psears

Hello,

I'm breaking in my newly rebuilt 3.0L SC motor w/Webers and GE-40 cams, and am experiencing backfiring through the exhaust, especially when the engine is cold, or when the weather is colder. I just bought a carb synchrometer because what is happening is commonly associated with out of balance carbs. But before I tear into the carbs, I thought that maybe I should check the timing. Now does anyone here know the correct procedure for establishing what the ignition timing should be for a particular engine-especially one that is modified? Please don't tell me that I'll know because it will just "sound right", because I don't make my living tuning Porsches!

Thanks

psears

Jeff Curtis

Psears, the SC is set at 0deg. at the factory, but seem to run a lot better at 5deg advance, at the distributor that is. Being that you have upgraded cams, you might try 10-12deg distributor advance...what was the advance on your cams??

I had a highly modified SC, using Webcams that were advanced to 2.1mm and my distributor, uh, er, distributorless ignition (Electromotive HPV-1) was set to 12deg advance...it ran like a scalded dog!

Setting the distributor timing is like any other car...disconnect any vacuum lines to the advance diaphragm on the distributor and temporarily plug them...I had none ...and hookup the timing light via a 12v lug underneath the black fuse/relay panel cover on the left side of the engine bay, hookup the timing light synch-sensor lead to #1 plug wire and your timing mark should be visible.

Be sure to reference the Z1 mark, that is 5deg?? (possible memory lapse) - "eyeball" the distance between "0" and "Z1" and add that amount for ~ 10deg. advance, that's where I'm guessing would be a good starting point for you.

Not a professional "P-Car" tuner either, just have tinkered quite a bit. Now I own a car that I CAN'T adjust the timing on, unless it's via a chip!

Howard

Psears,

Before I swapped engines I was running a 3.0 with CIS and it ran fine at 5 degrees btdc, and 30 degrees at 5,000 rpm. Then I modified the engine with cams and Webers and it ran like crap with the same ignition timing settings. After some trial and error I discovered the ideal settings to be 12-14 degrees at idle and a total of 34 degrees at 5,000 rpm, ran great! Be sure the vaccuum advance is working properly by connecting the vaccuum line and actually revving it up to 5,000 rpm, most crank pulleys will have a mark at 30 degrees btdc, and 1 mark at tdc and 1 at 5 degrees btdc. Never run the engine very long at 0 degrees, bad things could happen. Jeff is correct with the proper connection of the timing light, good luck !

psears

Thanks Guys for the info. By the way, since I'm using Webers, I had to have my stock '81 distributor recurved to '78 specs at the same time. So now I have no vacuum lines-just plugs. Any change in the timing instructions?

Jeff Curtis

Nope! As a matter of fact I had the same setup before changing over to the Electromotive setup.

psears

How do you like your Electromotive system? How much better does it work? Significant gains in HP? Was it worth the cost?

Jeff Curtis

I enjoyed the two years of use I got out of it...sold my SC back in May 2001. It really is a simple setup, not much can go wrong, although I hear of a crank trigger sensor going out on some people, an extra one costs about $70 or so.

There's a lot of juice delivered to the plugs and with the coil setup, similar to a lot of marine-type (boat) ignition systems...the coil fires on the ignition and exhaust stroke, keeping a cleaner combustion chamber.

I have a good friend using a twin plug setup, (two HPV-1 units) on a highly modified 2.7 with Webers...he really likes the setup and is able to adjust the advance differently on the upper/lower plugs...making the engine output more efficient.

Expect to spend about $1200 once you get the Electromotive unit, Magnecore wires and whoever makes your pulley/crank trigger wheel and distributor hole plug...I found Clewit Engineering in California to be "top notch"...he's a great guy (Richard Clewit?), easy to talk to and enjoys what he fabricates for the Electromotive type ignition systems.

***No affiliation, just a satisfied customer. If you go through Windward, they use a guy on the East Coast that makes some nice essentials for the setup as well.

The setup really gave my 3.0 some "umph", I've heard anywhere from 0 - 35HP gains...I honestly felt a good increase through my "butt-dyno".

Howard

I'm using the Electromotive HPx with a crank trigger, works great, no missing, complete flexibilty AND reliable !
You could go with am MSD-digital 6 and a Varicurve unit, lock out the distributor and adjust the timing advance with modules, works well........and I have both units for sale ! (used)

Nate71c

Hi guys,
I have a totally stock 78 SC (delivered new to Australia) which has the CIS injection, and no vacuum lines to the distributor. It's currently running 5 deg advanced at idle, and advances to 22 deg at 4000 rpm. My mechanic thought this didn't seem to be enough advance, and suspects the mechanism in the distributor as being the cause.

He thinks the factory spec is 5 deg after tdc at idle, not 0 as some have said. So, should I be looking for 30 deg advanced at 5000rpm, or another figure? I haven't run the car on a dyno yet, but I suppose that will be the best way to see what produces the best power curve. I don't want to spend money on the dyno tuning until I'm confident there is nothing wrong with my mechanical advance mechanism though.

Cheers,
Nate

Jdub

Nate:

Clean your distributor. You will be amazed how much crap gets in there. After doing this, I set my stock US-spec. at the standard 5degree and it advances to approx. 25+degrees.

Jw

Nate71c

Thanks JDub,

I will do that. But I am still confused about what the timing actually should be. Some say 0 degrees btdc at idle is factory, my mechanic says 5 degrees AFTER tdc at idle is correct, and it's currently set to 5 degrees btdc, and advancing to only 22 degrees at 4000rpm. If I were to set the timing to 0 at idle, would that mean I'd only get 17 degrees at 4000rpm? With 0 at idle, should I have 26 degrees at 4000rpm?

Confused...
Nate

Howard

Nate,

According to the book you should have 5 degrees BTDC at idle (900-1000 rpm ) and 24-28 degrees BTDC at 6000 rpm. If not, you have a problem !

Good Luck Mate !