Identifying RB modded head

Questions and Answers about the best carb and Head mods available for the KDX.
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Drewski51
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Identifying RB modded head

Post by Drewski51 »

Hey guys, I’m in the middle of a restoration on a 97 KDX220. The seller said he found an RB modded carb on the bike he was unwilling to part with. Now im wondering if the head was done by RB too, but I don’t really know what to look for to tell.

Anyone have any input to identify?

Thanks!
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Molly's 70
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Re: Identifying RB modded head

Post by Molly's 70 »

Take a picture & I will compare it with the spare I have on my shelf.
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Chuck78
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Re: Identifying RB modded head

Post by Chuck78 »

An RB modded head will have been completely rechambered, with a nice crisp transition between the squish band and the combustion chamber / dome, and a nicely machined and smoothed surface.
Most others I believe would have the stock chamber and squish band, and would just be milled on the head gasket surface to reduce the piston to squish band height ("squish height") & increase compression ratio as an intentional side effect.

The 220 runs significantly better with an RB head, but will also be well improved over stock with just a milled head, although the higher compression ratio vs an RB head will limit the top end power while increases low end throttle response and torque. The 220 does quite well on low end torque through it's porting, so a higher compression head isn't necessarily needed, but the tighter squish band clearance is absolutely critical.
'97 KDX220R - purple/green! - KLX forks, Lectron, FMF, Tubliss
'99 KDX220R project - '98/'01 RM125 suspension, Titanium hardware, Lectron Billetron Pro, Tubliss
'77 Suzuki PE250 & '83 Suzuki PE175 Full Floater - restomod projects
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Drewski51
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Re: Identifying RB modded head

Post by Drewski51 »

Looks like maybe not?
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Chuck78
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Re: Identifying RB modded head

Post by Chuck78 »

I'm fairly certain that is totally stock, not shaved, definitely not rechambered as Ron Black the great KDX tuning master once had done.
My apologies, I'd forgotten to go back and add a photo of what I believe is a Fredette head (milled only) vs RB head (milled & completely rechambered) vs stock.
Last edited by Chuck78 on 05:35 pm Oct 07 2024, edited 1 time in total.
'97 KDX220R - purple/green! - KLX forks, Lectron, FMF, Tubliss
'99 KDX220R project - '98/'01 RM125 suspension, Titanium hardware, Lectron Billetron Pro, Tubliss
'77 Suzuki PE250 & '83 Suzuki PE175 Full Floater - restomod projects
'77 Suzuki GS750-844cc, '77 GS400/489cc & '77 GS550/740cc projects
'62 GMC 1000 Panel Truck
'88 Suzuki Samurai TDI/Toyota swaps
'88 Toyota 4x4 pickup
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Chuck78
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Re: Identifying RB modded head

Post by Chuck78 »

Stock 220 head:
Screenshot_20241007-182143.png
Screenshot_20241007-182143.png (1.4 MiB) Viewed 2888 times

Milled 220 head (Fredette?):
(with some detonation damage marks, this is a fairly high compression head requiring high octane, octane booster, or race fuel)
Screenshot_20241007-182129.png
Screenshot_20241007-182129.png (1.41 MiB) Viewed 2888 times
RB 220 head, milled and rechambered, similar compression ratio to stock (higher octane pump gas recommended) but a tighter squish clearance and sharpened transition between squish band and combustion chamber dome):
Screenshot_20241007-182026.png
Screenshot_20241007-182026.png (1.47 MiB) Viewed 2888 times
Screenshot_20241007-182235~2.png
Screenshot_20241007-182235~2.png (2.87 MiB) Viewed 2888 times

Ron Black 220 vs stock 220:
Screenshot_20241007-182200.png
Screenshot_20241007-182200.png (1.63 MiB) Viewed 2888 times


All 3 220 head versions:
Screenshot_20241007-182235~2.png
Screenshot_20241007-182235~2.png (2.87 MiB) Viewed 2888 times
'97 KDX220R - purple/green! - KLX forks, Lectron, FMF, Tubliss
'99 KDX220R project - '98/'01 RM125 suspension, Titanium hardware, Lectron Billetron Pro, Tubliss
'77 Suzuki PE250 & '83 Suzuki PE175 Full Floater - restomod projects
'77 Suzuki GS750-844cc, '77 GS400/489cc & '77 GS550/740cc projects
'62 GMC 1000 Panel Truck
'88 Suzuki Samurai TDI/Toyota swaps
'88 Toyota 4x4 pickup
Drewski51
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Re: Identifying RB modded head

