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 XR400 High Performance Piston Kit?
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Blue250 has no Avatar

28 Posts

Topic started on 08/11/2004 at 7:37:51 PM  Member Profile
What kind of power upgrades would a high performance piston do to an XR400. Are they worse for the engine? Do they cut down on reliability? Is it worth the money and time to put in? Or are there other, cheeper, and less time consuming upgrades out there? Im just wondering so I can start looking for mods to do to my bike when I get it. Thanks!

1976 Honda XL250 with J&R Exhaust System - For Sale


ThumperTDC's Avatar

6556 Posts

Posted on 08/11/2004 at 11:25:58 PM  Member Profile  Visit ThumperTDC's Homepage  Send ThumperTDC an AOL message
There are all kinds of aftermarket pistons for the 400. You can get different compression ratios. Stock is 9.3:1 I have seen them up at about 12:1 which would require race gas to run properly. I have a 416 piston kit in my bike. This is an increase of 19cc's over stock. The compression ratio of the piston I have is 10.8:1 which is also an increase over stock. By increasing the compression ratio the piston is compressing the air/fuel mixture even more before the spark ignites it off to send the piston back down. By compressing it more it is going to make the ignition of the air/fuel mix more forceful, basically sending the piston down even harder than before. This will add more power, but over time could cause some parts to wear out faster than they would normally. To answer your question about it being worth it, I would say it is worth every penny. My XR400 felt like a rocket after I bored it out, and I have heard the same thing from others who have done the same thing.

2005 KTM 525MXC - The new canvas
1998 Honda XR450 - The master piece

In loving memory of my son Nicolas "Cole" Allen Carter 10/5/05


Blue250 has no Avatar

28 Posts

Posted on 08/12/2004 at 2:21:45 PM  Member Profile
do you have to use race fuel, or just premium 92 octane fuel for your bike thumper? Or can you get by with regular fuel?

1976 Honda XL250 with J&R Exhaust System - For Sale

Melbourne, Vic

booma has no Avatar

38 Posts

Posted on 08/14/2004 at 11:26:07 PM  Member Profile
I have a hi comp,standard bore piston and it pings if it isn't on PULP,but goes well,

XR75, DT250, DT400, XL250, XR250, XR600, KDX200, XR400, GPZ600, GPZ900, CBR1000


XRSheRider has no Avatar

10 Posts

Posted on 08/17/2004 at 5:27:40 PM  Member Profile
I unlike Thump have a 426 kit with 11:1 comp and it is awsome.. It runs OK with 91 octane but it really comes alive with 40% race gas mixed in. The giggle factor is worth it coming up next in maybe 5 years the big one the 440 with the 12:1 comp
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