Valve spring info?
 

I'm looking for specs for factory and aftermarket valve springs (diameter, wire size, no. coils, free length, tension @ installed ht., etc.). According to parts books, 911s used the same springs from 65 to 89 (or thereabouts). However, the spec book only lists installed height. Does anyone have any info? Am interested in the difference between the various versions and prices ($100-650/set).

I'm also wondering if a high-quality generic spring from a multitude of sources would work.

Thanks,
Sherwood

bump.

No info anywhere?

Hi Sherwood - the factory information on installed heights and compression strength is in the Engine Rebuild Book Appendices...

Not exactly what you're looking for, but the only thing out there...

-Wayne

Just go by the compression strength at the installed height, and at full opening, if available. Thats all there is to a spring afterall. All the other stuff is only relavent if you encounter spring bind, something you can measure, should measure, when you install new springs, thats all there is.

I'll take a look at the engine book, but it sounds like basic specs. I'm looking for dimensions and specs for free length as well. And what if I'm shopping for higher tension springs that don't have the letters, Porsche or "for Porsche" on the package?

Sherwood

I have some AASCO valve springs I can measure if that would be helpful.

As a data point, on my AASCO springs, the inner and outer springs touch/rub each other when they aren't compressed. I can't remember if stock ones do. The AASCO also have a different installed height than factory.
-Chris

Chris,
Yes, if that isn't an inconvenience. I hope they're not installed. There appears to be a limited info on 911 valve springs. Wonder why.

Thanks much,
Sherwood

I measured the springs but I couldn't find my data sheet with the installed height so I called AASCO and got that.

Spring height (outer/inner): 40mm/38.4
Spring diam (outer/inner): 32.8/24.6
Installed height: 34mm

-Chris

Thanks Chris.
I could have called too. Duh.

Sherwood

Welcome. AASCO wouldn't have had the dimensions and I needed the installed spring height for my own purposes anyway.
-Chris

Sherwood,

I have a valve spring tester that I used for many years. There never was significant variation in factory springs.

The limited information is because there isn't a need unless you use far more radical race cams than the Factory race cams.

I used factory springs, set to stock height, in my C6/910 cam GT2 914-6 race engines (66x91). However, they had factory 935 titanium retainers and RSR/935 rockers. Those engines turned 8300 regularly and occasional 8800 intentionally. I’m sure they saw 9000. There was never a sign of the valves contacting the pistons. Carbon shadow close but no contact.

Remember, those are race engines that had maintenance rebuilds every 25 hours or so. Never had a failure.

Best,
Grady

those aasco springs are some stiff sum bittches. you really fight the tension when turning the engine over for valve adjustments or cam timing. gee, i wonder if that's detrimental to cam and rocker life.

For me the AASCO springs and some Ti retainers were a safety thing. It is soo easy to miss a shift with a 915 at the track that I didn't want bent valves whenever I missed a shift. I would think that they would cost some horsepower and added wear.
-Chris

Chris,
Having the transmission pop out of gear is usually not a problem with a (several) good rev-limiter(s). I think the big issue is if you put it in the wrong (lower) gear and the inertia of the car spins the engine too fast.

I think it is better to have the transmission and shift linkage such that the mis-shift doesn’t happen than to spend lots of money to prevent valve float at 14,000 RPM. Besides, there are other things damaged at 14K than broken rockers and bent valves – rod bearings for one.

There is a big price to pay with stiff valve springs: horsepower loss, wear on valves, guides, rockers, rocker shafts, cams, chains, sprockets, and jackshaft. The whole valve train suffers.
If you have an engine where the piston is chasing the valve closed, the valve spring can take some slack out of the chain and have the valve smack the piston at low RPM.

I like stock valve springs and settings. Convince me otherwise.

Best,
Grady
gradyclay@hotmail.com

Grady,
I really appreciate you sharing your experience with the list.

It's embarrasing to admit but being the clumsy person I am, I can't avoid missing shifts on occasion. With a freshly rebuilt 915, shifting from 3rd into 2nd by accident is no harder than shifting into 4th.

