Rev kits and excessive spring pressure

[summit]

Been having an issue with my inner valve spring pulling my valve seals off. I have an old rev kit laying around that I can put in, allowing me to run dual valve springs instead of the triples I have now, but I would have to invest in new lifters and pushrods.

I have no idea why I have to run so much open pressure on the valves (close to 800 PSI with a .640 cam), but I do. If I even drop it 50 lbs it shows up on the datalogging-boost drops as rpm climbs. It's only a few pounds but it is measureable and goes away as I add valvespring pressure. Another option is to lighten the valvetrain, but I don't see where that is possible. Titanium valves already. Would something like the Shubeck lifter drop that much weight to ease up on the valvesprings? Any other advice? Standard single turbo stage 2 headed engine, solid roller cam. It is suposed to be a a street roller grind, but maybe it is ground too aggressive?

Greg Kring
87 GN
9.05 @ 150

 

[EightSecV6]

Originally posted by summit
Been having an issue with my inner valve spring pulling my valve seals off. I have an old rev kit laying around that I can put in, allowing me to run dual valve springs instead of the triples I have now, but I would have to invest in new lifters and pushrods.

I have no idea why I have to run so much open pressure on the valves (close to 800 PSI with a .640 cam), but I do. If I even drop it 50 lbs it shows up on the datalogging-boost drops as rpm climbs. It's only a few pounds but it is measureable and goes away as I add valvespring pressure. Another option is to lighten the valvetrain, but I don't see where that is possible. Titanium valves already. Would something like the Shubeck lifter drop that much weight to ease up on the valvesprings? Any other advice? Standard single turbo stage 2 headed engine, solid roller cam. It is suposed to be a a street roller grind, but maybe it is ground too aggressive?

Greg Kring
87 GN


FWIW greg, I dont think that spring pressure is too far out of line at that lift.
9.05 @ 150

 

[EightSecV6]

FWIW greg, I dont think that spring pressure is too far out of line at that lift.


Should have read like that....

 

[TurboTR]

Greg what pushrods are you running?

TurboTR

 

[summit]

Crower pushrods, full radius tip 3/8 diam. I don't think the 5/16 double wall would hold up. They are pretty long with the stage 2 heads. Little under 10 inches if I remember right. Maybe I should try a set in carbon fiber?
Greg

 

[TurboTR]

Well the few tidbits I've gotten from Lozano Bros, seems they had alot of fun with v6 valvetrain dynamics back in the day I think it then led to some Spintron or whatever testing, etc.

Wonder what the circle track guys say? Ron T?

Good that you have a strong 3/8" pushrod in it. They are very long; the ones in my S2/GN1's are 9.00 I think. I'm wondering what effect like a Manton tapered 4140 would have on what you are seeing? Like say a double taper 3/8-9/16-3/8, or a single taper like 9/16-3/8? Just curious. I do know that in some of the HD big twin racing the pushrods have gotten very large and strong Of course they have it even worse than we do though...

TurboTR

 

[summit]

So with all that being said would it be a mistake to try and use a rev kit with dual valvesprings instead of just the triples with no rev kit? I have had issues with valve seals being pulled up off the guides and I'm not sure if it the inner spring catching them or what. How can I tell if I need all 800 pounds on the valve or if I could split it up with a rev kit? Have most of a kit now, would need to get pushrods and the lifters checked out. The valve springs without the inner measure about 700 open depending on installed height.

Greg Kring
Arlington, Texas

 

[turbodave231]

Greg,

I'm battling a valve spring problem right now. What springs are you using? I'm looking at Comp Cams 948 triples. 332# on the seat and 744# at full lift. Seems like overkill for a .605 lift cam, but I don't want to do this job twice.

What rockers are you using? T&D or Jessel? Any rocker arm to retainer interference problems?

The circle track guys won't be alot of help because they don't pressurize their intakes. 25 psi boost places nearly 100 pounds of force against the backside of the intake valve. You can subtract that pressure from the spring seat pressure right off the bat.

Tim Cole at Comp told me not to use a rev kit...but didn't elaborate on the reasons.

Dave

 

[TurboTR]

Well this probably won't be popular, but here goes. Yes it does make an opening force on that side of the valve. But if you want the overall resultant force on the valve trying to open or close it, we *must* consider the pressure acting on the other side of the valve head as well.

At IVO, during overlap, the valve opens into pressure in the cyl = exh backpresssure basically. For the turbocharged case the exh backpressure is generally quite a bit higher than the intake pressure. Net result- more pressure force holding the valve closed than trying to push it open. We use this same principle ourselves all the time to change valve springs for example...

At IVC, the piston is already moving well on its way back up the cylinder on the compression stroke. The pressure in the cylinder is again already going much higher on the cylinder side than on the inlet port side as the valve cracks closed. I have cylinder pressure measurement traces from my own car that show this clearly. So the net result is again... more force pushing the valve closed than trying to push it open.

Sounds like, with 700+ lbs open force, you guys are probably venturing well into rev kit territory here

TurboTR

 

[TurboTR]

PS I had some issues with seals coming off the guides too, but a switch to a more stout type made it go away.

TurboTR