FE3 t3/t4 Miata - Page 2 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 05-16-2007, 11:01 AM   #21
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Was emailing with Jeremy regarding tuning after my dyno runs...

he suggests a 1400 degree EGT is pretty optimal and 1500 is about the max limit you'd want to run. I've seen people claim they run 1600 reliably but that's pretty hot.
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Old 05-16-2007, 11:20 AM   #22
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1400 at cruise or WOT? Seems high for cruise and low for boosted WOT run.
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Old 05-16-2007, 11:27 AM   #23
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I added in 4* of timing accross the board and no signs of knock. Need to do some datalogging, after looking at my map I'm still running pretty rich. I was surprised that I'm still very much close to FM defaults with a few changes here and there after coarse tuning. I expected to see some significant changes since the car drives better after the tuning session I did. Hopfully I can get on it this weekend and have some data logs.
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Old 05-16-2007, 01:29 PM   #24
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I dunno- everything I've read states 1600f being typical (if not optimal) under boost. 1400f @ mid rpm cruise is also regularly stated. Those are the numbers that I'm seeing... or were. Boost was still 1600, but cruise was about 80f lower.

Logging will give you the control to make those larger changes much quicker. I got to the point where coarse tuning wasn't getting any better. Good for getting the car running. Have you adjusted the AF targets yet? I'm aiming for the following with LC1 -
row 400 - 80 - 13.0
row 500 - 85 - 12.4
row 600 - 89 - 12.0

Last night was the first datalog run with those targets and my advance IGN map (referencing scott/maps IGN maps - which are both advanced over the fm defaults). I had no knock on the first run, then bumped advance 1* and came back with knock. That was after a full 4th gear run to 7k+, then 5th to ~6.5k (nobody in sight... except a turn). I'm going through the logs tonight.
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Old 05-16-2007, 04:09 PM   #25
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Go for the EGT that gives you the most power. I'm a fan of more boost, less timing, leaner A/F for power as are two very well known tuner guys I know pretty well.

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Old 05-16-2007, 05:14 PM   #26
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that's what I'm working towards - though less timing isn't applicable to what I had. I went to a full 5* advance and no knock- so I my IGN map had a major lack of advance.
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Old 05-17-2007, 08:08 AM   #27
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That's good. It's the "advance timing til knock then dump a bit of fuel on it to get rid of the knock" that I'm talking about. Too ragged edge close to det for me.

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Old 05-17-2007, 10:29 AM   #28
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Yep- and that too can lead to elevated EGTS. If the combustion can't burn all the fuel during the cycle, the ex valve opens and it finishes burning in the ex manifold. I am definitely following "very well known tuners" method, as it's the same as a "well known local tuner" here.
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Old 05-17-2007, 11:13 AM   #29
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burning in the manifold can help spool

actually I've heard reducing timing prior to spool can improve spool by heating up the exhaust earlier, but I haven't seen it documented anywhere. I wonder what pulling 5° 500 rpm before you reach 3 psi would do.
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Old 06-16-2007, 09:51 PM   #30
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Revelation?
Finally went back out and did another datalog. Taking a close look at my IGN Map vs. my actual IGN advance I noticed something. My actual advance starts dropping off right after peak torque (and peak boost) compared to the Map. By 7000k my advance is a full 10* less than the Map! Apparently this is compensation by the ecu (intake air) and maybe others? But this might explain my hp falling off with torque so soon.
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Old 06-16-2007, 10:21 PM   #31
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Just throwing it out there... Does your FE have a rubber damper at the crank pulley like the 1.6 does? When the rubber wears on the 1.6, it limits timing advance.

