ignition timing

[seniorchristo]

My engine is a 1700 with 10.5 compression and fast road cams (.420" lift and 275 degree rotation). I am using a Lucas 40953 distributor. When setting initial static advance at 12 degrees I get a total of 26 degrees which is aligned with the workshop manual specs. When I advance to 30 degrees total the car runs great but there is slight detonation at high load low RPM's. I would like to recurve the distributor for 12 degrees initial and 30-32 degrees total.

Has anyone experienced similar symptoms and made similar changes?

Thanks
Chris

[mbell]

I skipped the re-curve and just went to 123 dizzy where I can program the curve myself. I also found my standard big valve (i think) engine likes 30-32 degrees advanced and to get there quite quick rpm wise, as other as reported on here. (A few people have shared plots of there 123 curves)

I was exchanging messages with local shop that looks after exotics, inc older ones, one webber jetting and he suggested that modern fuels with ethanol burn a bit slower, so a bit more advanced helps counter that.

[seniorchristo]

123 ignition would be a good yet a very expensive solution. I think they are around $550.

[Quart Meg Miles]

Stop stamping on the loud pedal at low revs!

[JohnCh]

Another 123 convert here. It's not cheap but it has a number of features you won't get in a regular distributor. On US 92 octane fuel, dyno tuning my engine resulted in 32 deg by 2500rpm, increasing to 33 deg from 3000rpm to redline. The engine is a '68 SE with Euro-style intake manifold, Strombergs converted to adjustable needles, and an RD Enterprises exhaust manifold.

-John

[mbell]

123 ignition would be a good yet a very expensive solution. I think they are around $550.

Yes they are expensive and not for everyone. I classed buying it as treating myself. When you consider your probably $200-300 for a rebuild and re-curve on the standard lucus unit the price difference is a bit more manageable IMO.

You also get some features for the extra money, like better quality/reliablity, programmable curve, immobilizer functionality, gauges on your phone.So you are getting something for the extra money.

[seniorchristo]

mbell

What static timing do you use when running 32 degrees total advance?

Thanks
Chris

[mbell]

What static timing do you use when running 32 degrees total advance?

Looking at my graph, I am running 15@~1000rpm, and rise quickily from there, total advance is actually 34.

The static setting was found by adjusting the advance to find the advance that gave me highest rpm.

[JohnCh]

Here is a screenshot of mine from the 123 interface:

[seniorchristo]

123 looks like the way to go if money is no object
Thanks for the info!

[seniorchristo]

I'm going for the 123 distributor. Available at Holden's for 12% off

[rgh0]

On my Elan competition engine which runs on normal premium unleaded and 10 .7 compression ratio I have 32 degrees maximum advance with 12 degree static advance. The 20 degrees of advance comes in as a straight line from 1000 to 3500 rpm then flat 32 degrees above that.

Having 32 degrees at 2500 rpm would cause knocking in my engine at large throttle openings but it really depends on your local fuels and carbs ( Stromberg appear to want more early advance than Weber) and cams, so you need to test your settings carefully

cheers
Rohan

[mbell]

Far from an expert but I also think it has a lot to do with the fuels available. I run my car on US 93 (Ron + mon /2) premium which is quite a bit higher octane than UK premium (and maybe Australia) at 97 Ron, probably due to high ethanol content. Which also likely effects (slows) the combustion process.

I suspect that's why I can get away with similar aggressive advanced curves (see image) with no noticable problems. I tend not to stomp on the throttle at 2000 rpm thou. I'd probably need to charge out the curve if had to use different grade of fuel (another advantage of the 123).