Ignition advance and octane question

[gwagensteve]

I have been running Piggles 660 exclusively on 98 octane fuel.

These engines are tuned for 91 octane from the factory, and have no knock sensor (or in my case, 02 sensor either) so the engine runs in open loop continuously.

As you may be aware, I have a very free flowing exhaust and a much more efficient intercooler than factory. The car is also currently running very rich.

There is no movement in the temperature gauge at all regardless of load. It is running a mechanical fan and shroud, and the radiator is in good condition.

Is there any rule of thumb as to how much timing I can add? I have gone from 10 deg to 12 deg and the engine feels happer (and drivability has improved quite a bit) but doesn anyone have any ideas how much further I can go? I don't want to do it by ear as it's a noisy car and I my not hear detonation.

I know the correct answer is to put it on a dyno but I'm unwilling to do that until I am also willing to buy an interceptor to actually tune it properly.

Steve.

[cj!]

I don't want to do it by ear as it's a noisy car and I my not hear detonation.

I know the correct answer is to put it on a dyno but I'm unwilling to do that until I am also willing to buy an interceptor to actually tune it properly.

There go my first two suggestions. The other option is to build a device to hear what is going on more clearly. There is an article on Autospeed.com about doing this with a Walkman. http://www.autospeed.com/cms/A_2717/article.html

[gwagensteve]

Yes yes, thought you were going to say that.

I'd rather spend the money on a wideband AFR than dyno time ATM, as there is very little I can play with at the moment- I have the miniumum possible boost, (11-12 psi) the best intercooling I'm likely to come across and other than broad fuel trim (via the factory resistor) I only have static timing to adjust.

However, considering the car is breathing freer than stock, its well cooled and I have 7 more octane points than the factroy tuned for, I figured there'd have to be some room. How much is the key.

Steve.

[gwagensteve]

There go my first two suggestions. The other option is to build a device to hear what is going on more clearly. There is an article on Autospeed.com about doing this with a Walkman. http://www.autospeed.com/cms/A_2717/article.html

"The car on which the system was being used is a turbocharged Toyota Prius hybrid"

Ahem... cool.... I think

Steve.

[mightymouse]

A knock sensor is the best method.

There is(was) a kit around that provided a simple visual display, but it does require tuning for specific applications. Also many knock sensors are tuned to their vehicles knock characteristics bu internal masses which can render them less suitable on other vehicles. Easy to say - hard to do.

If you REALLY want to test it, put a pickup on you engine into the mic input, download a FFT scope off the internet and use a laptop. Knock is quite easy to visually detect ( the brain is amazing ).

Thats the way many of the aftermarket guys do it in the eary stages of develpment of knock detection systems.

But its not a 10 second job.

[mightymouse]

Not certain if you have read this Steve, but a bit more info.

Any Bosch knock sensor will do the job as they are NOT mechanically resonant. The bore diameter has a very substantial influence on the knock frequency and spectrum and so a sensor of a V6 holden ( Delco ) for example would be very difficult to apply to your 660.

Positioning is important, not on the head as valve noises will probably be a problem. In general ( and this is VERY general ) mid way along the block 3/4 way up the bore will probably be ok. They are piezoelectric and so can be considered as a special sort of microphone. Depending on the audio system of you laptop you may even be able to use earphones to get an amplified signal, but the background internal engine noise can be a challenge. Try and keep the signal wire shielded and away from noisy electrical systems, especially the ignition.

I personally like the through hole style as they provide a very tight coupling to the block, and of course you can select a fastener that is suitable if an existing boss is located. The contact surface needs to be flat as they can be damaged if bolted to a distorted surface.

And you will need to drive the engine into "ping" to ensure you know what you are looking for - ie the "baseline", so take it easy. The whole thing would be a lot safer and easier with someone else driving.

As you stated before this sort of thing is usually done on an engine dyno with a "disposable" engine ( or series of engines ) so the whole thing is not without some risk, but then finding out you had a problem afterwards isn't a wonderful idea either.