77, 2,7 S, ignition timing

[AndreasK]

Please advise a newbie on timing

Came across this image in another thread. Its a bit hard to read, but I think I may have my timing wrong, from what I can get from it. Should I have my timing set to 5 deg after TDC, with vacuum connected? I think that´s what it says? I believe I have mine at 5 deg after, with vacuum disconnected. Which I thought was correct, and is normal for most later models. (Mine is a 1977, 2,7 S)

A previous owner has had the cams changed/altered. Not 100% sure to what spec, but probably somewhere in between the SC/964 territory. Does that affect what timing I should have?

According to the image I should have 32-38 deg advance at 6000 rpm with vacuum disconnected. Is this also correct?

The car runs great, pulls nicely to redline, but I have some occasional backfires and some very mild bucking at low rpm´s.

[Flat6pac]

You want to set ignition spec without the vacuum connected.
The vacuum has to do with idle with the TB butterfly closed
Once off idle the vacuum is not a concern to timing.
Bruce

[manbridge 74]

From the tech spec book for 76-77. But you need to know what type engine you have, probably not USA by the way you use a decimal.

[Trackrash]

Make sure to check the points dwell.

[Ginger77]

good point Jeff. how does this affect us in Europe with a 911 imported from the US?
Should we stick to US spec or can we check engine numbers and such?
I'm assuming the difference in timing has something to do with emissions but I'm pretty sure that has now all been stripped from my 911 at least.

[manbridge 74]

I would check to see what distributor is there by part number and make sure it is a match for the engine. Get the timing and dwell set to what you have by the spec book. Make sure the advance is working by observing timing with and without line connected as you rev engine off idle. Make sure you don’t exceed max spec at 6000 rpm. Put a few drops engine oil underneath felt in distributor center shaft. See if shaft has minimal play up and down.

[AndreasK]

Tanks for all input. I see there is a lot to this and many small loopholes

My engine is a 911 S USA 1977. So from Jeff´s chart I should be at TDC +-2 deg at 950-1000 rpms. Vacuum hose connected? Am I reading the chart correctly?

[Bill Verburg]

Originally Posted by AndreasK

Tanks for all input. I see there is a lot to this and many small loopholes

My engine is a 911 S USA 1977. So from Jeff´s chart I should be at TDC +-2 deg at 950-1000 rpms. Vacuum hose connected? Am I reading the chart correctly?

I'd use the RoW spec, the reason that US cars were different was solely due to emissions regs, there was no material difference between a US and RoW 2.7 in '77. The US engines did have exhaust reactors SAI pump and EGR which hopefully have been removed(especially the exhaust) unless this is a show car that you want to keep 100% stock.

You can check the function of the distributor easily enough.
If it's at 5ATDC @idle then it should jump to ~0 if the vac is disconnected. Then check it at ~5500(vac still disconnected) timing should be a max of ~38 BTDC

do set dwell before hand, too low a dwell retards the spark timing a bit and too high advances it a bit.

[spyerx]

Can I pile on here?

2.7 S motor (in a 71)
Webers
SSI Headers
Distributor from Partzclassic, curved by them, with Pertronix, No vacuum adjustment
Stock cams, heads, CIS pistons

Should I target about 38 BTDC at 5500??

Thanks :-)

[Bill Verburg]

Originally Posted by spyerx

Can I pile on here?

2.7 S motor (in a 71)
Webers
SSI Headers
Distributor from Partzclassic, curved by them, with Pertronix, No vacuum adjustment
Stock cams, heads, CIS pistons

Should I target about 38 BTDC at 5500??

Thanks :-)

most likely, but use your senses and if possible check on a dyno

basic timing for all the early engines whether T, E or S was
TDC @900+/-50rpm & 38° +/- 3° max

They moved the 900 rpm spec a bit + & - so go by the spec for you year and experiment a bit tp get best idle but the max is fixed and actual values could be anywhere from 31° to 38° BTDC @6k
rule of thumb
all ° BTDC
100 3.5-6.5
1500 4.5-14
2000 16 - 24
4000 24 -31
6000 31 - 38

for the idle Ca cars were spec'd @ up to 15° ATDC which is really retarded and generates a lot of unnecessary heat

[spyerx]

Sorry i should clarify. My engine is a 77 2.7 911S. Same deal?

Won’t run this one on a dyno as it’s coming out in a few months for a swap. It will get refreshed then. Runs good, just been a long time since i used a timing light so looking to play around a bit lol

[Bill Verburg]

Originally Posted by spyerx

Sorry i should clarify. My engine is a 77 2.7 911S. Same deal?

Won’t run this one on a dyno as it’s coming out in a few months for a swap. It will get refreshed then. Runs good, just been a long time since i used a timing light so looking to play around a bit lol

yes, same deal for 2.4, 2.7 or even 3.0 C3

a dyno isn't necessary, use your senses, you can tell when it's idling comfortably and makes power through the rev range

[Bill Verburg]

I just double checked and 35° BTDC is the max @6k I was looking at the dwell #s in the above posts except for #10

the E & S was actually 30° while T's were 35° for all 911s from '65 to 77, The far right notch on the pulley is the 35° mark if there are 2 close together far to the right they are 30 & 35

[spyerx]

Originally Posted by Bill Verburg

yes, same deal for 2.4, 2.7 or even 3.0 C3

a dyno isn't necessary, use your senses, you can tell when it's idling comfortably and makes power through the rev range

Cool thanks!