Timing Retard Removal????

[signature65]

Ok this one has me confused and is the product of having a race car crew chief as a roommate.

My lowly 73T has a vaccum retard distributor.....from reading multiple posts it seems that I do not need it. Plus all the extra hoses look like crap. I propose this questions to those in the know.

In therory now......at RPM engines stop making vaccum. So if you remove the vaccum retard and then manually retart the timing arent you loosing the advance in the higher RPM range???

The thought is the mechanical advance cant make up for the 20 degrees or so of reverse spin you put on the distributor. Am I crazy here or did my roommate have a good point?

I mainly ask because yesterday after I figured that damn turn signal problem I ditched the vaccum retard hoses, capped them, and retimmed my car.

[Pele911]

Isnt it more PC to refer to them as "Mentally Handicapped"?

[equality72521]

Originally Posted by Pele911

Isnt it more PC to refer to them as "Mentally Handicapped"?

From someone with George Carlin as his avatar I'm surprised you said this.

[Pele911]

Touche'

[T77911S]

i am glad you asked this. i have been wanting to talk about this for a while. i am sure i will get hammered for my view on this.

a lot of people say to remove the vac retard. i did but have now connected it back up. i get about 15 deg mech advance and about 15 deg vac retard for an overall advance of 30 deg. when i set my timing for 30 deg at 6k, that puts me at 15 BTDC at idle. first, i did not like the way it sounded at idle. the tone was much higher. the retard gave it more of a low pitched sound. but mainly, when i retarded the timing, it made the idle mixture lean out, thus i was able to richen up the mixture even more which gives me a richer mixture across the RPM range but most importantly, richer at WOT. this was all measured with an LM2. my car seems to like the richer settings, maybe because of the retard. since i have fixed the fuel line i may have to go back and rerun some tests.
if you remove the retard, you would have to have the dizzy recurved, so why not just leave it on there? i dont know. 15 BTDC at idle does not seem like a good setting, doesnt the car start easier with less advance?
i wanted to get some recordings and post them before i brought this up.

[cmcfaul]

I think the roommate is 100% correct. Porsche would not have designed it this way if it was not needed. I believe correct timing is 5 degrees ATDC at idle with the retard hose connected. 20 degrees of advance greater than what Porsche recommends at idle can't be ideal (15 +5). The second the throttle is pushed the retardation / vacuum goes away.

Chris,
73 911 E

PS, does anyone really run the engine up to 6k RPM's and then set timing? I have seen this in the manuals but that is a screaming engine to be working on.

[Steve@Rennsport]

Originally Posted by cmcfaul

PS, does anyone really run the engine up to 6k RPM's and then set timing? I have seen this in the manuals but that is a screaming engine to be working on.

LOL,..All the time. No harm, no foul as thats the factory recommended procedure and done properly, works perfectly.

The key is that you don't need to hold it at 6K. One simply flashes it to 6K while observing timing marks to see where you're at. Rotate the distributor and repeat the process to observe the changes.

[911pcars]

Originally Posted by T77911S

i am glad you asked this. i have been wanting to talk about this for a while. i am sure i will get hammered for my view on this.

a lot of people say to remove the vac retard. i did but have now connected it back up. i get about 15 deg mech advance and about 15 deg vac retard for an overall advance of 30 deg. when i set my timing for 30 deg at 6k, that puts me at 15 BTDC at idle. first, i did not like the way it sounded at idle. the tone was much higher. the retard gave it more of a low pitched sound. but mainly, when i retarded the timing, it made the idle mixture lean out, thus i was able to richen up the mixture even more which gives me a richer mixture across the RPM range but most importantly, richer at WOT. this was all measured with an LM2. my car seems to like the richer settings, maybe because of the retard. since i have fixed the fuel line i may have to go back and rerun some tests.
if you remove the retard, you would have to have the dizzy recurved, so why not just leave it on there? i dont know. 15 BTDC at idle does not seem like a good setting, doesnt the car start easier with less advance?
i wanted to get some recordings and post them before i brought this up.

If I understand you correctly, your ignition system is set at 30º advance at 6K rpm; 15º of that via the mechanical advance and 15º via the static ignition setting.

While the total advance is within spec., it sounds as if there might be too much initial timing (15º) and not enough mechanical advance also 15º). Excessive timing at low speed loading may introduce unwanted detonation (depends on many engine and operating factors (i.e. ambient temperature, compression ratio, fuel octane, driving style, etc.).

I would suggest the mech. adv. be more conservative, e.g. 25º and dialed in 5º BTDC at idle - same 30º overall, but less at the bottom end. Even these numbers are slightly aggressive. With a stock engine, something closer to a stock setting might be better.

Sherwood

[rattlsnak]

Dont confuse this with the distributors that have two hoses. One is for advance and one is for retard. Many people confuse the meanings and results of these.

[T77911S]

Originally Posted by 911pcars

If I understand you correctly, your ignition system is set at 30º advance at 6K rpm; 15º of that via the mechanical advance and 15º via the static ignition setting.

While the total advance is within spec., it sounds as if there might be too much initial timing (15º) and not enough mechanical advance also 15º). Excessive timing at low speed loading may introduce unwanted detonation (depends on many engine and operating factors (i.e. ambient temperature, compression ratio, fuel octane, driving style, etc.).

I would suggest the mech. adv. be more conservative, e.g. 25º and dialed in 5º BTDC at idle - same 30º overall, but less at the bottom end. Even these numbers are slightly aggressive. With a stock engine, something closer to a stock setting might be better.

Sherwood

full advance is right around 30 deg. the spec says to set timing to TDC. full advnce includes the retard + the mechanical. if i unplug the vac retard, the timing jumps up to around 15 BTDC. the dizzy has been rebuilt and i recently had it back out to clean it. the car runs GREAT now that i fixed the fuel line. i thought i heard a slight bit of detonation at 5500, but i may be a bit on the lean side though. i am happy with the timing, i just never thought it ran as good with the retard disconnected. i look at it as part of the advance, not retard. plus, and what i really wanted to stress was the fact that with the retard, you can richen the mixture up and it still idles fine. when i connected the retard, with the same idle RPM my mixture went 1/2 a point or more leaner, which allowed me to go that much more richer with out surging at idle.
i have not messed with the mixture since i replaced the injector line, thats why i may be lean, plus i wanted to do another comparison between retard vs no retard and print the results.
sorry about the typing, i sit in the dark, my desk is back here where the controlers train so most of the lights are out.

[rattlsnak]

http://www.amazon.com/Saitek-Eclipse-II-Keyboard-PK02AU/dp/B000H6AY6M

it looks deceiving in the photo, but the entire keyboard lights up. Awesome for typing in the dark..