More Compression = More Low End?

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Jeb
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More Compression = More Low End?

Post by Jeb »

'Thought I might be interested in picking up another 220 head and having Ron do his thing, yet have the "spare" suited for race gas. Why? 'Cuz the more I ride this 220, the more I lust for just a bit more . . .

then I read some very interesting kdxrider threads about the increase in compression doing more to shift power as opposed to adding power. At least that's what I got out of the threads, which is somewhat disappointing given that 1) Ron's website states, " . . . I can give you even more compression . . . this will give more power and you will need to use race fuel . . . " and my hopes were elevated by this statement and 2) I don't want to sacrifice the upper end of things for more of the lower end.

Yes, I want my cake and to eat it, too! Actually, I'd settle for an increase in power across the board . . .

so did I understand the threads correctly? Here's one:

http://www.kdxrider.net/forums/viewtopi ... t=race+gas
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Post by Colorado Mike »

I noticed a good deal of added grunt on my 220 when I had Ron perform his magic. Mine was done so that I could still run pump gas, but I did tell him that I would not be lower than 5000' and to consider the norm to be 9000'. I imagine if I were to be riding at sea level I could well need better gas.
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Post by Green Hornet »

I picked up another 220 head on EBAY & had it shipped straight to RB. I just e-mailed Ron to let him know it was coming......For the woods guys, topend is not the riding factor....Low-end is what gets me through the Mud, Rocks, Hills & Such.....
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Post by Jeb »

Mike - I'll never know how much the head mod does because I did the carb + head at the same time. Any comments on what happened (or didn't happen) on the top end? Carb + head mods did wonders everywhere.

GH - I'm watching a "Buy it Now or Best Offer" head right now!! Is this other head you're sending to Ron gonna get the xtra compression?

I probably wouldn't do this if I wouldn't end up feeling some more on top as well as the bottom. Fact is I got about a 15 minute ride on a 300xcw within the last couple of weeks and I gotta' tell ya it made me want more out of my 220. Sure, the 220 is not going to ever be like that 300 - and that's allright - but I guess I'm considering some of the options.

I know there's the 240cc bore and recently another member made some positive comments about that.

Maybe if higher compression adds more overall power but it tends toward the low end I could have a little of the right kind of porting to shift some of the "extra" power towards the higher end? A synergistic kind of effect for more power everywhere? I don't know, guess I could use some schooling in how porting works . . .
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Post by m0rie »

Fuzzy can give you a good primer on how porting works to move around a 2t's powerband...
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Post by 2001kdx »

Jeb. You need to leave your KDX alone.

It's fine for what it is. You have a set of YZ forks, and your craving more power.

Let me put it this way - You need to add a bike to your stable - In the form of a YZ250! :supz:
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Post by Colorado Mike »

I did mine seperately, which is a waste of downtime and shipping. What I noticed was the carb mod gave me much better throttle response and opened the top end a bit more. It seemed to allow the bike to chug at lower RPMs much better and be easier to keep running right in changing altitudes and weather conditions.

The head mod was done about a year later, and the first thing I noticed was the bike took a good bit more effort to kick over. Nothing difficult, but just a more determined tromp. I would hesitate to put it on a small lady's bike though. Then I noticed a nice increase in low to mid RPM power. The bike was a good bit more willing to loft the front wheel over holes , water and rocks. Above the midrange, I think the benefits taper off. This is all subjective seat of the pants type stuff, perhaps a dyno would tell a different story. I seldom ride on a dyno though. it was also with a torque pipe on. I have switched to a rev pipe, and feel a bit more hit, but that's not comparing to pre RB head, just over the torque pipe.

Comparing this bike to my kid's YZ, there is just no comparison. He likes mine on trails since it is so torquey. Unless it is very tight and rocky though, I can ride the YZ a good bit faster than my bike ( this is not all, or even mostly due to the power). The hit on the YZ is an event you do well to be ready for. On my bike, you notice the surge, but as I said on another thread, it's pretty underwhelming. I've ridden the KTM 300, and agree it's a very nice motor. Personally, the chasis aggravates the crap out of me. Too bad Kawy tucked their tail and abandoned the 2 stroke trail rider instead of building a KTM killer that has a suspension that the average owner has a prayer of being able to tune (as in a linkage). Go ride a KX500 sometime. Kinda like a KTM 300 with a blower :supz: . Nothing like rolling on that throttle and seeing the terrain turn to blurriness. :lol: Just make sure you have room to pass your buds without sucking them in behind you, or roosting them off their bikes. The things are basically like Jetskis propelled by a stream of dirt and rocks.
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Post by Jeb »

Great feedback on the carb and then the head, Mike . . .

