The Great 61X/62T Debate, Philosiphized....

[Idok]

this may or may not be true...


but it seems as though the boats I have ridden with mild porting ESPECIALLY with slightly raised exhaust ports have that light switchy feeling.......

but just widening them keeps it a little smoother, more predictable?


the power on my LPW motor is so freaking smooth its not even funny....i still want to try it with a skat swirl..(thanks matt E :bs2: for snagging the first one ive seen in over a year) :biggthumpup:

 

[Matt_E]

thanks matt E for snagging the first one ive seen in over a year)

At a great price, I might add. Fark, I might just sell my Concord over that.
Tell you what, I am a numbskull when it comes to feeling power increases.
I dinged up my concord and had to send it to Impros, so I stuck an old-school skat 10/18 in (with an unported stator)....I can't hardly feel a difference.
Except the skat's faster on top.

Hummmh.

 

[WaveDemon]

this may or may not be true...


but it seems as though the boats I have ridden with mild porting ESPECIALLY with slightly raised exhaust ports have that light switchy feeling.......

but just widening them keeps it a little smoother, more predictable?


the power on my LPW motor is so freaking smooth its not even funny....i still want to try it with a skat swirl..(thanks matt E :bs2: for snagging the first one ive seen in over a year) :biggthumpup:

mine are widened and it's not smooth. it doesn't even matter where your throtle is(1/4 or WFO) when it hits that rpm it takes off like a raped ape.

 

[Matt_E]

Generally speaking, if the exhaust port top is more rounded (oval shaped), power delivery will be smoother.
With a flat port roof, it will hit like a switch.

 

[waxhead]

yup matts right about the porting
also the oval shape is easier on the rings as well

 

[Idok]

yup matts right about the porting
also the oval shape is easier on the rings as well

:dunno:

so, in THEORY...

if you were to change NOTHING on a stock X cyl except to raise the port timing by 1-2 mm..

what would be the change?

 

[waxhead]

Are you talking exhaust or transfer height here

 

[kid4now]

so, in THEORY...

if you were to change NOTHING on a stock X cyl except to raise the port timing by 1-2 mm..

what would be the change?

More top end, higher rpm. Loss of bottom end BRAPPPPP. Asumming your talking the exhaust port.

 

[waxhead]

More top end, higher rpm. Loss of bottom end BRAPPPPP.

Not always
it depends on the combination of parts and porting

It is better and more acurate to talk in degrees of duration

 

[Matt_E]

If you would raise the stock exhaust port roof by an even 2mm (retain the original shape) you will develop more power in the upper RPM's.

Just guessing.

Basically, any increase in exhaust port area is a good thing (to an extent, of course).
You can achieve that in a couple of ways.....raise it, or widen it.
If you raise it, you're altering timing, which changes power delivery.
As a four-stroke analogy, your valve's would stay open longer.
The powerstroke of a 2-stroke motor is from TDC to the opening of the exhaust port. The longer that stroke, the more torque (and bottom end power). However, for top end power (when the engine spins a lot faster), that's a limiting factor.
Raising the port shortens that powerstroke - see why it's bad for FS?

When you widen the exhaust port, you're not altering timing (much). You're just making the valve surface bigger - the dwell time remains (roughly) the same.
The powerstroke stays nice & long, and the engine can breathe better.

This, btw, explains the big advantage of strokers - they increase your powerstroke.


Of course, that was just a basic explanation. There are a lot more factors, such as exhaust port shape, transfer port area, port roof angles (very important!), boost ports, and port duration.

 

[waxhead]

the other part to that is the sooner you open the exhaust the longer scavenging time you get
so a better flush of the cylinder
to a certain extent i have found that going up a small amount has helped the skis bottom end
we are talking in small amounts of height changes here

The transfers are very low in a yamaha and there is a big gain there

 

[Matt_E]

Cleaning the transfers up properly raises them by a couple mm though.

 

[waxhead]

i dont measure the mismatch
i measure from the sleeve

 

[Matt_E]

*Crosses fingertips*

Excellent.