911sc 1982 Valve Springs Conundrum

[DoMeister]

Hi
I seem to be going around the houses on trying to find the best course of action here.
I'm doing a top end rebuild to bring things back inline, not chasing peak performance, I haven't even had a chance to drive the car yet! Serious rust repair underway, stripped to the shell...

I have one broken valve spring pair possibly from broken head studs (3) or heat related but I have also heard 82 was a bad production year for 911 valve springs...

I'm doing 6 standard exhaust valve guides but I'm told the intake guides are fine.
Nikasil cycliders replated, new rings. New steel lower head studs.
SSI exhaust which is a nice bonus.
Everything is pretty much stock with the addition of rocker shaft seals.

So I'm trying to decide do I replace all valve springs and if so with what?
Stiffer springs require other considerations so not sure that's the right route.
New set would be nice but which brand, that won't break the bank or worse break in the head!
Educate me - How critical is valve spring tension in the overall engine performance/consistency/longevity?

Where I live
Porsche VS = 550 euro
Eibach 20444 or 20701 = 400 euro
Hamburg Tech = just don't think this is a good buy (seems to be very available, sometimes called OEM!)
Labour is also a consideration, I want to make things simple (within reason) for the company rebuilding the heads.

Or good set of used? Not from the same production year.
Can used VS be tested to establish if they can be reused?

Any advice appreciated. And if there is something simple I should be doing that I have missed please jump in with that also.

Cheers
Dom

Because we all like photos

[Mark Henry]

A good machine shop will have a VS tester, but it only reads lbs at a certain height, no guarantee that a 40+year old spring will stay good after being pressed back in service.

I run the eibach sport spring in my 3.0 but it's fully balanced with 120/104 cam and 10.5:1CR twinplug. Be aware that the heavier springs will wear the cam components faster and they actually rob HP, one of those cases where you hope the HP gains are greater than the losses.

You're nowhere near that tune so I'd suggest sticking with the new stock springs.

[DoMeister]

Mark,
Thanks for your reply.
I need to look closer at cam specs, what does 120/104 refer to? I will look up SC cam profiles and get some education...

Eibach appear to be a good choice. They make 2 springs for the 911.


55lbs I think equates to the stock and 90lbs to the sport whereas racing might be 110lbs? I like the idea of a marginal increase that might compensate for other changes in the heads over time but not sure this applies in the way I think it does..

I think I recall Dougherty Racing saying that 90lbs is fine with stock retainers, cams, rockers etc... but can't be sure. I don't want to go down the titainiam retainer route.

Safe route is possibly 20701.212 @ 55lbs

Are there recommended online suppliers for Eibach in the US/Canada? Not many here which is crazy being they are made in Germany...

Good suggestions

[Trackrash]

Don't overthink it.

With stock cams, use stock springs set at factory height.

With performance cams use the spring and settings the cam-grinder specifies.

BTW, it is known that some of the early SC springs were known to break. So you are right track to replace them.

[mikedsilva]

Originally Posted by Trackrash

Don't overthink it.

With stock cams, use stock springs set at factory height.

With performance cams use the spring and settings the cam-grinder specifies.

BTW, it is known that some of the early SC springs were known to break. So you are right track to replace them.

I actually did a rebuild on a 3.0 a couple years back, and used all new valve springs from our host.
And 1 of those ended up breaking too...

[DoMeister]

Don't overthink it.
With stock cams, use stock springs set at factory height.

Good advice Gordon, thx

I actually did a rebuild on a 3.0 a couple years back, and used all new valve springs from our host.
And 1 of those ended up breaking too...

I'm afraid of this, picking a good brand I think is key, anybody know who supplied Porsche originally?
Other quality valve spring manufacuturers that people have used in their 911's would be helpful also.

I think I will be going down "the stock 55lbs" road...

Thx

[Mark Henry]

Originally Posted by DoMeister

Mark,
Thanks for your reply.
I need to look closer at cam specs, what does 120/104 refer to? I will look up SC cam profiles and get some education...

Web Camshafts 120/104 grind

[DoMeister]

Mark
Oh Sh$t is that a hole I fell into. Again!

I have the Euro spec SC which is 9.8:1 CR and the larger ports. With Mahle Nikasil P/Cs (replated) rated @ 204 HP, and w/ SSIs circa 220 HP. Supposedly!

I think there is opportunities here. Reading up on grinds (which I had before but conveniently forgotten $) there are a few of interest.

• Webacam 20/21 - might work with my setup
  SC330 - meant to be the SC cheater cam
  Mark’s 120/104 - race orientated?

Researching https://forums.pelicanparts.com/porsche-911-technical-forum/163860-best-cam-profile-stock-sc.html

It appears 20/21 might be a good match for CIS EURO CR. What do you guys think in terms of grind options?

So back to my OP “if I’m missing something, let me know” if a 20/21 grind was on the cards, would I be ok with ok with 55lbs spring or 90lbs spring?

If the 55lbs work well with the 20/21 then I see a nice gain with a smart budget spend…

Thanks

[Evan Fullerton]

I think the answer lies in how high you want to rev it.