On that YZ125 - fact: they develop as much horsepower these days as did my '83 YZ250.

The biggest post-Penton era big-bore 2stroke bike I've ridden, I believe, was that 300. 'Talk about some bull-snortin', snot slingin' torque. It was actually easy to ride off idle, one could make due in the woods as long as you didn't nudge that throttle very much (like off a bump or an ill-timed log!). I swear I felt the bones in my wrists and fingers separate as I would roll the throttle on. Ergos? If you get the chance try riding one in a standing position, 'course, hanging on gets darned tricky . . . :grin:

if only I could get some more of that on my 220.

RE: you need to leave your KDX alone - messin' with things was part of the plan with the KDX from the beginning!!
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Post by Rick »

I think we need to put my 250 motor in your frame Jim! PEEEEEEEERFECT!!!!!!!
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Post by quailchaser »

>|<>QBB<
Colorado Mike wrote:I did mine seperately, which is a waste of downtime and shipping. What I noticed was the carb mod gave me much better throttle response and opened the top end a bit more. It seemed to allow the bike to chug at lower RPMs much better and be easier to keep running right in changing altitudes and weather conditions.

The head mod was done about a year later, and the first thing I noticed was the bike took a good bit more effort to kick over. Nothing difficult, but just a more determined tromp. I would hesitate to put it on a small lady's bike though. Then I noticed a nice increase in low to mid RPM power. The bike was a good bit more willing to loft the front wheel over holes , water and rocks. Above the midrange, I think the benefits taper off. This is all subjective seat of the pants type stuff, perhaps a dyno would tell a different story.
I also had these mods done at separate times. Carb first...head second. The results of the seat of the pants test...Same as Co. Mike. After riding other poeples bikes and getting the same feeling as you Jeb, I picked up an '02 KX. I prefer the KX for the ST over the KDX. That was why the KDX went when we needed a better truck for the family. If I had it to do over, I would have liked to find a way to keep the KDX. The KDX was always a hoot to ride chasing the kids and worked well as a back up bike. The RB carb mod made it simple to jet for elevation changes.

I'd really love to have it back as it was street legal here in AZ. Makes those trips to Prescott and Flagstaff much easier not having to worry about LEO's. I've got a line on an '04 Husky WR250 that's plated. Might get back to 2 bikes again!

My vote, pick up an MX 250 2T set up for woods and ride that pace. Keep old reliable in it's current form for the pleasure days and kid chasing. It's a Great trail bike!
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Post by canyncarvr »

Re: 'Yes, I want my cake and to eat it, too!'

That's likely to lead to no cake and an empty tummy.

Nothing wrong with tweaking things..but when the desire to tweak exceeds the available envelope of tweakability...you end up with lowered reliability and more tuning headaches.

:hmm: Mrs. Jeb might appreciate the approach, 'I love this bike! It is PERFECT for what I need it for!' You know...as opposed to, 'Bigger! Better!! MORE!!! I want to trade in my 220 for two 110s!!!'

:wink:


Have you run toluene? That's a cheap high!


Don't relate Ron's head work to simply a compression increase. That's part of it...certainly not all....probably not even most of why his heads work so well.

Increased compression is one piece of an increasing complexity of puzzle that can make the engine run better...but it's just one piece.

That said, the 220 is known to have widely varying head volumes. Giving it a tuneup through RB-Designs would certainly be a plus.

Making the 220 run with a 12cc head? No cake in that!

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Post by fuzzy »

All above sugesstions sound good. Having the squish cut on the head to yield higher compression will help the power everywhere....Not necessarily just on the low end. The powervalve/porting/pipe will help take the power up top, but then detonation will occur w/o race gas. No trade-off for higher static compression other than having to run race gas....If you're willing to do that you will love it. You might be able to run a tolulene mix w/ pump gas to get you there, but for absolute max out of a compression mod have it setup to run on VP C-12 or similar.

I'm not too sure about what port jobs have sucessfully been done to 220's. Porting is like a camshaft on a 4T...There is always a trade off. More top end=less low end. You probably have some low end to spare, and this may be an option. Keep in mind that a port job (for more top end) along w/ a race-gas head cut may net you the same low-mid you have now. Also keep in mind that in most cases the squish will need to match the port-job so if you're planning on a port-job don't have the head cut first.

Most 'porters' go on the mid-top side of the equation. Eric Gorr is the only builder I know of that takes power-rance specifications when porting(a kdx). Fredette's jobs are known to be top-end emphasized (FWIW, I don't consider him an engine builder despite his vast KDX knowledge).

