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Old 07-20-2010, 09:26 PM   #11 (permalink)
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2 inch of mercury = approx 1 PSI

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Old 07-20-2010, 10:18 PM   #12 (permalink)
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Quote:
Originally Posted by Meph View Post
no EGR, JDM engine. I have a vac/boost gauge int he car and the values between my MAP sensor and boost gauge are comparable. The X axis is all in PSI, the conversion is somewhere around 2.03, I cant talk in -psi or in-Hg, but not many people use -psi.
Well, from what I'm seeing on your graph, your 7.74 PSI x 2.03 = 15.75 inches Hg seems about right for a steady cruise speed.
Without EGR and with your low compression the numbers I gave as an example should be pretty close. You said that you're going a bit slower than 60 MPH though, so unless your car has a lot of drag somewhere then you may be able to get away with a little more than what I have in my example for your cruise speed.

If you really want to tune to the edge and are worried you won't hear the knock, then there are aftermarket stand-alone kits that allow you to use a knock sensor and display the feedback for you. More sophisticated ones can also adjust the SA automatically, but they are more pricey.

As for a lean AFR: I have tuned a 1998 C5 Corvette that was very steeply geared at 3.15:1 with 29" diameter rear tires (the owner/driver weighed around 370 lbs) - it was a drag racer.

I set up an open-loop tune (no O2 feedback) with:
DECEL AFR of 16.5:1 or DFCO with less load (aggressive DFCO setting)
steady cruise AFR of 15.5:1
very light ACCEL AFR 14.5:1
moderate (but normal) ACCEL AFR 13.8
heavier (but not PE mode) ACCEL AFR 12.8:1

I never hypermiled it to test, but the car had a factory MPG gauge that averaged around 25 MPG with his normal driving.
The SA numbers for that engine wouldn't be comparable to yours so I won't even mention them. I just wanted to offer an example of AFR varying with engine load.
If you try to run 17.5:1 across the board, then you will definitely experience some lean misfire when you load the engine in your upper gears.
Very lean mixtures like that require excessive SA, and that will reach a point of being counterproductive in the search for efficiency. It will also be hard to keep the engine from surging when transitioning from cruise to light ACCEL.
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Old 07-21-2010, 12:01 AM   #13 (permalink)
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thanks again, i'll give everything we've talked about a shot. with my o2 settings I can controll the max throttle point, so I can set it to about 4-5% and pull the a/f ration back, say 15.5 to 16, and when i get into the pedal at all, it will revert back to my base map of about 14.5:1. Im still playing with the boost a/f, pulling it back slowly, still in the 9:1 to 10.5:1 range, once I get it leaned out to about 11.5-12 I think ill notice a bit of an improvement in power aswell, not that its slow by any means right now

I have dec fuel cut till 1400 rpm, i may increase that down to 1000 and see how ti works out.

Is my most efficient SA going to be right before audible pining starts to occur? Tomorrow ill bump the timing to 32 again and see how she does.
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Old 07-21-2010, 08:54 AM   #14 (permalink)
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Quote:
Originally Posted by Meph View Post
thanks again, i'll give everything we've talked about a shot. with my o2 settings I can controll the max throttle point, so I can set it to about 4-5% and pull the a/f ration back, say 15.5 to 16, and when i get into the pedal at all, it will revert back to my base map of about 14.5:1. Im still playing with the boost a/f, pulling it back slowly, still in the 9:1 to 10.5:1 range, once I get it leaned out to about 11.5-12 I think ill notice a bit of an improvement in power aswell, not that its slow by any means right now

I have dec fuel cut till 1400 rpm, i may increase that down to 1000 and see how ti works out.

Is my most efficient SA going to be right before audible pining starts to occur? Tomorrow ill bump the timing to 32 again and see how she does.
The only thing you might want to check is head/EGT temps .
With running ignition timing high with no EGR and lean A/F (17:1 ) .
You might get a condition were head temps raise during cruising , then when you go to boost your starting with elevated temps . not saying it will be problem but something to keep in mind . monitor water/oil and EGT if you have gauge . run baseline A/F and timing your running now (like 30-35deg) . then make your A/F and any timing changes (best to do each separate ) then compare if temps go any higher .

How much boost are you running ?
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Old 07-21-2010, 09:15 AM   #15 (permalink)
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Ive got an EGT probe but no gauge, I guess in the future its something Ill have to consider installing. Im only running 9-10 psi right now from a fairly large holset turbo. I have a 2 bar MAP sensor so I cant go over 14.7 psi anmyways, my final pressure will probably be around 12 psi. Ill hopefully try out some new settings today, thanks for all the input
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Old 07-21-2010, 09:24 AM   #16 (permalink)
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With 8+ psi of boost, even with the low compression (although it depends on the cam somewhat), you'll probably start pinging before you overshoot the optimum timing.
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Old 07-21-2010, 10:08 AM   #17 (permalink)
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thanks ill keep it in mind, but my a/f and SA in boost is more more conservative but ill do some tuning and testing as soon as i can
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Old 07-23-2010, 02:32 PM   #18 (permalink)
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Quote:
Originally Posted by Meph View Post
Is my most efficient SA going to be right before audible pining starts to occur? Tomorrow ill bump the timing to 32 again and see how she does.
Yes, for a lot of engines like yours it is for most of your driving.
It also depends on loading.
The more the cylinder is loaded, then the less it is true.
A loaded cylinder has more leeway between efficiency and knock.
That means you can get away with less SA than maximum and not lose a significant amount of vehicle fuel efficiency.
At low loads there is a greater % loss in vehicle fuel efficiency the further away from maximum allowable SA you get, though it often goes unnoticed.
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Old 07-23-2010, 07:35 PM   #19 (permalink)
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thanks, Im taking the car on tis first long trip tomorrow, about 100km one way, should be interesting since I built the car from the frame up in a garage 600miles so far without major incident, hopefully it will take it.

I had some issues the last few days with A/F ratios, it ended up being a disconnected signal wire causing the ECU to lean out, its sorted now and 15.35:1 has been programmed for the drive. Driving great once more

Ive got my Maps adjusted, gonna play with them till I start to dial in the optimum setting. I also did a couple Aero mods, grill block shown to reduce the Cd from .45 to .4 in wind tunnel tests and a front belly pan. Oddly enough the rear spoiler was shown to reduce drag vs a flat hatch, seems wrong but it was backed up by windtunnel tests as well.
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Old 07-23-2010, 08:17 PM   #20 (permalink)
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What ECU controller are you using ?

So this is basically first real running with it on .

Maybe you could post a higher rpm map, like 4k rpm so we can see how timing is for a rpm were light load to full boost would enter in (assuming 4k rpm is able to get max load ) .

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