View Full Version : advancing/retarding ignition.?
why would you
advance the ignition..?
retard the ignition..?
and also what are the pro's and cons of doing so.?
one leads to steam from your exhaust, the other leads to flames :D
there is an optimum ammount of advance (all ignition timing is "advance" since it always occurs BTDC) for any given point on a map of load vs. RPM.
usually OLD factory turbo cars won't be anywhere near the optimal point since the manufacturers don't want their cars going bang. Advancing a few degrees yeilds some extra power because you've brought the ammount of advance closer to optimal. If you go too far you run the risk of detonation. Normally you'd set your boost limit on your new engine then bring the advance up as far as you can safely. Boost should dictate the amount of advance, not the other way around. For this reason if you want to run a lot of boost you sometimes need to think about retarding the ignition. But, you need to keep those optimal values in mind, if you retard too much then you're wasting your time with that extra boost, you'd have been better dropping the C/R.
There's never any hard and fast values for a 1 off engine, only rules of thumb like the above, those that have tuned enough of a particular engine will have a good idea of how much advance they want and will probably have already chosen a suitable C/R with that in mind while building their engine.
jantheeven
08-11-2008, 14:12
(warning: ignition noob :D)
What's C/R? How can I check if the ignition on my 5 is retarded or advanced? And how do I adjust it?
c/r. cubic ratio.
cheers for the info scoff, i still find it a bit of a headfcuk to be honest! i think ill leave it as it is to be on the safe side...or is it the safe side:confused:
New poster! (less than 10 posts)
C/R is the compression ratio.
The ratio is the volume of a cylinder with the piston at BDC (Bottom Dead Centre) compared to the piston at TDC (Top Dead Centre). Hence 8:1 ratio, with the piston at TDC the volume is 8 times smaller than when it is at BDC.
Make sense?
jantheeven
08-11-2008, 18:51
Makes a world of sense ;)
But how can I see how many degrees my 5 fires BTDC and how do I adjust it, if necessary?
Rob@Backyardracing
08-11-2008, 19:32
The timing is fix on the GT but there are ways to adj it such as modifying the TDC pic up or swaping wires over on the lead.. The best way to check timing is with a timing strobe to the fly..
jantheeven
08-11-2008, 19:33
Thanks...
But maybe advancing isn't such a good idea for my engine... I run 23 psi... don't want knocking to happen!
jantheeven
08-11-2008, 19:35
Sorry Raj... I'm stealing your thread :laugh: :ashamed:
Rob@Backyardracing
08-11-2008, 19:45
Thanks...
But maybe advancing isn't such a good idea for my engine... I run 23 psi... don't want knocking to happen!
Get some det cans :)
Alastair
08-11-2008, 20:26
You could always run a mega squirt standalone ECU but only use the wasted spark ignition - although it would be a lot of effort not to control fueling too?
Sorry Raj... I'm stealing your thread :laugh: :ashamed:
its ok mate, its still relevant to the thread :)
jantheeven
08-11-2008, 20:39
Get some det cans :)
:confused:
det cans = earphones with a stethoscope pick up, or if your a cheap skate like me then just an engine stethoscope, bolted to the cylinder head.
jantheeven
08-11-2008, 21:18
I see... is that really necessary though? I mean... you can hear knocking from the cockpit whilst driving, can't you?
I see... is that really necessary though? I mean... you can hear knocking from the cockpit whilst driving, can't you?
detonation has to be really bad before you'll hear it inside the car. If your engine is under a lot of stress it doesn't take much to kill it, it'll often be dead long before you heard detonation by ear. If you want to push the limits of a tune you need some way of monitoring detonation.
in my case it's doubly hard since I have nearly no silencing, a 40mm screamer pipe, no interior or sound proofing and noisy tyres. You couldn't shout, let alone talk to a passenger in my car at wide open throttle, you definately don't hear what the engine's doing!!
Rob@Backyardracing
08-11-2008, 22:59
I see... is that really necessary though? I mean... you can hear knocking from the cockpit whilst driving, can't you?
:eek: Woooooooo
Rob@Backyardracing
08-11-2008, 23:05
Scoff you need a passenger ;). i feel it helps alot more as i struggle to look at laptop afrs, boost, rpm, speed, and try to hold the steph tight in my ears to cover the noise...
Scoff you need a passenger ;). i feel it helps alot more as i struggle to look at laptop afrs, boost, rpm, speed, and try to hold the steph tight in my ears to cover the noise...
I need a passenger seat before I need a passenger :cry: will have to invest in another silly allu chair next year.
I see... is that really necessary though? I mean... you can hear knocking from the cockpit whilst driving, can't you?
You can if you have a quietish car and are sufficiently perceptive and also have good working ears.
I made some Electronic det detectors using a Peizo sounder as a microphone and amplified it to headphones.
They were great, could hear every detail in the engine. Could hear the knock before it turned into a pink.
I was also able to deduce that it gave me no extra information as I could hear all that anyway.
But....with a larger cam and old rockers, ie, not re-ground to remove the edges worn by the smaller cam, the engine tapeting noise was overwhelming the knocking sound which could no longer be heard with the electronic detector. But I could still just about percieve it by naked ear and also one feels it somehow.
Rob@Backyardracing
08-11-2008, 23:14
I need a passenger seat before I need a passenger :cry: will have to invest in another silly allu chair next year.
Just get a GT seat and pull it out after testing. I take my seat from my 16v for testing, bit of a pain. Mined you dont you need two seats for TOTB
Just get a GT seat and pull it out after testing. I take my seat from my 16v for testing, bit of a pain. Mined you dont you need two seats for TOTB
yes, 2 seats and working belts for totb, I just fancy a matching pair. maybe the passenger chair could be on pins for quick release !
Rob@Backyardracing
08-11-2008, 23:23
mines only held in by 4x M8s.....mind you ive welded my frame to floor :crap:
its the ballache of getting the spanner/rathchet into the spaces under the seat, I'm a lazy sod, I'd just have it on bonnet pins or something, remove it for MOT :D
jantheeven
08-11-2008, 23:53
det cans = earphones with a stethoscope pick up, or if your a cheap skate like me then just an engine stethoscope, bolted to the cylinder head.
well I have absolutely no idea what to listen for... so probably best to let someone who knows what they're doing listen ;)
jantheeven
09-11-2008, 20:14
Final question... since I now have a wideband lambda kit I can see what the AFR is at all times. At full boost (23psi) and WOT it doesn't go leaner than high 11s, which is good, right? Doesn't this mean that there's very little or no det risk? I mean... isn't the det risk higher when you're mixture is too lean? Or is it really an ignition timing thing?
no, the det risk is there regardless of AFR.
jantheeven
09-11-2008, 20:54
thanks :agree:
dave j gtt
09-11-2008, 23:21
I need a passenger seat before I need a passenger :cry: will have to invest in another silly allu chair next year.
yeah when i came down wouldnt of been much fun to go for a a ride in your car like :( would of ended up doing tourqe head stands in the back no doubt :laugh:
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