SC Idle RPM at temperature

Vereeken · 07-25-2011, 12:41 AM

To all SC Owners; i would need some experience input.

At what IDLE RPM does your SC run when started from dead cold at ambient temperatues of 60F / 14°C.

I am looking for the average IDLE RPMS at this temperature for the first minute or two.

Thanks already.

fred cook · fred cook's Garage

When first started from cold, my 1980 SC runs at about 1600 rpm. After driving about two blocks (30 seconds), the idle will drop to around 1100 rpm. Another 2 miles (2 minutes) and it is at 950 rpm. Later, after a hot start, it will idle at about 800 rpm until brought back up to full operating temp (190-200 F) when it will be back at 950. Hope this helps. I try to always let the engine warm up by driving at a slow to moderate speed rather than letting it sit at idle speed. Hope this helps.

Vereeken · 07-25-2011, 04:33 AM

Thanks fred.

I would have expected 1600 RPM rather at lower temperatures.

Do you have any idea if the AAR is fully open at 60F and just closes faster then when in colder temparatures?

So in other words should I always expect the same start-up RPMS regardless of Ambient temperature and is it only the closing time of AAR that is variable with weather?

Michel

Scott R · Scott R's Garage

Mine is identical to the poster above, maybe 1200 or so RPM when it's 80 deg F out.

Vereeken · 07-25-2011, 08:22 AM

I pulled the AAR valve. It opens and closes when you warm/cool it but after half an hour in the fridge the opening was still very small. I suspect it has only about 20% opening left in which range it travels. When its hot it closes completely.

I will measure the resistance, but I suspect that the plate and or spring are not moving freely due to crud or something else.

With a small opening like that I guess I can only expect about 100 RPM above 900 when started at 60F.

Am I on the right track?

Michel

rgoodrich · rgoodrich's Garage

Scott,
I have the same set up on my 81 SC. How do you like yours?
Robert

fred cook · fred cook's Garage

Michel,

The AAR on my engine is fully open when the engine is cold. It doesn't seem to matter if it is 80 F outside or 60 F. Of course, the AAR closes faster in the warmer weather. It looks like you have found at least one issue/problem. After 30 minutes in a freezer, the AAR should be wide open. Maybe a little cleaning will make it work properly. If not, then the bi-metallic spring may have to be replaced. Good luck with your search!

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by fred cook

Michel,

The AAR on my engine is fully open when the engine is cold. It doesn't seem to matter if it is 80 F outside or 60 F. Of course, the AAR closes faster in the warmer weather. It looks like you have found at least one issue/problem. After 30 minutes in a freezer, the AAR should be wide open. Maybe a little cleaning will make it work properly. If not, then the bi-metallic spring may have to be replaced. Good luck with your search!

Fred,

AAR (auxiliary air regulator) does not completely open even at freezing temperature. The widest opening I've found on dozens of Bosch AAR's tested was around 50%-60% open (freezer test) and at room temperature @ 30% open (greater than a quarter moon. If you could demonstrate a good AAR fully open when cold (freezer), I'll buy you a good dinner for two because you have taught me something new about CIS components' properties. Thanks.

Tony

Scott R · Scott R's Garage

Quote:

Originally Posted by rgoodrich

Scott,
I have the same set up on my 81 SC. How do you like yours?
Robert

I love it, I just fixed a crazy distributor problem, had one good day of driving then the speedo died.

The 964 cams seem to pull forever compared to stock.

SchnellSchweitz · SchnellSchweitz's Garage

Mine runs around 1200 RPM before the AAR shuts and around 930 at warmed up idle. I believe this is the "preferred" settings.

Vereeken · 07-25-2011, 11:46 AM

Boyt911Sc might be right.

I have done a complete test of the AAR and opened it.

A. it gives me 22ohm between terminals. This is within spec for 83s. The earlier ones seemed to have 33ohms.
B. when 12 v applied it goes to fully closed in exactly 4 minutes
C at 60F I have about 30% opening, at freezing temp it seems about 40%
What is weird is that when I dismantled the AAR it is not a perfect round hole you find , it is actually a squared of triangle sort of opening and even if you would bring it completly in front of the hole it would give you only about 70% of the opening of the tube diameter.

