Air-Fuel-Ratio vs. power
Thread Starter
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From: Zurich - Switzerland
Originally Posted by miami993c297
Isn't the fuel different in Switzerland vs. USA?
Christian
Christian
I use what you guys call premium fuel.
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Originally Posted by dan@masportspeedshop
...test for brake mean effective pressure (BMEP) in the cylinder. BMEP acts on the crank and is measured on an engine dyno. Obviously, measuring BMEP is out of the question for most people ...
Note that BMEP is purely theoretical and has nothing to do with actual cylinder pressures."
Staging Lane
Joined: Mar 2006
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A few comments about knock:
1) Lean burns slower
a) This slower burn actually heats up the chamber due to loss of thermal efficiency (it's burning slowly giving more TIME to heat up parts, and since it's not making ideal power, it's less efficient, meaning less expansion work done).
b) The slower burn gives end gasses TIME to auto ignite - auto ignition is like dynomite exploding, not gas burning. It rings the bore, which is the knock sound.
c) The hotter chamber from knocking can lead to early ignition, prior to spark even, which puts so much heat in the piston that it can quickly burn a hole in it.
d) EGT can barely detect any of this, in fact EGT will often drop if it knocks. I only suggest using EGT for avoiding exhaust valve degradation/failure by richening it up or increasing timing (assuming you have knock detection).
e) 5 gas analyzers are pathetically slow, and barely portable. They're pretty much for dyno use only with a big budget and development engines, unless you're calibrating emissions on the road (which I often do, but we're no where near blowing holes in pistons), or just quickly checking some things like idle. It's a good problem detector / diagnostic tool, but hardly practical for tuning for joe streetracer. A wideband is a much better use of money and time.
Just my views on this. Gotta go.
1) Lean burns slower
a) This slower burn actually heats up the chamber due to loss of thermal efficiency (it's burning slowly giving more TIME to heat up parts, and since it's not making ideal power, it's less efficient, meaning less expansion work done).
b) The slower burn gives end gasses TIME to auto ignite - auto ignition is like dynomite exploding, not gas burning. It rings the bore, which is the knock sound.
c) The hotter chamber from knocking can lead to early ignition, prior to spark even, which puts so much heat in the piston that it can quickly burn a hole in it.
d) EGT can barely detect any of this, in fact EGT will often drop if it knocks. I only suggest using EGT for avoiding exhaust valve degradation/failure by richening it up or increasing timing (assuming you have knock detection).
e) 5 gas analyzers are pathetically slow, and barely portable. They're pretty much for dyno use only with a big budget and development engines, unless you're calibrating emissions on the road (which I often do, but we're no where near blowing holes in pistons), or just quickly checking some things like idle. It's a good problem detector / diagnostic tool, but hardly practical for tuning for joe streetracer. A wideband is a much better use of money and time.
Just my views on this. Gotta go.
Originally Posted by RednGold86Z
A few comments about knock:
1) Lean burns slower
Just my views on this. Gotta go.
1) Lean burns slower
Just my views on this. Gotta go.
Can you define "Lean" please...
Christian
Originally Posted by RednGold86Z
e) 5 gas analyzers are pathetically slow, and barely portable. They're pretty much for dyno use only with a big budget and development engines, unless you're calibrating emissions on the road (which I often do, but we're no where near blowing holes in pistons), or just quickly checking some things like idle. It's a good problem detector / diagnostic tool, but hardly practical for tuning for joe streetracer. A wideband is a much better use of money and time.
And, if you're anywhere near piston burning temps, you're in trouble anyways.
Using a gas analyzer just gives you an idea of where you're at tune wise, far before you get anywhere close to burning pistons.
Never said it was practical for joe streetracer.
Last edited by edcmat-l1; Jul 21, 2007 at 11:58 PM.
Staging Lane
Joined: Mar 2006
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Originally Posted by miami993c297
Hi RednGold86Z,
Can you define "Lean" please...
Christian
Can you define "Lean" please...
