288xp porting tips needed

[Yotaismygame]

My take is that your numbers are off.

Measured twice. I’ll measure a third time. The port shapes are interesting too. Exhaust is maxed out width wise but the intake is tiny

 

[cus_deluxe]

I imagine you mean your intake is 69 btdc, bummer about the exhaust being that high already, 98 atdc is prob higher than you would want for “work”.

 

[huskihl]

I think what he meant by your numbers being off is your intake opening. You measured in degrees after top dead center when it should open in numbers before top dead center

 

[Yotaismygame]

I think what he meant by your numbers being off is your intake opening. You measured in degrees after top dead center when it should open in numbers before top dead center

Can you explain that a little more? I measured in duration. As soon as it cracks open, until it closes.

 

[huskihl]

Can you explain that a little more? I measured in duration. As soon as it cracks open, until it closes.

Your intake duration is 138. That's 69 up and 69 down. Intake opens at 69

 

[cus_deluxe]

Well said kevin, i was preparing to write something longwinded and confusing. Lol

 

[huskihl]

Well said kevin, i was preparing to write something longwinded and confusing. Lol

That's okay. You beat me to it last time LOL

 

[huskihl]

The cylinder looks like a Stihl, the piston looks like a Stihl, I guess it would probably run pretty good at 100 - 120 - 80. But I've never done a 288 so I'm just guessing

 

[Yotaismygame]

I get you now. I was rushing out the door earlier trying to get to work. Now that i'm here I have more time to surf the net . So to get the intake height from duration its just duration divided in half? I had done 138/2=69, 180-69= 111. Is 111 the height of the roof?

 

[Yotaismygame]

For starters I'm thinking of taking 030 off the base and a 020 pop up. Hoping that brings the comp upward of 180. From there leave the exhaust alone, maybe lower the intake some more. Will have to see the numbers after the machine work. That would put me around Huskihl's numbers

 

[huskihl]

Huskihl's numbers

Like I said....just a guess. I'd pm rattler and ask for assistance

 

[Yotaismygame]

Ill post some pics of the cylinder tonight in case anyone is interested in the most recent version of a 288 hyway cylinder.

 

[mdavlee]

I imagine you mean your intake is 69 btdc, bummer about the exhaust being that high already, 98 atdc is prob higher than you would want for “work”.

Almost all of my work saws have exhaust from 94-99. A 288 will run fine at 98. It helps lower the compression on some a little bit. If you cut too much compression will be 220-240

 

[huskihl]

I get you now. I was rushing out the door earlier trying to get to work. Now that i'm here I have more time to surf the net . So to get the intake height from duration its just duration divided in half? I had done 138/2=69, 180-69= 111. Is 111 the height of the roof?

You were correct dividing 138 by 2. The ex and trans, yes. But the intake opening is measured by dividing duration by 2.
The intake roof is not measured.

 

[Fruecrue]

View attachment 166623 View attachment 166624 View attachment 166625 View attachment 166626 Heres my 281. @huskihl did machine work for me. This was meant only for play time so exhuast got raised a bunch, ex port width is “maxed out”...intake is funny on 2 series huskys, widened and increased intake duration a bunch as well.

Do I see a pipe peaking into one of those pics?
If so, more pics please.

 

[Yotaismygame]

Almost all of my work saws have exhaust from 94-99. A 288 will run fine at 98. It helps lower the compression on some a little bit. If you cut too much compression will be 220-240

Do you think a .020 pop up with .020 squish will net too much compression?

 

[Fruecrue]

Do I see a pipe peaking into one of those pics?
If so, more pics please.

I responded before reading the rest of the thread, OP doesn’t like de-rails.
De-rails are the best part.

 

[Fruecrue]

Do you think a .020 pop up with .020 squish will net too much compression?

I know you didn’t ask me, but that’s real tough to predict with inconsistencies commonly found in aftermarket cylinders.
Sounds like a good place to start, if compression is too high, you could raise the exhaust port some.

 

[Yotaismygame]

I responded before reading the rest of the thread, OP doesn’t like de-rails.
De-rails are the best part.

Depends on my mood. It's Friday, and I've had a lot of coffee.

 

[cus_deluxe]

Do I see a pipe peaking into one of those pics?
If so, more pics please.

Bertrand pipe i had made for my 281.