RedWS6 00

I hope someone can help, around 4000 RPM i have a dip in my table, this has NOT been adjusted by myself and beleive it to be the factory setting. Would the car go better is this was flattened out? or is it there due to the profile of the cam. I'm new to all this, so probably sounds like a newb. question.

Picture of capture should be attached......

tars7

iTrader: (3)

looks just like my 2000 m6 graph. I think thats factory, but I can't explain it at all, maybe someone else can jump in here.

Checkmate

iTrader: (2)

You can smooth it out a little. I've seen a few cars that don't need the dip at all and other that do, like mine.

WS6FirebirdTA00

iTrader: (33)

mine is totally smooth. why would you need the dip? only if you get kr right?

RedWS6 00

Thanks for the fast replies, I'll try to smooth it out and see what happens, I guess it will feel different and get some retard. I'm running on 98 octane fuel and off down the drag strip in the morning, this drag strip is only on once a year, not many others around. So trying to get much tuning done before hand, can also do some there.

I'll smooth it out and let you know how I got on.

WS6FirebirdTA00

iTrader: (33)

i think that was there at peak torque to prevent knock, or something like that, now that i think about it. someone posted something about it on here to my question about it

RedHardSupra

iTrader: (1)

that'd be me torque is a direct result of cylinder pressure, so you spot your peak torque, and might wanna take it a bit easier there on the timing.

WS6FirebirdTA00

iTrader: (33)

but you would know its too high by seeing knock right? i just dont like the jumpy values in the stock table, i feel like the smoothness helps the car run better

RedHardSupra

iTrader: (1)

If you're seeing knock then you're definitely too far with timing.
Timing doesn't necessairly follow the blackjack rules (go as high as possible without busting over a certain limit). Increasing timing is almost a dirty hack--it increases cylinder pressure that should've been there in a first place. Notice how timing changes from 853 to 241 to 243 heads. the better the head flow, the less the timing. you can go even farther, ask forced induction guys, how much timing they're running? 15 degs maybe? why? because they already have all the cylinder pressure they can handle, and pushing it any farther can be dangerous. When the engine can take Lots of timing to me it means it flows poorly. You shouldn't need ridiculous amount of timing to run well. Someone on vette forums took a stock z06 and run 22, 24 and 26 degs of timing, and it made NO difference. My car (853 head) made <5rwhp difference by going from 24 to 29deg timing. 29 still didn't knock, but I'm not gonna trade my reliability for 5hp.

the real bitch with timing is how it affects AFR. i completely don't understand the why and how of it, but don't expect to change your timing and have AFR stay the same. I did 13 pulls on the dyno, and i found NO rules that would make me able to predict which way and by how much AFR is gonna move based on my changes in timing. If anyone would like to explain this one to me, it would be greatly appriciated.

as for smoothness, yes, there is a point to having smooth tables in general. 'nothing in nature is jerky' as my physics teacher used to say. so just make sure you don't have any abrupt changes, but don't go crazy with the smoothing button either.

WS6FirebirdTA00

iTrader: (33)

i compaired my stock tables with the ones i have now and made sure if the timing went up it didnt go up but a degree or 2. most people i read doing timing changes increase until knock. i dont wanna go that far and back it off i just wanna get a little more down low with the cam and reduce it up top.


the afr changes because of waht im about to say, dont know if you know about the details or not but ill go into what i know at least. then fuel burn is not instantaneous it takes time to burn which is why you start the burn before tdc. you want to get the pressure built up enough in there to give you the most power but you dont want to run too high or it will detonate, which is why i think its safe to increase timing as long as you have no knock and dont go wild with it. well if you start the fuel burn too late you dont burn all the fuel and it will make you richer, if you start the burn too soon it burns it all up too fast and it goes lean and knocks. if you find a good spot in there where you can make power and not knock thats where you want to be, i think more timing is for the cars that dont have all the little tuning details figured out and may be too rich, leaning it out will give good power. but if you get everything in line then most wont see a diff above 26 deg. i have mine set at 26.5 and went up some and saw no difference in the way the car ran so i will back it out some, plus my pe is set too rich (wanted to be safe when i started to tune)

i just smoothed the timing out and added some to the lower airflow for the cam so it will help low end response, i still have to go back and rework my timing to not be so high at the other end. i compair it to stock and make sure my values dont vary by much. even though there is a big dip there isnt a big difference in the timing if you smooth it. i just feel smooth transistion helps the car run smoother. i don tknow if i made sense or told you anything new lol. with the cam im just making sure under 2500 i have more timing than stock and above it with the better heads i will decrease it some or put it around stock setting.

technical

Simply put. Pressure and temperature being directly propotionate will cause preignition with too much timing. You drop the timing *advance* curve somewhat proportionally to the increase in pressure which will in turn increse temperature thereby making it ignite faster. That's the reason you don't need as much timing in those "high pressure" areas. The reason AFR is affected is due to the efficiency at which the mixture burns via the spark. Too early or too late of a spark will cause changes in AFR. You're still putting the same amount of air and fuel in the engine, but will burn it differently based on timing causing your O2 sensors to think you're off the mark.

If memory serves, too late on the timing makes it rich. Pressure and temperature drop so it becomes harder to igite the entire mixture efficiently. Throwing extra HC's into the exhaust.