930 Ignition Timing

les_garten · 08-08-2003, 08:35 PM

Hello,
I just rebuilt my 1985 Euro 930. When it was originally imported it was fedealized. It however does not have the Euro distributer unit. It appears to haver the CA distributer for the US. It has a vacum retard and advance connectors on the distributer. What is the proper ignition timing setting for this setup? Itr has no air pump, and I have switched out the Euro headers for aftermarket SS headers, SC cams, Andial IC, and GHL muffler, Tial WG with 1 bar spring. The engine will be installed in the car in a week and it is a MIX of Euro parts with most of the federalization removed. It appears the only part left is the dual vacum distributer. Any thoughts on the timing?

Les

les_garten · 08-11-2003, 07:08 PM

anybody have a suggestion or two for me?

Les

snowman · 08-11-2003, 07:23 PM

At 6000 rpm the timing should be at the maximum which is typically between 32 and 36 degrees BTDC. I would choose the number that is the same as the engine in euro form.

The vacuum stuff shouldn't affect the settings at 6000RPM. I am ignorant of the exact function of any vacuum advance mechanism. In any case an engine is an engine and this type likes about 32 degrees max advance on pump gas and 36 degrees on race gas. Unless you are racing it I doubt you can tell the differance in performance between the two settings and I would go with 32 degrees max to protect the engine from needless knock problems.
Thats my 2 cents worth.

les_garten · 08-11-2003, 07:34 PM

Hello,
Just a feeling, but I believe these numbers you mhave given here are patently incorrect. The "book specs" for a "Euro" 930 with only the advance cannister is 29 degrees. I am asking the question because I do not have the Euro distributer and will be running on US pump gas not euro pump gas. It appears that I have a Ca. US distributer according to pictures in the Porsche manuals.

My initial impression is you are way off base, I would like some info from someone who has experience with a fedealized 930, not someone guessing. This is an expensive project for me and I cannot afford to experiment.

Any other takers who know what they are talking about??

Les

Wayne 962 · Wayne 962's Garage

Check the specs in the back of the Engine Rebuild book, and then make sure your distributor follows that curve. With a mix-match of Euro / USA, it makes solutions like these difficult...

-Wayne

snowman · 08-12-2003, 06:47 PM

These numbers are correct for ANY engine. If you can tell the difference between 29 and 32 degrees ignition advance at full RPM you are doing something amazing. The bottom line is it must NOT KNOCK. Otherwise it is tune for max speed or tire smoke. The place where the max advance starts, eg around 3000 RPM is determined by the distributor. Unless you are going into a dyno tuning session you take what you get there. Again it dosen't matter a lot as long as it dosen't KNOCK.

If there is anything wrong with what I just said I wouls REALLY like to hear what it is, specifically and with reasons for why it is wrong.

les_garten · 08-12-2003, 07:17 PM

With gas quality the way it is and a loud air cooled engine, this is a potentially expensive way to tune an engine. If this were a Chevy or Ford, I would tune it different, similiar to how you describe above. I was hoping someone would have some insight into the particular bastardization of Euro/US ver that I have. I don't want to tune this rebuild by ear and seat of the pants. I would like to leave some timing room to compensate for bad(schlecht) petrol. I just dropped a ton of money into the rebuild and don't want to detonate the engine. I am particularly sensitive to this question. THe car according to everyone was running great, except to me. It just felt not as edgey as it used to be. Durining the teardown nobody understood why I was rebuilding it. When I pulled off the cylinders, 5 of the 6 top compression rings were broken, and fell out on the floor.
I've rebuilt the engine/tranny, new flywheel, new lightweight clutch, new rocker arms, SC cams, New Intercooler, SS Headers, SS Muffler, K-27 7200, Tial wastegate with 1 bar spring, Heads reworked, new exhaust valves, C2Turbo head gaskets, RSR rocker seals, Micropolished the crank, New bearings, new gaskets, new seals, new rings, ARP studs, ARP rod bolts, New Cam chains, new tensioners, some new oil lines, Wevo shifter, blah, blah, blah. I just don't want to risk detonation on something that the distributer does not really match what I have. Call me cautioius. The ignition timing settings for the California distributer only really has staic timing specs, somethjing like 5 degrees BTDC at 900 rpm or something toi that effect.

