Rev Boxes

[jasonanderson1]

Hey everyone, im thinking about getting a rev box. What your opionons on rev boxes? is it true they blow your engine?
Thanks in advance.

[tri5ron]

Aftermarket rev boxes on a 400ex are not necessary, or beneficial by any measureable amount.
The 400ex makes all of it's torque and 99% of the HP, well below the rev limiter of the OEM box.

You can spend your money on far better performance upgrades,...
that will return greater gains,...
that will not inhibit the reliability,...

and, are a better "Bang for your Buck" value.

JMHO.

Example,
A bone stock 400ex puts out 27HP at the crank, and approx. 24-25HP at the rear wheels. (this is per the Dyno shop guru's).

My '03 400ex puts 32.7 HP (at the rear wheels/on the ground),
With a STOCK, OEM, Piston, Cam, and Rev box.

Here's a couple of threads you might be interested in...

http://www.exriders.com/vbb/showthread.php?s=&threadid=409169

http://www.exriders.com/vbb/showthread.php?s=&threadid=349499&highlight=sparks+advance

http://www.exriders.com/vbb/showthread.php?s=&threadid=314423&perpage=13&highlight=carb&pagenumber=1

Enjoy,
Welcome to the forum,
(and welcome to the disease, btw- there is no cure.)

-Ron

[bkelley]

x2 on all of the above.

There just isn't enough power left once you hit that stock rev limit to produce any gains. If you want cheap power, look into a nice slip-on (a new Lexx can be had for $200), Sparks key, EHS airbox lid, new tires, etc.

[jasonanderson1]

thanks guys...well i already have most of the basics done as i bought it from somone it came with for performance:
K&N filter
Motoworks Slip-on
FMF Powerbomb Header
What else can i do performance wise without boring or putting a new cam in it? What are some otehr opitons? i no the timing advance key does not work with aftermarket bores so it would be useless after i blow my enine corret?

[bkelley]

Originally posted by jasonanderson1
thanks guys...well i already have most of the basics done as i bought it from somone it came with for performance:
K&N filter
Motoworks Slip-on
FMF Powerbomb Header
What else can i do performance wise without boring or putting a new cam in it? What are some otehr opitons? i no the timing advance key does not work with aftermarket bores so it would be useless after i blow my enine corret? Wheelie, a member here, makes +3 keys that are high compression friendly. I'd say before moving on to a bigger piston and cam I'd look into suspension. Even some 450 shocks are way better than stockers. A nice suspension will in theory give you more power since you are able to ride harder and faster.

[nastyrider17]

I know this is a bit off topic but when installing the sparks key what happens if I don't hold the flywheel forward when tightening it?

[jasonanderson1]

ok maybe il try that...what exactly does the sparks key do performance wise?

[nastyrider17]

Originally posted by jasonanderson1
ok maybe il try that...what exactly does the sparks key do performance wise?

It improves throttle response.

[tri5ron]

Originally posted by jasonanderson1
ok maybe il try that...what exactly does the sparks key do performance wise? It fires the sparkplug 6 degrees earlier, on the compression stroke, relative to crankshaft rotation, compared to the factory ignition timing.
Thus resulting in a earlier flamefront in the combustion chamber, a longer and more complete burn time during the combustion stroke, and increased low end torque, without compromising any reliability.

or in other words, as mentioned above,...
Better throttle responce.

Naturally it does create a slight amount more heat, but it is a negligable increase, and will not cause any detrimental conditions, providing you have sufficient cylinder wall thickness, airflow, and oil cooling.

a +6 key will work just fine for a compression ratio up to, but not exceeding 10.5:1.

If you go to a higher compression piston, (11:1, 12:1, etc.), then it is advisable to use one of Wheelies +3 keys, or a stock OEM key.

[tri5ron]

Originally posted by nastyrider17
I know this is a bit off topic but when installing the sparks key what happens if I don't hold the flywheel forward when tightening it? nothing will happen. it will run the same as stock.
UNLESS, you install the key Backwards, AND rotate the flywheel backwards upon reinstallation.
In THAT case, you would end up with your ignition timing retarded from stock, and it would have lost low end torque, and overall HP.
or in other words,...
it would run like a slug.

... back to the OP's thread reguarding rev boxes...

[jasonanderson1]

Originally posted by tri5ron
It fires the sparkplug 6 degrees earlier, on the compression stroke, relative to crankshaft rotation, compared to the factory ignition timing.
Thus resulting in a earlier flamefront in the combustion chamber, a longer and more complete burn time during the combustion stroke, and increased low end torque, without compromising any reliability.

or in other words, as mentioned above,...
Better throttle responce.

Naturally it does create a slight amount more heat, but it is a negligable increase, and will not cause any detrimental conditions, providing you have sufficient cylinder wall thickness, airflow, and oil cooling.

a +6 key will work just fine for a compression ratio up to, but not
exceeding 10.5:1.

If you go to a higher compression piston, (11:1, 12:1, etc.), then it is advisable to use one of Wheelies +3 keys, or a stock OEM
key.

So what timing key should i get so in the case i blow my motor i dont needa replace it??

[quadmanw]

you said your 400 has a motoworks with fmf headers. is it still loud? or the sound decreases alot? thanks man

[jasonanderson1]

well its guna be louder then the stock exhaust obviously. And yea its pretty loud...np.

[monster400ex]

i have had a few rev boxs the moose racing one and the amr stage 2, yeah i agree with the minimal gain at high rev's but thats not what i bought it for, it does make a difference to the bottom and mid range not bad for spending 38 dollars on it (1 or 2 horse)
the moose one didnt have the rev limit on it so i sold it for the same price now i have the amr stage 2 with a 750 rpm gain which i would be happy with the stock limit i was just lookin to get a little more spark advance out of it, it helps out with the throttle response mainly.