liner material removal to reduce pumping losses

[baldrick]

hello, Way back in the midst of time i remember reading about some tuning houses  "windowing "the bottom of the barrel liners, in an attempt to reduce pumping losses. 

This usually involved  die grinding, i presume,  material off the  liners, below the travel of the pistons, between 1 and 2 cyl and again between 3 and 4.  this was in the shape of a sort of square/rectangle, with rounded corners iirc.

AFAIK, the idea was to reduce pumping losses and, allegedly, it did in fact help with power increases, although it was pretty marginal .

Anyone ever done thisor have any direct experience of what was involved, amount removed etc.

 

Cheers

[Gixer1460]

Yeah I've had it done with overbored GSX and GSXR barrels. From memory cut was about 30 - 40mm wide and 20 - 25mm deep. Whether it achieved anything was undetectable as it was done with other tuning work at same time but as the 1st shop that did it was a fairly successful race bike shop, I wasn't going to argue and demand proof LOL!

[Oilyspanner]

I'm a bit late on this one ! G1460 has said it all really.  Did it on mine, partly to help pumping losses and partly to reduce the amount of air shoved around the cases. It can't hurt, it probably helps a bit and it's easy enough to do. I tried to find an old photo of mine, showing the windows on 1 and 2, 3 and 4 facing each other, it must be on my old laptop ?!

[dupersunc]

Definetly worth doing. 

[Oilyspanner]

found the photo of when I was shaping the windows. I remember Suzuki saying they helped the gsxr1000k3  gain about 3hp (in crankcase on modern engines).

[bluedog59]

Many years ago John Robinson and Leon Moss conducted a series of tests to find the mechanical losses incurred driving an engine. The resulting magazine article found that crankcase "pumping" accounted for quite a large proportion of the losses and worthy of further investigation. 

Basically, the less power you waste between piston and sprocket,  the more power you have to drive the rear wheel. It may only be a small amount but lots of little gains all add up.

[baldrick]

Too true.

I remember reading an article years ago about it and said tuner deemed it worthwhile, so I'm gonna do it.

Thanks for your answers.

[gsxr1385]

On 11/3/2022 at 8:19 PM, Oilyspanner said:

found the photo of when I was shaping the windows. I remember Suzuki saying they helped the gsxr1000k3  gain about 3hp (in crankcase on modern engines).

Ok so I'll be the one to ask the question - how does cutting the liners in that way reduce pumping losses?

[imago]

6 hours ago, gsxr1385 said:

Ok so I'll be the one to ask the question - how does cutting the liners in that way reduce pumping losses?

Imagine the pistons moving next to one another, as 1 is going down, 2 is going up. Without the window the air below 1 is forced into the crank case which causes back pressure, and that in turn needs a bit of energy to overcome.

With the window the air can escape much sooner and goes straight into the 'draw' caused by 2 going up. So it shortens the track for the air, which reduces the delay between being forced out and drawn in. That reduction in time and pressure reduces the amount of energy needed to move the piston.

[Blower1]

On 10/27/2022 at 6:45 PM, Gixer1460 said:

Yeah I've had it done with overbored GSX and GSXR barrels. From memory cut was about 30 - 40mm wide and 20 - 25mm deep. Whether it achieved anything was undetectable as it was done with other tuning work at same time but as the 1st shop that did it was a fairly successful race bike shop, I wasn't going to argue and demand proof LOL!

It´s probably not working on GSX engines, because there are walls between the cylinders.

Or have you opened the walls and if so, doesn´t it make the engine block weaker?

[gsxr1385]

7 hours ago, imago said:

Imagine the pistons moving next to one another, as 1 is going down, 2 is going up. Without the window the air below 1 is forced into the crank case which causes back pressure, and that in turn needs a bit of energy to overcome.

With the window the air can escape much sooner and goes straight into the 'draw' caused by 2 going up. So it shortens the track for the air, which reduces the delay between being forced out and drawn in. That reduction in time and pressure reduces the amount of energy needed to move the piston.

I appreciate that explanation. I am not trying to be contrary, but the volume of air in the crankcase is not changing at all by the travels of piston 1 and 2, regardless of those windows. No new displacement is being added or taken away with those windows, and the argument of shorter path (and time) for crankcase volume to be moved via those windows vs. drawn from lower (perhaps 1 inch?) in the crankcase just doesn't account for lower or higher crankcase pressure.

That doesn't even take into account the crankcase is vented to either atmospheric pressure or into the airbox (less than atmospheric pressure). If the crankcase vent isn't large enough to reduce crankcase pressure, it would be more effective to reduce crankcase pressure in other ways. Engine temperatures are also a major contributor to increase in crankcase pressure.

