BVH flow bench findings...

[dub-disaster]

Hope this doesn't cause any problems for me , man in a shed put them in I assume he knows what he's doing !!

[hayesey]

hope what doesn't cause problems?

[dub-disaster]

Any difference in inlet valves between g40 and non g40 other thanthe little indent think my inlets are non g40 as they have no indent on them

looks like my inet valves are non g40 got a picture here do have to say lovley work on the head though and reasonably priced nice bloke too man in the shed

[hayesey]

there's nothing "g40 specific" about inlet valves and every big valve head ever made for a g40 doesn't have sodium filled exhaust valves to my knowledge.  At least all the ones using 31mm valves.

[PeteG40]

actually stock inlet valves on a 1.3 (gt etc) are part number 030109601D and '99.3'

inlet valves on a g40 py are 030109601B and are '101.4'   

so definately a different part number.

the 99.3 and 101.4 i think are length in mm of the stems. I can measure when i get home as i have both.  If g40 ones are longer then perhaps they would remain open longer perhaps.

[cheys03]

there's nothing "g40 specific" about inlet valves and every big valve head ever made for a g40 doesn't have sodium filled exhaust valves to my knowledge.  At least all the ones using 31mm valves.

How do they deal with the heat? Are they the same composition or different to standard Mk3 1.3L exhaust valves, albeit a different size obviously.

[hayesey]

I don't see how the length makes a difference, the cam lobe profile determines duration and lift.  Longer length will just mean the hydraulic tappets are more "compressed" as far as I can visualise.

[PeteG40]

wont a 1mm longer valve be like a 1mm longer cam lobe though?

[hayesey]

no because the lift is the ratio between the base circle of the lobe and the highest point of the cam.  If a 1mm longer shaft meant it was 1mm more open at full lift then it'd also be 1mm more open at "closed" (therefore not closed at all!).  That's why you shim solid tappets or have hydraulic tappets, they take up the slack between the cam and the valve stem top.

[PeteG40]

i get you yeah.  Unless the g40 cam would mean normal valves are slightly open?  I don't know.

They are a different part though for some reason.

[hayesey]

yeah there must be some reason, although it's possible that that size was just what was available from the manufacturer with sodium filled exhaust valve.

[PeteG40]

but the inlet isnt sodium filled, but is longer.... they could've just used all 3f ones.

[Andy]

If you can measure both sets of valves please Pete that'd be ace.

I wonder whether a G40 cam has a smaller base circle than a GT or AAV one? If it did for some reason, that might explain why the valves were different stem lengths to ensure the same tappets could be used across the range. Can't think why they'd have done that though!

Or maybe the base circle is the same, but it was done to keep the tappet more compressed on a G40?

[cheys03]

I wonder whether a G40 cam has a smaller base circle than a GT or AAV one?
Or maybe the base circle is the same, but it was done to keep the tappet more compressed on a G40?

I was thinking the same about the base circle. What be the advantage of a more compressed tappet, presuming it was intentional? Less float?

[dub-disaster]

I've been thinking about this, if the base circles are different as chest says doesn't this just put more pressure on the tappets ? The only reason for different valve lengths would Be different size head castings I'm probably wrong but just the way I see it.
  
   G40 valves are obsolete now anayway so standard polo ones will have to do for me anyway. Be intresting to find the difference, next time I'm passing vw Tps I'll pop in and ask the friendly blokes at the trade counter.

 I got a standard cam on my desk I'll measure the base circle with a micrometer tomorrow of any ones got a gt cam maybe they could do the same ??