Post by Drewski51 »

Well shoot. It was a nice thought. Thanks for the info. Nobody else is doing RB style work as I understand, correct? They seem almost impossible to buy from anyone already done.
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Chuck78
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Re: Identifying RB modded head

Post by Chuck78 »

Just milling the head via Jeff Fredette does similar enhancements, except that for one, it will require higher octane than an RB head as evidenced by the light detonation marks on the head I have pictured that's just milled and not had chamber volume alterations and squish band alterations done.
Also, on a 2-stroke, higher compression means more bottom end power AND more rapid throttle response, but at a compromise to high rom rev out / power. Lower to mid compression ratio means more top end power.
There comes a point where too much cylinder pressure through high compression not only makes an engine difficult to kickstart or crank over, but it also wears out big end rod crank bearings more rapidly. 200psi roughly is the cutoff for maximum desirable cylinder pressure for longevity and ease if starting.

Ignition timing advance is same type of relationship as compression on a 2-stroke, and opposite of what 4-stroje ignition timing advance curves are, due to the expansion chamber effects (read up on this as it's too scientific for me to recite from memory).
More timing advance means crazy fast throttle response and more bottom end, but less top end. Less advance means more high rpm power but at the expense of having a soft bottom end.
On a 220, even a soft bottom end through those two tuning variables mentioned above delivers "acceptable" low end torque due to the 220's unique porting.

To be continued...
'97 KDX220R - purple/green! - KLX forks, Lectron, FMF, Tubliss
'99 KDX220R project - '98/'01 RM125 suspension, Titanium hardware, Lectron Billetron Pro, Tubliss
'77 Suzuki PE250 & '83 Suzuki PE175 Full Floater - restomod projects
'77 Suzuki GS750-844cc, '77 GS400/489cc & '77 GS550/740cc projects
'62 GMC 1000 Panel Truck
'88 Suzuki Samurai TDI/Toyota swaps
'88 Toyota 4x4 pickup
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Chuck78
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Re: Identifying RB modded head

Post by Chuck78 »

Drewski51 wrote: 06:41 pm Oct 07 2024 Well shoot. It was a nice thought. Thanks for the info. Nobody else is doing RB style work as I understand, correct? They seem almost impossible to buy from anyone already done.

Fredette Racing Products will mill your head.

Tom Morgan Racing will take your cylinder and head and do an awesome porting job and reshape the head, as will Pro Circuit - Mitch Payton the top veteran guy and owner at PC has a well proven KDX porting and head combo.

