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Old 02-23-2009, 04:57 PM   #1
JSarv
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Join Date: Nov 2007
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Location: Effingham IL (Central IL)
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12.07@115.9mph-EJ205

Default MBT timing on the E vs Boost

I'm not a complete n00b at tuning, I have an 02 18g making just over 340wtq and 330 whp on a stock 205... E85 AND YES 85% even in the dead of Illinois winter been tested every 2 weeks with an average of 85% and as high as 88%

I've read up on and studies timing and its overall effects. MBT and how close one should be to mbt to keep things safe... I also realize that more timing = more cylinder pressure = higher torque = stress on bottom end = Lower EGTS.... So more torque and lower egts but more potential for disaster...

Its basically been tuned using feel - det cans - stock knock sensor - road dyno graphs for knock detection.....

No one really will come out and give a rough estimate of MBT on the 205, I realize with a dyno mbt can be found, or well it can be found with the proper fuel...

I'm running about 22psi in the midrange tapering to 20psi at redline (stupid 7cm2 housing)

When does one stop with timing? I do road tuning so there are some variables that make me a bit nervous on bumping up the timing, but everytime I do it seems like it just keeps making power...

I'm running E85 - which seems to make things more difficult/easier - Able to run more timing, but actually probably could run to much.

I see 22.5psi by 3300 rpms and timing is at 15*btdc basically slowly rises to 24*btdc at 7000 rpms...

With the stock td04 I ran about 16* of timing at peak torque and 34-35* at redline. I know the 18g is much different but were do I stop?

I'd like to have a good map to take to the track - and keep what I have now for street use.

I keep my afr's a bit rich for E - around 11.6-1 afrs under boost...

-Jerod

Hopefully once I reach a comfortable point I'll run it up to P&L and have Jorge do some runs on the dyno to back up my road dyno results..
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Old 02-24-2009, 10:49 PM   #2
bcblues
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You can roughly estimate when you are containing most of the combustion in the chamber, as opposed to the exhaust, by monitoring your EGTs as you slowly increase timing. They will (or should) drop until you reach your MBT, then plateau, or even rise. Anybody verify this?
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Old 02-24-2009, 11:26 PM   #3
JSarv
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Join Date: Nov 2007
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Location: Effingham IL (Central IL)
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l33t *******
12.07@115.9mph-EJ205

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Thank you! You definitely schooled me!

I knew EGT's dropped as timing rose but was not aware of a plateau or a rise once mbt was reached...

I have one in the mail coming my way, but until now (or until its in) I've kept things (what I honestly think) conservative.

I say conservative judging by other datalogs from tuned cars and reading and rereading anything I can find on tuning strategies. But it seems that the more timing I throw at the car- the more torque it makes...

Thank you!
-jerod
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Old 02-25-2009, 12:58 PM   #4
bcblues
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I am not certain on that statement, I am far from an expert, but I think it is correct. Subies run quite a bit of timing, even stock, and with the poor fuel we have around here (except, of course, for E85), I have never felt comfortable pushing the limits of timing. It does seem to reach a point of diminishing returns in terms of power, especially considering it increases your chance of knock.
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Old 02-25-2009, 09:17 PM   #5
JSarv
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Join Date: Nov 2007
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Location: Effingham IL (Central IL)
Vehicle:
l33t *******
12.07@115.9mph-EJ205

Default

well.. I haven't seen knock on more timing. I actually see knock on less timing....... Especially in low load regions...

I haven't PUSHED timing real bad in high load regions from mid rpms to high...

I run about 16* (give or take 1+2) depending on ambient temps - at peak torque and about 25* at redline.

Boost (sucks I want an 8cm2 housing so bad now) is around 23psi by 3300 holding till 5k and then slowly tapering to 20psi at redline.. (thats why I want an 8cm2 turbine housing)

I actually made 50wtq and 30whp on that amount of timing vs 13* at peak torque and 21* at redline.....

-Jerod
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