1976 911 2.7 dizzy curve for 123 Tune 6

[SunburntLobster]

Hi,
Does anyone have an example curve for a stock 1976 2.7 911?

MSD 6425 AL6 if that makes any difference?

The car was dyno'd but wouldn't rev cleanly past 5800rpm.

The MSD rev limiter was set to 0,0

I plan to check the base setting of the dizzy at TDC and work from there.

Thanks!

[Walter_Middie]

Here's an advance curve as a function of engine RPM:



Some curves are a function of distributor RPM, so be careful what you are looking at.

As it says in the picture, I set idle timing below 1000 RPM and check timing at 1500, 2000, 4000, and 6000 RPM. To get the 6000 RPM check, I just line up the timing light with one hand, and with the other hand, I quickly rev the engine and note the timing at which the advance stops advancing - I don't worry about what RPM I'm at - it's just a quick rev. No need to hold at 6000 RPM unless you really want to piss off the neighbors.

[unclebilly]

In the chump car, I installed distributorless ignition and could switch between the stock S curve above and the RS curve. They were pretty similar, it seemed like the RS curve was better with lower temps and the S curve was better when it was hotter. The engine was a 75 911 engine with early exhaust, modified zeniths (34mm chokes), and distributorless ignition.

[SunburntLobster]

Hi, thanks for the replies.
Is that curve too revvy for my 76 2.7? I believe it doesn't have the compression or cams to make power past 6k rpm?

[Hx911]

i have set mine 'by feel' for my 1974 911 targa. All stock, standard 2.7 with CIS.
first set it to what the 'picture' in the service manual said, worked it all out as a mid line between the two. It drove ok, but I felt i could improve - that is the beauty of the bluetooth 1-2-3.
after a few tries I settled on
NO Vacuum advance or retard.
rpm advance
500 0.0
1200 0.0
3000 27.0
5000 27.0
6100 25.0
7400 22.0
8000 22.0
edit: forgot to say
I have set the 123 for a 5degree static advance

using a CDI+ and its internal rev limit set as per default.

Unfortunately the Dyno near me is out of action so I have to wait to do this properly.

Engine is out ATM as we found a vacuum leak in the intake system and are waiting for parts.

[icarp]

Is this a 123 bluetooth dizzy?
There are set up steps to the 123 line . The are great systems in my experience

[SunburntLobster]

Hi, it is the USB version but all my laptops are so old they barely start up now!

[icarp]

First you must set the dizzy to 0 @ TDC, When you do this you can be sure of the timing degrees.
Start up @8* BTDC. - 16* @ 1,800 rpm - 24* @ 2,400 rpm - 31* @ 3,000 rpm
no need for more advance unless you have dyno access , then maybe 1*-4* more 4k-5.5k all in
I hope this helps
PM me if you would like to speak on the phone , the 123 can get confusing
Ian

[SunburntLobster]

Originally Posted by icarp

First you must set the dizzy to 0 @ TDC, When you do this you can be sure of the timing degrees.
Start up @8* BTDC. - 16* @ 1,800 rpm - 24* @ 2,400 rpm - 31* @ 3,000 rpm
no need for more advance unless you have dyno access , then maybe 1*-4* more 4k-5.5k all in
I hope this helps
PM me if you would like to speak on the phone , the 123 can get confusing
Ian

Hi Ian
Please see screenshot of my actual curve as set my previous owner.

[icarp]

SBL, if this were in my shop I would run the curve that I posted .
You are leaving a lot on the table , My curve is not aggressive . Yours is week .
Ian

PS. where in the world are you . I am in NM , Usa

[SunburntLobster]

Hi, I am in England!
When I drove the car home last night it was running really bad misfire etc.
I started altering the curve a few degrees a time and it now doesn't start.
I returned the curve back to what was on it originally but still wouldn't start.
I dropped out plug 4 and it looks rough. It was brand new about 100 miles ago!

[icarp]

SBL, remove all plugs are they all the same ? how old are the injectors? compression test? leak down ? Plug wires? distributor cap ? rotor and dist shaft? igniter wheel? cdi box? coil? ect... MS program?
It is not the fine tuning of the timing that is causing this problem . The timing at idle should be at 5-8* not 18* that can make it hard to start , although some race cars have Idle timing at 16-18*
let me know
Ian

The electrode on that plug looks rounded at the edge , that only happens with miles . I am stumped

[SunburntLobster]

It was on a rolling road last week and they weren't happy with it, only made 130bhp and misfired at 5.5k rpm. I only drove it a few times and got progressing worse, lumpy tickover, misfire, etc so think it isn't entirely what I have done.
I have fitted new diz and rotor arm but still won't start.
Bit nervous setting the curve to the expected levels now, 10 degree retard at idle from previous setting is quite a jump!
Injectors, etc were new last year when the MSD and megasquirt fitted.
I reckon I will reset the stock base megasquirt map, check TDC, put in your curve and fit new plugs!

[icarp]

SBL, the curve I suggested is very mild and safe . The curve you have is not good.
The timing should be checked to make sure the 123 dist is matched to TDC . This is a process that i can help you with when the car is running again . Spark plugs can be defective these days , so a new set is a good idea . 10 degree jump form bad to good is, GOOD! The PO did not know about engine ignition timing . The MS injection timing is very important as well. Do you know a good MS tuner?
MS can be very hard to get right if you are not a MASTER on a 911 .

[icarp]

Tell me about all 6 spark plugs.... pics?
Ian

[icarp]

Quote from Jonny H ...All three devices are programmable for ignition curve. I would be very careful, there could be curves lurking in the Megasquirt and the MSD box

This is what I mean about getting the 123 to match TDC on the engine
VERY IMPORTANT !
Ian

[Walter_Middie]

It is not the fine tuning of the timing that is causing this problem .

In the first post, you say it would not pull cleanly past 5,800 RPM. I was going to ask if that meant it was missing, or just stopped making power. If it is missing, your advance curve would not cause this. I think Ian can help get your 123 setup working, but you may have another problem that needs to be found.

[icarp]

To address the point from Walter Mitty. I do agree that fine-tuning will change the horsepower number and have the engine rev higher, my point about fine-tuning the timing at this juncture was addressing the fact that the car was not running well . Fine-tuning the spark at this point will not affect the starting rough running or missing

[mb911]

This is mine. It works really well.

[SunburntLobster]

So i popped all plugs out and checked the timing mark, I lined up Z1 expecting the rotor arm to point to plug 1 but it points to 2!
I tried 360 to see if it aligned with 4 but it lined up with 5.
Is my logic correct the PO may have got the timing 1 out and tried to compensate with 20deg of advance on the 123?