Adjusting timing
 

Call me the lazy mechanic, but can you adjust the timing by making a slight adjustment, driving the car, then making another adjustment, driving the car, until you sense a good adjustment?

What's wrong with the REALLY lazy method of using a timing light?

Isn't that really called "finding" the timing....or looking for timing in all the wrong phases..


Timing light costs 40-50 bucks, takes 5 minutes, and is right.

RazorRacer has a good point. Not every 911 engine is the same due to production tolerances, engine upgrades/modifications, compression ratio, fuel octane, altitude, air temperature/density, etc. Thus, some engines may provide better power with more or less advance.

You could maximize the baseline, factory specs by advancing the timing until you hear borderline knock (detonation), then back off (retard) the timing to provide a comfortable safety margin. The problem is, can you hear detonation under load? If you can't, disregard the above unless you have some instrumentation attached to the engine and/or are hooked up to a chassis dyno.

Advancing the timing changes the overall ignition advance. A somewhat better strategy is to lock out the advance weights, plot a HP/torque curve vs. ign. timing curve throughout the rpm range (still on the dyno), then modify the distributor accordingly. Some effort for a few HP, maybe. Modern engine management control systems use knock sensors to automatically provide the correct timing.

Timing to factory specs is the "by-the-book" method that works for most of us.

Sherwood Lee
http://members.rennlist.org/911pcars

Timing...
 

I noticed some of the ignition timing foil decals have different spec.'s for the same motor. European spec.'s for a '77 3.0 is 5 degrees ATDC and USA spec.'s are 5 degrees BTDC. Is there that much leeway for these motors? Can I run a USA motor at Euro. spec.'s and have no problems except for smog requirements?

JGL:confused:

Yes, you can run Euro specs assuming you don't increase the overall ignition timing (distributor advance + initial static timing). The difference between 5º ATDC and 5º BTDC is 10º. Typically, the 5º of retard (ATDC) is provided by a vacuum retard unit which only works at idle. Some folks disconnect this and use 5º BTDC for the initial setting. An adjustable advance timing light can verify the total advance.

I think you might have the specs crossed. US specs are usually ATDC for emission purposes.

Hope this helps,
Sherwood Lee

BTDC or ATDC?
 

I am looking at my foil engine sticker and it says to set timing at 5 degrees ATDC +/- 2 degrees for the Euro spec.s and when I look at a US version of a 3.0 the tag says to set the timing at 5 degrees BTDC +/- 2 degrees. That is 10 degrees difference. Is the distributor different in the two motors and is the distributor compensating? Or is one of those settings a higher performance setting?

JGL :confused:

Could this be a timing problem?

smooth above 6000 rpm, lousy under

pkfrdh,
What year is your 911?

My 911 year is...
 

a 1977 Carera 3.0, and I've seen tags for USA 3.0 SC's that say 5 degrees BTDC.

Check out the pic. below that shows a picture of a European spec.'s tag for a '76 - '77 2.7 and 3.0 engines. It shows that the Euro. spec.'s are 5 deg. ATDC.

JGL

At little help here?

Finally got the timing light and here's what I have seen:

mark was on 5, but you know the problems I've been having. See reply above with link if you don't know.
put mark on Z, and it seemed to improve.
put mark about 5 the other side of Z and problem is almost gone.

What's up with that? could someone have slipped in a euro engine in my 911?

Note: Z is left of 5.

I have a 72 911. Has anyone disconnected the vacuum advance\retard via just plugging the vacuum lines? If so, what does this do over all-idle and high rpm. I run 87 octane, have the timing advanced like crazy and it never pings. If I plug the lines, will I get more advance?
Thanks

RazorRacer,
 

...what is the type/series number that is stamped on the flat surface on your engine on top, to the right of the fan shroud, behind the oil pressure sending unit?

If you have a U.S. version of a 3.0, for '78, it should say : 930/06

JGLhttp://www.pelicanparts.com/support/smileys/yltype.gif

The number on the fan shroud says 911/06. Is this the location of the number I should be looking at?

RazorRacer...
 

The engine / suffix number is not on the fan shroud. It is on the top of the motor, at the right side of the fan shroud at the base of the fan shroud, behind the oil pressure sending unit. It is stamped into the aluminum and the numbers are small. You may have to clean up the area first to see it. It does have the format you mentioned, but it should read "930 / 06" . I will look up and check to see if there is a correct "911 / 06 ". Does your engine tag on top of the Fan shoud say it is the timing decal information for a 1978 SC in California? Your engine case numbers should be 930.101.104.4R and 930.101.103.4R (right and left halves) and there is a very small date code cast into the case next to the number on the right side case. It is a raised circle, split in half, about the size of an eraser on a skinny pencil...or even smaller. In one half of the split circle is the year like 77 for 1977 and in the other half is the week number of the year ths case was cast, like 24 out of 52. My engine was cast in the 10th week of 1977. That is the second week of March, 1977. The casting looks like
"10/77" on a small raised circle.

This gives you some information to try to decide if your motor is original for you car. Check to see what the production date of your car is...look at the plastic decal on the drivers door pillar. Your motor casting date should not predate the car by more than 30 days and certainly not be any less than 7 days prior to the build date of the car.

JGLhttp://www.pelicanparts.com/support/smileys/yltype.gif

FYI, early 1977 US-spec 930 Turbo tag (TURBO CID 182,6 Engine Family IV) states:

Ignition timing: 7 deg. +/- 2 deg ATDC at idle speed (vacuum line conn.)

While late 1977 US-spec 930 Turbo tag (TURBO CID 182,6 Engine Family IV) states:

Ignition timing: 5 deg. +/- 2 deg ATDC at idle speed (Vacuum line conn.)

The later decal has a part number in bottom right corner that states "930.??6.50?.05".

Holy smokes, I was 12 years younger when this thread started.

i was still in high school lol

Could have been directly related to the emissions nonsense the US cars were subject to.

On my 73S if set idle timing to 5deg ATDC(vac connected) then disconnect and plug line and time at 6000 RPM I only get 33 deg. what I have done is split the difference at idle to around 2 deg ATDC which brings my 6000 advance to 36 deg.

If I plug vac line and time idle to 5 deg BTDC my idle is so high I almost have to close the air screws. this does give me a more crisp idle, especially during warm up, but I loose a little throttle response. This is due to losing that immediate advance from ATDC to BTDC. Also, with the air screws turned closed I have to turn down the idle circuit which means less air and fuel in the combustion chamber.