Tom Morgan Racing might be able to do just the head for you, but unlike Ron Black, Tom may need a squish height measurement from you. You'd need to clean the gasket surfaces and reinstall the top end with the brand and thickness of base & head gaskets you plan to use, and take a piece of soft solder (look up the best kind to use, rosin core / flux core is hollow and will squish easier) and lay it across the piston side to side on the wrist pin axis, with the ends folded over in a u-shape pointed back towards the center, as to give extra measurement impression room and to keep any of the acidic flux core off the cylinder wall and rings. The solder needs to be a minimum of 1.6mm or maybe 1.8mm thick???? install head, torque head and base, and gently kick over the engine to smash the solder down. The solder must be laying right over the center of the wtist pin to be the most accurate. Kicking over a few times will suffice. Remove the head and solder, measure the smashed down solder now.
The maximum squish height to have any real effectiveness is around 1.6mm. you can run it much tighter, but rod stretch at high rpm come into play (10,000rpm on a hot engine may take a "tight" 0.75mm swuish height down to near 0!), as well as bearing service life wear and tear. 1.0mm is the tightest I'd go on a performance engine and that's with 90 or 93 octane minimum, as too tight will induce detonation even if the compression ratio overall isn't yet too high. 1.20mm is a pretty safe bet on a 2-stroke, and 1.4mm is still great. At 1.6mm or so, you're running out of room to go taller, as the squish band will lose it's effectiveness. It's purpose is to rapidly force out the air fuel mixture around the edges of the cylinder towards the ignited flame front in the center at the spark plug, and mix the air and fuel into the combustion very efficiently. Too large of a gap and you lose the effectiveness of the "squish velocity" - which is required to really benefit from the squish band design. The KDX220 squish height is pretty tall, and not as effective as what most of us desire. Kawasaki dumbed the 220 down a bit as it was more of a serious recreational trail bike tractor used for recreational riding more than racing, and the engineers knew that all pro tuners already know all the secrets to squish band height and squish band width reshaping and will do the necessary machining work to make the KDX220 more racey... Yamaha notoriously has very lame (tall) squish band heights on the YZ 2-strokes, hence why Apex Technical Innovations makes aftermarket YZ 2-Stroke heads!
The width of the squish band also comes into play heavily, hence why a 200 head has a narrower squish band width and percentage of total cylinder bore area, vs the 220 a wider squish band width. The width and height together create the total of the squish band effect, as the volume of air fuel mixture expelled from the edges nearing Top Dead Center as well as the velocity of the air/fuel being squished inwards both work together. Wider/shorter height means more rapid mixing and more low end torque and throttle response. Narrower and you have a more quick burst with less volume of air/fuel expelled at a lower velocity, as to arrive later to fuel the flame front. I hope I'm explaining this all correctly. And it must work in conjunction with the port timing as well... The delivery of the squished air/fuel being propelled towards the flame front. High rpm porting wont woek as well with a low rpm torque squish band configuration.

If you look at '94-'02 KX125 heads, they generally all have a pretty wide squish band. '03-'08 KX125 have narrow squish bands. The earlier models have decent low mod torque for a 125 and don't scream as high of rpm on top. The '02-'08 are high rpm screamers eith no bottom end, same as my brother's '00 Honda CR125R...
'97 KDX220R - purple/green! - KLX forks, Lectron, FMF, Tubliss
'99 KDX220R project - '98/'01 RM125 suspension, Titanium hardware, Lectron Billetron Pro, Tubliss
'77 Suzuki PE250 & '83 Suzuki PE175 Full Floater - restomod projects
'77 Suzuki GS750-844cc, '77 GS400/489cc & '77 GS550/740cc projects
'62 GMC 1000 Panel Truck
'88 Suzuki Samurai TDI/Toyota swaps
'88 Toyota 4x4 pickup
Drewski51
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Re: Identifying RB modded head

Post by Drewski51 »

You’re my kind of enthusiast with the level of detail of your knowledge! Thanks for the info! I’ll check out Pro Circuit and think about doing their service after I’ve ridden this thing for a little bit. Kind of doing phases of deeper dives with this project.
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Re: Identifying RB modded head

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Chuck, that's amazing! Great photos for e different cylinder heads & tons o' notes! Thank you.
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Chuck78
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Re: Identifying RB modded head

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Pro Circuit doesn't advertise their porting and head services, you have to call and see if they have the availability to schedule it.

Tom Morgan Racing has a proven KDX porting formula, as does Ted @ Boyko Racing. All 3 are very well proven for the KDX. Most professional veteran porting wizards always will turn down the base gasket surface of the cylinder in order to lower the 1990's Kawasaki transfer port height designs to a more acceptable standard height, and then they adjust the port roofs elsewhere accordingly. This really takes the place of milling the head for a tighter squish clearance, as the head gets lowered closer to the piston through this.

The 220 porting is really pretty excellent though for torque, and tighter squish improves the whole throttle range, as squish height/volume has a lot to do with targeting the peak RPM of the engine. On a higher RPM port layout like the 200, it's absolutely best to start with a 200 cylinder and remove material from the base to lower ALL ports including the notoriously raised '90's Kawasaki transfer ports, and then bore to 69.00mm 216.8cc, NOT necessarily the "225 Big Bore" 70.00mm 223.2cc size (no A, B, C sized piston options, only 1 size, A size for 70.00mm bore and no B or C for 70.01mm & 70.02mm to compensate for plating wear over the years - Wossner has 69.00mm bore A-sized, 69.01mm B, & 69.02mm C-sized bore options on their coated skirt forged pistons). Eric Gorr did not care for starting with a 220 cylinder for his porting recipe, as the ports are already lower for torque, except the transfer ports, so lowering the cylinder height to get better transfer port heights means welding up the cylinder to achieve what he was after.