Years ago I "monogrammed" some Euro 3.2 pistons (put big "C's" on the tops from the valves kissing) but didn't bend any valves. Now I run stiff springs because that was the only "fix" I could think of. With the deep valve pockets in my 98mm JE's am I worrying for nothing? I checked and the closest the a valve comes to the piston is 4.25mm; is that close or miles away from contact during an overrev?

The only two guys I know who have bent valves both did it with an SC. Hmm, I think it was different owners but the same car. Are SC's more prone to bending valves in your experience or it just a coincidence?

-Chris

Valve springs are critical and should be chosen with care for many reasons, the first and foremost is controlling the valve at high rpm's. It is very easy to miss a downshift and for the engine to see 9500+ rpm. If you have a valve spring that controls the valve, you have a better chance that the valve will not hit the piston.

Choosing the valve spring depends on: cam lift, rpm range, valve weight, retainer weight, valve lock weight.

While most of the aftermarket spring resellers (they do not produce their own springs) give you an installed height, that is not really the best way to set them up. You need to look at cam lift, clearance to coil bind and what type of driver are you. If you take a performance cam, there is a difference in lift intake vs exhaust. If you simply set the installed height to a given number, you are then going to have a difference in clearance to coil bind intake vs exhaust. The resellers give you an installed height number that provides enough coil bind clearance for both intake and exhaust.

The conception that a stiffer valve spring robs the engine of power due to the force it takes to compress the spring is false. You have an equal amount of force being returned to the motor when the spring unwinds.

If you run a spring that is to stiff, you will accelerate camshaft lobe and rocker arm wear.

Running a light valve spring, retainer and keepers will allow the motor to rev freer due to the reduced inertia. Yes this comes to play on the valve train.

I would make your valve spring choice wisely as it can and most probably will pay you dividends down the road. Remember, cheaper is not always better.

Porschetech; aren't you neglecting friction in your response. The loss in HP is not so much the result of pushing the cam against the spring (keep in mind that the engine is running 2x the cam speed), but the drag associated with that pressure on the cam. While it's most likely not a big deal at low RPM's, at higher RPMs it can become significant.

I'm not convinced by a benefit that is as ambiguous as being able to rev freer. BMW used very light valve springs (and as a result a lower red line) in their 528e series. They weren't concerned with revability but rather efficiency and mileage. Once again I believe that it is a friction thing.

Chris; Maybe I can swing buy and we can weigh a couple of my 2.4 intake and exhaust valves and hardware compared to your 3.2's. I suspect that your valves are a little bit heavier which would explain your observation about SC's. We can post the results for everyone to see.

My theory/belief: As in all things 911, bigger is not better. The objective is to shoot for "just right". I believe that the valve springs need to be matched to the valve train mass and the cams' profile - specifically the accelerations. Putting together Grady's observations as well as others, I suspect that the later IMSA era racing camshafts (such as the GE80 and GE100) have significantly higher accelerations then the 906 camshafts and as a result would require stiffer springs like Aasco's. This would allow the valves to flow more air for a given duration and provide a significant performance improvement. As a result Grady could use stock springs with his 906 camshafts without a problem. Replace the 906's with GE80's and the reliability may be something else entirely.

Unfortunately I don't have access to either 906 or GE80 camshafts (yet) to confirm my theory. Does anyone have either that they could plot???

Hi John,
I should arrange another P-car lunch. We can weigh valves while we're waiting for our order. :D BTW: I have a motor apart (3.2->3.4 twin plug) at the moment so the heads are available if you want to make port measurements.
-Chris

For what it's worth, I discussed this subject with Tyson yesterday. He stated the stock valve springs in the 911 engine are good past 7,300 RPMs, which was the redline (I think) for the '73 911S.

I imagine how high an engine will rev when a shift is missed, is relative to the modifications and how it's being driven.

I've heard 3.0s have reved to 8,000 after a missed shift, and not sustained any damage.

Ok, here's some data for folks to chew on. Chris and I got together and weighed some valves:

First, I grabbed a few intake valves that I have from a 2.2 - 2.7 engine and they all weighed within .2% of the average of 107.73 grams.

