Timing. What was Ferry thinking?

[Vereeken]

On a euro SC the Porsche label says to set timing vac hose off at full operating temp. So far so good. But than it says. Set timing to 25 degrees at 4000rpm.

I can interpret this in 2 ways and both actually seem to work ( at least stationary).

I can think : Ok they mean the timing should not be more than 25 ° when hitting 4.000 rpm or

You should get to 25° by the time you get to 4.000 rpm.

In the second case the timing at 1.000 will be retarded but the car still idles OK.
In the first case the idle timing is about 5°.

So is this my English that is limited? It says 25 degrees AT 4000 rpm.

What where they thinking? Am I missing something?

Kr

Michel

[mreid]

Perhaps you are over thinking it. By setting timing at 25 degrees BTDC at 4000 rpm and assuming your mechanical advance is working properly, you are setting the mechanical advance curve to optimize engine advance. It's a static measurement. Bring the rpm to 4,000 and check the advance, adjusting it to 25 degrees at that rpm. This is actually more important than idle rpm.

[wayner]

Checking oil when running?
Checking timing at 4000rpm?

I'm glad we don't have to check the valves with the engine on.

[RarlyL8]

These methods are the differences between a high performance engine and a grocery getter.
Not complicated in the least, just specific to the application.

[Dan J]

[QUOTE=wayner

I'm glad we don't have to check the valves with the engine on. [/QUOTE]

Back in my Mack truck mechanic days we did adj the valves with the motor running
little daunting at first but actually worked really well. I think it'd be a little messy on a 911

[kodioneill]

Mercedes diesel engines (old style 60s-80s) and the Audi 100 ls the valves were adjusted with the engine running.

[mreid]

You could buy a set of deflectors that attempted to keep hot oil from splashing on you while adjusting Chevy V8 solid lifters. The trick set up was to take an old stamped steel valve cover and cut a long section across the length. That way you could get to the rocker adjusters while the engine was running without getting sprayed by hot engine oil. Yeah, those were the days!

[OsoMoore]

Originally Posted by mreid

You could buy a set of deflectors that attempted to keep hot oil from splashing on you while adjusting Chevy V8 solid lifters. The trick set up was to take an old stamped steel valve cover and cut a long section across the length. That way you could get to the rocker adjusters while the engine was running without getting sprayed by hot engine oil. Yeah, those were the days!

And uphill both ways I'm sure.
I'm passively dreading my first valve adjustment.

[Vereeken]

How did a topic on timing become a valve job post?

The wonders of internet

[Bob Kontak]

Originally Posted by mreid

Bring the rpm to 4,000 and check the advance, adjusting it to 25 degrees at that rpm.

Would this be the case for a US SC? My engine lid only had a procedure for checking timing at idle and I would like to perform the higher RPM check to determine if mechanical advance is working right.

Edit: Here is a good read on timing and vacuum impact. I am thinking 25 degrees plus or minus a couple at 4k for my car is in the standard range.

Setting advance on an 83 SC: final word ?

[moneymanager]

Many of the experts here will tell you that timing at idle is pretty much irrelevant; the only thing that matters is advance at the specified RPM... 4000 here, mine is set at 5k.

[don gilbert]

Since you have a euro car, you should be able to go to around 31-33 at 4g, depending how good of gas you can get. Im running 9.5 on shell 93, 33 degrees, just hear a tiny bit of spark knock on a third gear load.

[Bob Kontak]

The link in post #10 above talks of mechanical advance beyond "stock" . Caveat from Bill Verburg is to get it checked on a dyno if you get brave with the mechanical advance as the spark knock may not be noticeable.

I don't know why or how, but assume the dyno will indicate something so that a pro would be able to tell when detonation begins.

I do know that the one SC I drove advanced beyond stock had really nice throttle response.

[Vereeken]

I am not going to set it beyond stock. I know 25° is fairly conservative with todays quality in gas.

I disagree with the idle timing being irrelevant.

If you look at my two interpretations of the porsche label you will find that when setting the timing in such a way that the 25° mark only comes up when you reach 4000, the idle timing will be TDC or even ATDC.

However in the other method reving to 4K and checking that advance is not beyond 25, you can realize that with an idle timing of 5/6°.

In the second case I find the car drives better.

This is the essence of my question. I can assure that I do not get beyond 25 but I have two means of accomplishing this and on the face of it I do not hear the car complain at either. I can only say that it feels better in the method whereby you get idle of 5°.

Michel

[PeterRT]

Originally Posted by Vereeken

I can interpret this in 2 ways

Why? Zündzeitpunkt bei 4000 U/min auf 25° - set timing at 4000rpm to 25°BTDC doesn't sound particularly ambiguous...

[Bob Kontak]

The mechanical advance has a defined amount of advancement from idle to 4000 RPM.

It sounds like that is 25 degrees - TDC to 25 advance in method one.

In method two you say idle is 5-6 before TDC and is "not beyond" 25 degrees advance at 4000 RPM. Not beyond means less than 25 (example 22 BTDC) and the math does not make sense.

In method two, if the 22 degree example is used, the mechanical advance only moves the distributor 16 degrees (22 less 6).

Is this what you are seeing? That seems not possible (only 16 degrees) but I have been wrong before. :-)

Also, vacuum line is plugged in all tests, right?

[Vereeken]

Originally Posted by Bob Kontak

The mechanical advance has a defined amount of advancement from idle to 4000 RPM.

It sounds like that is 25 degrees - TDC to 25 advance in method one.

In method two you say idle is 5-6 before TDC and is "not beyond" 25 degrees advance at 4000 RPM. Not beyond means less than 25 (example 22 BTDC) and the math does not make sense.

In method two, if the 22 degree example is used, the mechanical advance only moves the distributor 16 degrees (22 less 6).

Is this what you are seeing? That seems not possible (only 16 degrees) but I have been wrong before. :-)

Also, vacuum line is plugged in all tests, right?

When I say not beyond I see 25/26 degrees at 4000 rpm. Not more. If I attach the vacuum line I get to 30-ish at 4000 and stays at 30-ish even at 6000. So yes your math is correct. About 20/23 degrees of mechanical advance.
The vac hose is plugged with a T.

I assumed the little mechanical advance is perhaps due to an issue with the distributor, although I cleaned it and maintained it...
and I do not get any driving issues.

[TheCabinetmaker]

golly even the little 914-4 with the wimpy 1.7 motor has the timing set with engine running at 3000+ rpm I think the idea is that at this rpm, the advance is one which should not be exceeded, else engnine damage is possible. If you only set timing at idle, you would not know that if the advance mecanism was messed up, that you would be to far advanced at high rpm, and that can lead to destructive knocking. I like to adjust to the factory specification, at the given rpm, then I proceed to a higher rpm, just to confirm the total maximum advance does not increase any more as I go higher rpm.

[Bob Kontak]

Originally Posted by Vereeken

When I say not beyond I see 25/26 degrees at 4000 rpm. Not more.

This is when the idle is at 5-6 degrees advance, correct?

What do you see at 4000 when the idle is at TDC or slightly retarded? That should then be 20-23? Is that correct?

Sorry to keep asking what sounds like the same question. Just want to understand what you are seeing.

[Vereeken]

Bob,

Yes on both accounts.

What is wrong if anything?

It would help if I could the dizzy tested, but that became a lost art in these parts of the woods.

Kr

Michel