YZ 250 head mod

eric513anderson
Hey guys looking for feed back from owners who have sent there YZ 250 cylinder head to R&B designs for the "head mod". I have yet to buy any solder and do the test myself. I own a 2011 bike and swapped the head with a 2006. That head has the better compression ratio and helped my bike in the low end power some. I still want to be able to run the bike on 93 octane pump gas like I do now. Maybe mix pump and race gas 50/50 on ocassion. Thanks!

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adam8781
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adam8781 1/16/2017 10:17pm
1/16/2017 10:17pm
get solder, do the test and send it out, rd designs work is absolutely top notch, the 11 head is horrible, the 06 head is also garbage. keep going down the rabbit hole it gets so much better!
slipdog
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slipdog 1/17/2017 9:39am
1/17/2017 9:39am
eric513anderson wrote:
I thought the stock heads were decent...
They are not garbage in design, only in set up. They average between .076"-.082" on squish clearance depending on the year. General fix is .030" off the face and you'll fall into .040" +/- which is a good number, but the overall compression bump will be too much for pump gas. With .030" decked it will fall into the 18.5-19cc range and the dome will have to be opened up to about to get 20cc or higher to safely run on pump.
Monk
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Monk 1/17/2017 10:43am
1/17/2017 10:43am
Reshape the dome when you so the head and you can run premium octane pump gas all day...

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Monk
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Monk 1/17/2017 10:44am
1/17/2017 10:44am
eric513anderson wrote:
I thought the stock heads were decent...
slipdog wrote:
They are not garbage in design, only in set up. They average between .076"-.082" on squish clearance depending on the year. General fix is .030" off...
They are not garbage in design, only in set up. They average between .076"-.082" on squish clearance depending on the year. General fix is .030" off the face and you'll fall into .040" +/- which is a good number, but the overall compression bump will be too much for pump gas. With .030" decked it will fall into the 18.5-19cc range and the dome will have to be opened up to about to get 20cc or higher to safely run on pump.
+1
erik_94COBRA
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erik_94COBRA 1/17/2017 1:40pm
1/17/2017 1:40pm
slipdog wrote:
They are not garbage in design, only in set up. They average between .076"-.082" on squish clearance depending on the year. General fix is .030" off...
They are not garbage in design, only in set up. They average between .076"-.082" on squish clearance depending on the year. General fix is .030" off the face and you'll fall into .040" +/- which is a good number, but the overall compression bump will be too much for pump gas. With .030" decked it will fall into the 18.5-19cc range and the dome will have to be opened up to about to get 20cc or higher to safely run on pump.
Slip-
Any chance you have the stock head volume from a 2001 CR250?

***

OP-
Neat picture of that tree. My uncle in AR has one like that on his property. Supposedly bent by Native Americans while the tree was very young.

Erik
njracer46
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njracer46 1/17/2017 2:28pm
1/17/2017 2:28pm
Coming off of ktms I bought my first yz last year, the head mod was the first thing to do on my list. I put 70 hours on the bike since March with no engine problems running premium pump gas. I didn't notice any difference in performance but I'm a horrible test rider. Bike seemed to run pretty good from cold spring/fall to hot and humid summers. If you plan on running pump gas do not hesitate, it's cheap and RB is good to work with.
Ktm 5
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Ktm 5 1/17/2017 4:05pm
1/17/2017 4:05pm
J-Bone did the head on our ktm and my son loved it
slipdog
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slipdog 1/17/2017 4:22pm
1/17/2017 4:22pm
slipdog wrote:
They are not garbage in design, only in set up. They average between .076"-.082" on squish clearance depending on the year. General fix is .030" off...
They are not garbage in design, only in set up. They average between .076"-.082" on squish clearance depending on the year. General fix is .030" off the face and you'll fall into .040" +/- which is a good number, but the overall compression bump will be too much for pump gas. With .030" decked it will fall into the 18.5-19cc range and the dome will have to be opened up to about to get 20cc or higher to safely run on pump.
erik_94COBRA wrote:
Slip- Any chance you have the stock head volume from a 2001 CR250? *** OP- Neat picture of that tree. My uncle in AR has one...
Slip-
Any chance you have the stock head volume from a 2001 CR250?

