose just a tad of low rpm bottom end,
 

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Yeah around 1.5whp in the mid and top going from 39mm to 41mm. With no bottom loss. Going from 41mm to 43mm would net another 1-1.5whp up top but loses about .5-1whp down low. I think its a sacrifice id be willing to take on the xc motor. Its got alot of bottom end to waste but needs alot of help up top. In order to get 43mm to work right they need to do a few more mods, but can be made to work just as good as the 41mm.

I plan on doing a 42.5mm on my 505sx.
 

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Yeah around 1.5whp in the mid and top going from 39mm to 41mm. With no bottom loss. Going from 41mm to 43mm would net another 1-1.5whp up top but loses about .5-1whp down low. I think its a sacrifice id be willing to take on the xc motor. Its got alot of bottom end to waste but needs alot of help up top. In order to get 43mm to work right they need to do a few more mods, but can be made to work just as good as the 41mm.

I plan on doing a 42.5mm on my 505sx.
So with 570 Thumper kit - Full Port and +1mm Valves - 43mm bore Carb - Reground 807 Cam by Web to keep some of my low-mid - Full HMF System: I should have plenty of ponies to call on?
 

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Sounds like a screamer to me. :D
 

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I've got a 43.5 taper bored DRG carb on my 08. I can't tell you if it gains power, but heck I had the same setup on my 05 HOnda, and it was a nice upgrade on there.

Jay :D
 

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I've got a 43.5 taper bored DRG carb on my 08. I can't tell you if it gains power, but heck I had the same setup on my 05 HOnda, and it was a nice upgrade on there.

Jay :D
How much that run ya? Trade me for my 41mm LOL
 

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I think the last carb that chad did for me cost $280. His quality is impechable. I was recently did some dyno testing on a friends Big Trx557. I compared two carbs both bored to 43.25, one of them chad's(DRG), The Drg taper bore made .5hp more but 3ftlbs more torque than the other. That's good stuff, tells me that his quality of work is better.
 

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Yea it is about $300 or so to have DRG do the carb.. Chad does great work though, as I've had two honda motors built by him and my 08 is a full drg motor as well.

Jay
 

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Hey guys there is no better at carb boring than Chris Hanson - Sredrum Carbs a forum Vendor here on KTMATVHQ.com...he loves the 39mm KTM Carb for boring...
Does excellent work and has a new CNC Machine Shop...
419-618-5982
 

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Ive dynoed several carbs from sredum. On hondas and yamis. All made killer power and ran spot on. Ill probably use him.
 
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