sand_man,

I'm by no means an expert on 930's but here's my rough guess for what should be 'OK'.

A 7.5 or 8.5:1 motor should be able to handle similar ignition timing as a non-turbo 911 (when not under boost). So let's call it 30 degrees at around 3500 RPM which should be on the safe side. This can be maintained for redline (no real reason to back off a bunch as RPM climbs--this will just cause high EGT).

'Conventional Wisdom' calls for about 1 degree of retard per psi of boost. So 0.8 bar or about 10 psi would call for about 20 degrees under boost.

The problem is I don't know what this translates to for a twin plug engine. Twin plugs call for less timing because the flame front has less distance to travel. If you ignite too soon, the cylinder pressure builds up earlier than you want and your pressures become too high. This is hard on rod bearings and causes extra heat, which can impact the next engine cycle (causing pre-ignition).

I'm busy planning for tomorrow's trip to Le Mans so I don't have a lot of time to go into more details...

Good luck!

The new parts!

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VERY NICE, Craig!!!

Craig, have you thought about efi? im really no expert but the flexibilty to tune your fuel delivery to protect your engine may be helpfull, plus power gains with no increase in boost would be nice (although quite small)

Craig,

What are your thoughts on my ignition timing comment? What's considered acceptable for your setup? I really think stock ignition timing with additional boost + twin plugs put you over the edge.

24 was recommended by a Steve Weiner.

Hi Craig:

24 degrees is indeed recommended but that figure requires context for accuracy. :)

24 is correct for on-boost operation with twin-ignition since the original customer intended to use 100% race gas on the track. For street use, a blend of race gas & pump premium was highly recommended.

If these engine run (boosted) without functioning or disconnected boost retard and/or too much timing, it only takes about 30 seconds to break a set of rings and trigger ensuing damage.

Yes...what about a street engine. 7.3:1 CR, .8BAR, 3.4L...what should my Electromotive timing curve be on 93 octane?

I've recommended race gas (at least 50%) for ANY 930 that is used on the track, no matter what state of tune its in. For street use at stock boost, SOME race gas is strongly recommended especially in warmer weather for insurance.

Key issue here: Without question, this is a broad generalization but its mostly an indictment about the current sorry state of pump gasolines sold in the US over the past 3-4 years.

I've heard bone-stock, perfectly healthy 18K, 3.3 Turbo's detonate on 92 octane fuel in 85+ deg weather so I do not take this issue lightly. I've stated it before and I'll mention it once more; if one rely's on one's ears as the defacto "knock-sensors" to detect detonation in these cars, one is going to spend some serious money. This is especially important with 930's equipped with louder, aftermarket mufflers that easily mask the sound of on-boost detonation..

Bottom line: I offer recommendations based on personal experiences, but ultimately its up to each owner to decide what fuel to use in his or her car.

I hope this clarifies things a bit. :)

So what's the alternative? Is there a knock sensor for 930's that's proven to work?

If you could humor me, Steve......
Just for clarification:
That's total ignition timing, yes? In other words, if I'm running 2 degrees BTDC initial, then my advance at 4000RPM should be 22 degrees BTDC?

Thanks,

You could always add in a J&S Safeguard. If I need to boost octane say if I'm running way more advance and leaning things out on my race engine, I blend in Torco race gas conentrate. They make both a leaded and unleaded version. If I remember correctly, a single can will blend 20 gallons of 93 octane to well over 100 octane. i have also noticed that the spark plugs are cleaner and last longer when I run the concentrate, so I actually run just a tad in every tank.

Interesting indeed! Craig, I am sorry to have hi-jacked this! Not my intention at all! Maybe we can both benefit from the info. I've decided to cut my timing back even further. I'll be looking at around 18 to 20 degrees of total timing.

Where does one acquire the J&S stuff?

http://www.jandssafeguard.com/

I have only used their four-cylinder version and it performed very well. I would recommend getting the optional guage so you can see if you have any knocking and how much timing it is retarding.

Let's call this 'Timing 101' ;)

So my timing should be at 24 degrees, agreed.
Can you clarify what excatly this is (rpm range, disconnect etc) mainly as clarification for others?

How on earth do you actually check that 24 degree timing under boost? And how does it relate to the 'at rest' timing setting?

I would suggest checking timing on a Dyno (wheel dyno is fine) using a Snap-On type timing light that lets you dial in the advance. If your distributor does not use any sort of Vacumn connection, you won't need to use the Dyno - just rev and check accordingly.

Steve -

What is the proper timing method for a 930?

:) OK,..from the top:

Dave:

Yessir,..22 is what you'd see with 2 degs initial. Don't exceed that on single ignition.


Craig:

Chris's suggestion to set & confirm timing on a chassis dyno is a good one. We use our engine dyno as thats convenient for us, but a Dynojet, Mustang, Dynopack, etc all work very well. I use a dial-back Snap-on digital timing tight to check total timing at 4K without boost. I confirm boost retard either on my distributor machine or in the car using a hand-held vacuum pump to check the integrity of the cannister.

Your engine should be checked with the vacuum retard disconnected and then the cannister's operation confirmed as above. Other folks without the RSR distributor should refer to the Factory manual since timing figures and procedures vary with year and whether its US or ROW.

Here's what I mean:

Turbo ROW: 29 deg BTDC @ 4K, vacuum control detached.
Turbo US: 26 deg BTDC @4K, vacuum control detached.
Turbo US (CA): 31 deg BTDC @4K, vacuum control detached.

Further, there are other parameters for checking timing at idle, with or without the vacuum controls attached. Its VERY VERY easy for someone to misread the complex specifications and use the wrong values and/or procedures that will result in a handful of broken rings (and worse).

Charlie's suggestion about the J&S knock-sensor is a good one and we've used them on Motec-equpped 3.6 TT engines to integrate active knock-sensing into the engine management system. Obviously, the 3.0 & 3.3 litre 930's do not have the bosses & bridges to mount factory sensors so one must locate a suitable place for the sensors (one per side) and tune/calibrate them for that location. I've not installed one of these J&S setups on these particular cars so I've not crossed that bridge,.....yet. :) :)

Great stuff - thanks. This is with all vacuum devices disconnected and plugged?

Disconnected,..not plugged.