WS6FirebirdTA00

iTrader: (33)

so my map went from 99-98 kpa to 95-97 after pulling some timing. also, it was slightly rich. if i get the AFR right, would looking at the change in MAP be a good reference for how it changed the car? IE lower map means less power or bad changes?

Another_User

I think that you need to make your runs back to back and make more runs and use some averages. Pulling timing will make you run a little more rich, but you should have seen less vacuum...I would think. For example, at idle if you increase timing your vacuum goes up, so at WOT I would expect the same. Lower KPA is more vacuum. The only way I can see this happening for real in your case is if your timing exceeding the real max torque timing and your car actually runs more efficiently with less timing. Which could be proven on a dyno. How many degrees are we talking here (before and after)?

jimmyblue

iTrader: (11)

Lower MAP means you are drawing down the intake
plenum, against the inlet restrictions, more effectively.
I would take it that cylinder filling / evacuation has
improved. Though why that would result from -less-
advance, I have no idea.

Low MAP = higher vacuum, more vacuum signals more
efficiency.

WS6FirebirdTA00

iTrader: (33)

ok now you have me looking at it right lol. timing was changed by 3 to 4 deg depending on the rpm. it was also running slightly richer but nothing crazy, maybe 0.2-0.3 but thats just a guess based off my o2 numbers. i did this in 3 back to back runs today. the other night logging with more timing i consistently was at 98-99 kpa and today it was 96-97 and very consistent. just something i noticed in the logs and was curious about. maybe less timing gives more time for cyl pressure to increase so when it sparks there is better combustion? gotta think about this one haha but it is definatly consistent. im going to check my other logs as well.

Another_User

How many degrees are you running (before and after)? 28? 29? It sounds like it is time for a few dyno runs or quarter mile runs to see if less timing is more power for you. It sounds suspicious to me though. I was reading the other day that on pump gas you can't really advance timing and get less power before you get detonation, but it could have been B.S. (the source seemed very reputable and they had dyno charts to back it up though).

WS6FirebirdTA00

iTrader: (33)

i was running from 29-31* WOT and went down to 25.5-29*. although its hard to tell if the car is faster or not, but i had more wheel spin with less timing. so maybe the dip in timing helped out the tq? ive gotta get on a dyno to play with this just havent had the time or money.

Another_User

Based on what most people seem to run, it sounds like your timing was advanced too far. I always had good luck with 28 max at WOT.

WS6FirebirdTA00

iTrader: (33)

yeah i knocked it back some for that very reason.

redtail2426

iTrader: (10)

dont get caught up in the more timing is better thing.My car runs best at 26*,at 28 i sometimes get KR,not always but here and there.At 26 i get none,look for consistant timing.

WS6FirebirdTA00

iTrader: (33)

i got none at 31, but im trying different things and testing what other people said was their best. the curve i have now seems to be a lot better with less timing. i know most are getting best results 26-28

TPiS

At TPIS this is the way we do it on the engine dyno. After a warm-up and a base cal, which is usually the customers base cal. we will make a pull. find peak torque, say 4500 rpm. We use the dyno to hold the engine at that rpm. we note the timing at rpm. let's say 24 degrees. we make a change, say 22 degree, with it this low I would expect a loss of torque. next test we would raise it in 2 degree jumps untill we find the max. We would then go to peak hp and do the same thing. It is very important that the oil and water temps are at the temps you are going race at. and of course your using the fuel your going to use. Depending on the lenght of time at full throttle we may back that number down a smidge.

We built the engines that won the SCCA'S T-2 in 2003 & 2004 And the top finishing Corvette of Leighton Reese's in this years World challenge.

Myron Cottrell, pres--TPIS

WS6FirebirdTA00

iTrader: (33)

thanks for the info. thats waht i was thinking should be done. now i just need to find a dyno that its a million dollars to rent out haha.

MadBill

The MAP value has basically nothing to do with timing. It's really just a measure of how good the engine is as an air pump vs. how much restriction there is in the intake system upstream of the sensor. The most likely explanation is that the atomospheric pressure dropped betweeen runs. The MAP value should be a constant 'delta' (difference) from barometric pressure. e.g.: first run baro was 102, delta 3.5, thus MAP= 98.5. Second run baro was 99.5, delta 3.5, MAP was 96. BTW, a delta of only 3.5 kPa is really good in my limited experience...

WS6FirebirdTA00

iTrader: (33)

i understand what map is, and i can go out there right now and swap tables and see my map change, same day, same ATM press, same everything except for timing. it just stood out in the log as not being normal and figured i would ask about it, i thought it was quite strange.

Another_User

If that were true, then ignition timing would not affect engine vacuum at idle either. Sorry, but ignition timing affects the efficiency of the engine and could definitely cause MAP differences.

jimmyblue

iTrader: (11)

For example you might think that a charge that was
burnt late is still hot and higher pressure at exhaust
valve opening, blowing more of it out and leaving less
residual gas in the cylinder for intake dilution. More
inhale makes lower MAP.

Whether this makes more power, torque depends on
the pressure pulse in relation to crank angle. It's the
pressure -tail- that (plus piston push) evacuates the
cylinder. Don't know how strongly connected the
two are. Got to be many other variables.

WS6FirebirdTA00

iTrader: (33)

maybe ill get money for Christmas and can go to the dyno and find out lol

WS6FirebirdTA00

iTrader: (33)

this may work

78-88 mph, 29-31* timing WOT 98-99 kpa 1.038 sec
78-88 mph, 25-27* timing WOT 96-97 kpa 0.892 sec

both were WOT runs in 3rd gear, strait flat road. Dynamic airflow also increased from 345 g/sec to 352 g/sec at 6000 rpm. Granted there will be some sort of error in the numbers but the WOT run is a pretty damn close est, at least it shows it not slower lol. Both runs were done around 45* temps as well.

P Mack

iTrader: (6)

The reason timing affects your vacuum at idle is because your iac changes to keep your rpm the same. If you lower your timing, your rpm goes down, your iac opens more, your map increases. And vice versa. I don't buy the idea that a small change in timing at wot would have any measureable effect on manifold pressure.

WS6FirebirdTA00

iTrader: (33)

im not trying to make anyone buy ideas, i just wanna know why lol. EVERY SINGLE LOG i have with the higher timing, no matter what temp and baro pressure 98-99 kpa consistently. EVERY log i have with lower timing consistently 95-97 kpa no matter the temperature. if you can give reasons as to why please do so. i leaned this log out to the correct AFR and the map did not change. its odd but makes sense to me. those 3rd gear runs i had show somewhat of a truth to it. i chose 3rd gear compairison because i have the best traction in 3rd. my street and track runs were consistent with the times in 3rd gear, and my runs with this timing table are a good bit quicker every WOT pass i have made. and i compaired the time with several logs.