Dyno Video of Mike Simard's 427 c.i. 928 engine
08-03-2009 | 09:34 PM
#31
Three Wheelin'
Joined: Aug 2006
Posts: 1,765
Likes: 1
From: Atlanta
Mike and others --
Here's what I am planning to do, perhaps you can give me some pointers.
I am planning to use the stock 928 valves. I've collected a bunch of used valves, I probably have about 100 of each at this point. We'll pick a consistent set among those. This is for a turbo engine so the 37mm and 33mm valves are enough by my estimation. The intakes are magnetic steel and the exhaust have non-magnetic lower part and magnetic upper part. The stock exhaust valves are pretty thick and I haven't seen or heard of a burned one. Also, the weld surface on the exhaust valves should hold well as long as the valve guides are tight. This leaves the tripple groove tip as the weak spot.
On the groove, the plan is as follows. In stock configuration, the valves are loose in the keepers and the keepers butt, which allows the valves to rotate in the seat. This will presumably make the seat and valve contact surface wear evenly and seal longer. My plan is to take the keepers and grind/sand/whatnot them down a bit until the keepers no longer butt. Instead, the collet mechanism will hold/squeeze the valve the same way as with the single groove racing valves. By my estimation, this will hold the valve in a way that it can't bang its grooves up and down against the keeper.
What do you think?
Here's what I am planning to do, perhaps you can give me some pointers.
I am planning to use the stock 928 valves. I've collected a bunch of used valves, I probably have about 100 of each at this point. We'll pick a consistent set among those. This is for a turbo engine so the 37mm and 33mm valves are enough by my estimation. The intakes are magnetic steel and the exhaust have non-magnetic lower part and magnetic upper part. The stock exhaust valves are pretty thick and I haven't seen or heard of a burned one. Also, the weld surface on the exhaust valves should hold well as long as the valve guides are tight. This leaves the tripple groove tip as the weak spot.
On the groove, the plan is as follows. In stock configuration, the valves are loose in the keepers and the keepers butt, which allows the valves to rotate in the seat. This will presumably make the seat and valve contact surface wear evenly and seal longer. My plan is to take the keepers and grind/sand/whatnot them down a bit until the keepers no longer butt. Instead, the collet mechanism will hold/squeeze the valve the same way as with the single groove racing valves. By my estimation, this will hold the valve in a way that it can't bang its grooves up and down against the keeper.
What do you think?
I would sleep well with stock 928 valves that have been looked at. It's not just that they are a little better than currently available ones, the only way a triple groove can survive is with a tight keeper fit and I've seen no others that were anywhere as good as original Porsche ones. The original Porsche valves fit so well that the retainer doesn't rock, that's what breaks them. Rocking of the retainer will fatigue the root of a groove and break, it doesn't matter how good the material is either. The TRW valves I broke had just .002-.003 excessive clearance but that translated into a lot of retainer rock. The tolerances of the manufacturer should have been one tenth of that crap. I've also measured some other valves that had varying groove spacing(!) as well as the groove not being very round.
In other words, I agree with Mr. Glerb
If you were so inclined to fit keepers, you can use a belt sander to 'lap' them. If you did that you must deburr them either by a vibratory finisher, tumbler or something. You can also order new keepers from 928sRus, they are surprisingly cheap too and seem to be original stock. Don't even think about ordering valves from Porsche. They cost twice a custom Ferrea and they are not original anyway. The originals have engraving near the tip, modern crap has electro etched lettering.
BTW, if you had to make valve guides, SI has 7mm blanks that can be finish machined. That's their one good product, their valves are hideous. Can you not use Porsche replacements?
08-04-2009 | 09:17 AM
#32
Nordschleife Master
Joined: Jan 2009
Posts: 5,610
Likes: 82
From: MA
Improving the valve-keeper connection
The valve guide issue has been solved, we got guides from SI Industries. Others have not been happy with their valves, but nobody has complained about their guides. In contrast, people justifiably bitch and moan about the stock guides which are made of the same material as the Swedish fish candy.
I'll fit the keepers such that the valves don't rock or rotate, whether or not I get new keepers. The non-rotating connection is so much stronger. I have a bunch of used keepers and a bunch of used valves, and will get some new keepers as well. I planning to sand the keepers down in a way that the contact area is maximized and that the valves neither rotate nor rock.
Here's one web reference to what I am talking about:
I'll fit the keepers such that the valves don't rock or rotate, whether or not I get new keepers. The non-rotating connection is so much stronger. I have a bunch of used keepers and a bunch of used valves, and will get some new keepers as well. I planning to sand the keepers down in a way that the contact area is maximized and that the valves neither rotate nor rock.
Here's one web reference to what I am talking about:
Last edited by ptuomov; 08-04-2009 at 12:12 PM.
08-04-2009 | 05:42 PM
#33
Nordschleife Master
Joined: Oct 2006
Posts: 8,575
Likes: 3
From: Orange, Cal
Something not to loose sight of when using racing parts, many racing engines are disassembled every few thousand miles, some after every race. Most of us require more reliability than many racing parts are designed for.
