lift vs valve spring life?

[John Milmont]

Hey guys,

Looking for a little advice. A friend of mine picked up a c5 z06 corvette he's primarily going to use for track days. The car has an aftermarket cam that has quite a bit of lift. I believe the car has a texas speed ms4 cam, the specs are 239/242 .649"/.609".

I'm thinking that .649 lift is quite a bit for a ls6 thats going to spend a lot of its time at RPM. My question is: whats a good estimation of how long the valve springs are going to last/how often should they be changed?

Any advice on the topic would be much appreciated.

 

[Cliff Beer]

John,

Well, there's a lot of variables here that affect spring life....

I'd say the most significant factors are:

1. Spring pressure. Generally, the higher the spring pressure, the shorter the life.
2. Usage. More time at high rpm dramatically shortens the spring life. Valve float also lessens service life as it's hard on the spring (as well as everything else).
3 Conditions. High heat, and higher lift cams shorten spring life.
4. Metallurgy and construction. There's good springs, and there's bad springs. Good spring will last a very long time, bad springs might not go more than one track session. Needless to say, go with the best springs you can buy.
5. Miscellaneous. Valve weight...lighter valves require less spring pressure thus longer life.

Net, for what you're describing, personally, I would check the springs after every five track sessions. Just pull one out and inspect and put it on a spring gauge. If it's more then 5% off it's spec then replace all of them. Pick the one that gets the hottest...usually that's the one right up against the firewall.

Just my $.02.

 

[Ron Earp]

Seems excessive for a non-drag car. I'd check them, but probably not based on the number of sessions. I install hour meters in my track cars and build a log of MTBF (or close to failure) of various consumables and parts. In this fashion he'll figure out how long the springs last and he can replace them well ahead of time.

 

[Mike Huddart]

The LS engines run a Bee Hive spring so traditional thinking on spring pressures doesn't really apply. The retainers etc, because of their small size, are incredibly light compared to a traditional set up, plus the LS uses an 8mm valve stem further reducing weight.
Stock GM performance springs will only cope with .600 lift but there are plenty available up to about .700 with all sorts of trick stuff like oval wire.
A typical LS spring for that sort of lift will be about 60 lbs less seat pressure than a normal roller spring.

Mike

 

[Ron Earp]

The LS engines run a Bee Hive spring

I didn't know that. My SCCA ITS Mustang has beehive springs in the 3.8L engine. 94-95 Mustang V6 motors have traditional springs, 96+ engines use the beehive springs and the difference is fairly dramatic with respect to size and weight of the components so we used those. Valve stems were smaller diameter, the keepers were much smaller, etc.

 

[John Milmont]

I talked to Texas Speed today and asked them some questions about their cam. They said that the cam was never intended to be a road race cam and was intended for drag racing. They said the normal street life of the springs was about 30,000 miles.

I told him the car was used primarily for a track day car - he said that I should periodically test the springs and probably replace them every season.

I don't think they do any road racing at Texas Speed, so I don't think they have a good understanding of how long the springs will last in a road race environment.

The valve springs on the ls6 are the ones Texas Speed recommends, which is a dual spring design and not a beehive. They said they put a ton of R&D into choosing this spring and that it was engineered much stronger than what was needed.

This whole issue came up because we had some sort of valve train failure. Today, my friend told me his mechanic found one of the valve springs was broken - my only guess is that whoever installed it didn't get the fitted height correct. Before this, we were thinking that it might have been a lifter failure since it was making a buzzing sound at higher RPM's and because this car is running LS7 lifters which have a track record of failing on bigger cams. I thought the hydraulic portion of the lifter collapsed and could not pump up anymore, thus the buzzing at higher RPM's.

We dont know the extent of the damage, but I think hes going to find himself very lucky.

 

[Mike Huddart]

That isn't much of a cam for drag racing, it's actualy less than GM put in their top end crate engines.
Also you can't go putting valve springs on hydraulic roller lifters that " are much stronger than what was needed" it doesn't work like that.
Maybe your friend should be talking to someone else about this.

Mike

 

[Randy V]

When checking the springs (I would recommend every few events), remove them in order and catalog each spring. Note its free height and pressures at .250", .500" and finally full lift.
Don't make the mistake of judging loss of pressure as the sole cause to toss a spring out. Springs will often times get stiffer just before failure. I use 10# delta from original as the guide on a racing engine. Springs are a lot cheaper than replacing pistons, heads, etc..

Rocker arms should also be replaced in cycles. Depending upon the service, annually or as part of the refresh cycle for the engine for any aluminum rockers. Steel rockers get an extra cycle if they magnaflux well and the rollers are sweet.

Consider also using a spray bar system for the springs. A lot of hassel, but spring life is increased many fold.

 

[John Milmont]

That isn't much of a cam for drag racing, it's actualy less than GM put in their top end crate engines.
Also you can't go putting valve springs on hydraulic roller lifters that " are much stronger than what was needed" it doesn't work like that.
Maybe your friend should be talking to someone else about this.

Mike

Sorry, I didn't quote them accurately. I believe they said the springs were over spec'ed.. Not sure what that means.

Yes, it isn't much of a cam for drag racing. It is still supposed to be a streetable cam. I can say that its right on the edge of being comfortably drivable on the street. The thing about it is that the lift is pretty big. In the corvette forums, it seems like no one is running over .590-.595 lift in track day cars.

 

[Howard Jones]

When I was selecting the valve train on my SLC motor (old school SBC) I talked with Brodix and Comp cams tech line guys. They were so helpful I still like to tell people about them and recommend them both.

I would call comp cams and ask them about your particular configuration. I would bet on them being very helpful. Ask for their recommendation on a valve train using comp cam parts and then you can make some baseline comparisons to your stuff.

I would also think they could work out a maintenance program for you if you use their parts.

That also seams like a lot of lift for a hyd roller lifter. Also the total weight of the valve train, spring, keeper assembly, pushrod, and lifter, is very important. But the really big thing is max revs, rev range, and total time running in that range.

 

[John Milmont]

Yeah, I have worked with comp cams for my personal car. All I can say is that those guys are pros.