If it were me, I would've run the ebay 220 cyl bone stock (as the 'spare'), and sent the fried 200 off to Gorr for a 225/port/head overhaul. The 225 is reportedely the best combo to solve the 200/220 debate as it 'does it all.' However, even w/ pump gas squish spec most have had to run race gas or at least tolulene. The head probably reaches a limitation at the 225 bore size making it hard to get it right for pump gas. In order to truely do a 'mild' 225 for 93 octane a 'blank' head might be required(never heard of anyone doing this). Point is I think this combo is the best bet for those looking for 'all out' without sacrificing woods ability...Problem=race gas. After that it's methanol(NO range even with large tank), or another bike/engine combo.

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Post by kawagumby »

My head mod (no carb mod) slightly dropped hit just right off of idle, but added significant power everywhere within the rpm range that I tend to use. The thing carburetes better with the head mod too. The loss off of idle wouldn't even be noticeable to most riders I think, it just requires a little more clutch in extreme conditions like steep uphill rooted sections.

I've read that increased compression generally decreases low rpm power, which seems to be my experience.
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Post by Green Hornet »

>|<>QBB<
Jeb wrote: GH - I'm watching a "Buy it Now or Best Offer" head right now!! Is this other head you're sending to Ron gonna get the xtra compression?
I had the head cut for pump gas. The stock head is just that stock & I'm leaving it until I need it or decide to do anything with it. Porting is what will have the most effect on top vs. lowend...My 220 just pulls, pulls & pulls. I stall it once in a while & thats usually becuase I hit the rear brake
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Post by m0rie »

Kawa - Try an EG plug and gap it a bit on the large side of the spec. Might find some of that low end hiding... A rewound lighting coil also gives some extra low end pull...
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Post by kawagumby »

mOrie,
I'll give the gap increase thing a try - honestly though, I am very satisfied with my bike's current performance - the weak link is always me. I'm such a skinflint by nature I'm actually still using the same plugs that were running in my 2smokes back in the 80's, I just keep cleaning them with a spark plug cleaner.... mebbe that'll help by "naturally" increasing the gap - something else that I don't check much.. (if I can see air - it's good to go!) LOL
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Post by m0rie »

Get a new BR8EG! You'll like the difference!
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Post by Jeb »

Great stuff guys . . .

For the record, I have an RB-modified head . . . for pump gas. When considering options for more power, one that seemed most likely for success was Ron's head modification for race gas. I recognize that Ron does more than raise the compression and so it seemed reasonable to expect more power for the higher-compression head (in fact his website indicates this very thing). Some searching yielded some threads indicating that more compression would mean more low end at the expense of high end . . .

If I send a second head to Ron (so I can switch the heads when and if I don't run higher-octane fuel) would the Ron-Black-modified, race-gas-compression-level head mod result in more power all around or more low end?

RE: No cake and an empty belly - I'd settle for licking off the icing, you can have the spongy stuff!

Toluene? I've got some and I'm gonna try it next go around. 5% a good starting place?

Wait a minute . . . Kawagumba suggests that it's the high end that benefits most. That would work for me.

A 250? Someday, maybe!
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Post by canyncarvr »

Re: 'would the Ron-Black-modified, race-gas-compression-level head mod result in more power all around..'

Yes.


'Your results may vary...' but 5% works for me. I've tried higher percentages (7% and 10%), went back to 5%.

It's real easy to get into a seemingly endless list of possibilites. I found quite by accident that one brand of pump gas works much better than what I have been using. First put it in my Honda. Wow! Immediately noticeable. Must be my imagination...but I found the same effect in my Tracker and the KDX. Wibby noticed it in his V-Strom, too.

Riding last week with a CRF450X..there was a stretch of pavement we rode going to/from trails a couple of times. Honda-man said, 'That 200 scoots along pretty quick!' He asked it I had any throttle left...I told him, 'That was only 1/4 throttle.' He thought I was kidding. I wasn't. And it was 4-stroking at that. It was happy!!

The point is...a simple fuel change (it being just another pump junk choice) made a big difference. How many fuel, oil, witch's mixes can you come up with?

That doesn't cover timing, spark, air, jetting, etc. etc. and on and on.

Get your head done. Buy a jug of C12. Have a lot of fun!!

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Post by Jeb »

Won that 220 head . . . $45 + shipping.

'Gonna get it to Ron next week. I'll have a jug of VP 110.

'Can't wait!!
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