I may be off base and it could just be IAT correction. What is your IAT? Could be knock correction too.
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Old 06-16-2007, 10:23 PM   #32
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Well im glad you got that sorted
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Old 06-17-2007, 01:26 PM   #33
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It probably does- that's the "harmonic balancer" on most 4 bangers. The difference in MAP vs. actual definitely increases as the IAT goes up. Check out the attached log graphic of accel 2nd-5th. AIT starts out ~32c and by 6k rpm in 5th it's 58c. Air Temp compensation starts at 40c. My advance at around 6k is supposed to be 17* and the actual advance is 7*. That's a huge difference. The rise in IAT definitely follows the trend in IGN advance reduction.

In comparison a local LINK'd AVO 1.8 is making more power at the same boost level. The primary difference between the two cars - the AVO 1.8 has an intercooler that's nearly double the size of mine.

We had some IAT threads going, I need to dig back through them and focus on the actual temp rise vs. starting temp compared to ambient.

Not sorted yet, but I definitely feel like I'm on to something. And I've got an IC that's double my existing core size - just need to make the time to install it.
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FE3 t3/t4 Miata-ait.jpg  
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Old 06-17-2007, 06:50 PM   #34
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Yes the harmonic balancer is what I was referring to.

Sounds like you are on to something. I'm curious to see your results...
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Old 07-03-2007, 07:43 PM   #35
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I have the EGT probe right at the turbine inlet, where it meets the collector from the log. I report the same high EGTs as you all. I have an obiwan link. I inspected my turbine blades after >3 years of subjecting my crappy small turbo to these temps and it still looked brand new. The compression on my motor is still fine. I haven't taken it apart to inspect though.

Cold start it is about 200F cooler everywhere until it removes the cold start richness.

Warm:
Cruise under vacuum is in the 1300-1400 degree range, depending on how fast I am going. This is with advanced timing and normal stockish AF ratios. Cruising at 2500 rpms gives me 1250-1300 egts. Going up to 4000 rpms gives me 1350-1400 EGTs. Beyond that and I am going at highly illegal speeds but it still goes up a bit.

Under boost, temperatures rise to 1500-1600, especially towards higher RPMs.

Note that behavior of EGTs is the same under vacuum or boost (they rise with RPM). Any explanation for this?

Last edited by beerslurpy; 07-03-2007 at 07:55 PM.
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Old 07-03-2007, 08:35 PM   #36
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Quote:
Originally Posted by beerslurpy View Post

Note that behavior of EGTs is the same under vacuum or boost (they rise with RPM). Any explanation for this?


Just a few guess:

In order to maintain a constant EGT as RPMs increase, you need to add more timing to keep the entire ignition event before the exhaust stroke. But due to detonation and the fact that you don't want to blow your engine up, you have to take out timing. So more heat into the exhaust?

Or...there's more ignition events per unit time, so everything gets hotter?

Or... you spin your waterpump impeller so fast that it cavitates the coolant and therefore more heat goes out the exhaust?
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Old 07-03-2007, 08:56 PM   #37
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I personally suspected that the pressure at the collector was higher at higher RPMs because the same volume of gas was being pushed through it more often.

The only part that confused me was how vacuum EGTs were about the same as boosted EGTs but that it varied under RPM. I guess I wasn't satisfied with my personal explanation that although there is a much higher pressure of gas, it is also cooler because the engine runs richer under boost.

It seems that the only reason advance is risky at higher RPMs is because we can't accurately control either the rate of combustion or the timing of the spark. Which one is weak on a Link controlled NA?
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Old 07-08-2007, 12:07 PM   #38
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Basically the two variables are the spark timing and the fuel. Changes in either of these can raise or lower egts. Using extra fuel is going to "soak" detonation is going to raise egts at higher rpm because the excessive fuel isn't getting fully burnt in the cylinder and passed on to the exhaust. There it continues to burn past the exhaust valves, in the manifold and so on. A similar issue occurs when the ign timing is retarded to the point where combustion starts so late that it completes outside the combustion chamber.

I had high egts at 4k and just moved my advance up manually and literally watched the egts fall 300f.

Newer/bigger IC should be installed this month
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