Rasing exhaust when settin squish???

[wigglesworth]

I recently lowered the jug on my 038 mag. It had a rather large squish, at nearly .045 I took it down to .025 and was wondering, should I raise the exhaust the .020 difference? I did not have to adjust the H needle, it was still reving out fine and 4 stroking. It seemed to have more pep, which it should with the increased comp, but im wondering if im loosing some hp/rpm by not raising the exhaust (i.e. timing) back up. Thoughts? Experiences? Ponderings?

 

[wigglesworth]

I guess I should also add, that I do/did not want to port this saw. I am only looking for the compression bump. If the exhaust is raised, it will only be back to bring it back to stock timing, and all else will be left stock. I have had good luck dropping the jug on others while leaving ports stock, but the squish was no where near as big as this. I actually had planned to go smaller (.020 or so) but stopped at .025. I personally like to leave the gasket and turn the bases down. The most I have had to take from previous jugs is around .013 so .020 seems like a lot to me to not touch the ports.

 

[AUSSIE1]

Wiggs, some say yes, some say no.
Have you done a compression test?
You would normally only raise the exhaust if your compression says you can.
When you drop the jug you raise the compression.
When you raise the exhaust, you loose that compression you gained, or some.
It is said that the compression gained is better than the exhaust timing lost.
Depending on your compression, you could even do a compromise at .010.

 

[wigglesworth]

Wiggs, some say yes, some say no.
Have you done a compression test?

No comp test yet. I usually run a few tanks thru them to verify everything has settled back in. Comp is noticibly more.

It is said that the compression gained is better than the exhaust timing lost.

That statment better asks my question. Is the timing I lost worth more, or the comp I gained?

 

[AUSSIE1]

No comp test yet. I usually run a few tanks thru them to verify everything has settled back in. Comp is noticibly more.



That statment better asks my question. Is the timing I lost worth more, or the comp I gained?

Wiggs, I'd wait until you've done a comp reading.
Then you can determine if and how much you can raise the exhaust.

 

[blsnelling]

I would not raise it. You lowered the squish to gain compression. Raising the exhaust back up will only serve to lower the compression. I doubt you lost enough RPMs to notice.

 

[Dibbs]

I would not raise it. You lowered the squish to gain compression. Raising the exhaust back up will only serve to lower the compression. I doubt you lost enough RPMs to notice.

:agree2:
The 038 Magnum was one of the Stihl saws which had a choice of base gaskets (as standard) for low or high compression depending on what the user wanted, You may have had the "low compression" gasket fitted from new.

 

[CHEVYTOWN13]

Wiggs, I'm curious to know what your numbers are on the wheel, especially ATDC.

Do you have any numbers by any chance?

 

[wigglesworth]

Wiggs, I'm curious to know what your numbers are on the wheel, especially ATDC.

Do you have any numbers by any chance?

Not yet. Ive never ran a wheel on it. I think ill print one out tonight and give it a go.