So I guess that my AAR is working as it should and I should not expect more RPMs at 60F then what I have now (maybe a 1000; 1100 at the most.

Weird that FRed gets 1600. AL the rest of the warm-up seems to be as i would expect, only the high start-up rpm is off.

All very confusing.

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by Vereeken

Boyt911Sc might be right.

I have done a complete test of the AAR and opened it.

A. it gives me 22ohm between terminals. This is within spec for 83s. The earlier ones seemed to have 33ohms.
B. when 12 v applied it goes to fully closed in exactly 4 minutes
C at 60F I have about 30% opening, at freezing temp it seems about 40%
What is weird is that when I dismantled the AAR it is not a perfect round hole you find , it is actually a squared of triangle sort of opening and even if you would bring it completly in front of the hole it would give you only about 70% of the opening of the tube diameter.

So I guess that my AAR is working as it should and I should not expect more RPMs at 60F then what I have now (maybe a 1000; 1100 at the most.

Weird that FRed gets 1600. AL the rest of the warm-up seems to be as i would expect, only the high start-up rpm is off.

All very confusing.

Vereeken,

Remember one thing about these CIS components, they are not precision devices like we have today. These are old technology yet still reliable and dependable. The resulting idle speed will depend on your idle setting (baseline) and level (degree) of vacuum for the system. All the AAR does is by-passed the metered air during cold idle. Any amount of unmetered air (leak) would affect your final engine speed.

Spent a great deal of time testing these components operate under different conditions (cold, warm, and very warm) to fully understand their behavior and performance.

Tony

MotoSook · 07-25-2011, 02:13 PM

Not sure why you woul dowrry about the idle at warm up.

fred cook · fred cook's Garage

I've only checked one AAR, the one on my engine. When I say it was "all the way open", I mean that it would not turn any further after a stay in the freezer. I assume that the bimetallic spring is the limiting factor there. It has been several years since I had it off the engine, but I think that it made an opening that looked like about a 3/4 moon. When warmed up the opening was completely closed. I was not trying to imply a full circle of opening. Sorry if I confused anyone. I guess the important thing is that it works!

Vereeken · 07-25-2011, 11:11 PM

Quote:

Originally Posted by Soukus

Not sure why you woul dowrry about the idle at warm up.

Driveability. I just redid the whole CIS-thing on my SC and want to be as close again as possible to when it was new.
That and the fact that the weather is bad over here.

Vereeken · 07-25-2011, 11:15 PM

Quote:

Originally Posted by fred cook

I've only checked one AAR, the one on my engine. When I say it was "all the way open", I mean that it would not turn any further after a stay in the freezer. I assume that the bimetallic spring is the limiting factor there. It has been several years since I had it off the engine, but I think that it made an opening that looked like about a 3/4 moon. When warmed up the opening was completely closed. I was not trying to imply a full circle of opening. Sorry if I confused anyone. I guess the important thing is that it works!

No problem fred. Indeed 3/4 moon is a good way to describe it when fully open. It is like a full moon with a pie-piece taken out (or left in if you prefer).

It just seems strange that you are getting 1600rpm.

The AAR has spent the night in the freezer. I will install it this afternoon and then start-up , see what it gives me in RPMs.

Vereeken · 07-26-2011, 03:43 AM

Well the delta between my start-up RPMs at 60F and now after a night in the freezer is only 100.

I was expecting more.

The way I see it now is that (if all else is well) the AAR on my EURO SC 83 only gives me about 200-250RPM in extra idle.

Perhaps I should forget about it. Starts up nicely idles well. Hell.

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by Vereeken

Well the delta between my start-up RPMs at 60F and now after a night in the freezer is only 100.

I was expecting more.

The way I see it now is that (if all else is well) the AAR on my EURO SC 83 only gives me about 200-250RPM in extra idle.

Perhaps I should forget about it. Starts up nicely idles well. Hell.

Vereeken,

What's the Bosch number on your AAR? Do you have a 0-280-140-218 or something else? Thanks.

Tony

Vereeken · 10-13-2011, 10:59 PM

Tony,

I will let you know when I start on the right bank of cilinders. I think the AAR is just fine. It is just my Intake runners that let through air at the gaskets. I have identified 2 definetes and one maybe. So I guess that is a lot of false air.

I think once that is solved my cold start idle is going to go up like it should.

Michel