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spuggy spuggy is offline
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Join Date: Jul 2003
Location: Glorious Pac NW
Posts: 2,770
Ignition timing for modified 930?

What you guys running?

'78 RoW 930, SC cams, 8.0:1 static C/R, GHL headers, K27/HF, EVO MS intake, Kokeln intercooler, .8 bar (factory wastegate with dump pipe), adjustable WUR from Brian Leaske. (RPM solenoid fitted but not needed or used/connected).

My local Porsche wrenches, whilst highly experienced with factory cars, aren't 930 tuners.

They set the car up to factory spec, i.e. 29 BTDC @ 4000 RPM.

It started great hot or cold, pulled like a train from idle/everywhere, good throttle response and didn't go at all badly in boost (in moderation, what with running it in and not knowing what the AFRs were).

I ran it in for 1800 miles and was very happy.

Just took it to a respected 930 tuner with a dyno (mostly to get the AFR's checked/adjusted), who says he wouldn't run more timing than 20, 22 tops, on a modified 930 under boost, to avoid detonation.

He reset the timing and the WUR control pressure (in conjunction with pressure gauges, wide-band and the dyno).

The car then felt incredible on-boost over 3000, really crisp exhaust/wastegate note - and pulled 395 BHP @ 6100 RPM, 350 ft/lbs @ 5700. So it seems pretty happy there.

Trouble is, it had little power off-idle, throttle response was sluggish, it was a pig to start and keep running from cold, hard to drive in town even when warm etc.

As the '78 930 distributor has no boost retard can, whatever the dynamic ignition timing is at 4000 RPM is what I get under boost as well.

Right now, I've split the difference to 24 degrees BTDC. The car starts fine from cold and has throttle response, and is well-behaved in town. Although all not quite as good as before (with 29 degrees). I'm gonna pretty much stay out of boost until this is sorted.

Spoke to the tuner today (I wanted an overnight cold start to confirm the difference from the new setting), who listened to the symptoms/description and said he's a little surprised it makes that much difference, but sticks to the retarded on-boost figure.

His suggestion is to use the later distributor with a boost retard can to pull the timing back for safety under boost and get the best of both settings. (I'd actually asked about that when he was adjusting the timing after checking it, and he'd replied that it doesn't normally matter that much).

This seems pretty logical to me - and I certainly can't deny that the motor was very different under boost at the more retarded setting - and I really like "safe", "safe" is good - but can I get some opinions here?

What timing - on-boost - is ballpark/safe for that build sheet, and does this all sound right & reasonable?

How much does the boost retard can pull the timing back anyway, I'm guessing 9-10 degrees?

What do other people with 78-up 930's and no boost retard do?

Anyone got a dual-can 930 distributor for sale?

Thanks!
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'77 S with '78 930 power and a few other things.
Old 06-22-2007, 07:41 AM
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