350HP930 · 08-12-2003, 07:22 PM

OK Boys, here are the specs right out of the factory manual for US cars.

With the vacuum advance disconnected the ignition advance should be 26 +-4 BTDC @ 4000 RPM

Since you now have a lot more free flowing plumbing it certainly would not hurt to run the high end of the above range.

snowman · 08:58 PM

Well the numbers I quoted are very conservative. Especially the 32 degrees. An american engine, like a chevy might like as much as 45 degrees! Thats a LOT. You will not detonate your engine at 32 degrees at 6000 RPM, especially with what you say you have done to it. If you are really that concerned the ONLY way to go is to Dyno tune it, PERIOD. No one can argue with that method.

Broken rings are usually a symptom of overheating and or incorrect ring end gap. The usual symptom of to much spark advance, ie engine knock, is broken spark plug insulators, broken ring lands, pistons, and then rings. I would vote for overheating in the case of a Porsche.

I run my 912 race engine at 38 degrees, with 12 to one compression and 115 octane race gas. no problems. I run one of my 912 street engines, 9 to one compression at 30 degrees, pump gas (91 octane) no problems. My 911 engine, 8.6 to one compression, 87 octane, 35 degrees, no problem.

If you are really interested in gettiing the most out of your engine, and protecting it as well, get an Electromotive ignition systemhttp://www.electromotive-inc.com/products/hpx.html. They make one for the 911. The system includes a knock sensor so you do not have to worry about the gas, enough instructions to make you a Real expert ignition systems and the worlds best ignition system, period. Their top of the line, crank fired system, includes enough software for anyone to do whatever they want to and not hurt the engine. Its not all that expensive either.

Racer Wholesale is one of the best sources for this system.

350HP930 · 08-12-2003, 08:11 PM

les_garten, if you want to play it safe when it comes to detonation on your tweaked 930 you may want to invest in a knock sensor and timing controller from a manufacturer like J&S (http://jandssafeguard.com/).

I have one on my 930 and it appears to have done a great job of protecting the motor (130K+ miles with immaculate internals).

Have you had a chance to put the car on a dyno yet to check your power and A/F ratios?

With the mods you have listed you really should.

les_garten · 08-13-2003, 04:14 PM

Thanx for the feedback!

Les

Type961 · 08-14-2003, 05:16 AM

Hi,
I agree with Snowman.
30° @ 4000 rpm is a good conservative stock setup.
As Snowman tells it, there is no real difference between 29 and even 35° except maybe exhaust temperature, that is significant for turbo engines

On a 'basic' tuned 964 engine I put 40° advance to get a reliable and torky engine :

The map on this engine has been done until 6500 rpm and note that the 'secure' value I use for unmapped RPMs is 32°.

The knock limit is somewhere around 48-52°. The power really increases until 45° but changing from 45° to 50° the engine doesn't deliver more than 3% bonus tork.
So to get the last 3% is expensive and dangerous, only top-end racer should do it.

All this to tell you that the limit is far from stock setup, that you can win tork adding 5 or 10° advance at relatively high RPM, and then you don't have to go and search the knock limit since it won't give extra power. Power more becomes from good timing than from good fuel/air ratio...

Regards,
Luc.

les_garten · 08-14-2003, 06:32 PM

The guy who normally does my car says to set them at 25 degrees.

Les

snowman · 08-14-2003, 06:36 PM

Les,

Your loosing a lot of power, needlessly. Even the factory spec allows 29 degrees.

Mr Beau · 08-17-2003, 07:58 AM

Snowman,

Do you realize this engine is turbocharged? You do know turbocharged engines use less timing under boost, right?

Les,

With that said, I'm not sure if the distributor has vacuum retard or not. When you apply pressure to the hose, does the timing retard?

