valve spring pressure determination ?

[toolmakeron]

When setting up springs, I go by the cam mfg, or usually PAC suggestions. Question is , why do we always use the same spring for both valves? The ex is usually lighter than the intake.Is there some formula that a guy can use to see what will be the correct spring #'s needed. I was told that Vizard wrote how to do this years ago in some British mag.I haven't had any problems yet, but it still seems like common sense to have different spring( seat & over the nose) pressures for the different valves. Is there a program out there that is available? Any info or discussion would be great. Never seem to stop learnin' . Thanks guys

[T-flow]

A lot more to it, but I have several of my engines with two different springs on it. Lift and weight for sure make a difference, but lobe rate or aggressiveness of the lobe will tell you something to.

No an easy question to answer.

Whats the springs?
Whats the cam?

[bigjoe1]

I ALWAYS run a much smaller spring on the exhaust


JOE SHERMAN RACING

[randy331]

When setting up springs, I go by the cam mfg

That will get you a mean spring every time.

I have a considerably different spring on my ex than I do intake.

Randy

[MadBill]

One consideration is that from a load/wear standpoint, the typically lower/slower/longer exhaust lobe is usually going to be easier on float RPM and potential wear with the same spring, so the main benefit of a lighter spring might be that only the inlet lobes wear/fail, while giving up the safety factor of having the inlets float well before the more contact-prone exhausts*. Slightly lower friction losses could be a mitigating factor..
*Another way to look at it: in a deliberate over-rev situation, floating the inlet valves will give the driver positive feedback via temporary power loss. Badly floating the exhausts usually results in permanent power loss.

[wyrmrider]

Ayymetrical cams also allow different springs
BVVC with heavy Motor Home/ Truck exhausts
lots of variables to consider

[jim_ss409]

Badly floating the exhausts usually results in permanent power loss.

As Larry the Cable Guy would say,,, That's funny right there!

[JoePorting]

I always wondered about heat. Since the exhaust valve spring is right above the exhaust port, I assume it must run a lot hotter than the intake spring. Maybe even twice as hot. Therefore I wonder if the light weight of the exhaust valve is offset by the heat it makes when it comes to setting the exhaust spring pressure.

[Greenlight]

There are several software packages that do a good job of calculating valve spring load vs. RPM using the weight of the components, acceleration values of the cam lobe, moment of inertia of the rocker arm, and a few dimensions.

Performance Trends has a good one.

I know Kip at Cam Motion has one, as I am sure all the other cam manufacturers do as well.

I have a DOS based program that I have used since he mid-90's that has never failed me.


Joe,
From what I have read, most automotive valve springs operate between 175F and 250F (ref: Symposium on Effect of Temperature on the Properties of Metals by SAE/ASTM), which is below the temperature where the material properties are significantly affected (~400F). I'm sure the valve spring temperature can get over 400F in applications where the oil is restricted to the top of the engine. As you know the endurance engines spray oil directly on the valve springs to keep the temperature at bay.

[PackardV8]

Just to clarify, doesn't an endurance spring generate it's own destructive heat from continuous high-RPM internal forces? The oil spray is to remove the heat they generate, not just the heat they conduct up from the exhaust ports.

[Greenlight]

Just to clarify, doesn't an endurance spring generate it's own destructive heat from continuous high-RPM internal forces? The oil spray is to remove the heat they generate, not just the heat they conduct up from the exhaust ports.

Absolutely, the majority of the heat is generated by the spring. The relatively small contact surface at the spring/spring seat interface and the spring/retainer interface is only a minor contributor.

On dual or triple springs, the friction between the moving coils is also a big contributor.

[piston guy]

Valve material ( steel vs Ti) is an important factor here IMHO.

[CharlieB53]

Valve material ( steel vs Ti) is an important factor here IMHO.

Same goes for top collar, Ti much lighter than steel.

Newer conical springs have a lighter upper sectional weight, supposed to increase RPM capability for a given spring rate of pressure.

It can get expensive fast to combine all the best light weight high strength parts, coupled with the right cam should make a noticeable difference if the heads, intake, and exhaust all match.

[toolmakeron]

Other than the Perf Trends program, what other ones are there out , that I can try? Perf trends program that I have is , for me , a bit confusing. Hope to find another program that will work.Thanks

[Greenlight]

Other than the Perf Trends program, what other ones are there out , that I can try? Perf trends program that I have is , for me , a bit confusing. Hope to find another program that will work.Thanks

Check your PM.