vent holes in cylinder skirt

[jmw76]

Hi Guys,

Has anyone attempted to modify the cylinder skirts on their block by cutting the skirt back to the block on the no thrust sides (as is done on the later GSXR engines)? I believe that this assists in reducing pumping loses and freeing up some extra horses.
Does it make a noticable difference or is it just a waste of time?

Peter.
[?]

[Chris41]

Here it is done on a ZRX (not mine)
It depends on what your going to use the bike for it apparently does give drag and race bikes a few more HP and quicker revs

http://i227.photobucket.com/albums/dd102/chris-41/baseporting.jpg

[jmw76]

Great stuff.

Anyone with personal experience and that might have an understanding of what the power gains are?

This engine is in a race application.

Every bit of power is a bonus.

Cheers

Peter.:D

[Stocky]

It does help. BUT

The new Hayabusa barrels have it done stock and tend to crack there when they are over sized.

That suggests that it does make it a little weak and gives the barrels an excuse to crack.

You get simliar gains from achieving a vacuum in the crank cases.

You can do this by fitting a reed valve to the crank case breather. You can use a Krankvent (I don't think they flow well enough, maybe the big one would work) or even retro fit a aftermarket Ducati breather with reeds like the Nicoles or STM.

Maybe even fit stock stuff from a newer model.... the new GSXR 600/750's and the new Busa engine all have reeds in their case breathers.

http://www.asfphotos.com/upload/1251850931.gif

[Stocky]

If you are serious (race engine) then you run an electric vacuum pump from a Yank car. More vacuum less pumping losses.(to a point)

If you aren't running any Lambda sensors in the exhaust then you can vent the cases into the exhaust with a Morosso vent kit. It uses the negative pressure pulses in the exhuast to pull the air out of the cases. Not as good as a pump but pretty good.

Ultimate is a dry sump. Not only do you get more power from the crank etc not bashing oil around, they pull huge vacuum in the cases. Only drawback is COST LOL.

[jmw76]

Some interesting thoughts.

Breather reeds. Maybe worth looking at. The late Busa and GSXR 600/750 may have these but they also have the cutaway cylinder skirts.

I would expect the inserted steel liner skirts of the old GSXR to be stronger than the cast skirts of the Busa. Are they not?

Pulling a vacuum on the crankcase may help give a bit more power by reducing the average pressure below the pistons. Improving air flow between adjacent ports must surely also help reduce pumping losses?

Anyone else have an opinion?

Cheers

Peter.

[jmw76]

Any further info on this topic?

Is it really necessary to cut through both sides of the cylinder sleeve? I had thought that I would only need to cut through the sleeves between 1-2 & 3-4 as this is where most of the air is going to flow.

Cheers
:)

[Chris41]

" I had thought that I would only need to cut through the sleeves between 1-2 & 3-4 "

Yeh that's what I thought when I copied that pic, and you would probably not be able to run teflon buttons if the wrist pin passes the cut out. Check out a dragbike forum you might find more onfo

[jmw76]

With standard stroke lengths, the wrist pins are a long way above the cutout. Its only the piston skirt that comes down this far and provided the cutouts are kept to about 30mm wide x 20mm high, there is no part of the piston that makes contact with this part of the skirt (at least not with my wiseco pistons). With generous radii I would figure that the risk of cracking is small.

Thanks to all.

I will post a quick note in the drag bike sections.

Cheers

[Issues]

Booster has put pics up before re- this subject. Maybe try search his build.

[jmw76]

Hi Guys,

Here is a pic of the mods I made to my clinder skirt.
The cutouts are between 1-2 & 3-4. The width of each window is 32mm and they are cut right up to the block. At 32mm they are clear of any part of the piston that contacts the skirt. The cutouts below the gudgeon on the Wiseco pistons is 35mm wide.

Cheers

Peter.
:D

[jmw76]

Oops

Here is the pic this time.

http://www.asfphotos.com/upload/1252342132.jpg



Cheers

Peter.
[:I]

[Booster]

Yep mine looks similar
from below block mounted on cases
before
http://img.photobucket.com/albums/v378/maj750/DSC01985.jpg
and after
http://img.photobucket.com/albums/v378/maj750/DSC01984.jpg
Don't know how much it helps but its free and can't hurt......

[Stocky]

AND it's less weight LOL ;)