Setting timing at 6000rpm

[RyanH]

Hey, just curios how many 911 owners that work on their own cars actually set their timing at 6000rpm? I find it a terrifying experience and haven't had the courage to get the revs up there yet, my timing is set at TDC at idle. I have a 1970 911T, runs really well so I wonder how much better it would be setting the timing to spec?

[Lyndon302]

Ive just got mine going after a rebuild. I've set mine at idle and then ear. Ive advanced it so much and it makes a lot of difference. It does not ping. Will do for the run in. I would definalty check it at six thousand. Won't hurt it a bit.
Lyndon

[BK911]

Full advance happens well below 6000 rpm, probably closer to 4000 rpm. So no need to rev all the way to 6k. 4k is bad enough with your face next to the fan belt!

[gomezoneill]

It's just to check full advance, not to set the timing.

[911pcars]

Originally Posted by gomezoneill

It's just to check full advance, not to set the timing.

If distributor adjustment needed, then you rotate it at some speed. Then re-confirm at speed and at idle. If nothing wears, that idle timing should be set going forward.

Sherwood

[RyanH]

Yes full advance not timing. If I adjust the distributor for full advance (35btdc) will this not affect the idle setting? If it does is this telling me there is wear somewhere or is it aback and forth procedure getting the idle and advance as close as you can?

[Trackrash]

You can't hurt the motor by revving to 6000 rpm. The timing at 6K rpm is to check the maximum advance, which in your case is 35 * BTDC.

I am assuming you have the rev limiting rotor installed....

[RedCoupe]

My late father who had a masters in mechanical engineering and worked on experimental engines at GM before going into aerospace used to say that it was much harder on an engine to take it to high revs unloaded than it was under load, say on a dyno. I don't know the technical answer why, but I always keep that in mind. That said, 911 engines have a very stout bottom end and I have witnessed them taken to screaming revs with zero load.

[911pcars]

Originally Posted by RyanH

Yes full advance not timing. If I adjust the distributor for full advance (35btdc) will this not affect the idle setting? If it does is this telling me there is wear somewhere or is it aback and forth procedure getting the idle and advance as close as you can?

Total advance is the sum of initial timing (distributor location) and the centrifugal advance mechanism inside the distributor.

After checking total ign. timing at 4500 rpm +, check again at idle speed (~800 rpm).

You now have the timing specs for idle and distributor ignition advance.

[E Sully]

If you look at the ignition curve for the 2.4 and 2.7 engines, total advance does not happen till about 6000 rpm. I would check your advance at various rpm to make sure the distributor weights are moving smoothly. If not it may be time to do a little distributor maintenance.

[David Inc.]

Originally Posted by RyanH

Yes full advance not timing. If I adjust the distributor for full advance (35btdc) will this not affect the idle setting? If it does is this telling me there is wear somewhere or is it aback and forth procedure getting the idle and advance as close as you can?

I think what you're doing is setting the idle timing, and then just checking to make sure that the distributor is getting full advance. If it isn't getting full advance you don't adjust it, you fix your distributor.

Or am I wrong on this one?

[cmcfaul]

just dont keep it there long. Hard part is seeing the tack and timing light. Rev it and confirm it wont over advance. It can take it. its a Porsche. Neighbors love it also.

Interesting the chart does not show correct timing at idle. Should be 5 degrees ATDC with retard hose connected.

73 911 E

[E Sully]

David Inc. is correct in his assessment.
cmcfaul, if you read the text at the top of the picture, timing is set with vacuum line disconnected. At idle with vacuum line attached yes, it should retard the ignition. If not the vacuum pod could be malfunctioning, or the distributor plate could be sticking, in which case it would be a good idea to have it serviced.

[BK911]

Originally Posted by E Sully

If you look at the ignition curve for the 2.4 and 2.7 engines, total advance does not happen till about 6000 rpm. I would check your advance at various rpm to make sure the distributor weights are moving smoothly. If not it may be time to do a little distributor maintenance.

That is for a 2.4/2.7 engine.
A 2.2 engine only advances about 1 or 2 degrees past 4k rpm.
Most of the advance is in the early revs.

[Ian Comerford]

Originally Posted by gomezoneill

It's just to check full advance, not to set the timing.

The other thing you get out of the check at 6k revs is confirmation that the distributor shaft isn’t worn. My garage did this check on mine in the last week in an attempt to eliminate an issue.

[Bill Douglas]

Originally Posted by RedCoupe

used to say that it was much harder on an engine to take it to high revs unloaded than it was under load,

My thoughts too.

I live in a town which is really just a whole lot of hills stuck together. So I get to do a lot of 6,000rpm under full load Italian tune ups. Plus we have a white trash town called Wainuiomata nearby with a very big steep both sides. So kind of handy.

[Walter_Middie]

Interesting the chart does not show correct timing at idle. Should be 5 degrees ATDC with retard hose connected.

The chart only shows the advance portion of the total timing. Your total timing consists of the initial timing (idle), vacuum advance/retard (depending on the type of vacuum timing), and the centrifugal advance ( shown on the chart above).

To check my total timing at high RPM, I don’t linger at high RPM, I line up my timing light on the timing marks, reach over with the other hand at briefly open the throttle and then close the throttle. The engine will just rev up then immediately go back to idle. If you are watching the timing marks, you will see the timing advance and then stop advancing - this is your total advance. If there are any adjustments that need to be made, I rotate the distributor at idle and then check total again with a quick rev. I don’t worry too much about what RPM the total occurs at.

If I adjust the distributor for full advance (35btdc) will this not affect the idle setting? If it does is this telling me there is wear somewhere or is it aback and forth procedure getting the idle and advance as close as you can?

Yes, if your initial timing (idle) and total timing cannot be adjusted so that both are correct, then something is wrong. If they are close because of normal wear and tear, set the total and the idle is just whatever it is. Idle timing is not all that important.

[E Sully]

Originally Posted by BK911

That is for a 2.4/2.7 engine.
A 2.2 engine only advances about 1 or 2 degrees past 4k rpm.
Most of the advance is in the early revs.

From what I have found, it continues to advance to 6,500 rpm. Note distributor shaft speed is half of engine rpm.