I would set it close to what is recommended for the distributor you have. Because of the aditional boost and and possibly inferior fuel, you could reduce it 2 degrees to be safe.

Some 930 distributors I've seen have the ability to advance timing but not retard it, so you have to set the timing to "worst case" (i.e. boost), which means its running retarded from where it should run normally. This results in max timing somewhere in the 20's.

350HP930 · 08-17-2003, 08:50 AM

Yes, 930s have boost retard assuming that the lines and dashpot are operating correctly.

Warmed over 930s have a lot to worry about, so unless you have a knock sensor ignition retarder set it at spec. +-4 is just there so a technician does not have to beat him self up about if it is adjusted perfectly.

Now if you do get something like th J&S you can start tweaking it up since it will inform you when you have detonation and take action to keep the engine from being damaged.

les_garten · 08-20-2003, 04:29 PM

Mr Beau,
I think you understood my question completely. I am looking at probably a 25-27 degree safe zone. Euro gas was when I lived there, a lot better than the "swill" our motors have to digest. My distributer appears to be a Californiua distributer, it has advance and retard on the distributer. I am inmterested in the electronic solution mentioned above. All of my compression rings were broken, this was discovered during the rebuild. I don't want to break them again. I will drive the car for the first time this friday. I ran it for 20 minutes on break-in oil and changed it, and am now ready to put a couple of miles on it and see how it does. Running with no load, it runs and sounds magnificent. I have a mixture adjustment to do and do some more roughing in of the timing. I was looking for some advice from some folks who knew "Turbo" engines. I believe running thios engine with 35-40 gegrees advance is asking for trouble. I don't want to open it up for at least 50-100K miles. No leaks b y the way, thanx Wayne, awesome book!!

Les

p.s. during this rebuild I subsidized this web page considerably!!

350HP930 · 08-20-2003, 05:40 PM

Wow, broken piston rings are definantly a sign of either bad detonation and/or severe over heating.

Its likely that the piston ring grooves were also shot.

My car had beautiful rings, pistons and cylinders at 130K miles and that was after running almost 80K miles with almost 100 more HP than stock and a lot of moments of WOT and heavy use.

On an air cooled turbo I know I have my J&S to thank for the good mechanical condition of everthing. Since the J&S would keep the detonation prone cylinders from holding back the rest of the motor my timing was set to the agressive end of the spectrum.

When my Andial Fuel Enrichment System pooped out instead of burning and breaking stuff I could tell something was up since the unit started super retarding the motor at the peak powerband.

Mr Beau · 08-20-2003, 06:00 PM

Les,

It sure sounds like you were running too much advance. Was anything melted, or just broken? Its suprising how well and engine can run with broken rings, no?

What I would do is determine the total advance of you system under boost. To do this, you need to take the total amount of advance due to the mechanical portion, and subtract the amount the vacuum lines can adjust.

So, set your idle to some number (lets pick "0" for simplicity). Disconnect all lines to the distributor. Rev the engine and determine the total advance caused by the centrifugal advance. Write this down (BTW, this is much easier with an advance/dial-back timing light). Next, take a Mitivac or equivalent and pump the amount of boost you're running into the vacuum lines. The timing will retard by some amount. If you take the mechanical and subtract the retard, this is the amount it runs under full boost. I don't know the specifics of the 930 system, but hopefully this will work. Ideally someone with a "stock" 930 could do the same.

Most what determines the allowable advance is the temperature of the gas in the cylinder and the octane level. Temperature is mainly affected by boost, I/C efficiency, CR, and humidity (more humidity=more timing). What I/C and CR are you running? Once we determine this information, we should be able to make an educated guess based on what the factory ran.

Hope this helps.

les_garten · 08-21-2003, 04:20 AM

The ring grooves were perfect. Thew cylinders showed no scoring, taper or wear of anykind. The rings however fell out onto the floor. The car ran remarkably well, just not crisp like it used to. The car had a loud exhaust system and detonation would have been impossible to hear at WOT. I'm convinced that boost and one bad tank of gas can cause this. I am interested in the JS knock sensor sytem mentioned above.