RB Head and low low end torque?

[ebeck]

Love my RB head. Makes it more like an MX motor, more throttle snap, pulls harder hits harder.

I just spennt the day riding frieds stock KDX and he rode mine. Actuallly same pipe and silencer on both just the head is different.

Is it more or does the RB head take away some of the low end tractor pull (torque). Seems the stock KDX was more luggable and went up hills lugging where I have to attack them a bit more with the RB head motor, mor elike a MX bike.

No complaining, everywhere the R hed is great but the loss of low end was pretty niticable. And I mean real low end, lugging in a hugh gear WAY off pipe. It just pulls up a hill like a big thumper. The RB motor needs to be wound up a bt more for the same hill.

Fast riding the RB head is better, slow or lazy riding seems the stock KDX is better. Anyone else notice this or is it just my imagination?

Not complaining I love the head just trying to confirm what I felt.

[2001kdx]

Each bike is not the same. The RB head can't compensate for different factors such as jetting and whatnot.

If you can build a KX/KDX hybrid, why won't ya shell out $160 for the RB carb? Fellas on here on NUTS about it.

[Indawoods]

What was the difference in gearing?

[skipro3]

The added compression should have boosted low end power. I'd compare jetting then look into rejetting with the new head in place.

What needle are you running? DEK and CEK are great with the DEK more for torque and CEK more for excitment.

[Indawoods]

His carb is not RB'd.... therefor the DEK and CEK do not apply.

[skipro3]

I thought the needle selection was independent of carb modification. CEK and DEK only work well with an RB'd carb and not a stock carb?

[GS]

I'd bet jetting and/or gearing made the difference.

Funny how you can think it's running JUST PERFECT.....then ride another and wonder 'what the hell?'

[Indawoods]

I thought the needle selection was independent of carb modification. CEK and DEK only work well with an RB'd carb and not a stock carb?

Correct. CEL and DEL work with stock carb.

It has to do with the cut of the slide I believe.

[m0rie]

I thought the needle selection was independent of carb modification. CEK and DEK only work well with an RB'd carb and not a stock carb?

Correct. CEL and DEL work with stock carb.

It has to do with the cut of the slide I believe.

The cut of the slide and the jet nozzle height are what determines the base needles that work for the different carbs (ie. E series, H series and RB)

[skipro3]

Well, thank you for the correction.

Now, what about compression. I thought the higher the compression the better the low end power and the lower the compression, the better the high RPM power.

[Jeb]

FWIW, when I replaced the RB-modded head with Ron's race-gas-cut head (more compression) I noticed a distinct difference from mid to high; low end improved but not as much . . . BUT I did also retard the timing a bit in an attempt to accentuate high RPM power at, perhaps, the expense of some low-end power. Meaning that had I NOT retarded the timing I likely would have noticed MORE low end power.

My direct observation of Ron's work is that not only is compression changed but the shape of the head is fairly different and based on seat-of-the-pants as mentioned above power is improved overall.

Based on my personal experiences with Ron's work I'd say that ebeck oughta' be getting more low-end power with that head . . .

[ebeck]

Now I thought the lower the compresion the more the torque. The KDX220 has less compresion thatn the KDX220 along with a smaller carb to make it a torque monster. One would think it would have higher compresion if that were benificial. Maybe I am thinking non NA motors....

As far as the RB carb, I may get it I may not on my second Hybrid. On my first hybrid stock pipe and stock carb are staying. It is my loaner bike.

why don't I get it RB carb? I could say why doesn't everybody get Talon hubs everyone raves about those. I have em...

I have a 40 pilot he has a 42 pilot. Both have the same pipe, I have a 48 tooth rear he has a 47 tooth rear. I do seem to loose traction easier as well. I wonder if the stock gearing is not optimal? Was thinking of using a 49 on the new bike but maybe not?

[Jeb]

why don't I get it RB carb? I could say why doesn't everybody get Talon hubs everyone raves about those. I have em...

What does a Talon hub do that warrants them over any other hub? Besides lookin' good?

Apples to oranges bro . . .

[scheckaet]

why don't I get it RB carb? I could say why doesn't everybody get Talon hubs everyone raves about those. I have em...

What does a Talon hub do that warrants them over any other hub? Besides lookin' good?

Apples to oranges bro . . .

yep, bling vs performance...the choice is easy for me

[canyncarvr]

Ron's modified head will increase your pull off the bottom.

Comparing one bike to another..them being 'the same' or not... isn't too productive. Fact is they are not 'the same'.

I've got a couple of Banshees. One of them I broke in using the 'hard' method..and I am convinced it runs better than the machine I broke in using a 'conventional' method. Two machines...exactly the same..and NOT the same.

Gas matters. Premix oil matters. Air screw adjustments matter. Air filter oiling matters. Lots of thing matter if you're trying to make two different machines 'the same'.

There is one thing you can count on...your bike will run better in the 'low end tractor pull' range with a head modified by RB-Designs. If it so happens that it does NOT..then you need to tune your bike so it does! run as it can..and that is better'n it does now.

Re: 'I do seem to loose traction easier as well.'

That could be due to all sorts of things, too...including more of what you feel you have less of.

Ride something like a YZ250...maybe a bit older punkin 300 and you will have gobs of traction 'loss' compared to the KDX.

Heck...follow a CRF250X and watch the back tire. It's breaking loose all the time, but doesn't feel like it is. It's also putting power pulses out at 720º engine intervals as opposed to the 360º your KDX does. That's what makes the CRF a lot 'easier' to ride in a lot of situations.

...a lot less fun, too!

[ebeck]

yeah I see your point. Makes sense. It may indeed just feel that way. Thanks fo rhte replys.

What does a Talon hub do that warrants them over any other hub besides add bling?

Look I am not trying to start an argument but that is like saying an aluminmum frame does nothing but add bling. I think you are confusing full Talon wheel set with mods like graphics.

They are not cheap, not for the faint of wallet and they do not make you go faster I'll give you that but then again neither does an aluminum frame.

[TWMOODY]

I sent my head to RB back in December and had cut for race fuel.
I retarded the timing about 4 degrees to the best of my measurement
and after taking a few rides I can say without doubt that my low end has
a mild improvement however midrange has a very noticeable improvement in response and torque and will hit the highs faster.
I enjoyed the RB pwk mod improvement but IMHO the head mod did
more for it. I also purchased a new RB mod AS but have not tried it
out yet.
Gotta dial in what I have then change out the carb and do it all over again.

[fuzzy]

By retarding the timing you probably took low end out of it so to say that it's still stronger is a great testamant to a hand worked head. Sort of a quick 'blueprinting' item for a 2-cycle. The other main workable item is the porting, and it's debatable that kawi already has this 100% correct outside of a little hand-cleanup.

The talon hubs are surely superior to the OEM ones, but IMO should only be installed until you've wore out the OEM hub...Not that common on a KDX that hasn't totally been thashed by a racer.....Unless you just have the cash to spend....Then more power to ya!

[ebeck]

Hmm it must be an auditory illusion. I am sure you guys are right on this.

[skipro3]

Something as mundane as tire selection, heck, even tire air pressure differences can make one bike perform different than another.

Swap the head between the bikes and see what the effect is. Of course your buddy with the stock head may not want to give your modded head back, so it might cost you a few dollars. Ha!!

Ride Oregon April 11, 12, 13!!!!!!