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Join Date: Jul 2005
Location: Atlanta
Posts: 809
Quote:
Originally Posted by faapgar View Post
Some other choices have the outer of the inner spring already rubbing the inner of the outer spring in a resting situation.Not cool for a stress free environment that the spring needs to live in.The quality of the heads makes the motor.Fred

There is some nominal benefit in harmonic dampening with the two springs having a very slight interference fit, but that is outweighed by the stresses placed mostly on the inner spring so in modern designs it's not done these days, and the heat it generates. The inner spring design for about every 911 aftermarket spring on the market now is very overstressed even without the interference fit, and that's because they're based on decades old designs with no thought given to recent advances. I can't blame them really, if it works don't fix it, but if modern design can make it better then that should be pursued.

The spring metallurgy around these days is a big changing factor, as they are far superior with alloys containing vanadium, nickel, silicon, and chromium. The material is also far cleaner than ever before resulting in ultimate tensile strengths being far higher. A modern design likely would never have worked decades ago simply due to materials. Advances are obvious but some of the fuddy duddies need to pipe down and let the engineers handle it.
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Old 08-24-2018, 11:11 AM
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Fuddy Duddy

I have been called a few things before.So I will take this as a new form of endearment.But since I am old it is probably fitting.Ciao Fuddy Duddy Fred
Old 08-24-2018, 12:13 PM
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titanium retainers

Neil, your take on titanium retainers seems to conflict with Steve Weinerís experience and advice. For instance, you say that most titanium retainers are cheaply made and full of sharp edges and are not coated.

Yet Iíve seen posts by Steve where he points out that titanium is an excellent choice for retainers and he further explained that the OEM sintered Metal has the propensity to crack and therefore the Ti retainers are more durable and lighter, too.

There are a number of us that use Ti retainers from AASCO, EBS, etc., and I havenít experienced these wearing any quicker than OEM ones.

Is there some brand that we should stay away from? When did you discover this and in what engines? I understand that valve seat pressure must be optimized but Iím not in agreement yet on the use of Ti retainers.
Old 08-25-2018, 02:34 PM
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Functionista
 
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A clarification..

The 3.0 & later ones are sintered, not machined and that means they can fracture if you ever miss a shift. The 2.7 and earlier ones are machined steel and will not break.
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Old 08-25-2018, 04:57 PM
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Originally Posted by Rusty911 View Post
Neil, your take on titanium retainers seems to conflict with Steve Weinerís experience and advice. For instance, you say that most titanium retainers are cheaply made and full of sharp edges and are not coated.

Yet Iíve seen posts by Steve where he points out that titanium is an excellent choice for retainers and he further explained that the OEM sintered Metal has the propensity to crack and therefore the Ti retainers are more durable and lighter, too.

There are a number of us that use Ti retainers from AASCO, EBS, etc., and I havenít experienced these wearing any quicker than OEM ones.

Is there some brand that we should stay away from? When did you discover this and in what engines? I understand that valve seat pressure must be optimized but Iím not in agreement yet on the use of Ti retainers.
We all have our comfort levels. I certainly do not wish to disagree with my learned friend Mr. Steve Weiner. He is one person I have a lot of respect for.

Titanium has its place and its very common to run retainers made from this material, but here are some requirements when using these. They need to be inspected and crack checked often and replaced when any sign of wear exists. The trouble with selling them to the customers with street engines, inspection is never done unless the engine comes apart. Unlike race engines. If you have these retainers I would be shocked if there is not wear or damage to the contact face between the retainer and the spring.

For sure the sintered streel retainers are junk and are known to fail. My suggestion for street engines was to consider a lighter tool steel alternative where the wear rate is a lot lower than Titanium. The use of this along with well design cam profiles will make a big difference.

Yes we want to lighten up the valve train. No issue with this. Mine concern is, the retainers are often sold as an high performance upgrade, with springs that put 100+Lbs on the seat at installed height, and a poorly designed or copied cam is driving these parts. The cam induces huge harmonics, unknown to the driver, the springs go nuts trying to stay connected to the cam lobe, and the lighter retainer does not do what it was intended to do.

The correct fitment of a retainer to a spring is with some interference so the spring does not move. But the springs are often with sharp corners too, and these dig into the retainer along with the contact faces. There is no way titanium running hard against a vibrating spring does not show signs of wear.

Last edited by Neil Harvey; 08-25-2018 at 08:29 PM..
Old 08-25-2018, 08:26 PM
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Thanks Neil for the detailed post. It’s a good discussion for considering potential use of Ti retainers.
Old 08-26-2018, 09:02 AM
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Hi Neil,

I understand and agree with what you are saying about not using more seat pressure than necessary, and that a bad cam design could be compensated for by using heavy springs.

I know you are being very diplomatic by not naming names. But I took a high performance engine building class with Dema Elgin (of Elgin cams) in 1990, after which he invited me to a tour of his cam shop in Redwood City. And even then he was using software that allowed him to analyze the velocity, acceleration and jerk of the cam shaft and he took all of that into consideration in his designs, even in the 90s. If other cam makers made poor copies of his cams or the GEs, I could understand, but the way you are presenting your analysis of existing cam designs seems to cast doubt on all currently available Porsche cams.

If the improvement you are making is due specifically to the fact that you are able to CNC the cam to spec vs grinding a master with imperfections or that wears out of over time, that makes sense. But I'm less convinced by a general statement that currently available air cooled cam designs are generally bad copies and you can do better with no supporting documentation or examples.

Looking forward to hearing more about the new products.

cheers,
dug
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Old 09-01-2018, 06:33 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #27 (permalink)
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We have started to compile a full list of the air-cooled cam profiles we will offer. This includes all the standard stock profiles, but our intention is to offer our improved versions of many of these along with some profiles we have done in the past years for custom engines.

These include starting with, 356, 904, 951, and 928 cams we have created. The later water engine profiles will also be included dating back to the custom 962C grinds up and including the very latest 991.1 GT3 solid finger profile.

We intend to offer both 47.00 and 49,00mm journal sizes, including a 3-journal cam with a bolt instead of the early style large nut. All cams will be supplied on new billets with DLC coated lobes. A re profiling service is also offered, but welding repairs are not something we wish to offer.

I have also authorized new Valve covers to be designed that include a secondary oiling system for the camshaft.

We have all the stock profiles, including the 911E, 911T, 911S, 911 SC, 964, 993 Hyd. Profiles.

Of our custom grinds we have many variants of the following including some of our A symmetrical designs.

356, 904, 911 improved, SC Ĺ step, 911 race, 930, 930 race/GT2, 964 improved, 993 Hyd improved, 993 non-hyd. All 911, 964 and the 993 non-hyd cams can be used with our solid version of the forged 993 rocker arm.

Of the water profiles we have 962C, 951, 928, 996 and 997 GT3, street and race, 996/997 Turbo street and race, and the very latest 991 GT4 and GT3 non-hyd. These later 4V cam shafts are being manufactured in house and we do intend to make the 2V shafts the same way in the future. This will lighten up the shafts, allow for additional performance to be added and center oiling if ever required.

I will have a more complete list up on our web site every soon with the seat durations and lifts included. We will not show the 0.050” durations on any of our improved, Ĺ step or custom designs.

Our sales model is to offer a better match for each engine with modern designs, lower manufacturing tolerances, and quicker turnaround times. Custom designs will continue to be a large part of our business and with the Landis CNC grinder up and running shortly, we will be able to do this without the need for masters to be made each time.

Neil Harvey
Performance Developments
Old 09-09-2018, 02:17 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #28 (permalink)
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