I wouldn't bother to cut those windows

[imago]

14 minutes ago, gsxr1385 said:

I appreciate that explanation. I am not trying to be contrary, but the volume of air in the crankcase is not changing at all by the travels of piston 1 and 2, regardless of those windows. No new displacement is being added or taken away with those windows, and the argument of shorter path (and time) for crankcase volume to be moved via those windows vs. drawn from lower (perhaps 1 inch?) in the crankcase just doesn't account for lower or higher crankcase pressure.

That doesn't even take into account the crankcase is vented to either atmospheric pressure or into the airbox (less than atmospheric pressure). If the crankcase vent isn't large enough to reduce crankcase pressure, it would be more effective to reduce crankcase pressure in other ways. Engine temperatures are also a major contributor to increase in crankcase pressure.

I wouldn't bother to cut those windows

OK. Thanks for sharing. 

[Gixer1460]

1 hour ago, Blower1 said:

It´s probably not working on GSX engines, because there are walls between the cylinders.

Or have you opened the walls and if so, doesn´t it make the engine block weaker?

I'm only responding to the question asked. If done with a GSX then obvs the web is cut also and seeing as the GSXR did away with that feature I don't personally think block integrity is compromised.

[dupersunc]

51 minutes ago, gsxr1385 said:

I appreciate that explanation. I am not trying to be contrary, but the volume of air in the crankcase is not changing at all by the travels of piston 1 and 2, regardless of those windows. No new displacement is being added or taken away with those windows, and the argument of shorter path (and time) for crankcase volume to be moved via those windows vs. drawn from lower (perhaps 1 inch?) in the crankcase just doesn't account for lower or higher crankcase pressure.

That doesn't even take into account the crankcase is vented to either atmospheric pressure or into the airbox (less than atmospheric pressure). If the crankcase vent isn't large enough to reduce crankcase pressure, it would be more effective to reduce crankcase pressure in other ways. Engine temperatures are also a major contributor to increase in crankcase pressure.

I wouldn't bother to cut those windows

The volume isn't changed but you do have displacement and flow. As it's actually an oil air mist, it's quite dense, so takes even more energy to move it the air volume around the crankcase. The energy required is squared as the speed of the piston doubles, so at 10,000rpm you are using a lot of energy to move the mist around the crank case, that energy is turned into heat, which causes more power loss.  Shorten the path via windows in the liners, or by smoothing the edges of the webs in the crank to improve flow for the displaced air/oil mist reduces the energy it takes to do so.

all well proven physics. It's why race engines run dry sumps with a depression in the crank case and have huge amounts of detail work on the inside of the cases.  Ducati even run vacuum pumps on wet sump engines.

[bluedog59]

Basically it's "gas flowing" for crankcases. The less energy you use moving the displaced volume, the more you have available to drive the rear wheel. 

[Jdeac]

Way above my knowledge!!

@dupersuncis that why you can get a knife edged crank???

[dupersunc]

4 minutes ago, Jdeac said:

Way above my knowledge!!

@dupersuncis that why you can get a knife edged crank???

Yes, in simple terms.

[Jdeac]

Cut through the air oil mix?? Would the crank loose any strength by being knifed??

Sorry for a sort of high jack on the post @baldrick

[bluedog59]

In both cases,

If there is resistance to movement, it will require energy to overcome.

It's not above your knowledge, you've just not thought about it in this type of application before.

[Jdeac]

I don't want to high jack the thread. I may not have seen a build thread of @baldrickand the intentions of the build.

i have a motor. With above crank (knife edged) busa rods and pistons. Ported head. Adj cam sprockets etc. For a turbo build. ( shall update tomorrow) curious about things

[baldrick]

I feel it's worth doing. I must admit that I'm also doing it because a liner has a very smalll bit of damage, way below the piston contact path, and it was only when I looked at it I remember, I think pdq, or some other reputable tuning company do it and mention it was well worth doin tbh.

[Jaydee]

14 hours ago, baldrick said:

liner has a very smalll bit of damage

Nope, that's clearance for the primary gear. 

[Swiss Toni]

@baldrickThe amount of information this post has un-earthed is unreal! As they say, which in this case most certainly is correct, ‘Every day is indeed a school day!’ Long may it continue!

[Gixer1460]

3 hours ago, Jaydee said:

Nope, that's clearance for the primary gear. 

Yep - that gets everyone first time as it looks like it's been whacked with a hammer!

[baldrick]

 

4 hours ago, Jaydee said:

Nope, that's clearance for the primary gear. 

Doh! 

 

cheers for clearing that up, in all the years ive had these ive never even noticed before, worra nugget eh ?