EGT and AFR Tuning Gurus- need your input

[miniman82]

First off, thanks for any input or advice you guys can give about tuning. I've got the 1915 turbo to the point where it drives really well all the time, so now I'm focusing my efforts on the 'fine tuning'. First the specifics:

1915cc
42X37.5 SS valved CB 044 CNC roundports
Megasquirt EFI, Ford EDIS distributorless ignition (crank fired)
375cc/min injectors
single TB common plenum inlet manifold, stock dual port style end castings with injector bungs (multipiont injection)
Garrett T3 turbo, .48 turbine .42 compressor, mated to a modified CB buggy header
Currently no intercooler
Techedge 2A0 wideband logging AFR's, and 1 EGT probe as close to #1 exhaust valve as I could get it (approx 3" away from the flange), and 1 probe post turbine (about 4" from the turbine outlet)


During the past week or so, I've been driving around trying to get a handle on what the 'normal' temps and AFR's are. It idles smooth at exactly 14.7 AFR, at 11* BTDC. At idle, the EGT from #1 probe reads around 730-740*C (~1350*F) with the engine fully warmed up. The post turbine probe reads around 350-400*C (~750*F).

During hard runs (10lbs boost pressure, 12.5~12:1 AFR, around 140*F inlet temp), EGT on #1 gets to around 850-900*C (~1575*F), and post turbine shows about 500*C (930*F). This sounds a tad on the high side to me, conventional wisdom saing you shouldn't top somewhere in the neighborhood of 1400*F.

I can tailor the ignition and fueling curves to whatever I want, so suggestions on what to run will be appreciated. Also, I have a few different turbos I can try, so if swapping in a larger turbine housing would help, I'll try that.

Thanks again,
Nick
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[The Noof]

Oh, man..how we've come to rely on electronics.lol
If we take the gauges at face value, anything over 1350 degrees sustained at the exhaust port window is high.The best of aluminum alloys are pudding at 1400 degrees sustained.It depends too much on exactly the placement of the probes, and accuracey of the electronics.

[miniman82]

Thanks, Noof. I thought the same thing, but the problem is it IDLES at that temp, so I figured it's normal. No matter what I do (more/less timing, richer/leaner) at idle, it starts to run like poop once I start getting away from 14.7 AFR. Timing doesn't seem to have a large effect at idle either way. 14.7 AFR, 11* BTDC, and 1350*F seems to be the sweet spot at idle.
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[miniman82]

Bump.
Anyone got any input on this? The internet isn't a whole lot of help with this, it's mostly stuff about tuning diesels.
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[SRP1]

Well there is plenty that comes to mind, the issue here is where the problem lays.
I only use the tuning electronics as a guide, and tune from there with the spark plug. First issue that comes to mind is timing, you said you have 11* at idle, what is it at 3000rpm. Personally I would advance the idle timing to 18* and adjust the total to 24*, that should cool things off a little at idle.
Second go ahead and put a little more fuel in it at across the board, shoot for 12.0:1 threw out the rpm range. Your turbo housing should be ok IMO, and I would work with that later if need be.
BTW what cam and head combo? Also comp ratio?

[[email protected]]

back out the idle timing to 7, you'll have to add air and fuel to kick the idle speed up. More than 10 degrees is too much timing. Get A/F around 16-17:1 under light loads. 14.4:1 is fine for idle, that's where mine runs sweetest. You are not trying to make it idle the fastest, you want the MOST STABLE condition for idle, so idle speed doesn't hunt. If you have too much timing it will be all over the place.

and most of the A/F advice you are going to get is going to be wrong, so watch out who you listen to.

John
Aircooled.Net Inc.
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[miniman82]

Thanks, guys.

Cam is CB#2241, heads were listed in my first post (65cc chambers), stock rockers, compression is set at 7.2:1.

John, I've got the AFR's setup how you describe. It runs around 15.5 under light load (cruising), and under boost it's usually at ~12:1.


Also, I found out today that the Techedge software I was using was corrupt. The EGT's weren't being reported accurately for some reason, so I upgraded to a new program that gives EGT's in *F instead of having to convert from *C. New data shows normal idle at 14.7 AFR at 1000*F EGT from #1, and 1300*F under boost at 12:1 AFR. This sounds a little better than I previously reported, but I'd like to cool off the idle a bit more. I'm thinking 900*F would be just about perfect, so I'll give the timing and fuel adjustments a shot, and report back.

The new program allows me to run the wideband logger and Megasquirt software at the same time, so now I should be able to see the results of my tuning in realtime. Wish me luck.
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[[email protected]]

you should not be trying to run a "cool" EGT at idle. By its very nature, EGTs are hottest around Stoic. But the VOLUME Of exhaust and air is so low, you should not care that it's "hot". The engine is under no load, it is going to run cooler at idle than at any other situation when you are driving the car, so don't worry about it.

If running cool EGTs at idle was the goal, we'd be running 8:1 A/F at idle, it would be so cool it might not even run. Don't worry about EGTs at idle it's a meaningless #.

John
Aircooled.Net Inc.
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[miniman82]

OK, got it. I just thought running it slightly cooler at idle would somehow help, due to the lower temps. How do my loaded EGT's look? I figure 1300*F is about right for a boosted engine, most people say to keep it under 1400*F.
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[The Noof]

Keep it close to 1300 max.

[miniman82]

Sweet, sounds like I'm on the right track.
That means once I get the head temp sender and knock sensor installed and calibrated, I can throw more timing at it, and really see what it has!
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