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? :D

Thanks!

You could actually replace your dizzy with the electromotive XDI. The timing can then be adjusted with a screwdriver. I appreciate this isn't a cheap solution.
Check out the pdf here http://www.racetep.com/hpx.htm
Stephen Kaspar of www.imagineauto.com can fix you up with one.

A good tuner with the correct dyno can find out what the timing needs to be at any RPM under full load.

How did you get 8.0:1 CR?

Anyway, I would stick to stock timing for your year model, staying at .8 bar boost. And the mechanic who said he was suprised it made that big of a difference, well um.....well, now you know for sure. Its a big difference. The stock equipment works, and works well for your config.

Mine is a '78 w/Euro CIS/dizzy and stock 7.0:1 C/R set at 26 BTDC @ 4000rpm using stock boost. With your C/R I would set it at the factory specs and see if you can make up for the off-boost lag by timing the cams to pick up some torque.

8.0:1 was achieved with fly-skimmed heads by the PO; that and the SC cams were the only mods from Euro-spec in the first incarnation.

But this isn't stock? It's the tuner, not the mechanic, who says I should retard the ignition - on boost, he could care less about stock timing off-boost - to stay safe with the modifications.

I guess I must have explained it really badly. Probably just too verbosely.. :)

(BTW, 26 BTDC is factory setting for a US 930, according to my info.)

Stock Euro timing (29 BTDC) is too advanced to be safe on-boost (according to the tuner), it runs very, very, nicely off-boost with that setting.

He's pretty clear; he advises 22 BTDC is absolutely as far advanced as he would go (when on-boost) and counsels less - 20 BTDC.

Don't know how much is down to my specific modifications, I get the impression he would set any '78 930 - even a stocker - to those numbers. He says most people/motors don't notice any effect off-boost from being that retarded. Maybe the higher C/R is the significant factor here?

Retarding the ignition to 20 degrees BTDC, it seems to run very well (noticably better) on-boost and makes good dyno numbers, but it makes it horrid off-boost, cold starting suffers etc.

Hey Brian, are you not using the '87 dizzy (presumably with the boost retard can) you bought from SCHNELLE?

If you just wanted a spare, I got a perfectly good '78 euro dizzy on the motor - swap ya? LOL

A post-83 930 distributor really does look like the easiest way to reconcile the two different settings I seem to need for optimal/safe running both on and off boost. I'm starting to think that's probably why the factory did that, huh?

Your mechanic does not fully understand these engines.
My engine is very similar to yours - SC cams, K27-7200, Euro exhaust, Euro CIS, Euro '78 dizzy, but has stock C/R. I can run more than 26 degrees if I wanted to but 26 is safe for any fuel and ambient temperature for my application. Unless you have some detonation issue I see no reason why you can't run 24-26 degrees of timing with good gas at only 0.8bar of boost.
As you have stated, the dizzy on the early 930s did not retard the timing on boost. That makes setting the timing really easy because you know exactly what your timing will be at 4000rpm and above. As you know you cannot produce boost by revving you engine when it is not under a load (such as when setting the timing). Using pressure to check the retard is a PITA.
I have not received Schnelle's dizzy yet but should get it any day. It is for the Evil Engine.

Another option is to consider using a Ford EDIS system with a Megasquirt II ECU. This allows you complete control of the ignition. It has the added benefit of supporting an EFI conversion later, if you choose to go that route.

For me, this one change made a huge difference in throttle response, especially when the engine was cold. My total cost was about $900. It can cost you more or less (+/- $150), depending on how you approach it.

http://forums.pelicanparts.com/uploa...1182622753.jpg

http://forums.pelicanparts.com/uploa...1182623327.jpg

I could be way off here, but my opinion is that you aren't running rich enough below boost, due to your AFR change. Maybe you need more overall idle fuel mixture, and therefore less on-boost mix to compensate and keep your AFRs equal.

The reason I say this is twofold. First, timing advance is not generally going to be more than a 5 hp difference within a fairly close range like you are talking about. Second, I have had my car tuned to try to run less rich during idle and all of your symptoms showed up in my car, no power at all until I was on boost, and then the boost worked normally. It was a simply spectacular difference in performance when I tried to tune the richness out of my idle mixture. Huge difference in off boost power, there simply was none....

Just a thought, maybe if you look over the situation this makes some sense, but I am only relating my personal experience with a lean bottom end killing my CIS power off boost.

The cure for me was just tuning back in the rich idle and de-tuning the boost richness a bit. Now my car happily smokes again on idle and runs correctly down low.

Hope this helps.....

Did they monitor AFR while on the dyno ?

Checking AFRs under load/boost were safe were the primary motivation to go to the dyno, there was a gas analyser on the car before it was strapped down.

This was the earliest I could get the car in this shop after running it in.

There's no doubt in my mind that the guy tuning the car knows what he's doing with a warmed-over 930, he's been doing it a long time. Both his advice and his reputation have been endorsed by other people who do the same thing for a living, so that's good enough for me.

I'll be going with a later dizzy as soon as I can find one, just because it'll do what I want, and is the simplest, bolt-on fix - safe, minimal faffing about and using factory parts, yet.

Thanks everyone, some good input here. Bouncing ideas around really helps sometimes. It's more fun in the garage with a cold beer or two, but hey... :)

Hey Turbobert, did you post a thread on your EDIS conversion? Must've missed it, and I'd like to read up on that...

Hey Turbobert, did you post a thread on your EDIS conversion? Must've missed it, and I'd like to read up on that...

No, I haven't posted anything - not yet anyway. I took my lead from Mike Pickett's write-up (see link below). I used his spark table and it worked perfectly. Great guy.


http://forums.pelicanparts.com/porsche-911-technical-forum/279322-megasquirt-setup-930-dual-plug-edis.html?highlight=.msq

Ah, right, I read that thread when it started, excellent stuff... :)

my new setting is 32 degrees advance and on boost is 28degrees.. this was set by supertec so pretty sure they know whats going on. but again I run high CR then you guys and lower boost

Ben, do you think you have better fuel than us here in the UK?

good question??