Christian
We use AVL's Digas 440. Pretty portable (12x10x3.5 or so) but $5000. Still is like a 10 second delay and 1 second update rates, and some sensors faster than others, and there is a little mushing of the gases through time. It's portable, yeah, but jeesh, running a tube from an exhaust bung (or stuffing the probe into the tailpipe), getting it to the unit, expelling the waste gas, combining/synching log files, etc... it takes an engineer with/or lots of experience to do it all right.
Also, I wasn't saying you're wrong or anything - I love the EGA (I use it mostly post cat, though, unless on the engine dyno), but it's not practical unless you are working for a company that needs perfection and validation. Knock sensors and widebands keep most gasoline engines guys out of trouble. A good ear and seat of the pants are also necessities.
Originally Posted by RednGold86Z
We use AVL's Digas 440. Pretty portable (12x10x3.5 or so) but $5000. Still is like a 10 second delay and 1 second update rates, and some sensors faster than others, and there is a little mushing of the gases through time. It's portable, yeah, but jeesh, running a tube from an exhaust bung (or stuffing the probe into the tailpipe), getting it to the unit, expelling the waste gas, combining/synching log files, etc... it takes an engineer with/or lots of experience to do it all right.
Also, I wasn't saying you're wrong or anything - I love the EGA (I use it mostly post cat, though, unless on the engine dyno), but it's not practical unless you are working for a company that needs perfection and validation. Knock sensors and widebands keep most gasoline engines guys out of trouble. A good ear and seat of the pants are also necessities.
Yeah, they def take experience to operate, interpret, etc. And in the grand scheme of things, 5-8 grand is a drop in the bucket when you have a shop with a couple hundred grand in equipment. and to me, its my opinion more pro tuning shops should use one. They make a huge difference in nothing more than idle tuning big cam cars. Compared to a wideband that is.
And as far as knock/ping/detonation/preignition, whatever you want to call it, just monitoring your NOX will give you a "view" that you cannot possibly have/get any other way. You can actually watch you NOX increase as you add timing, lean the mixture, etc, far before you're at the point of audible knock. What you are doing by monitoring the NOX is actually watching the combustion temperature increase.
Your EGA seems slower than mine. Both in delay, and sample rate. by several seconds in the delay, and I'm pretty sure mine updates a couple times a sec. It def seems faster than once a sec. Shortening up the hose will decrease the delay too.
Because my background is emissions/diagnostics, the info I get from mine is invaluable to me. I have trimmed idle HC values by 30% on some cammed cars, with almost NO CHANGE in wideband readings. That to me means a wideband is worthless at idle. Dropping the HC level does nothing to the left over oxygen. So the wideband has no idea that you've "leaned" it out.
]QUOTE]That to me means a wideband is worthless at idle. Dropping the HC level does nothing to the left over oxygen. So the wideband has no idea that you've "leaned" it out.
Try telling that to some of my customers! You should hear some of the phone calls I get, like "You have my car idleing at 17-1!". If the fuel trims are OK, it isn't. Same guys that want to use the wide band for VE tables. I have an old 4 gas Sun analyzer I use for open loop idle tuning a lot. If you know how to interpret the data, it's an invaluable tool. I'm amazed more shops don't use them.
Try telling that to some of my customers! You should hear some of the phone calls I get, like "You have my car idleing at 17-1!". If the fuel trims are OK, it isn't. Same guys that want to use the wide band for VE tables. I have an old 4 gas Sun analyzer I use for open loop idle tuning a lot. If you know how to interpret the data, it's an invaluable tool. I'm amazed more shops don't use them.
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Originally Posted by Ed Wright
]QUOTE]
Try telling that to some of my customers! You should hear some of the phone calls I get, like "You have my car idleing at 17-1!". If the fuel trims are OK, it isn't. Same guys that want to use the wide band for VE tables. I have an old 4 gas Sun analyzer I use for open loop idle tuning a lot. If you know how to interpret the data, it's an invaluable tool. I'm amazed more shops don't use them.
Try telling that to some of my customers! You should hear some of the phone calls I get, like "You have my car idleing at 17-1!". If the fuel trims are OK, it isn't. Same guys that want to use the wide band for VE tables. I have an old 4 gas Sun analyzer I use for open loop idle tuning a lot. If you know how to interpret the data, it's an invaluable tool. I'm amazed more shops don't use them.
