Gasgas 300 s3 cover squish guestion

[chrille79]

Hi there does anybody know how much a s3 covers there are 3 inserts?decrease the squish? What difference in performance is to squish with head or
squish with the cylinder gaskets. I had my messaured and it was 1,95 mm
with 1 mm gasket and i mounted 0,5mm so it is now squish is 1,5mm.
I feel the bike runs smoother but on very low rpm i feel the exhaust port its not matching correct? heard some people is going with 3mm cylinder gaskets. so is that better to lathing the head. hope you understand my english is not so good thanks Christian

 

[Zman]

Can you explain more about your exhaust matching comment. What is the bike doing or not doing?

 

[(F5)]

Ignore people trying to match the exhaust floor. It is the very least factor.

Ideally squish should be 1mm but 1.5 is. . . OK. If you get it down to 1mm the compression will be too high.

 

[chrille79]

Can you explain more about your exhaust matching comment. What is the bike doing or not doing?

I have no rpm but, up to lets say 3000 rpm its great and then a little dead
up to 4000k and then fine. before it i squished it was great up to 4 k, but not as strong that it is now.

 

[chrille79]

Ignore people trying to match the exhaust floor. It is the very least factor.

Ideally squish should be 1mm but 1.5 is. . . OK. If you get it down to 1mm the compression will be too high.

ok great than i will not do anythin more to the bikes top end

 

[Zman]

We had the same problem with a EC300. The stud weld broke on the power valve actuator plate behind the small cover on the exhaust side of the cylinder. Another option is that your power valve is stuck and does not move.

 

[Zman]

I also agree with F5 that the piston to exhaust port floor alignment is not critical because the piston spends VERY little time at that point in the cycle and because the majority of the exhaust is already out of the cylinder by that time.

That being said moving the cylinder higher, changes the port timing in favor of top end performance and moving the power band from low end power toward high rpm power. If that is what you are looking for you are better off correctly setting the port timing with a degree wheel.

Moving the cylinder up (away from the crank) will require you to cut the head to correct the squish and compression which is already low on most stock GG engines.

People looking for more low end performance will actually cut material off the cylinder base which changes the port timing in favor of low end performance this also corrects the compression / squish at the same time.

 

[chrille79]

I also agree with F5 that the piston to exhaust port floor alignment is not critical because the piston spends VERY little time at that point in the cycle and because the majority of the exhaust is already out of the cylinder by that time.

That being said moving the cylinder higher, changes the port timing in favor of top end performance and moving the power band from low end power toward high rpm power. If that is what you are looking for you are better off correctly setting the port timing with a degree wheel.

Moving the cylinder up (away from the crank) will require you to cut the head to correct the squish and compression which is already low on most stock GG engines.

People looking for more low end performance will actually cut material off the cylinder base which changes the port timing in favor of low end performance this also corrects the compression / squish at the same time.

oki thanks for answer now i understand.buy a S3 head will not gain any pwrformance? I had the DEP exhaust before, i tested the original gasgas pipe now and the bottom is very good. now and smooth the top is also good i felt. The DEP pipe looks good and the sound is good, but thats all.
i think the valve is working great, i had just mounted a new piston also

 

[(F5)]

You would be better getting the head reshaped by RB or similar. You may have already made the comm too high tightening the squish up that close.

 

[chrille79]

Aha oki. I dont know anybody here that can fix the head, and send it to someone will cost to much, the bike runs fine now anyway..

You would be better getting the head reshaped by RB or similar. You may have already made the comm too high tightening the squish up that close.

 

[motopsycho87]

Exhaust port height is damn important, that's what governs your top end power and over rev. It's the first port of call to raise exhaust height for a peakier motor. That being said, I matched mine at 3x0.5mm gaskets.

But, if you don't have the machining facilities, choose the squish over the port height, but if you're gonna do a job, do it properly!

 

[Jakobi]

Exhaust port height is damn important, that's what governs your top end power and over rev. It's the first port of call to raise exhaust height for a peakier motor. That being said, I matched mine at 3x0.5mm gaskets.

But, if you don't have the machining facilities, choose the squish over the port height, but if you're gonna do a job, do it properly!

Really? I would have though that the exhaust port area would have much more impact on top end performance than the relationship between the edge of the piston dome to the bottom of the exhaust port, given that if you look at a complete cycle of the engine, the time that the piston spends at the bottom of the stroke is very small. Almost every tuner I have spoke with has said this too. However, in saying that it does change the timing and duration in which the port is open (and reduces area by a small amount) but that is also only a couple variables in a complete setup. You still have the relationship and flow of the transfers, boost port, port angles, etc will play a part as well.

The other consideration is purpose. As much as I'd love to be able to ride a 2T around at peak rpm all the time for the sound alone, in the bush/endure/technical riding you will only spend a small portion of time in these revs. In many cases a more linear power curve with the gains being shown in the mid range will be more usable and translate to a faster, more manageable engine.

 

[barossi73]

Changing exh port height will/should require a corrected squish anyhow.otherwise how do you isolate any benefit as youve immediately raised or lowered the compression ratio also
Not saying theres no benefit,just you need to compare apples with apples and keep your cr safe

 

[(F5)]

Really? I would have though that the exhaust port area would have much more impact on top end performance than the relationship between the edge of the piston dome to the bottom of the exhaust port, given that if you look at a complete cycle of the engine, the time that the piston spends at the bottom of the stroke is very small. Almost every tuner I have spoke with has said this too. However, in saying that it does change the timing and duration in which the port is open (and reduces area by a small amount) but that is also only a couple variables in a complete setup. You still have the relationship and flow of the transfers, boost port, port angles, etc will play a part as well.

The other consideration is purpose. As much as I'd love to be able to ride a 2T around at peak rpm all the time for the sound alone, in the bush/endure/technical riding you will only spend a small portion of time in these revs. In many cases a more linear power curve with the gains being shown in the mid range will be more usable and translate to a faster, more manageable engine.

Erm, no you misread that I think. He was specifically saying the top of the port, therefore the timing of opening and closing. Assuming the power valve . . . anyway let's not overcomplicate.