CDI+ advance/programming issue

[mysocal911]

Originally Posted by Jonny H

Many have done, here's one:

Classic Retrofit CDI+: Dyno Results

Read post #106;

"Thanks Johnny H, at last, for the good comparative data. Some of the very small increase in torque
at various points can possibly be explained by the very small increase in advance of the CDI+ over
the Bosch CDI, i.e. for every one degree in advance, the typical increase in HP is about 3-4 HP.

Bottom Line: The 50 year old Bosch CDI technology doesn't "leave much on the table". "

and review the dyno data;

[Jonny H]

Originally Posted by mysocal911

Surely you're aware that simple timing changes can be made by just re-positioning the distributor.

Simple timing changes yes, but a distributor cannot produce a curve with a mid range 'bump' and then a reduction in advance at high RPM which is what these engines respond to.

If you were to maximise advance for mid range power by moving the distributor, there would be too much advance at high rpm and the engine would detonate.

Real world example: a 911RS has peak torque at around 5000 RPM, but the distributor is not fully advanced until 5800 RPM. The factory spec max advance for this engine is around 35 deg. This car was mapped on a rolling road using headphones to detect knock. It responded exceptionally well to having almost 40 degrees of advance at peak torque (5000 RPM) without any signs of knock. Beyond 6000 RPM, knock was evident so the advance was reduced down to 35 degrees at the top end. The rate of acceleration of that car is phenomenal now, even though the headline max HP is no different.

[mysocal911]

Originally Posted by Jonny H

Simple timing changes yes, but a distributor cannot produce a curve with a mid range 'bump' and then a reduction in advance at high RPM which is what these engines respond to.

If you were to maximise advance for mid range power by moving the distributor, there would be too much advance at high rpm and the engine would detonate.

Real world example: a 911RS has peak torque at around 5000 RPM, but the distributor is not fully advanced until 5800 RPM. The factory spec max advance for this engine is around 35 deg. This car was mapped on a rolling road using headphones to detect knock. It responded exceptionally well to having almost 40 degrees of advance at peak torque (5000 RPM) without any signs of knock. Beyond 6000 RPM, knock was evident so the advance was reduced down to 35 degrees at the top end. The rate of acceleration of that car is phenomenal now, even though the headline max HP is no different.

You're joking, right?

[Jonny H]

^ No joke. I guess you haven’t been to many dyno sessions.

Pretty much all profession dyno tuners use headphones. Your ear / brain has more signal processing and computing power than any chip.

There are lots of system out there such as the one below, educate yourself:

https://phormula.com/product/phormula-ks-pro-audio-knock-detection/?gclid=CjwKCAjwyryUBhBSEiwAGN5OCCg_HjiewfZLzqLJS6k F30zGHjkZJfcQC0rPKoYnaOP09dyACzUgZxoC7-4QAvD_BwE

[mysocal911]

Originally Posted by Jonny H

^ No joke. I guess you haven’t been to many dyno sessions.

Pretty much all profession dyno tuners use headphones. Your ear / brain has more signal processing and computing power than any chip.

There are lots of system out there such as the one below, educate yourself:

https://phormula.com/product/phormula-ks-pro-audio-knock-detection/?gclid=CjwKCAjwyryUBhBSEiwAGN5OCCg_HjiewfZLzqLJS6k F30zGHjkZJfcQC0rPKoYnaOP09dyACzUgZxoC7-4QAvD_BwE

Not really! Tuning engines without knock control is problematic, e.g. the 911 3.2.
The variables which are not controllable, typically contribute the most to detonation and can't be fully simulated during dyno runs;

1. High engine load conditions like climbing a long steep grade.
2. A hard acceleration on a very hot day in the high RPM range, e.g. a track day.
3. Compounding conditions 1&2 is having a fuel octane level which is less than what's presumed, i.e. a lower octane than what's listed on the pump. It happens!

Those also buying the so-called 911 3.2 "performance" chip typically overlook these issues too!

[Jonny H]

^ I think you'll find that ears have been around a lot longer than knock sensors. Ears are old tech so you should really like them, no? I'm quite attached to mine.

p.s. Hijacking every thread about CDI+ is getting pretty tiresome.

[Fixer]

Originally Posted by Jonny H

^ I think you'll find that ears have been around a lot longer than knock sensors. Ears are old tech so you should really like them, no? I'm quite attached to mine.

p.s. Hijacking every thread about CDI+ is getting pretty tiresome.

I think it's pretty entertaining !

My CDI+ is working well btw.

[groovydude]

I'd rather end this discussion of the merits of a CDI+.

Getting back to what this thread started with - setting ideal timing/spark advance using a CDI+ in full control mode. I think Jonny H's manual is confusing. I appreciate the greater knowledge for sure. But, in his manual Jonny goes into great detail about the trigger point and an explanation of why half of that is the ideal rotation of the distributor.

My understanding is DON'T CONFUSE ROTATING THE DISTRIBUTOR TO SOME VALUE IN DEGREES THAT'S HALF OF THE TRIGGER POINT WITH DEGREES OF ADVANCE SET AGAINST THE FLYWHEEL WITH A TIMING LIGHT. One is twice the other. And, there's no easy way that I can see to measure degrees of rotation of the dizzy, although I'm sure it's possible.

What I've done is to set my trigger point to 35 degrees by Jonny's recommendation. I used a dial-type timing light to set spark advance to 28 degrees when the engine is at the top of my curve (23 degrees), at 3K rpm. If I were able to physically measure the rotation of the distributor past TDC, I'm guessing it would come out to 17.5 degrees at this mark. But I don't see any easy and accurate way of measuring the rotation directly.

Btw, I believe an advance of 28 degrees at 3K is what Porsche suggests for the 3.0 Euro. We could have a whole other discussion about what's ideal for a 3.0 US with ITBs, SSI headers and a cat delete. I have a dyno session scheduled in a month or so, perhaps I'll have more accurate info after that.