Looking for thoughts on what sort of ignition curve is required for the following motor spec:
1275
270 Degree cam
lightly modified head with S sized valves
98 Octane fuel

Sort of information i'm intersted in are ideas on static advance, advance at 1000rpm idle speed, maximum advance, quick advance, vacuum assist or not? etc.

Not currently interested of what is the best system to use (black box/petronix/123 etc) just what the basic requirements are to having a car that starts easily and drives well.

I gave my S dissy to an old skool tuner who put it on his Sun machine and played with the centrifugal weights and springs to create an advance curve that matched the spec of my engine.

And you could really feel the difference in how the car went afterwards, much more lively, crisper pick up.

While Sun are no longer around I believe King is making these machines again in the US for the local muscle car market. Places like Performance Ignition Services in Melbourne and Kent Town Classics in Adelaide still have them, though I doubt many modern garages do.

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Slide
1965 Mini Van (1360)
1970 Mk2 Cooper S (1310)
1978 Rover SD1 V8 (4.6)
1996 Land Rover Discovery V8 (4.0)

Thanks, I have a friend with a distributor machine who has offered to assist, so I’d like to give him a starting point to work from. What has got me interested is that I just pulled a distributor out of a box of spares, threw it in the car without much thought, gave it a quick strobe timing to 10 deg at idle, and the car went better than before, so I was amazed.

As a starting point use a 10 deg advance plate and have full advance by 4000rpm.

Max advance would be about 32deg at 4000rpm but will depend on the C/R.

Here is the spec for the repro 23D dissy by Accuspark. The issue with a 16deg advance plate is you can't bump up the idle advance or it will ping at high rpms.

Here is the Accuspark 43D dissy and it looks like a 13deg dissy advance plate. Still a bit too much total advance if you want to run a 10 deg BTDC advance at idle.

Swiftune CSI dizzy curves:

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The swift tune charts seem to be more realistic. I have done a fair bit of experimenting with advance curves using the Stealth Black Box. It is way easier than using the spring change method. Only snag is one needs a windows seven laptop for them because that is the only program they ever made. I have an old Windows 7 Laptop which I only use for this. Running too much advance might make the motor sound like it is revving harder and stronger but also hammers the crank shaft bearings which has serious consequences.

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Thanks guru's, gives me a few ideas.

I'm running a 266 cam in 1293 about 9.75:1 CR and S valve sizes in ported head. Dizzy is set up with 10 deg advance plate and modified springs, using about 12-14 degrees static advance on 99 octane fuel. What I found is changing the rockers made a big difference to advance requirements at low rpm:
- A+ sintered rockers ran fine with fairly slow initial advance
- fitted 1.25 ratio rockers and had to use lightest standard Lucas primary spring
- with '1.5' forged rockers ran best with custom very light primary spring
With all of the above the secondary spring was medium strength, and full advance with a 10 degree plate is probably all in by about 3,500rpm.

I also have vacuum can fitted, but here it is important to select a can which does not advance too quickly or by too much. There are a lot of different can specs, check on the 'nose' and you should see three numbers such as 6-13-7 which is start advance at 6 inHg, finish at 13 inHg and gives total 7 degrees of distributor advance. This is probably about the limit for a well tuned fast road motor - would suggest avoiding 3-10-10 and similar cans which give a lot of vacuum advance and are probably best suited to low compression motors.

Thanks Carbon - great information. The distributor i’ve throw in has a vacuum can but I haven’t currently hooked it up. For those of you following this post, I can’t believe the difference a change in distributor/ advance curve has made. Car is much more drivable at low revs, easier to start etc. Has really opened my eyes to how critical this basic stuff is.

I bet your motor will run cooler too. Stock Cooper S dizzy had way too little advance at idle and above, which meant more heat going into the exhaust ports on the head. Probably why they had a reputation for running hot in traffic....

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.