***

OP-
Neat picture of that tree. My uncle in AR has one like that on his property. Supposedly bent by Native Americans while the tree was very young.

Erik
Sorry, I don't have detail for those older motors. Back then I was still learning under a "head of engine dept" and I made all my cuts and changes according to his spec sheets. Didn't start recording my own data until a handful of years later.
eric513anderson 1/18/2017 1:55pm
1/18/2017 1:55pm
slipdog wrote:
They are not garbage in design, only in set up. They average between .076"-.082" on squish clearance depending on the year. General fix is .030" off...
They are not garbage in design, only in set up. They average between .076"-.082" on squish clearance depending on the year. General fix is .030" off the face and you'll fall into .040" +/- which is a good number, but the overall compression bump will be too much for pump gas. With .030" decked it will fall into the 18.5-19cc range and the dome will have to be opened up to about to get 20cc or higher to safely run on pump.
erik_94COBRA wrote:
Slip- Any chance you have the stock head volume from a 2001 CR250? *** OP- Neat picture of that tree. My uncle in AR has one...
Slip-
Any chance you have the stock head volume from a 2001 CR250?

***

OP-
Neat picture of that tree. My uncle in AR has one like that on his property. Supposedly bent by Native Americans while the tree was very young.

Erik
I have no idea what happened to this one. We always call it the "L" tree. It's at Haspin Acres in Laurel Indiana
WileCyot
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WileCyot 1/22/2017 10:07pm
1/22/2017 10:07pm
slipdog wrote:
They are not garbage in design, only in set up. They average between .076"-.082" on squish clearance depending on the year. General fix is .030" off...
They are not garbage in design, only in set up. They average between .076"-.082" on squish clearance depending on the year. General fix is .030" off the face and you'll fall into .040" +/- which is a good number, but the overall compression bump will be too much for pump gas. With .030" decked it will fall into the 18.5-19cc range and the dome will have to be opened up to about to get 20cc or higher to safely run on pump.
erik_94COBRA wrote:
Slip- Any chance you have the stock head volume from a 2001 CR250? *** OP- Neat picture of that tree. My uncle in AR has one...
Slip-
Any chance you have the stock head volume from a 2001 CR250?

***

OP-
Neat picture of that tree. My uncle in AR has one like that on his property. Supposedly bent by Native Americans while the tree was very young.

Erik
Erik, I have 2 I can CC if you need. Been saving these parts for a future AF build. 09 crf250r frame.
Bruce372
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Bruce372 1/22/2017 11:05pm
1/22/2017 11:05pm
50 % squish, so record the volume stock, measure the squish and calculate how much you need to take off the face to get 1.0mm.

Take twice that amount out of the bowl to keep the same compression ratio
erik_94COBRA
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erik_94COBRA 1/23/2017 5:08am
1/23/2017 5:08am
WileCyot wrote:
Erik, I have 2 I can CC if you need. Been saving these parts for a future AF build. 09 crf250r frame.
Would be much appreciated. I think I'm going to be stuck running avgas for the time being, but knowing the stock setup will help me know what direction to go with this head next. (head modified to correct squish, tuner setup head for avgas not pump gas).
WileCyot
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WileCyot 1/23/2017 5:22am
1/23/2017 5:22am
WileCyot wrote:
Erik, I have 2 I can CC if you need. Been saving these parts for a future AF build. 09 crf250r frame.
erik_94COBRA wrote:
Would be much appreciated. I think I'm going to be stuck running avgas for the time being, but knowing the stock setup will help me know...
Would be much appreciated. I think I'm going to be stuck running avgas for the time being, but knowing the stock setup will help me know what direction to go with this head next. (head modified to correct squish, tuner setup head for avgas not pump gas).
I'll keep you posted. I gotta get a burette.
sebastianer 1/23/2017 2:16pm
1/23/2017 2:16pm
how much should i take out in the bowl area ? just keeping the bowl shape the same and just take say 1mm of the bowl ?

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