Starting with a 200 cylinder for a "more power everywhere" type porting is a better idea if the veteran pro porter is looking to mill the base to lower the transfer port heights, but Mitch Payton the top vet engine tuner/builder & boss guy at Pro Circuit did his porting wizardry on Carson Brown's 220 cylinder and not a bored out 200 cylinder, as witnessed by photos showing KDX220 casting numbers on Carson's cylinder.

All of those guys can do an awesome job, but for a 220 I might lean towards Pro Circuit if available, or Tom Morgan Racing. Don't hesitate to phone Ted Boyko and even Ken O'Connor Racing to chat about KDX220 porting options though...

I'm personally planning to make a fixture for a 4-jaw lathe chuck to hold a '95+ KDX head (& perhaps '89-'94 also, only slightly different in head stay setup). I'll utilize the coolant flange as the fixing point, as the spark plug is not centered in the KDX head, unfortunately for DIY/aftermarket shop machining purposes. I have a 70mm ported cylinder that a guy was running with a 69mm stock 220 head, and need to enlarge it to a 70mm head and may as well just learn to cut down and rechamber heads for tighter squish transition and corrected head volume. Ordering a graduated acrylic burette with valve to use with plexiglass to measure head volume.
Last edited by Chuck78 on 01:08 pm Nov 06 2024, edited 1 time in total.
'97 KDX220R - purple/green! - KLX forks, Lectron, FMF, Tubliss
'99 KDX220R project - '98/'01 RM125 suspension, Titanium hardware, Lectron Billetron Pro, Tubliss
'77 Suzuki PE250 & '83 Suzuki PE175 Full Floater - restomod projects
'77 Suzuki GS750-844cc, '77 GS400/489cc & '77 GS550/740cc projects
'62 GMC 1000 Panel Truck
'88 Suzuki Samurai TDI/Toyota swaps
'88 Toyota 4x4 pickup
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Re: Identifying RB modded head

Post by Molly's 70 »

Here is my spare RB head.
DSCF0030.JPG
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DSCF0032.JPG
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Re: Identifying RB modded head

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DSCF0022.JPG
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DSCF0033.JPG
DSCF0033.JPG (1.96 MiB) Viewed 2362 times
If you lend someone $20, and never see that person again, it was probably worth it.
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Re: Identifying RB modded head

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Molly's those are amazingly clear photos and it's amazing you have the 2003 paper invoice. Thank you.
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Re: Identifying RB modded head

Post by Molly's 70 »

How does that plug look? VP VPR w/ 45:1 Amsoil. VPR is an oxygenated, ethanol free, leaded (tetraethyl lead) fuel.
Plug looks to rich for me. Bike runs fantastic. RB carb responses seem good. I think it's the fuel.

https://vpracingfuels.com/products/vp-vpr-race-fuel
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Chuck78
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Re: Identifying RB modded head

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Interesting, your older RB head looks to use the stock dome, for much higher compression than the RB heads I have here... Your VP Race Fuel's higher octane is necessary then...
'97 KDX220R - purple/green! - KLX forks, Lectron, FMF, Tubliss
'99 KDX220R project - '98/'01 RM125 suspension, Titanium hardware, Lectron Billetron Pro, Tubliss
'77 Suzuki PE250 & '83 Suzuki PE175 Full Floater - restomod projects
'77 Suzuki GS750-844cc, '77 GS400/489cc & '77 GS550/740cc projects
'62 GMC 1000 Panel Truck
'88 Suzuki Samurai TDI/Toyota swaps
'88 Toyota 4x4 pickup
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Re: Identifying RB modded head

Post by Molly's 70 »

The RB head I have on the engine now Ron did May of 2022. No pictures of it. I had purchased the top end from a member here & had Fredette
port the cylinder & he sent it to Millenium for replating. Also, May of '22. I have receipts for that work also.
If you lend someone $20, and never see that person again, it was probably worth it.
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