Valve spring question

turn 'em upside down LOL


you only bought the outer spring and were going to use the original inner? . . could be a costly experiment.

edit: and you mentioned in another thread you only want to do this once

 

In theory as long as you don't have any interference between the inner and outer there shouldn't be a problem. Are they well retained (stepped retainer / seat) so they can't move? The best choice would be to have one left hand and one right hand spring so the inner spring coils can't get 'caught' between the outer spring coils.

 

IMO I would try to find some springs that coil in the original design orientation. If by some chance they do get caught in each other, the results would be very bad....... broken rockers or worse.......

Here is an interesting Vid that could help you make that decision to use the new ones or not:

http://www.youtube.com/watch?v=i_NpzU4pGjc&feature=related

 

Are you sure you need stronger valve springs?
The spring pressure is designed in relation to the camshaft profile and valve train weight to keep the valve in contact with the cam when it's opening & closing.
The extra pressure in the inlet manifold due to the supercharge will virtually only act on the valve when it is shut at which time there is pressure in the cylinder anyway.
If you are using standard cams stay with standard springs. Stronger springs will sap power and could lead to increased wear.

 

246tasman,
While your argument might sound reasonable, the experience of Norwoods & others with boosted 3x8 engines is that with OEM springs, the boost can cause the valves to float. The guys running boosted the Japanese 4 & 6 cyl. DOHC engines have found the same thing.

This is why Bert & I are increasing our intake valve spring pressure.

The rule of thumb fix is to increase the intake valve closed position spring pressure by approximately the amount of force the boost pressure generates on the valve's face.

Bert,
The 308 spring retainers & seats have steps to keep the inner & outer springs centered. The steps are why the inner spring's valve closed length spec is shorter than the outer spring's valve open length. The springs are short enough so that sideways bending is very unlikely. However, it IS YOUR engine & your risk decision.

 

just one other note .. a proper spring manufactuer designs the inner and outer springs to cancel out harmonics in the springs . . . . I'm not sure at what rpm this is a real problem but I thought it was more spring specific like number of coils and diameter of wire .. .. which after doing some research convinced me you are getting something more when you pay for quality springs . .. that whole subject is also like an onion . . just layer after layer to keep peeling back

cheers

 

stating it another way . .. you can have 2 completely different springs with the same force but completely different winds/# of coils/material properties ... and they will have different harmonic frequencies .. . thought this was an issue when you started rev'g Chevy's which is where our engines live . . sometimes I miss the days when the only harmonics I cared about were those in the intro of "Mean Street" (Van Halen . . the band).


cheers

 

how'd you like it? .. I can't play anything that resembles the intro . . but the rest of the song I do a pretty good job of hacking

cheers

edit: first time I heard it I was hanging out in a Burger King parking lot on the cruising strip in Portland, Oregon .. . ohhh the memories
edit2: I think I got in a fight with Kid Rock LOL!!!
edit3: considering the time line more like Kid Rock's dead beat dad LOL again . .okay back to work

 

The outer should be carrying approx. 2/3 of the load, the inner 1/3. Compress each one individually to the same height and see what you have. It's not an absolute rule but a good guideline. Quite honestly there's no special relative dynamic control designed into a 2 spring assembly; you try to maximize the natural frequency of each one while keeping the stress level low enough to avoid a fracture. i.e. you wouldn't lower a spring frequency just to keep it different because that would cause it to go out of control sooner. Best to crank them both up as high as you can (in the design phase).

FWIW, many enthusiasts are running big boost pressures through STi and EVO motors without changing springs and so far (knock on wood) seeing no spring problems. I went from a stock 14.5 psi max to 22 psi and have 30k miles on the engine so far. I fully expect to break a piston first Of course if you're going from naturally aspirated at -10 psi to a +18 psi, well that's quite a change!

 

any thoughts on double springs that have inteference between the inner & outer spring? . . is this common now?