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Crankcase breather Question

GabrielGoes

GabrielGoes

Forum Mentor
I noticed the xr69 had its crankcase breather venting right into the clutch cover oil fill cap. And apparently a lot of race guys do this. What would be the advantage and why would this be done? I thought the idea was to RELIEVE pressure so from the crankcase back into the clutch oil fill cap area wouldn't you just be building a pressure cooking machine? Or in other terms you might as well just cap it off with that idea.

For example:

http://m.ebay.co.uk/itm/361331801197?_mwBanner=1

Like in that description he even says it would be a GOOD idea for performance bikes. Like why in the world is this a good idea lol

https://youtu.be/0Nq1xplQVBw


This guy has run like that too


If anyone has any ideas that would be great
 
So I wrote an email to the seller and asked him why that routing is a good a idea, looks like he doesnt know either lol





GabrielGoes said:
I noticed the xr69 had its crankcase breather venting right into the clutch cover oil fill cap. And apparently a lot of race guys do this. What would be the advantage and why would this be done? I thought the idea was to RELIEVE pressure so from the crankcase back into the clutch oil fill cap area wouldn't you just be building a pressure cooking machine? Or in other terms you might as well just cap it off with that idea.

For example:

http://m.ebay.co.uk/itm/361331801197?_mwBanner=1

Like in that description he even says it would be a GOOD idea for performance bikes. Like why in the world is this a good idea lol

https://youtu.be/0Nq1xplQVBw


This guy has run like that too


If anyone has any ideas that would be great
Click to expand...
 
it doesnt vent INTO the clutch cover, it vents FROM the clutch cover, usually into a catch tank or a small pod type filter
 
It's easy to do and looks effective. But in my experience it isn't.
Some years back I'd built a GSXR1100 for a speedway car and the owner had a long dyno session available. He'd fitted an extra breather from the oil filler on the clutch cover so the engine had two breathers - the normal Suzuki one exactly the same as the GS's from the cam cover - and this extra.
The one from the clutch cover had oil comiing from it - with the clutch under it, there's always oil flying around. So I clamped it off.
Instant 6 HP gain.
I can only speculate why it was so, but we did back to back runs and it was a consistent gain blocking the extra breather.
For those interested, it was bullt to the local minisprint rules, stock parts, careful assembly, legal head work, FCR39's and alcohol...149hp at 9900 rpm.
 
GregT said:
It's easy to do and looks effective. But in my experience it isn't.
Some years back I'd built a GSXR1100 for a speedway car and the owner had a long dyno session available. He'd fitted an extra breather from the oil filler on the clutch cover so the engine had two breathers - the normal Suzuki one exactly the same as the GS's from the cam cover - and this extra.
The one from the clutch cover had oil comiing from it - with the clutch under it, there's always oil flying around. So I clamped it off.
Instant 6 HP gain.
I can only speculate why it was so, but we did back to back runs and it was a consistent gain blocking the extra breather.
For those interested, it was bullt to the local minisprint rules, stock parts, careful assembly, legal head work, FCR39's and alcohol...149hp at 9900 rpm.
Click to expand...


thats crazy would have never imagined
 
GregT said:
It's easy to do and looks effective. But in my experience it isn't.
Some years back I'd built a GSXR1100 for a speedway car and the owner had a long dyno session available. He'd fitted an extra breather from the oil filler on the clutch cover so the engine had two breathers - the normal Suzuki one exactly the same as the GS's from the cam cover - and this extra.
The one from the clutch cover had oil comiing from it - with the clutch under it, there's always oil flying around. So I clamped it off.
Instant 6 HP gain.
I can only speculate why it was so, but we did back to back runs and it was a consistent gain blocking the extra breather.
For those interested, it was bullt to the local minisprint rules, stock parts, careful assembly, legal head work, FCR39's and alcohol...149hp at 9900 rpm.
Click to expand...

6HP gain, that is a lot !

I spoke to Nick Pepper couple of years ago, talking about GS1000, he told me the breather relieves overpressure in the engine and iirc the advantage was it prevented blown oil seals. But Nick uses stroker engines with much more power than normally seen for road bikes. May be the GSXR1100 engine is not affected because already built for more power.

He still advertises the breather as a must.

http://www.suzukiperformancespares.co.uk/product/suzuki-crankcase-breather-180-degree/2126/

"a must on tuned and raced bikes...killer looks on stock bikes!!"

Just throwing this out there, any of you guys have experience either way ?

I would happily sacrafice 6 HP for engine health on my 130 HP GS1000, but if not needed it is a shame to lose that much just for looks ..
 
Last edited:
6 bhp sounds a lot to lose just for a vent on the crankcases. I remain sceptical about that claim.
 
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