Stroker Crank

[nakomis0]

I would like to put a rod and crank in my 400ex. Not sure which one to to get. I don't know alot about them. All my mods are in my sig.

Stroker? Long Rod? Does port timing come into effect? How many mm?

Any suggestions on this?

[JOEX]

There's some info here.....
http://www.exriders.com/vbb/showthread.php?s=&threadid=97271

[nakomis0]

That did help. Pretty technical as I skimmed through it.

What gains should I expect from adding a 4mm stroker crank to a 440 with 11:1 comp.?

[SnellCRP]

As JOEX said check out that thread it got very indepth. One thing though, only in a 2 stroke engine is there port timing, not a 4 stroke. Check out that post and if you still have questions I would be more than happy to help. ;)

[nakomis0]

I dont want to get to technical I'm really just hoping for someone that knows to tell me the best set up for my quad. And maybe a little explination on why. Stroke size rod size ect.

[SnellCRP]

With the bore already at 89mm I would not suggest going any bigger there. By adding a 4mm stroker you will be gaining low to mid power assuming you don't have a cam that has an extremely long duration. High RPM cams have long duration, and low is the opposite. You may not actually increase max HP and its possible that the motor might not rev as high, but you will move your power curve up in the low to mid area which will give you that "roll on the gas" kind of power. As far as actual HP/torque #'s I don't know. The bottleneck of the engine will be its ability to breath, so I would be very particular about the cam, carb, and head mods that are made to feed the beast.

[SnellCRP]

With your current setup you should make good power now assuming it has been tuned on a dyno. You can find ALOT of HP/torque in tuning a 4 stroke that you could never feel if it wasn't tuned on a dyno. If you are looking for more I would look to initial ignition timing, cam timing with a adjustable cam sprocket, and maybe in the cylinder head. Just curious, but was your head ported on a flow bench?

[nakomis0]

It hasn't been dyno tuned ... I was actually considering that recently but was gonna wait to see if I was gonna try and do another mod.

I have never messed with any of my timing. Wouldn't know where to start with that. Your not talking like a timing advance key, right?

I'll look into that adjustable cam sprocket. If that would help.

I really don't think my porting was done on a flow bench. It was done by Magics Racing. Is there other head work I could do?

Thanks for any help, I'm just looking for more power.... somewhere, somehow....

[SnellCRP]

If you dyno tuned your current combination you would find more HP/torque just in tuning. With the timing, if you don't mind running a higher motor octane fuel, there are power gains in adding initial timing (exa. Sparks 6 degree flywheel key), or with a cdi box with a custom timing curve that will advance or pull timing depending on engine RPM. With adjusting the cam timing you can make the motors powerband "hit" harder, by advancing, like you would want for mx or have the power come on "softer" by retarding cam timing. I have seen cylinder heads that have been "hogged out" with the builder just thinking the bigger the port the more HP. WRONG, the idea with cylinder head porting is to flow the max amount of air through the smallest port. That maintains your velocity. Its like trying to force 25 cfm of air through a straw (great velocity, but volume is low), or 25 cfm through a 4" tube (terrible velocity, but high volume). On a flow bench you can find the best of both worlds, and thats the only way to make power with porting. I know of $1000 port jobs that made less HP than the stock head. When you get into cam, and initial timing there will be alot of clearance checking and careful fuel selection to resist preignition and detonation, but there is good power to be found in those areas. Next time you have your motor apart check the thickness of your squish band (the distance between top of piston at TDC and cylinder head) try to get it to about .030 - .040 by having .030 taken off the bottom of the jug or by using thin gaskets this will increase your compression and reduce the squish band. By reducing the squish band you are reducing the chances of fuel being left in the squish band where it cannot be reached by the flame front and therefore unburned and spent as exhaust gas. It also will increase the turbulence in the combustion bowl improving burn and reducing detonation. Zero squish is optimal, but mechanically impossible. This kind of power is almost free you just have to find it. ;)

[nakomis0]

Thanks for the help Snell.

I guess I'm going to try the degree key Possibley the cdi with timing options (if I can find one under $200) the and a dyno tuning.

I looked into the squish awhile back when I put the Ross piston in it. But decieded to hold off because I just wanted the thing together fast, and I was concerned with stock rod and heat issues.

I cured my heat issue now but still have a stock rod that I'm really not that confident in. But like I said I'm gonna try those other things you mentioned hopefully that will satisfy me for this summer.:)

I was kinda looking for alternatives to taking my motor totally apart. Its costly and my bike is finally reliable. thanks man.

[SnellCRP]

Get the advance key, CDI, and take your bike to a dyno and tune it. Make sure you have many different needles and jets so you can get it tuned in "perfect". Don't be afraid of leaning it on the dyno, but watch the air/fuel ratio. You will be surprised what you will find. ;) Let me know how it goes.

[nakomis0]

So a degree key and the cdi.... ok ok.

Any recommendations on what CDI box. Maybe the best bang for your buck. I seen one on ebay the Dyna FS with 4 timing curve adjustments, 4 rev limit adjustments, and options for nitrous and a bunch of other stuff I really dont think I would need, for about $280... You know off hand a basic one that would be good? Thanks again.

[SnellCRP]

I would want something I could adjust, but not for $280. I have a TC racing CDI on my quad. They are all probably good (if not all the same) the only drawback is the quad won't start as easily unless the battery is fully charged. If the battery gets weak you'll be stuck in need of a charge.

[nakomis0]

Well wait a minute. I do already have the White Brothers CDI. Wasn't sure it that increased the timing.

And I just bought a Sparks degree key.

[SnellCRP]

The CDI changes the spark curve, and increases the advance throughout the RPM's. You will be fine with the Sparks key just make sure you listen for "pinging" and if its there you need to increase the motor octane of the fuel you are running. Check out the post "Degree key" I explained a little about timing in that post. Good luck with the mods let me know how it goes. :)

[nakomis0]

Hey does your TC cdi change your spark curve? Cause my WB one doesn't.

[SnellCRP]

I assumed most aftermarket cdi's had a "aggressive" spark curve, but I think that maybe the WB only increases rev limit. If you get one with a "aggressive" curve you will pic up on the low to mid and will have better throttle response.

[Teufel]

The WB cdi box does change the timing curve

[nakomis0]

Originally posted by Teufel
The WB cdi box does change the timing curve

I called WB to ask and they said it doesn't.

Then I asked the someone that knows alot about this stuff and he said that almost all of them are just re packaged XR CDI.

SOooo.. I'm thinking they are all pretty much the same. And the guy I talked to at WB prolly didnt know what he was talking about.

[honduh440]

u r a smart man snell......lol

[SnellCRP]

Thanks.:p