power w/ these enexpensive mods?

[maxamillion]

I was curious how a Sparks degree key, xr400 cam and gaskets, grinded header welds, and an EHS lid would perform in my '02 400ex. I would be using 93 octane and would probably put in fresh rings and valve seals. My only motor mod is an HMF slip on. I want this motor to stay reliable. Does anyone have a similar set up?

Thanks

[wilkin250r]

I would throw an extra $100 into it and get a high-compression piston, and then additional few bucks to get a better filter (probably UNI).

If you get the high-compression piston, you're better off WITHOUT the Sparks timing key.

[maxamillion]

i forgot to mention i have a UNI filter. i thought the key and thinner gaskets would raise the compression enough so i wouldnt need a piston.

[Fortman_400]

key won't raise compression,, and the thinner head gasket does but only slightly,, not enough to really notice a difference at stock.

[maxamillion]

alrite thanks, i read the key advances the timing 6 degrees but i thought i heard it would raise the compression slightly, i guess thats wrong. So a 10.6:1 piston, xr400 cam, grinded header welds, and EHS lid (rejet) would be the way to go? I dont want to go to wild on the cam so its not so hard on the valves/springs. Another reason i want to do this is to get more experiance with these motors.

[Fortman_400]

instead of an advance key u could get a CDI box instead,,, would give ya a benefit from stock to however far u want to mod it.

[khen]

Sounds like a fun build.. If I had to guess I would say you'd grab an additional 3-4 HP and a couple ft lbs of torque with these mods. So maybe 33-34 hp peak..

[04'400ex'er]

well im not too experienced in the cam mod field, but from what I've read the xr cam is just slightly hotter than the ex cam.
If I were you I'd do a hotcam. you can keep everything stock.

[Fortman_400]

if i ever put an agressive cam in mine i'd go on the safe side and get stronger valve springs atleast,, worst thing to happen would be valve float after u got ur engine back together

[Eddiesanders250]

hey wilkin why do you say a uni air filter? why not a K&N?

[wilkin250r]

I prefer K&N, but they are more difficult to oil. As such, if they are not oiled properly, they present a significant risk. How many times have you seen posted here about K&N filters passing dust? Lots.

UNI filters provide nice gains, and are much easier and less critical to oil. As such, they present less risk from a recommendation standpoint. I would truly hate to recommend a K&N filter, and then have it destroy his new engine because it wasn't oiled properly.

[wilkin250r]

As far as aggressive camshaft profiles, heavy-duty valve springs and such, I think the XR400 cam is a perfect compromise between performance, cost, and reliability.

It's true, there are MANY better camshaft profiles out there to provide more power than the XR400 cam. However, with such radical profiles, they often require stiffer valvesprings and/or hardweld of the rocker arms. I'm not sure I would trust the stock valvesprings to handle a radical cam. However, I would certainly trust the stock valvsprings to the XR400 cam.

I don't think I would feel comfortable dissassembling the valves to replace the springs without lapping the valves to ensure a good seal. And me personally, I don't have the proper equipment to lap the valves, and it's about $200 for your local shop to do it.

If cost and reliability are more important than performance, I say leave it all intact, with the stock springs. With that, you are severaly limited in your choice of camshafts, and the XR400 cam is certainly better than stock.