Interesting discussion on timing, fuelling and det

[Chris Wilson]

Techie and long, rather than summarise, have a look at the messages from the forum yourself at:

 

HERE

 

Many of the participants are very well respected professional engine tuners and their input is pretty much de facto.

[Digsy]

Interesting stuff. I kind of skim-read it (seemed to be getting a bit heated part way through).

 

Did anyone actually answer Horatio Williams from Jamaica directly (2nd post from bottom)? His description of how to map the engine seemed like the best approach, but I wonder how many people actually do it this way?

[TLicense]

Seemed to be going in cricles a little.

 

Heres a quick run down of how I saw the conversation:

 

Q. OK you've got detonation how's the best way to sort it out using timing or fuelling?

 

A1. Don't get detonation in the first place. (Obviously didn't read the question, probably fails written exams on a regular basis)

 

A2. (Quite insulting I thought, but I am a touchy barsteward) Don't get detonation in first place. P.S. You deserve to have you engine melt for asking about this.

 

A3. (Slightly off topic) Who cares, just tune the car (Use the force I guess)

 

A4. (Seemed quite condesending) Decide what's causing the detonation, fix it. ie too little fuel - add fuel, too much advance - retard timing.

 

A5. (At last we're getting somewhere) Don't bother advancing the timing, it take's so long to actually work you'd have blown your engine by then.

 

A6. (Not really an answer to the question but a brief how to tune your car)

 

So From what I read between the lines I guess the answer is to add fuel over timing advance?

 

I know you engine tuner guys keep your method's kinda close to your chest, otherwise everybody would be tuning their own car's, but do you think someone would be willing to write a reasonable brief guide of the best way to tune an engine? Perhaps a post for the techinical section of the site as a lot of questions seem to be cropping up about this stuff.

 

Regards

[Chris Wilson]

I believe what they were saying was add octane to stop getting det at your desired boost level and compression, and at a level of advance that offers efficient combustion. Rather than run an insufficient amount of octane and try and fudge things by throwing more and more fuel at it, or retarding timing to extremes and generating a mass of heat. That's how i read it anyway. It's a very interesting mailing list, "Matt" travels Australia and the globe mapping engines, although he specialises in rotary engines.

[Digsy]

Originally posted by TLicense

A5. (At last we're getting somewhere) Don't bother advancing the timing, it take's so long to actually work you'd have blown your engine by then.

 

This is the way it's done on the engine dynps at work, but you're right, you have to run the engine into det to know where to back off. When you're done you have an optimum fuel / spark map but also a partially detted-out engine. Maybe not the best method for one-offs after all, I suppose.

[Chris Wilson]

Originally posted by Darren Blake

This is the way it's done on the engine dynps at work, but you're right, you have to run the engine into det to know where to back off. When you're done you have an optimum fuel / spark map but also a partially detted-out engine. Maybe not the best method for one-offs after all, I suppose.

 

Indeed, a truly optimally mapped engine will have seen many of its siblings sacrificed to the dyno. The real problem, to which i have never seen a satisfactory answer, is how do you map rotary turbo engines? Even a beat of det under high boost usually kills the tip seals, often taking the housings and turbo(s) with them as pot hard material is exhaled down the ports. Only answer i have seen is "experience". Yeah... right! Expensive experience

[Digsy]

Well by bizarre coincidence I'm going for a beer and a curry with our head of R&D on Friday, and he just luuurves rotary engines. Not sure if he's ever worked on one in person, though. I'll ask him.

[Chris Wilson]

I have found that people who love rotary turbos have rarely worked on them, and vice versa

[Justin]

I'm reading a book on Forced induction performance tuning by Graham Bell at the mo. I've just got to the bit about det and retarded timing etc etc. I'm on page 14 so will post back this time in 12 months when I understand it all

 

J.

[Chris Wilson]

If it's the book I am thinking of it's very good indeed. He's written ones on two stroke performance and N/A 4 stroke tuning too.

[Matt B]

Guys,

Am I right in thinking detonation is the same as Knocking??? If so then according to my newly fitted S-AFC II my car Knocks at high boost and when idleling after a good blat. Any ideas what the level is before you need to worry?

Thanks

[Chris Wilson]

Originally posted by Matt B

Guys,

Am I right in thinking detonation is the same as Knocking??? If so then according to my newly fitted S-AFC II my car Knocks at high boost and when idleling after a good blat. Any ideas what the level is before you need to worry?

Thanks

 

Engines only knock at idle if they have about 60 degrees advance in them. Yours won't have, the knock reading form these things is utterly worthless, you might as well look to a crystal ball.

[Ian C]

I thought that the soundest advice was to run a bit less boost so it's safe, if you haven't got the octane.

 

Doesn't someone mention that you start to lose power advancing the ignition timing too far and *then* you get det slightly beyond that? In which case wouldn't a Thor Dyno tuning sesh be ideal, i.e. when power drops off, back the ignition timing off and there you have it, with no detonation occurring?

 

Glad to see professionals get stroppy in emails too, heh.

 

-Ian

[Adam W]

Originally posted by Chris Wilson

I believe what they were saying was add octane to stop getting det at your desired boost level and compression, and at a level of advance that offers efficient combustion.

 

This would be about 20 degrees advance, right? Good info/post, thanks.

[Matt B]

Thanks Chris, I'll just ignore it from now on..... Makes me fell better.

[Keith C]

then increase timing from max boost to 0

psi linearly one degree at a time

 

Didn't quite follow this sentance. What does he mean?

[Ian C]

I think he means:

Starting at max boost, you add 1 degree of timing, and check for det. If there isn't any, add another degree. Continue until you've got the optimum ignition timing, then drop the boost by 1psi and repeat. Do this until you hit 0psi.

 

-Ian

[Keith C]

Ahh. Makes sense.