boost retard ignition timing

[CHB]

I'm not clear about ignition timing on a turbocharged engine.
take example my 3T-C, i've converted to MS2 and all EFI bits. from what i'm understand,
for the ignition map at vacuum "area", we should reached maximum ignition timing by 3000RPM, take 30degree BTDC.
by that time my turbo already start making up boost. now we've enter boosting "area". we should retard 1 degree for 1psi of boost. if i'm making 30 psi, at full load i'll be at 0 degree ignition timing?? that is impossible won't it.
i've referred to Microtech forum, ppl advance their ignition to the max degree by 3000RPM from the Trpm, then they will retard the timing 1 degree for 1 psi of boost too. but they retard until 24 or something they won't retard it further no matter how much they are boosting. will this cause the engine to detonate?

[thechuckster]

at a guess - yes, setting an arbitrary retard limit like that is likely to make it detonate.

Unless the meant to say retard a total of 24 degrees?

My timing map pulled out a lot of timing in the higher boost areas (e.g. down to <10 degrees) but i never got anywhere near 30psi so it's a bit academic.

[JZA70 R]

Put your car on a dyno with some form of trustworthy knock detection and use the dyno to tell you what timing vs hp vs knock you can run.

for example.

you keep adding timing until either peak hp is reached, or detonation starts to occur. then you can remove 1 or 2 degree's of ignition timing for reliability's sake.

peak horsepower can be achieved much earlier than your engine is willing to take timing so dont ever tune in timing to detontation without checking hp because you could have peaked horsepower and then started to lose it at the detonation threshold.

[CHB]

the MAIN problem is, i can't access to any dyno here at my area, the nearest i can go is 1000km away in Brunei. so all i can do is "butt dyno" hehe

[MS-75]

Order yourself a knock box and do the knock detection on the road then.

Road needs to be reasonably smooth and straight so you can load the motor up smoothly without too much road noise.

There's no hard and fast ignition retard rule as all set-ups are different.

Sean

[YLD-16L]

you keep adding timing until either peak torque is reached or detonation starts to occur.

Fixed.


Without access to a dyno take Seans advice and get your hands on some decent knock detection and then get a logging device that can accurately log vehicle rpm against time (and MAP if possible for reference sake) and perform single gear runs (i.e. 4th gear from 2000rpm to xxxxrpm) on a flat or inclined road (that doesn't change gradient during the run) at WOT on preset boost levels eg. start at minimum boost the wastegate can run and work up by 0.5psi - 1psi increments adjusting timing as you go until you reach your target peak boost level.

You will need to do a lot of passes to get it right and for the areas of the timing map you can't access using the above technique you should be able to extrapolate from the data you have gained anyway.

You are aiming to acheive the shortest times to move through the selected rpm range as this is the indicator you are increasing torque (increasing times mean torque has decreased). You just need to keep an eye on knock and as JAZ70 R said back off 1-2 degree from the point you detect it.


The above is tedious but doable, just try to limit the environmental variables as much as possible and use the same stretch of road each time.
Controlling the boost by means of the wastegate/controller and doing runs at WOT (instead of simply controlling by throttle only) is used to minimise boost variance during the run and make the runs easier to repeat (hence logging MAP can be useful for validating the other logged data).

[CHB]

lets assume, if i'm in 4th gear, at 2000RPM, i keep my right foot all the way down, i still need to wait the boost to build up though. i think i need to find a really long section of road to do this tuning, may be on an isolate highway...

[YLD-16L]

Using an incline or riding the brakes a just little to begin with will create additional resistance and will help build boost quicker.

You can do it in 3rd or even 2nd gear but everything will happen much faster and minor variations in time V rpm will be harder to detect.

It's all pretty hard and dodgy to do on a public road though so be careful/do it at your own risk.

I have no idea what Sarawak roads or laws are like though?


NB. You are only interested in the time lapse for the rpm range where you are at the desired boost level for your test run.

[CHB]

one more thing, if we adding ignition timing throughout our tuning, do we need to richen the AFR also? so which one comes first? AFR or ignition timing?
i guess once we adding timing, it will lean out the AFR also isn't it?

[YLD-16L]

This is a common method but someone may have a better way:

Set conservative timing values
Tune A:F (I start on the slightly richer side of my target at this stage)
Fine tune timing values while also monitoring A:F
Fine tune A:F while monitoring for knock
Check through load and rpm values for knock and any A:F values that need tidying.