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Boost pressure

I am new to 930 and turbo gasoline engine in general.

My question is, why Porsche designed 930 to boost only to .8 bar and anything over 1.0 bar is considered dangerously high when at the same time my 14 yrs old diesel VW TDI engine boosts sustained 1.3 bar without any problems at all?

Old 05-08-2013, 06:54 PM
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Can't ever compare tdi or any diesel to gas power because of the difference in energy in the two fuels but......
It's mostly because the fuel head is designed to flow safely to 1 bar. Above that it goes lean and dangerously so at high rpm. I'm not an expert but not very long ago it seemed pretty common to see guys grenade the pistons or rings and heads from going lean on sustained runs. Before efi and wideband o2 sensors and afr gauges it was said to just not go ofer 1 bar. There was the andial fueler system to enrich the mix at a higher boost level and that would allow higher boost. Bigger inter coolers help up to a certain point but basically not higher than 1 bar.
These days we watch things closer with afr and egt gauges. Even then it's not a good idea unless you have a high flow fuel head, andial enrichment or efi.
That's the simple answer from a distance.
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Last edited by quattrorunner; 05-08-2013 at 08:32 PM.. Reason: Forgot
Old 05-08-2013, 08:30 PM
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also: Air-cooled engines. High Boost also causes excess heat, which can lead to all sorts of fun stuff like detonation. Your V-Dub was a water cooled engine, so its apples to oranges.
Old 05-08-2013, 08:49 PM
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Related side question: at what nominal boost level does the over boost sensor activate to sever the fuel pump ground?
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Old 05-09-2013, 02:57 AM
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1.1 bar
Old 05-09-2013, 06:11 AM
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Quote:
Originally Posted by Miguel Antonett View Post
1.1 bar
I thought new was something like 1.2-1.4, but I could be mistaken. Old and tired, 1.1 or so is probably true. I've had mine trip only a couple times early on when I was 'messing with things'. I'm sure it was over 1 bar but my eyesight became blurred as my face hit the dashboard with the sudden shutdown.
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Last edited by mark houghton; 05-09-2013 at 07:28 AM..
Old 05-09-2013, 07:26 AM
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Factory manual p21-11:

Quote:
6. Increase pressure carefully. Check that ohmmeter goes to (infinity symbol) at about 1.5 bar.
7. Drop pressure slowly, until ohmmeter again goes to 0. Now read pressure which should be between 1.1 and 1.4 bar. If necessary, replace pressure limiting switch.
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Last edited by spuggy; 05-09-2013 at 05:33 PM.. Reason: Bah, list numbering doesn't work.
Old 05-09-2013, 05:30 PM
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Thanks!

Btw, getting back to boost in gas vs diesel, I only run .8 in my 8 liter Cat diesel. 300hp, 600 ft lb, per specs.

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x: 62 356, 64 356, 76 930, 84 911 Targa, 85 ROW 911, 00 996, 07 Cayman S.

Last edited by M5guy; 05-10-2013 at 05:23 AM..
Old 05-09-2013, 06:19 PM
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