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426 Q's.....

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OK... To get a 426, is it bore to 88mm and get an 11:1 piston??

For the people who run this size, what cam are you running??? What are the performance differences in the Stage 2, 3 Hot Cam's??? How does the stock cam work with this???

I want to up the HP's, but too much extra is needed for the 440 kit... (pumper carb etc) So I'm really liking the idea of the 426... Much cheaper to do too...

Any info would be greatly appreciated...

Thanks!!!!!!

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Even going to 416 makes a huge difference over stock. The difference between 416 and 440 is mainly some roll on torque. If you plan on keeping the bike a long time I'd go 416 so you can bore it again to 426.

A pumper isnt a requirement for any big bore kit, although they are nice.

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I run an 11:1. You can see the mods in my sig. I have the stock cam.

Huge power difference. You never ever run out anymore. Lots and lots of torque. Completely worth it.

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OK... To get a 426, is it bore to 88mm and get an 11:1 piston??

For the people who run this size, what cam are you running??? What are the performance differences in the Stage 2, 3 Hot Cam's??? How does the stock cam work with this???

I want to up the HP's, but too much extra is needed for the 440 kit... (pumper carb etc) So I'm really liking the idea of the 426... Much cheaper to do too...

Any info would be greatly appreciated...

Thanks!!!!!!

Yes a 426 is an 88mm piston that uses the stock engine sleeve. JE and Weisco both make 88mm pistons. A "440" is actually a 89mm piston with 435 cc's. When I redid my engine I went for the 426 because it wasn't worth putting in a new sleeve for 9 ccs. The displacement gain gives you roughly 3 hp but where you gain most of your power is from a compression increase and a high performance cam.

The stock cam is too restrictive on the XR 400 partly because it is a green sticker. An aftermarket cam will have more duration and lift. The difference between the hotcams 1,2,3 is the amount of duration. More duration gives you more mid-top end but you loose a little low end which isn't a big deal. The hotcam stg 3 is probably the best bang for the buck. I have a web cam but I had to get new valve springs and hard welded rockers.

Pumper carbs are expensive but they are worth every penny IMO. I have an Edelbrock and it really is awesome. It makes pulling wheelies unbelievably easy and the throttle response is always crisp which is worth a lot. Also the edelbrock works really well with elevation changes. If the bike is running too rich you reach under the seat and turn the mixture knob leaner and your back to perfect carbonation. No more tearing your carb apart and changing jets!

Have fun with your XR project :thumbsup:

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I discussed this with several experts prior to having mine 440ed. This research led me to believe that the sleeve required for a 440 gives you cylinder wall thickness equal to or greater than stock specifications, boring a stock cylinder thins the walls of the cylinder and could make them more prone to cracking and porosity. Bigger bores produce more heat. I dont knock the guys that choose to bore their cylinders and I know it works but I chose the long route. Just my .02

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Great info.. Thanks... Is there a reason to do the 11:1 vs. the 10:1 piston???

The 11:1 will give you some more low end torque and top end power than the 10:1. I have a 11:1 piston and have had my bike ping only once when it was really lean (my bike was backfiring constantly; chose the wrong jets for Nevada :ride: I ordered my Edelbrock soon after that :thumbsup: ). 11:1 is about the highest you can go without your bike pinging..

Rockjockey is right, the sleeve on the 426 is getting thin but I've never heard of a bored out sleeve cracking.

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I was running a little rich before the 426. It runs perfectly since then, with no other changes.

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I have USDs, but since I toasted my xr(currently pulling engine apart) I guess its time for a 426 kit!

btw -- Rannoch where in cali do you live? And where did you buy your piston kit

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