My stock SC motor would rev to 7000 without floating a valve. Some of the 3.2L guys rev to 7200 or 7300 on stock springs and cams........ but there isn't much headroom. Miss a shift and buzz it to 8500 and you will probably break a rocker and or bend a valve with stock springs. With stiffer springs you might just get away with it...... but things won't last as long, a little more heat in the oil, and you might loose 2hp.

A hotter cam will likely accelerate the valve a little faster and float sooner. Light weight rockers that are now available and or going with lighter valves get some of the headroom back with stock springs but they aren't cheap.

It's all a compromise.

[Mark Henry]

IIRC you can't use the 120/104 Web cam with CIS pistons.

[G450X]

Originally Posted by Evan Fullerton

I think the answer lies in how high you want to rev it.

My stock SC motor would rev to 7000 without floating a valve. Some of the 3.2L guys rev to 7200 or 7300 on stock springs and cams........ but there isn't much headroom. Miss a shift and buzz it to 8500 and you will probably break a rocker and or bend a valve with stock springs. With stiffer springs you might just get away with it...... but things won't last as long, a little more heat in the oil, and you might loose 2hp.

A hotter cam will likely accelerate the valve a little faster and float sooner. Light weight rockers that are now available and or going with lighter valves get some of the headroom back with stock springs but they aren't cheap.

It's all a compromise.

What modifications did your SC have to rev to 7k rpm’s? My stock ‘82 (with SSI’s & M&K 2/1) falls off cam at around 5.5k rpm’s - it drives me nuts.

I am planning on a rebuild in January with M1 cams which should remedy the low redline, but I am curious about your set-up. I also have 964 cams if the M1’s don’t work out.

I plan on “backdating” my late SC to early SC specs with large port heads (recently rebuilt by CGarr), early CIS with the higher flow fuel distributor, Max Moritz short stroke P&C’s, etc.

The recent rocker arm quality problems have me worried of late, since WebCam recommends new rockers with their camshafts. The M1 cams are new billet, which is supposed to be slightly softer then their hard weld cams, so maybe rebuilding my stock cast rockers would suffice? I’ve thought about Pauter rocker arms, but they’re expensive and back ordered - I guess I’m not the only one worried about rocker arm quality…

Thanks

[Evan Fullerton]

It was a totally stock small port 3.0L. It didn’t make power up there but for Autocross, not having to shift is often much faster.

I’m currently in the process of getting parts together to build it into a short stroke 3.3 with modified twin plug heads by Xtreme. Bill was thinking he would open them up to 43mm intake ports and 39mm exhaust with bigger 8mm stem valves. Not sure when I will see them though as I shipped them out 6 months ago.

Figuring out cams and rockers is something I need todo still. Neil at Performance Developments I believe makes his own rockers also but I’m not sure of the availability or if he will sell them for use not with his cams and recommend springs.

[Neil Harvey]

Camshafts, Rocker arms and Valve springs all need to like one another.

PD has developed many new Cam profiles for these Porsche air cooled engines. These are at another level to what is currently offered by the other suppliers. They are not cheap, come only on new billets and are DLC coated.

All the performance comes from your Cylinder head. The cam makes the head work. Opening up the restrictions helps a lot.

Controlling the valve through its motion is extremely important. We have worked really hard in developing cam profiles that provide the air flow performance, along with minimal harmonics. This has allowed us to lower the spring pressures and make springs that were on the critical stage of stress become a lot more usable.

Calculating the spring pressures is really something that your camshaft provider should do for you. You need to give them all the mass weights including the spring you wish to use, the valve seat margin widths, engine use and the RPM limit you are wanting to use.

But, don't get involved in any of this if you do not know the airflow. What's the point of spec'ing out a cam etc, if you have no idea of the flow numbers. The flow numbers need to be measured with all parts used in the car. Filters, Intake manifold etc.

Camshaft lobe design can lower the harmonics or increase them. Then you can either lower the pressures used or have to increase them to dampen out the noise. Increasing them hurts torque and increases the wire stress levels.

If you gain 2-5 ft/lbs per Cylinder by lowering spring pressures, and any other means, you can gain quite a significant amount of performance. The little things do help.

Rocker arms get expensive as you need 12 of then per engine. There are some out there that cost well over $ 400.00 each. There are some billet ones that are way less but I have no experience with them to give any advice on use. We have never used them by choice but others have so seek out their experience. We offer a modified 993 arm that is billet but these too get expensive. My advice here is to have your rocker arms checked for the correct ratio and condition before doing anything. I have seen some that should not have been repaired put back into service. Your cam supplier will provide this service I'm sure.

[RobFrost]

If your engine's unusually low on power at high revs I'd check for ignition advance, fuel delivery and air flow.

Check the mixture at high revs, check the timing advance is working, and check for obvious flow restrictions such as defective silencer, air filter, or throttle not 100% open.

Leaning out at high revs can be as simple as a blocked fuel filter, low fuel pressure, crud in petrol tank, worn pump, etc.

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