hey guys... I'm thinking about uping the gearing to 16/38 on my 400EX

if I do that, will I be able to get most of my bottom end back buy installing an aftermarket silencer, and re-jetting??? I already have a K&N and some airbox mods

 

It depends on the pipe. But with the right pipe you should get most of it back with the benifit of a high top end speed. We are talk about a 400ex with stock 20 inch rears right?

 

right, stock 20" rears.....

BUT... the pipe I want is the new FMF IVQ.... dirtwheels says it's the most powerful "quiet" pipe they've tested...
Now I know I'd get more power from say a DMC double-barrel full exhuast, but I don't want to spend that amount of money or have it be that loud.

FMF IVQ = 93dB & only $189

 

If you buy an aftermarket CDI box you can bump up your RPM limit and you would not have to regear.

 

I would not get the same increase in top speed with a CDI box VS higher gearing..... if any gain at all..... HP only increases 1hp with a pipe... I don't think it'll change the top speed but 1 or 2 mph.... but gearing changes could get me around 5 mph

AND gearing is about $60 for 5mph... a CDI box is what $99? for 2 mph..... what would you do?

 

I doubt a 400EX with just a pipe will pull a 16T front, with any ***** off the line.

With the mods I have, my 400EX has no problem pulling the 16T 1st thru 5th, and still wheelies like a son-of-a-beeoch...in other words, due to the engine mods, I didnt lose power/acceleration (bottom thru top), but I did gain a higher top speed in each gear.

I also dont hit the rev limit quite as fast in each gear...hence why I didnt bother with a rev kit. Again, stock 400EXs make no real use of a rev kit, and even modded 400EXs--unless they were modded to produce power above 9000RPM--make no use of a rev kit....other than to wear out the internals faster.

 

I am use to duning. The aftermarket cdi is needed to make it up some of the dunes. If you dont have it you dont get the R's to get to the top of the hill. It made a big difference for the people I ride with. They did have to get a pipe and a k&n to make use of it though.

 

On a 250R...I totally agree with you on the CDI.
On a 400EX...no way. Does nothing for a stock to mildy modded 400EX.

 

In the dunes the CDI made a big difference getting up the dune hills on three of my fellow riders bikes. They have aftermarket headers and pipes and a k&n. they were unable to make it up many dunes until they put the aftermarket CDI in. We didnt think it would make much difference either but it did.