[cobra2326]

This post on h-t has caused my interest and question:

More boost certainly doesn't make a safer tune. Adding fuel and retarding timing will make a safer tune but retarding the timing too much can cause excessive cylinder temperature which isn't good either. Having a good standalone and a good tuner are the keys to a good tune.

Can you explain why retarding timing increases cylinder temps? Think about it, overretarded timing would mean that peak burn rate would occur too far after TDC, which simply means that less of the pressure generated by the burn would contribute to pushing the piston down, as the piston would tend to "run away" from the burn. However, the burn *should* still be complete. Perhaps this delay in burn, when delayed too far, can cause the burn to happen into the exhaust stroke, which would mean *much* higher EGT's. HOWEVER, this is really not detrimental to the actual combustion chamber and should NOT have an effect on peak cylinder temps, as the peak temp is still the same (possibly less). The only real effect is that the EGTs are higher b/c the burn happened closer to the exhaust stroke...

Am I correct in my reasoning here? I mean, theorhetically, you could retard the timing to all hell and it shouldnt matter since the next stroke will always be the exhaust stroke, and there is basically no stress on the engine during that stroke.

 

[tepid1]

You are correct and you basically, minus adding more fuel, explained how EMS's use anti-lag to spool a turbo....

You will put more heat and stress on the turbine wheel and manifold with the increased heat.... I have yet to see a damaged turbo though. I have this feature on my stock ECU with Neptune. There are other EMS's that support it too.

EDIT: You are also correct in assuming that the EGT's are higher because you are moving the burn closer to the exhaust stroke....

Great post!

 

[cobra2326]

Ok great, so Im going to start with a base retard of 1* per psi and Ill know its safe. Everyone has a damn opinion and people have been saying "retarding too much is bad as well, because EGT's are higher...". Of course, I beg to differ, lol...

 

[Far_From_Stock]

I've been reading alot of your stuff concerning FI and tuning, etc. and you seem to have a pretty strong grasp of what you're talking about. By posting stuff like this, it's helping me with my tune too, assuming it's accurate, which it sounds to be. Thanks!

 

[cobra2326]

I've been reading alot of your stuff concerning FI and tuning, etc. and you seem to have a pretty strong grasp of what you're talking about. By posting stuff like this, it's helping me with my tune too, assuming it's accurate, which it sounds to be. Thanks!

I dont claim to be the ultimate source, Ive basically just taken my knowledge from the articles on here, on evans-tuning, and on pgmfi.org, and on reading of a few books and applying it. Hopefully someone will correct me if Im wrong as to not spread misinformation...

 

[tiger6386]

you ever heard of paulo freire? I wonder if tuan has himself

you never know to spread misinformation if you don't critically think about it. The quote you quoted probably came from a question itself, and matured into basic information; you're the effect of it making it into refined information, or possibly knowledge if it can't be further simplified into more critical thought.

~P2P

 

[tepid1]

Ok great, so Im going to start with a base retard of 1* per psi and Ill know its safe. Everyone has a damn opinion and people have been saying "retarding too much is bad as well, because EGT's are higher...". Of course, I beg to differ, lol...

It sounds like you know what to do....

1* /psi is a great starting point....

I find it easy to tune a car on a dyno (of course) and find the motors MBT. once you do that then you can back your timing off a little bit, about .5* or so then tune your AFR's to the boost tables. Of course it is not just that simple as you most likely know, but that is the rough deal.

Are you tuning a VTEC motor or will you be on one map only?

 

[cobra2326]

Yeah, its a VTEC motor. Right now I have the rev limit set @ 6500, vtec disabled and a really rich tune b/c I have an open dp. Soon I will tune the low cam to a flat 11.8-12:1, then tune the other cam separately and merge the two where the fuel maps cross.

Already the motor is fast as crap and I love it! Full boost is around 5k rpms and there is definitely some lag, but Im happy with it.