SC Distributor Specifications

[Mothy]

I have spent all day searching both this site and the WWW trying to find the standard distributor advance/retard details for my car. I can find all sort of suggested modifications but not the original starting point.

I have a 1983 SC USA spec (180hp) engine - with vacuum operated retard and advance on the distributor.

I'd like to know for an original dizzy:

• how much mechanical advance it has
• how much vacuum advance it has
• how much vacuum retard it has.

If I assume 5deg BTDC @ idle I should be able to calculate the total advance range at say 5k revs (depending on vac condition or no vac condition)

Thanks

Tim

[Flat6pac]

If you remove the pod, there is a number stamped into the arm. That number is the significant description of the pod by the manudacture. I havent ordered anything in recent years but I did have problems with a distributer years ago and calling the wholsaler I was able to order the pod I needed by specification.
What the reference available now, I dont know
Bruce

[psalt]

Tim,

The 1983 US SC distributor has 10 degrees of mechanical advance (20 at the crank). The vacuum retard pulls out 5 degrees at idle and the advance adds 5-10 degrees at cruise, depending on the condition of your engine. The US SC was detuned to run on 87 CLC octane fuel and the timing spec is 19-25 BTDC max at 6000 rpm.

Paul

[Mothy]

OK - that helps a lot.

With the 19-25 - is that a range for maximum advance because the 5-10 advance at cruise? If that was the case it would mean the mechanical advance is approx 15 degrees - am I on the right track?

Tim

[psalt]

Tim,

No, the max advance spec is with both vacuum lines disconnected and plugged, 19-25 range because of slop in the distributor (new). Vacuum lines do get mixed up, the advance uses ported vacuum (no vacuum at idle), the retard, manifold vacuum (full vacuum at idle). The timing of this engine was retarded to meet the low octane fuel spec with a margin of safety from detonation. A wide VIA hemi headed engine with domed pistons needs a lot of advance for optimum power and early high octane leaded models used 38 BTDC. Porsche's response to the low octane mandate in the US was first to use low compression. This resulted in poor mpg, so they changed to raising compression and retarding timing through the 80's. Most of these engines respond well to advancing the timing if you have the octane and temps are in control. The vacuum retard is strickly a device to meet the then current US HC curb idle emission test and the engine will run cooler and cold start stronger with it disconnected and plugged.

Paul

[Mothy]

Ok - so measuring at the crank (with a strobe light) and using the dizzy details provided asssuming that dizzy degrees is half crank degrees:
at idle I should see 5 deg BTDC with no vac tube connected and 5 deg ATDC with vac tube connected (retarded by 10 deg at crank)

At say 6k revs I should see 25 BTDC (original 5 plus 20 mechanical) with vac tube disconnected (=top end of 19-25 timing range spec) and potentially up to another 10-20 with the vac tube connected under certain conditions (cruise) - that seems a lot.

Or are we mixing crank degrees and dizzy degrees here?

I have 98 RON octane available in Australia and my retard tube is already disconnected, so was looking to increase the static advance as a test with a view to having the dizzy recurved if it proved worthwhile. Just wanting to know where I am starting from with the dizzy I have.

Tim

Tim

[psalt]

Tim,

Yes, the vacuum specs I gave were crank degrees. You set the timing at 5 BTDC, it should retard to TDC with the vacuum retard attached. You cannot get accurate vacuum advance figures blipping the throttle, you need to test it on a distributor machine. The factory spec for your car is 25 BTDC max advance. The vacuum advance will add 5 to 10 crank degrees under light load cruise. Your 98 RON is 93 CLC, some cars will tolerate a few more degrees, but this varies widely with heat, so you have to pay attention to pinging. Most US cars can be set to 8-10 static on premium if you set the open loop mixture on the rich side. Does your lambda system work ? You can set the mixture off of the test port dwell reading. On race gas, this engine will continue to make more power out to the mid 30's BTDC and peak cruise efficiency is in the 40's under light load.

[Mothy]

Great - thanks for clearing it up.

My lambda system has been disconnected and fuel head changed to a ROW one - the old one started playing up and ROW is what's available as spares in Australia. Cat converter gone and using a Fabspeed bypass.

Tim

[5String43]

So if I'm reading this correctly (and I don't mean to hijack the thread), on my '82's distributor, I want to disconnect the vacuum retard and leave the vacuum advance connected?

[psalt]

5String,

Yes, you will need to reset the idle speed with the large bypass screw on the throttle body. You can use you fingers.

[Flat6pac]

The vacuum retard only works at idle so there is no reason that it has any effect on acceleration.
Bruce

[Mothy]

My AFR was being tested on a dyno run and that's where we picked up the problem with the fuel head - was leaning out way too much up high.

Has since been tested and adjusted on a second dyno session when the fuel head was replaced.

I'll do the same test again if we end up changing the initial advance - much cheaper than an engine rebuild if we get it wrong!!

Tim

[Mothy]

OK - so we have now changed the static to 9 deg BTDC and adjusted the mixture slightly richer till we can get it onto the dyno for checking.

Initial impression is a noticable improvement accelerating thru the gears - and the car now just keeps going. It used to run out of "puff" at about 5.5k revs now it wants to keep going.

Not sure if that is me being wishfull - what is the expected outcome from slightly advanced setting?

Tim