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Join Date: Jan 2001
Posts: 539
I'm so scared
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Mark
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Old 05-17-2010, 03:07 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #21 (permalink)
3 restos WIP = psycho
 
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I can't wait to see this bad boy running those new ITBs!
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- 1965 911
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- 1979 930
Old 05-17-2010, 03:36 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #22 (permalink)
GJF GJF is offline
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Mark built the motor well. Good fasteners and a balanced assembly. The rockers would only be the weak link but I 'd rather have a rocker break than bend a valve. Rockers are like a fused link, safe to fail without catostrophic failure. Mark is just cautious and I can respect that, but TOO cautious 1 bar atleast rev'd up to 7500 RPM w/ ITB's will be a rocket.
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87 911 Carrera platform
Twin Garrett's, Big Valve, Xtreme Cylinder Heads, JB Racing cylinders and machine work, custom JE pistons, GT2 EVO cams, GT3 oil pump, modified 3.2L intake, 80mm TB, custom Intercooler, equal length headers, DFI, KEP Stage 2 custom twin disc, G50 custom gear set, LSD, Tilton trans pump, Fluidyne cooler
Old 05-17-2010, 04:44 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #23 (permalink)
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I officialy protest the title of this thread!
Old 05-18-2010, 07:22 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #24 (permalink)
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Quote:
Originally Posted by GJF View Post
The rockers would only be the weak link but I 'd rather have a rocker break than bend a valve. Rockers are like a fused link, safe to fail without catostrophic failure.
You and I have had different experiences with rocker failures.
I had one break, like you described, and no other damage.
But on 2 other Turbos all the valves were bent, and both cams damaged. Best guess is that the broken rocker pieces jammed into the camshaft thus destroying the cam, also applying resistance against the chain and affecting cam timing momentarily (overcoming the tensioner?) on both sides, thus the bent valves.
With the age of these engines, we now magnaflux all rocker arms as a precaution during engine rebuilds.
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Old 05-18-2010, 08:44 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #25 (permalink)
3 restos WIP = psycho
 
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Quote:
Originally Posted by TurboKraft View Post
we now magnaflux all rocker arms as a precaution during engine rebuilds.
Great idea - another thing to add to the list.
Thanks!
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- 1965 911
- 1969 911S
- 1980 911SC Targa
- 1979 930
Old 05-18-2010, 09:17 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #26 (permalink)
 
GJF GJF is offline
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Hey Chris,
I usually buy new ones to start, mag, debur and shot peen them. It is a little more, but insurance in the end. (not that rebuilt rockers won't work) I always wondered why the factory discontinued the forged rockers. I also no longer run hydraulic tensioner's ( I know there are a lot of people who aren't fans of mechanical tensioner's) But I have never had one fail. I would have to agree with debris floating around in the cam boxes wiping everything out. I have to be careful on my wording. The rockers aren't always just going to break and it has safe margins. But rather to at least hope for just a broken rocker. The two that wiped out the boxes I have to wonder how hard they twisted them and after the frappe, how long they drove it? ( and not to discredit anyone)
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87 911 Carrera platform
Twin Garrett's, Big Valve, Xtreme Cylinder Heads, JB Racing cylinders and machine work, custom JE pistons, GT2 EVO cams, GT3 oil pump, modified 3.2L intake, 80mm TB, custom Intercooler, equal length headers, DFI, KEP Stage 2 custom twin disc, G50 custom gear set, LSD, Tilton trans pump, Fluidyne cooler
Old 05-18-2010, 10:23 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #27 (permalink)
GJF GJF is offline
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Juan had a valve or two bend a few years ago due to an over rev'd when a tuner missed a shift. No broken rockers just slight contact with the pistons enough to show a good jump in leak down numbers. I would say both motors you speak of, would have to been healthy runners to say the least.
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87 911 Carrera platform
Twin Garrett's, Big Valve, Xtreme Cylinder Heads, JB Racing cylinders and machine work, custom JE pistons, GT2 EVO cams, GT3 oil pump, modified 3.2L intake, 80mm TB, custom Intercooler, equal length headers, DFI, KEP Stage 2 custom twin disc, G50 custom gear set, LSD, Tilton trans pump, Fluidyne cooler
Old 05-18-2010, 10:29 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #28 (permalink)
Wo ist die Rennstrecke?
 
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Quote:
Originally Posted by GJF View Post
Hey Chris,
I usually buy new ones to start, mag, debur and shot peen them.
[snip]
Are you kidding?
Old 05-18-2010, 05:44 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #29 (permalink)
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No... for the price I can get them for it is just a little more than refurbishing used ones. I feel it is kinda a toss up due to the price. If I couldn't get the rockers at the price I get them for then I would use the used ones and have them mag'd, hard welded deburd, peened and re-bushed.
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87 911 Carrera platform
Twin Garrett's, Big Valve, Xtreme Cylinder Heads, JB Racing cylinders and machine work, custom JE pistons, GT2 EVO cams, GT3 oil pump, modified 3.2L intake, 80mm TB, custom Intercooler, equal length headers, DFI, KEP Stage 2 custom twin disc, G50 custom gear set, LSD, Tilton trans pump, Fluidyne cooler
Old 05-18-2010, 06:27 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #30 (permalink)
Wo ist die Rennstrecke?
 
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The newer ones I buy don't seem to last as long. I now buy used pieces from DC Automotive and inspect. The older ones seem to keep their faces intact longer. Maybe it's me....
Old 05-19-2010, 05:53 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #31 (permalink)
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I see no problem with the air mass calculation.

For VE I use a value in the range of 0.87 to 0.95. The lower is for a stock 930 cam with a muffler. The higher is an all-out effort with no muffler.

For BSFC I use this curve:




For 500 HP @ 5000 RPM I get (372.9 x 365)/1000 = 136.1 kg/hr of fuel, or 2.268 kg/min

For a target A/F of 11 that is 11 x 2.268 = 24.95 kg/min air or 55 lb/min, which is about what you were getting with your unofficial squirrel calculator. The pressure ratio is what is jacked.
Old 05-22-2010, 01:04 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #32 (permalink)
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