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stock compression xr400 etc

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Hi dudes,

sorry but i need some info on the stock compression ratio..

any1 here knows? :applause:

if i changed to a 12:1 stock bore high compression piston what other things should be recommended to change? 🤣

how bout a satge 1 cam?

any bearings to change also? :banghead:

bearing numbers?

i bloody new & green at this so pls guys/gals pls bear with me as i'm scouring the pages but to no avail 🤣

thousand apologies & many thanks in advance

des 🤣🤣🤣

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Well first off I wouldn't go any higher than 11:1 compression and maybe even think about just going 10.5:1. You will have to go to race gas with the 12:1 and I have seen pictures of blown up XR400's because the connecting rod was not designed for that. The rod gave way and grenaded the cases. They do make heavier connecting rods which are excellent but then instead of a top end rebuild you are looking at splitting the cases. The other consideration is the clutch. At the least you will need heavier clutch springs and should go with a billet clutch basket, i.e. Hinson, Barnett, or better yet I hear the Wiseco is best because it is forged, don't know the exact difference but there again I read an article saying it was the best for the 400 app and it stuck in my mind. As far as pistons, Wiseco and J&E seem to be the top choice that I know of. I would not go with the 440 it needs a re-sleeve. If your bore is still fairly fresh you might want to go with the stock piston size and just up the compression, I hear this will really wake the bike up. Lastly I have heard good things about Hot Cams both Stage 1 & 2 (1 for trails riding and 2 more for wide open desert). They do not have an automatic decomp on them if that makes a difference to you, not to me. If you want a HRC replica cam, you can get one from XR's only, it is supposed to be a good choice and still has the decomp on it. I heard Hot Cams is coming out with a Stage 3, but I haven't looked into it yet. Don't forget the Gordon Mods" consider a Mikuni pumper (another great addition) IMS footpegs, gold valves, GPR damper, Renthal Bars, etc. etc. etc. By the time you are done you could have bought a brand new spanking USD fork wearing, Austrian or Japan made bike. But then again, I love my 400, always gets me back. 12:1 compression I wouldn't be so sure.

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i guess yr right maybe a 10:1 would suffice first as i do not know the stock compreesion of the piston.will stick to what you said should be good enough

as for the cam i'll go for the stage 1 first to see if my bike really needs a wake up call.also am hunting for an fcr or something as the freight to singapore for the mikuni is downright insane!!!

then again you may have one up for sale to poor old me?

thanks for the advise i kinda read wrongly as the 12:1 needs to resleeve

whereas the std bore compression 10.5:1 or 10:1 would do just nice

cheers & ride safe

des

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