Which cam,piston,and bore should I use?

[leasureryan]

I am currently gethering all the parts to upgrade alot of HP. I don't want to jump straight to a 440 though. Thinking about 416 or 426.

Also, who makes the best 11.1 piston? I don't mind running a race fuel mix or straight race fuel

And stage 2 cam?

I do alot of hill climbs, trail riding, and a little MX here and there. Which is best combo.

[zrpilot]

Right on Ryan, glad to hear your not afraid to run race gas.

Given that fact here is what I'd do:

416 piston 11:1 (wiseco or Ross Piston)
CRF450 timing chain
GT Thunder HD studs (for relibility)
Stage 2 cam
Sparks X6 Exhaust
450R carb
Head porting by C&D or GT Thunder.

Should make 40 HP

[blue_ex_rider]

I would go ross 416 11.2 to 1 compression

Sparks x 6 exhaust

Tc national Cam

39 fcr or 450 carb

good port and polish
hd studs and crf chain

[leasureryan]

I am going to stick with my HMF full system.

Already have my CRF timing chain, XR400 head gasket, 450R carb, throttle cable, a ZRpilot adapter. I'm off to a good start

I plan to port and polish, and use HD studs


Why 416 and not 426???

[dariusld]

Originally posted by leasureryan

Why 416 and not 426???

Why 426 and not 416??? They both are going to make the same power and you will have another bore to go before replacing the cylinder:) I don't know if this is true, but they say the 426 gets hotter than the 416.

[leasureryan]

so how many MM would the piston be?? I would think that that would be more than just 1mm over...right? Is't 416 like 2mm over?

[dariusld]

Originally posted by max400EX
BORES

Stock 85mm - 397
.040 - 86mm - 406
.080 - 87mm - 416
.120 - 88mm - 426
.160 - 89mm - 435 (440 Kit)


I get all my info from this site, just search, its fun:)

[shallow518]

whats the diffrence between a 400ex head gasket and a xr400 gasket? also how high of compression can i go till i need to use race gas?

[AZ440ex]

Originally posted by shallow518
whats the diffrence between a 400ex head gasket and a xr400 gasket? also how high of compression can i go till i need to use race gas?

Both the XR400 gasket and the cometic 3 piece stell gasket are a little thinner.

After 11:1 I would consider race fuel. Not only will you eliminate detination issues it is a better quality fuel, burns clean and consistant.

There is alot about 400ex compression most don't realize. 11:1 is usually not really 11:1.

Read through here. It explains it pretty well and Micky Dunlap is one of the best 400ex builders around so I would believe his answers.
http://www.atvriders.com/articles/askmickey1.html

[leasureryan]

adding the XR400 head gasket will "True" your compression ration. Compression is lost when using aftermarket cams, so using a thinner gasket compensates for that