Valve springs
 

I received a telephone call yesterday from a home builder asking, what Valve Springs should I use?

He made reference to some of the springs sold in the aftermarket as well as the springs offered for his engine type from Porsche.

I am unaware of the steel used in many of the aftermarket springs but have done some research into the steel used in the stock springs. If you step back and look at both, you will be hard to find any springs from any company that have failed “just” because they were poorly made. I’m sure some have as there is always some mis use, Coil bind issues and maybe one or two that slipped through QC.

More important to me is the actual application and how they are used. Not who made them. The caller made mention of watching several You tube video’s on cylinder head rebuilding which I’m sure, they all did it differently. Confusing to say the least.

There are several areas that I consider important to remember.

Not all springs for the same application are the same. The wire size, number of coils can be equal, but the rates and pressures at the seated and open dimensions can all be different.

Coil bind height is a constant. There is nothing you can do about this.

Seated pressure is all about the valve seat and valve contact and the open pressure is all about the engine’s RPM safe capabilities.

It’s easy to state the following when you have a shop full of tools. A little different when you are building in your garage with nothing more than a set of Craftsman wrenches and a floor jack.

Seat pressure is more important than installed height. Setting all the valves, with the same seat pressures is far more important than just assuming the pressures are the same by setting all the installed heights the same. Note, Intakes and Exhaust will be different.

Why, as the springs are often slightly different, equalizing the seat pressures makes sure the valve seal the same, the over the nose pressures are the same, and the engine uses the same amount of torque to open each valve. No more, no less.
But at home, all you can do is the installed height method. You then have to assume that the pressures are the same and go with the shimming to obtain the same heights.

Professionals should be looking at all the parameters when setting up springs. The retainer height should be known, valve train weights and seat and open pressures calculated, and each spring tested for its pressures at both the seated and open dimensions. The distance to the spring coil bind should also be checked. This becomes important if you are changing the cams lift numbers.

The retainer height is somewhat a fixed dimension. It’s the distance between the seat base and the underside of the spring retainer when the valve is on its seat. This can be changed with different seat depths, base thickness, retainer step differences and lock position on the valve.

Another check often forgotten is the distance between the underside of the locks/retainer to the guide seal at full valve lift when seals are installed.

A professional shop will probably have a modern digital tool providing huge amounts of data easily manipulated by changing any parameters in software. Or, something like the more common Rimac tool or its equivalent by other manufacturers. These give height and pressures only.

There is no way I can write this and find fault with any pro shop assembling cylinder heads with the installed height method. This is more the common way when using stock parts and no changes made to the cam etc. It’s your typical production shop, where time is more important than quality.

But if you are thinking about changing parts, using any aftermarket spring, spring retainer, a different cam lift, you should be checking the pressures and not just assuming all things are Ok.

Also, if the person who called yesterday would call me back. I have information on the springs you are considering. I did not get your contact info.

The springs we use are Aasco. Randy had them designed back in the early IMSA days to provide the seat and over the nose pressures required for the 8000+ rpm 2.5 GTU engines.
We've used them successfully for 35 years with zero failures from breakage and good results post over-rev. I believe part of the success lives in the lowest over-the-nose pressure possible for high lift applications. Most of the after markets [racing] springs we've tested have stupid high pressures. Silly numbers like 400+lb @ .500" lift. Things change, engineering and materials evolve over time but to date, we've have never seen a better spring for two valve 911 engines. .

Indeed.

Like I said, its not about the spring, it is about the way they are setup.

My point was never to disparage any spring sold, but the correct way to set them up. Particularly when changing to aftermarket types.

Neil and Harvey, thank you for providing your expertise on this topic. Question for you both: Have you ever seen a broken genuine Porsche valve spring on a non-modified Porsche engine, either OE factory or correctly rebuilt? My limited perception is that the OE springs are excellent for OE lifts and virtually never break.

There was a bad batch of factory springs that broke in the 3.0L era (78-82). Changed a few of them when I worked at the dealership. In the early 2000's, there was another "bad batch."

Yes we have installed these before when customers have them shipped to us to fit.

A couple of observations we made. Wire diameter and the number of active coils. They seem to offer a wider range of possibilities in pressures.

As our cam designs have become more "modern", so too has our springs designs.

Even our stuff is nonsense if the correct way to assemble is not followed. Cam designs today have come along way since the 70"s. We are now down in the high 50's for Intake seat pressure and in the mid 70"s - 80"s for the Exhaust. When you get this "light" you have to know what you have and be accurate.

As best as we can, there is a limit to the amount of air you can pass through these ports. High RPM's should always be limited to the air flow capabilities, not because it sounds good. You just wear out parts making less torque.

Running high RPM's has to be because the heads flow enough to allow. The flow has to be measured with all of the Intake attached. These heads suffer from some weird reversion effect when you start lifting the valve too much. Its a function of large port opening and slowing down the air speed in the Intake. The air does some odd turns and tumbling between the Intake and Exhaust. Keeping the percentage between the two is extremely important in any head but these 2V Porsche heads its critical.

Having good control over the valves is a huge part of controlling this phenonium. Cams and springs become your friend or your enemy.

I had a 1978 SC that had 5 intake valve springs replaced, they all had broke (at different times). The previous owners kept very good maintenance records

This was very common on the early 911 SC. There was a bad batch of springs. The issue was addressed by the factory and spring failures were greatly if not completely resolved.

This is good to know. Before my time with Porsche engines.

I have not seen any heads or engines with a failed springs since working on these engines. However, we have seen springs broken where the spring was placed into Coil bind after the cams were changed and no change made to the set up. Cannot blame the springs for that.

We have on occasion discarded new springs that showed a odd spike in the force/lift graph.

The stock Retainers are something that do need to be checked. We have seen many that have cracked or failed completely. Be careful of the Titanium Retainers as well. Many heads that we have seem had these fitted and the underside showed serious wear, where the spring was working against the material. Common I think. Always check this.

There is not a lot that anyone can do but check.

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Apologize for the poor quality of the images. Screen shots of the software we use.

I found a spring we discarded and ran the test against another good spring. Both are new unused springs for 911/964 engines. Both have the exact same appearance.

As can be seen, one measures what a good spring should, the other has a lot less force. The force/lift graph shows the odd spike the bad spring shows mid lift, the reason we did not use.

This is rare but shows it can still happen. The reason I suggested, that when ever springs are replaced or reused, not only is the installed height measured but the force/lift checked as well.