Guys I'm having a real odd problem with my car.

In the attached data log there is a 1st though 3rd gear pull. 1st gear starting at 20mph..

Heres what i want you to look at.. in 2nd gear @ 5500 and 258 load. My car ran 9* of timing. And didn't knock at at all.

In 3rd gear at around 5500 and 258 load my car decided to run 7* of timing and caused a little spur of knock.


Now heres what i want explained to me. Why did it do that. The octane rating hadn't changed. Why did it just make up that it needed 7* of timing there when it is tuned for 9*

Had the car not decided to run 7 there there would've been no knock at all that pull.


By the way I'm running 280's and a 2.3 Do you guys feel this is about my threshold of 93octane. Or should i back it off a bit?

 

cant say a whole lot w/o seeing your map. I'd go back and look at that area and see if you have some weird low timing cell that pulled it down to 7, and if not I believe what is happening is the logger isnt picking up on the knock as quickly as the ecu is picking up and correcting for it, meaning that 7 is there b/c the ecu already pulled some timing but the logging didnt pick it up.

 

typically the lower the gear the leaner the car, so in the next gear it was richer that got rid of the knock.... the higher you go up as far as gearing the less knock youll notice.....

if you were tuning very aggresively for 3rd gear, you would getting a little knock in 2nd and a little more in 1st, but none in 4th and 5th.


if you make that area a little richer youll fix your 2nd gear knock, but will make the rest of the gears richer in that area and it may end up slowing you down in the long run even though you lose a little power in 2nd.


if you drag race i would leave it how it is, because ur in 2nd gear for a very short amount of time, youre in 3rd and 4th much longer and thats where you need the power.

cheers!

 

opps i misread what you wrote, for it not to knock in 2nd then knock in 3rd is aqward and doesnt make sense... lol

what are you afr's? do you have a wideband?

 

why would he pull it down to seven if its running 8... the ecu basically tells you exactly what it wants....

if youre going to change it.... try 9 see if it knocks, it shouldnt, if it does then put it to 8 where the ecu dropped it down to.

 

its nine all around pretty much a small version of block timing in that area.


my afr's are all different depending on the temp but that night it was like

11.9 1st 11.7 2nd 11.5 3rd and so on.


Cass.

 

Logger may have been slow... The knock caused timing to be lowered to 7 if you really had 9 on the table...

 

I'm not having a go at you here, but for crying out loud- the ECU pulled 2 Degrees of timing BECAUSE it detected knock.

The knock made the timing go from 9 to 7, not the other way around.

MB

 

try running 8* in that area and do a few more pulls to see if you get that knock. if you still do, take another degree out, OR you can try to richen up the AFR a tiny bit. maybe instead of running 11.5 in 3rd, try running 11.3.

 

I'm not having a go at you here,

But for crying out loud.

... The octane rating hadn't changed so the ecu shouldn't of pulled any timing.

As the octane rating gets below 255 the ecu will start to take an average between your low and high octane maps the lower the number obviously the more it will pull. but at 255 it is running 100% off your high octane map.

That is my understanding of how things work. Correct me if I'm wrong please.


Cass

 

Hi

Sorry onrails, but your wrong. The ECU will pull timing without decrementing the octane number, if I remember rightly the ECU will pull deg for every 3 counts of knock and decrement the Octane number once 9 counts have been seen. I'm sure those better at the disassembly will know the exact figures.

MB

Looks like 6 counts will lower the octane number.

 

^ +1

yes, this is true. your car can still pull timing from the knock, and your octane flag will not change. i've seen this in my logs numerous times and i've seen it posted in other threads. from what i've experienced 1* of timing is pulled for every 3 knock counts. once i hit 6 knock counts, my octane flag will start to decrement (ex. 255 to 254...and so on).

i still think you should take out a degree or two out in your map and relog.


btw...when you log your runs, make sure you do a complete pull. 2500rpm-7200rpm (in 3rd gear) on a nice flat EMPTY road, and try to do at least three for comparison.

 

I'd like to see some timing patters for other 280 cam cars. Do bigger cams seem to make these motors more knock prone with less timing.

 

lol at the misinformation in this thread...

not having knock in 1st and 2nd is common, they are short gears with little time in big boost and do not create as much heat... as you get into 3rd and 4th gear the engine is getting very hot and will often knock. This is why you tune in 3rd and 4th...also you'll get much more data per rpm range in a longer gear.

the timing was lowered due to knock

for good measure I often make 3 or 4 pulls in 4th gear back to back and then tune out the knock. This ultimately gives me a margin of safety.

 

also if you're using an MBC (not sure with any other type of boost control) I typically see a higher spike of boost in the higher gears. So that can play a factor.