YZ250 / 250X Head Swap

quadmx301
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quadmx301
Edited Date/Time 9/9/2022 5:41pm
Doing a top end on my ‘05 YZ250, discovered some damage that will need to be repaired. Can a YZ250X head be used? Is the squish or dome any different?

Thanks
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RGaede
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RGaede 8/13/2022 10:26pm
8/13/2022 10:26pm Edited Date/Time 8/13/2022 10:27pm
The 250x head will be lower compression. Even if it shares a head with the mx model, the yz250 got a global spec head in 2011 that was lower compression than the earlier ones.
quadmx301
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quadmx301 8/23/2022 8:46pm
8/23/2022 8:46pm
Would this noticeably affect power? Would it be worth it to have the squish corrected for higher compression?
FGR01
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FGR01 8/24/2022 7:44am
8/24/2022 7:44am
So, the differences are all in the height of the gasket surface relative to the combustion chamber. So, if you shaved the gasket surface of an X-head .026" (.100 - .074") it would end up being identical to a stock 2005 head?
quadmx301
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quadmx301 9/7/2022 10:06am
9/7/2022 10:06am
Do those of you who have corrected the squish and corrected the dome for the same compression ratio see a difference in top end life? I’m looking to lower the compression for less engine stress and longer engine life, and if I could get away with using the stock X head, I don’t mind saving a few bucks

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RK Tek
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RK Tek 9/7/2022 11:02am
9/7/2022 11:02am
The squish clearance is just one "player" in the overall head design and function..

Having a better squish clearance does not necessarily mean you will have a better functioning head... It can help, but there is MUCH more to ombustion chambers than the squish. Seem most everybody is under the assumption that "correcting the squish" "corrects" the shortcomings of the head.. Again,,, this is not the case..

The chamber's design is much more complicated..

Being in this biz for decades and also being an owner (current) of MANY YZ 250's.. I can assure you that the head (X or not X) leaves a lot on the table in terms of peformance.. Getting the correct HEAD design will make a workd of difference across the entire RPM band.

There are a few other mods that really help out the YZ 250 and put it in a 250 league of its own.. Once you get a properly set up YZ 250, it is a joy to ride.. The head is the best place to start and just milling it is not going to get you there.


RK Tek
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RK Tek 9/8/2022 7:05am
9/8/2022 7:05am
I hear these "squish set for octane" or "corrected squish" phrases quite often..

Would anybody like to discuss these phrases (and any others) in detail?

I think it would be a good discussion


dedi684
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dedi684 9/8/2022 9:14am
9/8/2022 9:14am
After 6 yz 250s I'm finally modding one and just put an apex with an xc dome. Always ran Pump gas too. I'm about 145 pounds now and pushing 50 so I'm trying to tame it a bit and make more usable power. Ran most of my bikes stock over the years besides randomly trying a pipe reeds or 51t gearing. Just recently stopped using an 11oz fww weight I ran for 10 years or so.

UGOTBIT
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UGOTBIT 9/8/2022 1:05pm
9/8/2022 1:05pm
RK Tek wrote:
I hear these "squish set for octane" or "corrected squish" phrases quite often.. Would anybody like to discuss these phrases (and any others) in detail? I...
I hear these "squish set for octane" or "corrected squish" phrases quite often..

Would anybody like to discuss these phrases (and any others) in detail?

I think it would be a good discussion


Drop some knowledge Kelsey, we're listening
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RK Tek
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RK Tek 9/8/2022 1:39pm
9/8/2022 1:39pm Edited Date/Time 9/8/2022 2:03pm
RK Tek wrote:
I hear these "squish set for octane" or "corrected squish" phrases quite often.. Would anybody like to discuss these phrases (and any others) in detail? I...
I hear these "squish set for octane" or "corrected squish" phrases quite often..

Would anybody like to discuss these phrases (and any others) in detail?

I think it would be a good discussion


UGOTBIT wrote:
Drop some knowledge Kelsey, we're listening
Again, I think it would be a worthwhile discussion..

If you guys want to get into the nuts and bolts of all of this.. I think we should start a new thread with the corresponding title?, then we can dive into it.. So, if somebody wishes to get that rollin... that would be great!
Mr. Robinson 9/9/2022 11:59am
9/9/2022 11:59am Edited Date/Time 9/9/2022 12:00pm
Start a head thread and eliminate all the misconception.
RK Tek
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RK Tek 9/9/2022 12:09pm
9/9/2022 12:09pm Edited Date/Time 9/9/2022 12:14pm
Mr. Robinson wrote:
Start a head thread and eliminate all the misconception.
I am trying to HELP ,via the discussion, eliminate the mis-information out there on this subject and others, if they come up .. IF the riders are not interested , that is fine as well..

I asked that somebody start a new thread IF there is interest in this topic.. We KNOW you are not interested in this discussion... Again, I think it would be very informative for those that are under false assumptions like squish clearance determining octane requirements etc
sandman768
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sandman768 9/9/2022 5:41pm
9/9/2022 5:41pm
RK Tek wrote:
Again, I think it would be a worthwhile discussion.. If you guys want to get into the nuts and bolts of all of this.. I think...
Again, I think it would be a worthwhile discussion..

If you guys want to get into the nuts and bolts of all of this.. I think we should start a new thread with the corresponding title?, then we can dive into it.. So, if somebody wishes to get that rollin... that would be great!
Done…. I would like to learn and look forward to your comments, thankyou..

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