I'm sure this isnt a true advanced tech question but I was hoping to attract the more experienced crowd with more credible answers. How will an engine run with valves springs that have gotten weak and no longer have the springs pressures they started out with due to too large of a cam and FI? Would low vaccum be an indicator of weak valvesprings? Any other indicators?

 

I think the only thing that would happen is float at lower and lower RPM's. The springs purpose is to make sure the lifter follows the cam profile, but it has the mass of the valve assy slowing it down. I don't think FI would come into play.

Does it float right now in a useable RPM band?

 

I agree. Eventually the spring wouldn't be able to keep up, and it would have to open again before it fully closed.

 

It just feels like it missing all the time, no power at all at any rpm really. I have checked everything else but the spring pressure. I am running a .606"/.628" cam on COMP 26918s good for .600" lift for about a year now with 11 psi of boost. My gut tells me the springs just cant get the valves closed in time anymore but Im not sure. Its really the only thing I have left to check is the open and closed spring pressures.

 

It certainly does sound as though spring seat pressure is low. First, the spring does function to keep contact between the lifter and lobe, but its second job is to make certain the valve does not bounce (everything vibrates to some magnitude) excessively when the lobe returns to the base circle. If this happens, the process will increasingly degredate the valve and valve seat fit, the strength of the valve itself, and the action of the lifter. In a hydraulic lifter engine, the spring must have enough pressure to keep force on the plunger; otherwise, lifter pump-up will occur and the valve will not seat fully.

All of this creates poor power, vacuum signal, and in more severe cases, misfiring.

 

Uh, yeah, I'd definitely say that you need to get some bigger springs...

 

Unfortunately this is an easy one as I just got done changing springs yesterday and still need to adjust the valves.

The car will run fine (not sure if you go forever, before changing) but the top end will go flat. Instead of a nice smooth curve up on top, the dyno sheet will just start flatening out loosing peak power.

Your springs may have gotten weak but it sounds like you have other issues.

 

My car is at the dyno tuner this week and he suggested the same thing. He's changing the springs and retainers (and porting the heads) to solve a flat-top dyno graph. I'd be interested to see if it's the right fix or if there's something else going on.

 

2 things....

1. 11lbs of boost
2. wrong seated height

You basically need more seated pressure and you can't get there from here with .628" lift. You need to drop the rocker arms back to 1.5's or 1.52's to drop the lift and increase the crap out of the seated pressure. Should make for MORE power and better valve control.

Bret

 

Would weak valvesprings effect the curve before valve float happens? IE if a car had a nice flat torque curve of 330ftlb, then sometime later it dynod a curve of 290ftlb up till valve float at 5500rpms which didnt happen in the begining.

 

I would think that it definetly would! Especially with a high lift cam. As the RPM's increased, it would land the lifter further and further back after the lobe. This would continue until it is taking off of the lobe and landing back on it. Full float. Weither or not to get springs with higher seat or compressed rating... I would think a higher compressed rating would be the primary target. Higher seat rating will wear the cam/lifter out faster unless a roller lifter is used.

 

blue got it right.

Denny knows all about soft valvespring dynos..... easily put him from 480rwhp to 445rwhp.

Bret

 

It was 447 rwhp. Missed two.

Ya, well.........New springs and dyno time awaits but there ain't no free lunches. ***, grass or gas, someone pays.

 

Did you ever figure out what those springs are?

 

Think you know this; getting hold of Trevor is like trying to place a personal call into George Bush thinking he'll get right back. It took getting a security agent named Lloyd Elliot to stop by his shop to find the part number.

It's PSI CT1225 - Dual late model stock valves springs. Seat 140 @ 1.950 and open 435 @ 1.200. Max lift .750.

Great big plans of hitting the dyno today to get that new baseline but when scanned with a Tech 2 it showed an exhaust leak and weak 02 so instead it was off to the muffler shop to fix the leak in the new off road pipe and new GM 02's.

Hey, we'll eventually get it as unless something strange happens, (It's happened before) think I've got whooped to the point of being on the downhill slide.