ptuomov

If you're building an optimized race motor (or in fact very efficient modern passenger car engine), you'll build it to "loft" the lifter over the nose at the redline rpm such that the cam and lifter almost but not quite lose contact. You build it such that the seated load just controls the bounce. You build it such that the optimal shift point is very close to the redline. You build the combustion chamber to optimal burn. In such a motor, one spring breaking during a race will lead to valve to valve and/or valve to piston contact.

This may not be the case for hot rodded street cars. That I grant.

Lizard928

After the fiasco with the springs from another supplier (most didn't even last 600miles), I switched to the PAC springs and have had zero problems.
A full set of PAC springs with all retainers etc are around $670 last I bought them.

Be very careful with any valve springs. You can have them made at a local company, but you're going to be relying on them to buy good wire.

The springs which had all the failures were from racing spring in CA. They were properly wound, and heat treated, and shot peened as yours are as well. However, the wire they purchased was deefective and had issues. Looked fine, worked great, but alas failed really fast. Thankfully they were dual spring setups so there were no dropped valves.

Make sure you have a disclaimer on your site stating explicitly that you have no warranty on these springs, or that your warranty is for the springs only and that you won't be held responsible for any damages.

On the PAC springs, before I ran them, I contacted over 20 of their suppliers, stated that I was looking at possibly reselling their springs in Canada, and was wanting to know roughly what their failure rate was so I could compare.
Every company but one that was willing to talk to me stated that they had never had a PAC spring failure come back to them, but they had loads of other springs come back. The one company had one spring come back to them broken. It had clear signs of impact damage on the side of it where another component let go and smacked the side of spring, then got in between the coils of the springs.
I also searched the forums, and there are many who got other brands of springs which are about 1/2 the cost of the PAC springs, there was countless threads on broken springs. All from other companies, none from PAC though.
An additional note is that PAC does all their own wire in house too, so they have consistent metal, and are therefor able to control all facets of the manufacturing of the spring.

With the labor to change these in the cap, as well as the cost of potential failure. I would strongly urge everyone to research all valve springs they might get.
If the source of the spring and wire is unknown, RUN.

mark kibort

or street based race cars.

"valve to valve " contact? how is that possible.
one valve spring busting, still leaves another to close the valve, albiet with a less force. however, at the engines speeds concivable for a 928, i dont see how even a broken outer or inner spring can not do the job, albiet with some valve float at redlie. valve float, doesnt equal piston to valve contact. the intake valve has plent of time to retract . the exhaust valve , not so much. at 45 degrees before TDC, the exhaust valve is maxed out and starting to close. it cant make contact, with a 928 valve, unless the valve didnt move .2" upward to the seat, because the total distance that the valve extends to the piston is .3" on a .5" lift cam. maybe at 9000rpm, this can be a problem, but do you really think a 6500rpm 928 race engine is going to have issues? i think the helper spring is a good safety net for a broke valve spring.... especially for how long these things stay in our cars! heck, my valve springs are 30 years old right now.

ptuomov

With high lift cams, big valves, steep valve angles, maximally compact and low volume combustion chambers, and long overlap periods, it's possible for the valves to hit each other when a spring breaks. That list of characteristics is usually found in an optimized race motor.

I grant you that when you're making something like 66 hp per liter, you may be quite robust to valve spring issues. But that doesn't sound like an optimized race car motor to me. An optimized race motor will drop a valve in no time if either of the springs break.

I don't think the rpm per se is what matters. What matters more is whether yuo've taken everything out of the engine that you can. If nothing bad happens when one of the springs breaks, then you're either running way too much spring or you're leaving money on the table in terms of what the rest of the engine could do.

Carl Fausett

The rev limiter is set to 6700. I built the engine to run at 7000 because of Bonneville.

But with these cams (different) and road racing, we note the torque starts to drop off at about 6500 and I should select the next gear. So - 6700 rpm rev limiter.

Because of the HP, I get to it very quickly. Note how little time is spent in 4th before I have swept all there is and its time to grab 5th.

ptuomov

Poking the beehive, pun intended..

mark kibort

well, the torque is dropping pretty significantly in that range anyway, but i suspect that the hp is great enough and broad enough were you dont have much more than a marginal gain for shifing higher. my engine, runs out of HP after 6600rpm (redline) and i shift close to that to get the most possible out of it.

yes, if you drop a valve, but the other spring would keep that from happening, right. as far as geting the most out of the engine. if its breathing best it can and its only 6700rpm, then a valve spring break shouldnt effect even the most stout of race engines. i guess its how you define " getting the most possible out of the race engien". again, there are plenty based on rules and limits that dont even allow you to have these issues, especially if its rev limiters or cam lift, etc. many can be maximized and not hurt themselves if a spring breaks.

ptuomov

But Mark if you're running too much spring with your "stout" double springs to the point that either one of them would protect the engine, then aren't you usually leaving some power on the table by higher friction losses?

mark kibort

again, if we are talking about engines like ours, the friction losses are miniscule compared to the final product.... if you are talking miata, where 1-2hp makes a difference, then maybe. one great thing about the V8 is that if it is a lower reving type, then valve,and spring weights and frictions for springs dont have a lot of value. the main things that most V8 racers are concerned with is longevity and max power. this can happen at lower relative revs than a Porsche flat 6 counterpart or a BMW/Acura engine. dual springs dont have to be over sprung, its just that the helper spring is there in case of a failure.. ......and the little things that move , like retainers, dont have to be that light either, as they are not moving as fast as they would in a car with a 9000rpm redline.
so, my "stout" double springs are not that stout at alll... just stock stuff

ptuomov

Flat tappet cam interface friction is a meaningful part of the total engine friction at midrange rpms.

No factory puts double springs in an engine as helper spring for the case of failure. They are (or more accurately were) there to reduce resonance.

Racing teams used to do double (or triple) springs and sometimes still do because they can't get enough load and clearance without reducing the number of coils to a low level. Since fewer and fewer race engines now have two valve heads (that require a lot of lift) and one can get ovate wire single springs, that use is down too.

I get it why you and others run old Porsche double springs. They are good enough for most purpose.

mark kibort

they worked great for scot and his racer. they were not stock, they were eibach springs. a devek high performance replacement ... i forgot what the S4 has on it.. it might be a single spring. do you know?

Carl Fausett

Agreed. Say in the design envelope Porsche has provided, and you should be good. Change cams, change your rev-limiter, add boost - whatever - then consider it.

FredR

Interesting thread- does this [in part] explain why GT cams seemingly have lobe wear issues compared to the S4 [lower lift] that seemingly does not?

Rgds

Fred

Carl Fausett

I cant say. I have not had my head in enough GT motors to know for sure. I own one, and it has no lobe wear issues.

Yes, valve springs, valve weights, and camshaft profiles all would/could have an effect on lobe wear. Then there's oiling... we know that Porsche played with the oiling on the GTS... did they tinker with some GT's before they did it to the GTS? They often do put a few of something out there pre-release to see how it goes I have noticed. They might have.

Carl Fausett

Myles: numbers still coming. My guy is out till tomorrow and the numbers are on his desk. We think we remember the numbers, but we want to be sure.

Trouble is I'm racing a BMW 325 at Road America Friday and Saturday. I'll get these to you as soon as I am able.