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View Full Version : Performance V's Reliability. XR400.


keg07
06-06-2005, 04:22 PM
I've got a small dilemma and I just can't figure which way to go. I currently have a '00 xr400 that has just clocked up 10 000 k's and I would like to freshen up the engine. I just bought a stage 2 performance cam and was thinking about a high compression piston(11:1) to go with it-with a rebore one size up. But would these mods put extra stress on the other parts not designed for the extra load, mainly gearbox, compromising reliability??? The reliability is the reason I bought an XR and it served me well on a Cairns to Cape york trip and back, and I plan on doing it again, so obviously reliability is paramount. But I do like the idea of a few extra horses as well. Has anyone done similar mods? What do ya think?

johnno
06-06-2005, 04:29 PM
The only thing i have to say is with the higher comp piston

You need to make sure you use good fuel as it will start to need it
and if you go on a ride and the servo you stop at doesn,t have prem unleaded
What then.

Whilst the head is off maybe a head work just a little clean up
also the exhaust ports ground out for better flow.

Thats all i have

Kris73
06-06-2005, 04:38 PM
What do ya think?

Sell it mate and buy my WR.... ;)

Arbo
06-06-2005, 05:06 PM
keg07,
I have a JE High Comp piston in mine. It is less than 11:1, but I can't remember by how much. I think the HRC piston is 11:1 though. I have had this in the bike for about the last 12,000 k's or so. IMHO this is about the best engine mod you could do to an XR400.
I still have std cam. In sand, I need to run good fuel, but apart from that I haven't had any problems.
As far as the gearbox goes, yours being an 00, it already has the stronger gears. I also run heavier clutch springs in mine. Hope this helps.

keg07
08-06-2005, 08:41 AM
Thanks Arbo,
12000k's is a lot of work, does it run alright on standard unleaded?
I think the standard compression is 10:1 so your might be 10.5:1?

Does anyone know if a stage 2 cam will work ok with standard compression, I do have the figures somewhere as to what the cam does, but I'm not mechanically minded enough know what real differences or other modifications, if any, would be required if I did fit it?
Oh yeah, Arbo, have you replaced your cam chain at all? Just asking 'cause I thought my 10000k's was a good time for it???

Jeimbo
08-06-2005, 09:34 AM
Thanks Arbo,
12000k's is a lot of work, does it run alright on standard unleaded?
I think the standard compression is 10:1 so your might be 10.5:1?

Does anyone know if a stage 2 cam will work ok with standard compression, I do have the figures somewhere as to what the cam does, but I'm not mechanically minded enough know what real differences or other modifications, if any, would be required if I did fit it?
Oh yeah, Arbo, have you replaced your cam chain at all? Just asking 'cause I thought my 10000k's was a good time for it???


Gday Keg07

My thoughts are while the engine's in bits, replace the camchain and tensioner so you know what you have. After that you know you'll have pretty much rebuilt it and won't need to worry about things you could have replaced when it was in bits.
I may have arebuild due soon so am thinking Wiseco pistion, head cleanup, port job, camchain and tensioner and valve guides. Luckily all we need are the bits as we can do it in the garage.
A higher profile and altered duration on the cam lobes will affect how long the valves open for and how far they open. It will affect how the bike behaves as well so if you like the way it is I'd stick with stock or go for a mild cam if you want more poke. I'm no expert but from a mate's experience it'll add about $200 to the cost of the bits. Sometimes it's almost worth considering a newer bike but if the rest of the unit's good then go for it.

diZco
08-06-2005, 10:38 AM
11:1 isn't that high when you consider that the new 250F's are running 12.5:1... I think it's unlikely you would have to change your fuel in normal riding conditions.

A high performance cam is going to be more aggressive, keeping the valves open for longer - this means that they will open sooner and slam down harder at the end.. possibly resulting in faster valve wear. So you would have to keep an eye on this.

But keep in mind a new bike such as a WR already has a high comp piston and cams etc standard... so your XR probably still wont be a "close to the edge" as one of those even after the mods.. as it prob still has smaller valves and an over engineered driveline.

Obviously though when you increase power you will decrease reliability (but not to a massive extent)... you will be increasing the heat that the motor generates, the valves will be getting hotter, the oil will be breaking down sooner, there will be more stress on the crank, clutch, gears etc.

But that just comes with the territory....

turtle
08-06-2005, 07:11 PM
mine was 11.2:1 stroker with stage 3 cam, ports, 3 angle valve job and noleen exhaust. It had a massive torque gain and the cam made it rev much higher. As with any mods get your fuel system tuned to suit. The only draw back is its hard to start when cold, absolutly no throttle on start up.Still wasnt as fast as the wr426/450 but would smash them to bits on hills. The power went from 26 rwhp to 42 rwhp with no failure of any mechanical componant.As said above good fuel is a must , but that said i used to carry a small bottle of octane booster and nothing ever went wrong.The oil was changed at 750k's instead of 1000k's.Dont waste money on polishing the ports as the gain was almost nil. Port match the headers and a good "D" port job will serve u well.
ps: get the headers and muffler HPC coated to reduce the heat.

wazza
08-06-2005, 09:27 PM
I ride a box stock '98 model XR400, de-restricted and thats it apart from getting Terry Hay to weave his magic on the suspension. I have no trouble passing KTM's, Husky's, WR's, "Bergs etc. Terry's work lets you hold it open wider for longer and hit the brakes harder and later. Best money I have ever spent on improving a bike.
It almost Maico's, it's that good!!!

keg07
09-06-2005, 10:51 AM
Hey wazza, if you don't mind me asking, how much did the suspension work set you back?

wazza
09-06-2005, 02:04 PM
It was 12 months ago now, I can't remember exactly but about $400 I think.
Have a chat to Terry, its money well spent.

TEDISTHEBEST
11-06-2005, 02:48 PM
If i had the money i would rebore the cylinder to a 426 or 440. Probably a 426 because it gives you a few more rebuilds before a sleeve is required. JE piston which is about 10.6:1 (somewhere near that) Hotcams stage 2, mikuni 36mm flatside with pumper and a full exhaust system, head and valves ported and polished. Dyno tune to get jetting absolutely spot on. Should be good for about 35-40 RWHP.

go to www.thumpertalk.com and ask also found this. http://www.thumpertalk.com/forum/showthread.php?t=263352

Arbo
16-06-2005, 10:34 AM
Thanks Arbo,
12000k's is a lot of work, does it run alright on standard unleaded?
I think the standard compression is 10:1 so your might be 10.5:1?

Does anyone know if a stage 2 cam will work ok with standard compression, I do have the figures somewhere as to what the cam does, but I'm not mechanically minded enough know what real differences or other modifications, if any, would be required if I did fit it?
Oh yeah, Arbo, have you replaced your cam chain at all? Just asking 'cause I thought my 10000k's was a good time for it???

Sorry about the late reply, just got back from Finke last night.
The XR runs ok on std ULP. But I try and run PULP as a minimum. You can make it ping in the sand on anything less.
I did replace the Cam Chain. For the minimal cost, it seemed like false economy not to.

Arbo
16-06-2005, 10:39 AM
I ride a box stock '98 model XR400, de-restricted and thats it apart from getting Terry Hay to weave his magic on the suspension. I have no trouble passing KTM's, Husky's, WR's, "Bergs etc. Terry's work lets you hold it open wider for longer and hit the brakes harder and later. Best money I have ever spent on improving a bike.
It almost Maico's, it's that good!!!

I agree wazza, getting the suspension sorted on the XR is the best money I ever spent on it. More power on a poor handling bike only makes it handle worse.