More HP for SC owners

RazorRacer · 11-30-2002, 02:46 PM

More HP for SC owners: If you start your car cold and it doesn't idle at 1800-2000 rpm for a few minutes and then drop to 950 rpm then you are missing some HP. Advance the timing to 10-15 degrees BTDC at idle with vacuum advance disconnected. Leave vacuum advance disconnected. Take a drive and feel the extra power. I drive with my vacuum advance disconnected at all times now.

History: My car started and idled at 950 rpm with 5 degrees BTDC at idle. I disconnected my vacuum advance and changed the timing to 15 degrees BTDC and now it starts at 1800-2000 rpm for a few minutes and then drops to 950 rpm.

Warning: The downside to this is that if you advance your timing too much it will begin to pre-detonate. This sounds like bb's being shaken in an aluminum can. Please be careful if you make this adjustment.

pbs911 · pbs911's Garage

Quote:

Advance the timing to 10-15 degrees BTDC at idle with vacuum advance disconnected.

Doesn't that work to about 35 degrees BTDC @ 6,000 RPMs with the vaccum advance hooked up . . . the setting JW has recomended.

RazorRacer · 12-02-2002, 04:44 AM

Dr. Paul: JW offered advice while I was finding out what was wrong with my car. Several people helped me find the problem and increase the HP. I don't know if anyone has offered a check based on initial start-up idling rpm. It might help if you included a link to JW's suggestion.

Timing at 6000 rpm: Using a fixed timing light, you can estimate the timing at 6000 rpm. You can do this by measuring 10 degree increments and marking it on the pulley with nail polish or paint. It's better to get an adjustable timing light.

My 6000 rpm timing: I have estimated it to be near 35 degrees BTDC without vacuum advance and with 10-15 degrees BTDC at idle.

Leland Pate · 12-02-2002, 07:37 AM

My car idles high for the first few minutes of warmup... I'm still thinking it is a faulty Aux. Air Valve. Cary and i looked at it briefly but didn't get a chance to test it.

My car will idle at about 2K for about a minute or so before dropping in a stair step fashion to 1K.

wckrause · wckrause's Garage

Quote:

My car will idle at about 2K for about a minute or so before dropping in a stair step fashion to 1K.

It's supposed to do that on a cold start. Why is that a problem?

Superman · 12-02-2002, 08:57 AM

That's what it's supposed to do, Leland. Sounds like your AAV is working, since that device is responsible for increased idle during warmup. This time of year, the last thing that a Boise-dweller needs is a car that has no choke or idle increase during warmup. If these systems were not working, you would need to keep your foot on the gas for a few minutes, in the mornings. It would die at intersections and perhaps exercise your popoff valve as well.

jmohn · jmohn's Garage

Quote:

Originally posted by Leland Pate
My car idles high for the first few minutes of warmup... I'm still thinking it is a faulty Aux. Air Valve. Cary and i looked at it briefly but didn't get a chance to test it.

My car will idle at about 2K for about a minute or so before dropping in a stair step fashion to 1K.

I must agree with Bill and Super, that's exactly how mine performs on a cold-start. It appears to me, (from everything I've read) to be the correct operating procedure.

Jerry M
'78 SC

RazorRacer · 12-02-2002, 09:32 AM

Leland and others: What is your SC timing settings without vacuum at idle and 6000 rpm?

pbs911 · pbs911's Garage

I received an adjustable timing light this weekend (thanks mom) and checked my timing @6000 RPMs. I had previously timed the car at idle at 10 BTDC thinking it would get me to about 30-35 BTDC with full advance. When I checked the timing with the adjustable light I was pretty close, but it needed to be advanced about 3-4 degrees to get it between 33-35 degrees BTDC. If set to 15 BTDC at idle, the advanced timing was beyond 35 BTDC at full advance. this is with the vacuum advance connected.

RazorRacer, with disconneting the vacuum advance you may not running into greater than 35 BTDC and running where JW says these cars run best. Here is one of the threads w/ JW's recommendation on timing.
If it the vacuum advance was connected you would probably have detonation. I didn't check the timing with the cvacuum advance disconnected at 6000 rpms, but I'll check asap.

FWIW, my cold idle did not raise to about 2000 rpm upon start up. I threw a emissions analyzer in the car and discovered I was running really really rich, in excess of 14. Upon setting the fuel mixture to 3.5 the cold idel rose to about 1500 RPMs and dropped to 900 RPMs at idle in about a minute. At least on my SC, if the fuel mixture is way to rich, the ability of cold idle to work properly was impeded. Just thought I's throw this out.

ebrownson · 12-02-2002, 10:38 AM

PBS911:

Do you have a pop-off valve installed?

Eric
83SC

pbs911 · pbs911's Garage

Quote:

Do you have a pop-off valve installed?

Yes, and I've been grateful on more than one occation.

Leland Pate · 12-02-2002, 12:08 PM

Well .... that goes against everything i've always believed.
I thought the idle was supposed to stay at a constant 1K regardless of hot or cold condition and that all of these pesky little devices are designed to help keep the idle and mixture stable during different conditions.

I feel soooo cheated.

http://forums.pelicanparts.com/showthread.php?threadid=61777&highlight=high+idle+at+start

Ok, then... no worries...

Superman · 12-02-2002, 01:19 PM

Late SCs are timed with the vacuum line disconnected. I think early SCs are timed with the vacuum line connected. 5 degrees BTDC on late SCs, 5 degrees ATDC for early SCs. I could be wrong. Mine is set at about 12 degrees BTDC with vacuum line disconnected. That gives me about 35 degrees full advance. Runs much better than stock spec.