[Tim M]

Originally Posted by JROC

Just a quick question, but does boost really hurt or cause faster wear or premature failure to a valve spring? I would of thought boost would be irrelevant towards spring life on a motor with a stock cam, run stock RPM's?

NA motor operates at atmospheric pressure.

Supercharged/turbo charged engines operate with positive intake manifold pressure. This pressure acts on the back of the intake valve in an attempt to open the valve when when seated (area of the valve times boost equals pressure attempting to open).

This pressure on the backside of the valve negates the pressure from the valve spring...90 psi on the seat minus ~35 under full boost means your effective spring is only ~55 psi on the seat and something similar over the cam lobe.

I'm not a engine scholar and there are probably more variances, it is an issue especially on an engine that doesn't just slice thru the rpm like a drag run or stoplight vice road course and/or top end.

Don't think boost has an effect on wearing the spring out unless it is in a valve crash/valve 'float' condition. The rule of thumb is each time you experience these events, the spring loses tension.

I'm concerned as valve issues seemed to be the only thing that our LT1's have any issue with (and even then pretty darn rare).

Keep in mind the LT4 version uses the same spring at a reduced installed height (more overall pressure and the valve is made of titanium for reduced weight and thus less required spring pressure).

Simply, I'm going to spin the engine higher, longer than it was designed on the road course and autobahn. It will still probably blow up due to the DOD lifters...

[JROC]

Got you, and that makes sense.

I was thinking the pressure would be in the cylinders pushing up on the valves and that would put more stain on your rockers/pushrods/lifters but not really the springs since it's all riding a cam lobe and the spring is returning the valve to being closed. But I wasn't considering that when the valve is closed that the incoming pressure would be pushing on the backs of the intake valves.

Thanks,

Jesse

[Tim M]

Used a visit to Nurburgring as a validation of my valve spring change...seemed successful - no defects and nothing came apart on the 400 mile round trip. Feel much more confident on redline shifts. Only the DOD lifters are a concern...

I ran into another forum member - FNxR3DNECK...for some laps.



Will say, the LT1 is no different than the LT4 (gen 3) or Gen 1 I've worked on. The Bluegrass spring compressor makes the compressing a fair bit easier...not seamless, but easier.

And no air/rope is required...will suggest putting piston at TDC plus 1 inch of rotation on the balancer. Gives a bit more room for spring recompression/valve drop before it releases the locks. The valve notches are not very deep in the piston and you may touch the piston while compressing the springs (especially the intake valves).

Thanks for the suggestions folks!