XR440 kit

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#1
Hey all,
I was advised to ask Eric Gore if he has an XR440 kit. Anyone know? I rode Cuzs' 440 this last weekend and it rocks. I guess Thumper Racing has a kit? Thanks for any info.
 
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#3
My son has a 440 kit,and I have an 280 kit from Thumper.We both have been very happy. Largest single improvement you can do to an XR.Don't forget the SUSPENSION.:cool:
 
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#4
Powroll offers the kit in either 10.5:1 or 12:1 compression. Question: does it go: the higher compression ratio you run, the higher octane fuel required? or the other way around? What would be the assets and tradeoffs of one over the other? Thanks.
 
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#5
The higher compression, the higher octane required.

With 12:1 you'll have to run straight, leaded race fuel - at least 110 octane.

Another option is the 415cc bore kit. This will create quicker reving power than the 440 kit, and some riders like it better. The 440 kit is best for torque and smooth power. The 415cc for rpm and quick power.

In a drag race on pavement, the 415cc kit will beat the 440cc kit. But in mud, the 440 kit will be better.

Hope this helps you out a little!
 

Rodzilla

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#7
Hey Derek,

Check the XRs only website they have several different kits to punch out your XR. You may consider doing the valves and such while the jug is apart. I think I remeber Eric Gorr replying a Fellow DRN rider saying that going through him would be cheaper. But I may be talking out of turn on that.

I'm looking at the 430 kit as opposed to the 440. I hear you don't have to resleave with the 430 (again I'm not positive)

Looks like I'll be splitting cases this winter to replace my shift shaft so I might have Eric do a 430, port and valve deal on my 400 as well.

Let me know what happens

Rod
 

SFO

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#8
The 400 is another motor that likes Stainless exhaust valves.
If you are popping it apart for a big bore, you might consider dropping good valves in it.
You will notice that your valve lash will require less attention.
 
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#9
Originally posted by DualSportr

With 12:1 you'll have to run straight, leaded race fuel - at least 110 octane.
Keep in mind the MON (or motor) octane rating of the fuel is the significant spec in this case. There are a number of race fuels with high overall octane numbers (> 100) but a large gap between RON and MON octane ratings. High RON rated fuel without comparable MON rating is fairly useless in an air cooled XR.

PJ - Don't forget to remind these guys that the (MON) octane the engine will require is dependent on the CR and the cam they are running, specifically how late the intake valve closes. The later the intake valve closes the lower the MON octane required (all else being equal). Running a 12:1 CR with the stock XR cam run (at stock lobe center angle) will generate very high cylinder pressures and an enormous amount of heat and in my opinion it's not a good idea regardless of the fuel you are running. It's not a coincidence that Honda matched a relatively low stock compression ratio with the stock early intake close timing. :)

Trailryder - Unless your rides are short and the engine only sees light loads it's best to be conservative with the CR on these engines and make sure you match the compression ratio and cam timing carefully. Don't forget it's still an air-cooled engine :)
 
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#10
I'm looking at the 430 kit as opposed to the 440. I hear you don't have to resleave with the 430
This kit leaves the stock liner VERY thin.

Not recommended for long piston life.

Rich, right as always - sometimes I just don't like to get that involved unless asked - I talk too much anyway (or should I say type too much!).

;)
 

Rodzilla

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#11
Originally posted by DualSportr


This kit leaves the stock liner VERY thin.

Not recommended for long piston life.


;)

See this is why I spend time here. It reveals my ignorance.

So what you're saying is go ahead with the 440 as it will, in the long term, provide a better lifespan?
 

mtngoat

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#12
I visited and chatted with the XRs Only crew last month and they were pretty hot on their 430 kit, which doesn't require the sleeve. They've always been pretty forthcoming with pros and cons of different approaches and didn't "con" the 430 solution because of thin walls. It'd be worth investigating that option and asking them IMHO. I know it's not the same since Al Baker passed away, but they still seem to have competent and honest staff.

I also recommend against very high compression. The XRs already run very high head temps and commonly "embrittle" valve seals causing them to smoke at start-up.
 

Wolf

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#13
I am extremely interrested in this thread.
Since I have not been very successful at selling my xr I may keep it and go to one of the above mentioned options. I wasn't sure I wanted to sell to begin with...
I am looking for a little more in order to have a chance at staying at least midpack at the starts, and have a little more snap out of corners in order to be able to clear some of these jumps that you don't have much time to set up for. Top end is of no significance to me since I am used to not having any to begin with. If any of this rambling made any sense, wouldn't that mean that by the above posted descriptions of the kits, the 415 would be better suited for me??
 

Rodzilla

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#14
"The XRs already run very high head temps and commonly "embrittle" valve seals causing them to smoke at start-up. "

Yep, experiencing it now.

Rod
 

SFO

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#15
I must confess, I can't figure out how a brittle valve seat would create smoking on start up.
I have seen high head temps on air cooled motors, turbocharged drag bikes and single cylinder rotaxes.
What I have seen is valve seats lose concentricity to the guide in high heat situations.
Also I have seen valve seats fall out. Putting new seats in a rotax head we would use .008-.010" interference, or press.
One or two mile races on a rotax and check your leak down.
The new liquid cooled stuff is nice because the heads keep a valve job longer.