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Question Low power under 3500 - why?

My '86 930 seems very flat below 3500rpm (compared to my '85 930 and other 930s), so I am taking the opportunity to delve into its innards while I fix a few oil leaks and a very heavy clutch pedal.
The car has been checked over by local specialist and without doing a major investigation they were stumped as to why it was so low on power while off boost. Over 3500rpm and with plenty of boost it performs normally. They set timing and CO at idle but car would hardly run at all with correct idle timing so they had to shift timing back (clockwise) to what it was (= advanced?).

As I stripped the motor over the weekend, I have been on the lookout for potential causes of low power and have found two issues so far:
1. the small vacuum hose from bottom side of distributor was squashed flat between the IC neck and manifold.
2. the cam timing (with std cams) was at 0.20mm (should be between 0.65 and 0.80mm).

My question for the gurus is ... are these two issues likely to be sufficient to significantly reduce power below 3-3500 rpm? Or should I keep looking?

I already have the "while I'm in there" bug and I will be fiddling with stuff like porting, deleting air injection, etc. as well as the usual cleanup of twenty years worth of crud. Is there a list of stuff worth doing that doesn't cost heaps while I'm in there?
Old 04-20-2008, 10:00 PM
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Check if distributor gear jumped tooth.
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Thank you for your time,
Old 04-20-2008, 11:15 PM
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The engine is in bits all over my garage floor at present.
Checking the static timing was one thing I forgot to do before I pulled the dizzy out so I'll address the issue of correct timing when I rebuild.
Old 04-21-2008, 01:09 AM
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2. the cam timing (with std cams) was at 0.20mm (should be between 0.65 and 0.80mm).

That was the problem.
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Old 04-21-2008, 05:21 AM
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Quote:
Originally Posted by billjam View Post
My '86 930 seems very flat below 3500rpm . . .The car has been checked over by local specialist . . . They set timing and CO at idle but car would hardly run at all with correct idle timing so they had to shift timing back (clockwise) to what it was (= advanced?).
1. the small vacuum hose from bottom side of distributor was squashed flat between the IC neck and manifold.
2. the cam timing (with std cams) was at 0.20mm (should be between 0.65 and 0.80mm).
My question for the gurus is ... are these two issues likely to be sufficient to significantly reduce power below 3-3500 rpm?
1. If timing was set at idle with the vac line pinched off, the engine was missing a bunch of timing. Even under boost, it was still missing timing as it had only centrifugal advance. (Advance due to loss of vacuum and centrifugal advance with distributor shaft speed are additive.)
Turning the distributor clockwise advances timing.
2. Not knowledgeable about cam timing.
3. I'm no guru, just a gear head.
Old 04-21-2008, 06:57 AM
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