Author Topic: Head mod question  (Read 644 times)

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Offline storie585

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Head mod question
« on: February 05, 2019, 01:08:15 AM »
Has anyone ever run a "Gore mod" 1983 YZ 490 head on a 1983 IT cylinder? What could I expect?
Dave

Offline T.RexRacing

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Re: Head mod question
« Reply #1 on: February 05, 2019, 01:46:59 AM »
Have you measured squish clearance? That's where I would start.
Whatever you do will be insignificant, but it is very important that you do it.
- Mahatma Gandhi

Offline storie585

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Re: Head mod question
« Reply #2 on: February 05, 2019, 12:40:37 PM »
I haven?t. It?s pretty clear that the heads are different. The IT head is more open than the YZ. I?m assuming the YZ head will bump up the compression.  I assume the porting is the only difference between the two cylinders . I just wondered if anyone has experimented ..
Dave

Offline 2old4this

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Re: Head mod question
« Reply #3 on: March 21, 2019, 07:43:25 PM »
  The  IT490K  I  bought last year came with what I assume is a YZ head (marked 23X) with an IT cyl.(marked 26A) with a Wiseco 89mm  YZ piston.Unfortunately  it was bought  as a non runner off
previous owner who had never had it running while owning it &  I didn't get it running before I  bought a replacement cyl.(26A) which came with a 26A head, I got new cyl.block bored out to suit a 88mm Wossner piston but haven't decided which head I will end up using (I am going to have a decompression valve fitted to which ever one I decide on using) So I can't even tell you if/how it worked out with IT/YZ combination,though I may well decide to run the YZ  head when the time comes soon.
                                                            Dave H.

Offline storie585

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Re: Head mod question
« Reply #4 on: March 24, 2019, 10:38:35 PM »
I read on a previous thread that someone had run the YZ head. It made a little positive differnce or at least that?s how I took it.. it seems to me that if the port height was lower ( ITjug) that would cause more mixture to be compressed which would bring the compression ratio up... maybe higher than running the YZ jug.. and I can?t imagine that would be good.
Dave