An Exhaust valve weighed 89.7 grams

A Keeper weighed 17.35 grams

Chris had an intake valve from a Carrera 3.2 and it weighed 118.4 grams (7.7% more) while the exhaust weighed 105.2 grams. I believe that the SC valves were the same size as the C2's

As a for example, taking Grady's example of a 906 cam with stock springs (abiet light weight rockers and retainers), if you were to put that exact same set-up into a 3.2 Carrera engine, you would find that forces have increased proportionally to the weight of the valve since...

Kinetic Energy = (Mass * Velocity^2)/2

So this would say that if Grady's arrangement would survive an occasional spin to 9000 RPM in his GT2 engine, in a C2 engine with C2 valves it would have reached the same forces when spun to only ~8411 RPM. If you change to a cam with faster valve velocities, the problem will get significantly worse since the valve velocity term is squared. It wouldn't be too difficult to believe that you could run into valve problems at speeds below 8000 RPM using stock springs.

So Grady, do you remember what you were measuring for spring pressures on the stock valve springs?

Now you need to look at wire diameters, materials, natural frequencies of the inner and outer springs, acceleration rates of the cam profile, the changes in acceleration rate(jerk),
valve seating velocities, moment of inertia on the rocker arms, the interference fit between the inner and outer valve springs, does the retainer fit the springs tight enough to dampen vibrations, and a few others im too tired to remember.
The 906 is what I would call a slow acting camshaft, low lift with lower velocities.
In comparison our 306/288 cam at 8000 RPM would need a lot more valve spring pressure to survive.
Our race spring sets up at 39.5 mm with 100 lbs and has 410/ in rate. It was designed by us for the 306/288 and larger cam grinds and made with a very high quality wire.
To calculate open pressure take the spring rate and multipy it by the valve lift and add the closed pressure.
410lbs x .500 = 205= 100 = 305 open pressure.
I believe the higher open pressures and increased friction is a fair trade off for a stable valve train. If the spring is not up to the job and the rocker arm leaves the cam lobe (lofting) the rockers wear, the valve springs get beat up, the valve stem tips and get hammered etc etc.

If Dema was your teacher, I will second, third, any info you provide. Was he?

Yes!
He was when I was at De-Anza college,
and for the last 14 years at Elgin Cams.

Then with all the authority I have ( please don't challange this..OR ELSE!!) I pronounce you a true cam expert. If anyone wants to look into my pronouncement, you will find one of the most respected and knowledgeable people in the world, of cams, is Dema Elgin, of Elgin cams. Any student, or accomplis, of his, especially one with such longevity is worth listening to, very closely.

And hes Irish to boot! Can't be all bad.

Welcome aboard.

Okay Camgrinder - I'd like something a little more radical than a 330 cam, but something that'll still work with CIS induction and pistons, and also work with a stock valvetrain. 20/21 is what Webcam offers. Do you guys offer a similar cam to the Webcam 20/21?

Thanks.

The next step up from our 330 or Sport SC is the 964. I believe the 20/21 lies between our Super/C2 grind and our Sport 964.
Both I wouldnt use in your case.

Thanks for the endorsement Snowman.

Why? Too hard on the stock valvetrain?

Both of those grinds should have an upgraded valve spring. The Super C2 works good if the compression is raised to 9.8-1
The other variable is the CIS.
The 964 grind is stable with stock valve springs up to the usual rpm limit of 6500 with CIS so it works nicely. Regrinding the SC cams to 964 specs remove very little from the base circle (.030")
by far the most popular Porsche grind we do in the last 2 years.

Camgrinder(John) what have you got for the 3.6 and 3.8 in general?

and more specifically what have you got for a 3.8RS mostly street use?

Bill,
there are a few options available.
Super C2 248/236 duration @ 1mm
.475"/.455" valve lift
Sport 964 254/236 duration @ 1mm
.490"/.455" valve lift
284/274 254/244 duration @ 1mm
.490"/.460" valve lift
All of these grinds work well in the 3.6 litre and up engines and the choice depends on your mods and driving style.
The sport 964 is a little more than the 3.8 super cup cam. and the 284/274 is another step up.

John - can the sport 964 cam work in an SC engine? If so, how would it behave?

Thanks.

The Sport 964 cam needs over 9.8-1 compression and might have a choppy idle in the SC. I have not sold it to anyone that has put it in an SC.

Thanks, I'll do that:)