Does anyone really rev up to 6000 RPMs to check timing?
 

Does anyone really rev up to 6000 RPMs to check timing?
Just curious as I have never had the guts to.:D

Yes

6000 RPM w/ no load=bad idea, IMHO

Beside, don't you get max advance way before 6000?

The books say check at 6000, but that is just screaming my little 2.7.
I just can't bring myself to do it.
Is it necessary?

I do 5,000 max even though my modified redline is 7,500, but I think if you have two experienced people, one on the throttle and the other on the light, you can do it in a short burst quite safely. Trying to attain and hold 6,000 no-load and at the same time aim and read the light is too much for me.

Never once. Too loud.

YES, EVERY SINGLE TIME.

Free-rev at 6000 rpm is no-big-deal for a 911 engine – just noisy.
It can sit there hovering between 5800 and 6300 as long as you want.
The key is having appropriate oil temperature.

Sure, having some load is better. When I did this on the dyno, I always added 5% or so load but that was mostly to have the mixture better, not any mechanical issue.

There isn’t a 911 that can’t sustain 6500 rpm at FULL LOAD for long periods. Race engines do this at 8000 for 24-hour events.

The reason for this is our 911s are very sensitive to the ignition timing at peak power and above. Individual distributors have sufficient variation (manufacture and wear) that you can’t set the timing at idle and know the timing at high rpm is within spec.

Most of the time we want to position the 6000 rpm timing at a specific part of the spec range (high, middle, low) depending on the circumstances.

There are ways ([i]ve hav vays) to reduce the fiddling at 6000 rpm. You can remove the distributor from the engine (remember to position the engine at TDC compression on #1 cylinder). You can then easily clean and service it. You can then ‘run’ it on a distributor machine. This runs the distributor at various rpm. This is so you can observe the advance curve at as many speeds you want – low idle to above engine redline. Keep in mind the distributor runs at half engine speed – 4000 rpm distributor = 8000 rpm engine.

The key is to know your distributor’s actual advance curve. This way you know the relationship between static (0 rpm), idle (whatever) and 3000 rpm distributor (6000 rpm engine). You can then re-install the distributor in the engine and set the timing at the same idle speed. The timing at 6000 rpm should be right on.

Every place has distributor machines – metro areas and John Deere. If you can’t find on, UPS the distributor to ‘someone in the know’.

I then still ALWAYS check the timing at 6000 rpm.


Some other tips:
It is useful to have a clean crank pulley. You can use a scribe to clean the timing marks. During assembly, many partially fill the marks with white paint.
There is no substitute for a good, powered timing light. The 12V is available at the relay panel to the right of the engine.

In general I don’t care for ‘adjustable’ timing lights. It is much more sure to observe the 30° or 35° physical marks on the pulley than rely on someone’s ±?? calibration of a timing light.

Time the engine in the dark. Look for sparks elsewhere.

Be careful. Neckties in the fan lead to serious injury. :eek:

EDIT: BTW, shooter's ear protection is a must.

Best,
Grady

Try it with a 912 engine sometime! Thing sounds like it going to come apart :eek:

[QUOTE=Grady Clay;4471018]YES, EVERY SINGLE TIME.



There isn’t a 911 that can’t sustain 6500 rpm at FULL LOAD for long periods. Race engines do this at 8000 for 24-hour events.


i have had a few 2.7s that i was affraid to push over 5k during tune due to the fact it sounded like it could shat itself right then and there on me!:eek:

so i go by motor to motor basis as IMO some older motors just havent been maintained and it sounds as if the chains are going to throw them selves out of the case.

i use the 6000 RPM most of the time:D

cheers ed

I don't do that with a 912/356 - or 914-4.

If you want excitement, time a 914-6 at 6000. You put your head down in the engine compartment. Unless you are 7'2", your feet are off the ground. The timing marks are on the flywheel and observed through the notch in the top of the transmission housing. The air filter must be off so you have three intakes in the chest. This is where you are really happy to have set-up the distributor on the bench and machine. You only have to check at 6000 rpm.

BTW, shooter's ear protection is a must.

Best,
Grady

OK, Thanks for the input.
My engine is rock solid, so I'm going to give it a shot this spring just as a check, and because I've never done it.
The dizzy is newly rebuilt, so I don't anticipate any trouble.
With the M&K 2in/2out my neighbors are going to love me.:D

Left hand on the throttle linkage, peek through the rear window to check the tach, timing light in the right hand.

That is pretty much all there is to it.

That's how I do it. Wife says too noisy so I'm on my own.

It is noisy as hell tho. I too have a 2 out sport muffler.

I was nervous at first but then I thought who the hell wants a porsche that can't run 6000 rpm? If it sharts on you then at least it was in your garage!

Ditto on engine temp.

Btw if you can manage it use the triangle linkage piece on weber cars.

Why the heck not? I rev mine to 6500+ all the time although I can't hear the valve train over the wastegate screaming.

Every porsche owner should be required to free rev the engine to 6000 rpm and hold it before being released into the public. Makes 5000 seem much more relaxing. 7000 sounds better though must be the harmonics. By the way I don't free rev mine to 7000 but it holds real nice in 2nd gear.

It's much better to rev it to 6000 RPM w/o load (=no chance of knocking) and discover that timing is wrong than to rev it under load and discover it the wrong way (=eroded pistons)

6,000 is no big deal. Maybe a little intimating, but that's it.

in context to a small boat V8 engine that spends much of it's engine's 1,000 hours of load work at 4,000, 6,000 free rev is still no big deal for a flat 6.

There is also something about the geometry of the flat 6 that enables it to be more balanced than a V8 to start with. Some do take notice that it revs almost like a sewing machine.

And if the flat 6 is very worn better it blows up in your garage than on an interstate. Kinda like taking your rebuild to the track after you rebuild it to see what it's make of.

Novice on this subject. You don't time a DME motor do you?