Valve Springs

[gerge]

I see a lot of people with turbo Busa's are using stiffer valve springs? Why? Most of the cams in use appear to be stock so I wouldn't think that you would need a stiffer spring to prevent float.....

I am sure someone here can enlighten me!

 

[BA BUSA]

Under boost you have positive pressure working against the valves...also with a turbo motor a valve spring upgrade is cheap insurance

 

[gerge]

Thank you, that makes sense...

 

[fstbusa]

usually only the bigger hp guys are running stiffer springs... up around 350+ hp guys. Anything below that you can run stockers just fine.

 

[gerge]

Thanks!!! The turbo dragbike is coming along well, waiting on the last big pile of parts, hoping to see some high 7's in the 1/4 this year...

 

[NearDeath]

(gerge @ Apr. 10 2007,23:52) I see a lot of people with turbo Busa's are using stiffer valve springs?  Why?  Most of the cams in use appear to be stock so I wouldn't think that you would need a stiffer spring to prevent float.....

I am sure someone here can enlighten me!

Under that much preassure, you want the valves to open and close completely and quick, you don't want any sloshiness in valves closing...

 

[OZBooster]

A simplified way of understanding what valve float does to an engine would be to rest a hammer on your finger, even a big hammer can rest comfortably , now lift it 1/2 an inch and let go .... thats valve float and its realy hard on parts...

 

[mountainmotor]

A plus is that when using either set of the APE springs at recommended seat pressure for example , there still won't be excessive pressure on the nose of the cam at full lift when using the stock Busa cams that come in @ .345I and .292E

Sometimes increased spring pressure can come at sacrifice to valve train longetivity but not so in this given example .

 

[thugimmortal68]

 

[gerge]

Does anyone just shim the stock springs?

 

[OZBooster]

I have shimmed tlr springs on my racebike,.040 shims bumped the seat pressure ~5psi ,just be carefull of coil bind... that would damage things quickly.
Not recommending TLR springs, they were a best option at the time i built my motor, i have Carpender to put in when i make the time.
For the time and effort to shim just put in some middle of the range APE or Carpender springs .