Launching!
Joined: Jul 2004
Posts: 204
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From: Arizona.
After a lot of esoteric reading I have this to say:
Try to run a few different AFRs from low 12s to 13 on a hot day. The cool air right now will really change things, the density is just a lot higher and the tune will be different. By tuning on a hot day, you ensure that your tune is safe even in less than optimal conditions. For each tune, maybe try playing with the timing a bit. But I can say right now that 17 degrees advance on an FI application on pump gas is pretty good. Good power but still safe.
You should post all this data up. I think vids of the Double-D acceleromoter would be best
Try to run a few different AFRs from low 12s to 13 on a hot day. The cool air right now will really change things, the density is just a lot higher and the tune will be different. By tuning on a hot day, you ensure that your tune is safe even in less than optimal conditions. For each tune, maybe try playing with the timing a bit. But I can say right now that 17 degrees advance on an FI application on pump gas is pretty good. Good power but still safe.
You should post all this data up. I think vids of the Double-D acceleromoter would be best
Originally Posted by Sparetire
After a lot of esoteric reading I have this to say:
Try to run a few different AFRs from low 12s to 13 on a hot day. The cool air right now will really change things, the density is just a lot higher and the tune will be different. By tuning on a hot day, you ensure that your tune is safe even in less than optimal conditions. For each tune, maybe try playing with the timing a bit. But I can say right now that 17 degrees advance on an FI application on pump gas is pretty good. Good power but still safe.
You should post all this data up. I think vids of the Double-D acceleromoter would be best
Try to run a few different AFRs from low 12s to 13 on a hot day. The cool air right now will really change things, the density is just a lot higher and the tune will be different. By tuning on a hot day, you ensure that your tune is safe even in less than optimal conditions. For each tune, maybe try playing with the timing a bit. But I can say right now that 17 degrees advance on an FI application on pump gas is pretty good. Good power but still safe.
You should post all this data up. I think vids of the Double-D acceleromoter would be best
You want to tune in cold air because if you tune in hot air it will knock when you switch back to cold.
I am lead to believe that leaner is more power, but when does the heat produced get to be too much? People run 12:1 at WOT power because it cools the engine and doesn't make alot of heat. I am sure 14 to 1 would make more power at a risk of safety. As lean as you can run it yields the best power. It doesn't mean to knock or auto ignite when it is lean like previously stated on the dyno if you tune for it to be like that. I have ran 10 12 and 13.8 to one on the dyno and leaner made more power.
I think sparetire is onto something with this DD meter.
Last edited by 2002_Z28_Six_Speed; Jul 27, 2007 at 12:31 AM.
:slap-me-now: 
Teching In
Joined: Jun 2007
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Originally Posted by tici
Looking here and there on the web I find different opinions about the optimal AFR (NA engines):
12.8 at torque peak
13.0 at HP peak
12.5 for auto X-ing
A local tuner uses 13.2-13.5
...
Nice numbers, but wo made a test?
I'd like to see a dyno graph of the same car with different AFR (like 11.0 - 11.5... up to 13.5)
Thanks!
Stefano
12.8 at torque peak
13.0 at HP peak
12.5 for auto X-ing
A local tuner uses 13.2-13.5
...
Nice numbers, but wo made a test?
I'd like to see a dyno graph of the same car with different AFR (like 11.0 - 11.5... up to 13.5)
Thanks!
Stefano
Here are a couple pics of recent dyno runs, fairly stock Honda 2.0L 4cyl 91 oct, only change was the header.
The first run was with the original header, lets call it Header#1.
Header#1 was A/F tuned and the resulting power and torque can be seen in the first picture as well as the A/F ratio. You will see that the A/F is smooth.
This run was overlayed in the second picture, and Header#1 is represented as a RED line on the torque plot.
Header#2 was then installed. Nothing was changed on the fuel or ignition maps. Header#2 is the YELLOW line on the torque plot, and the resulting A/F from the header change is to the right of the torque plot.
First picture: Header#1 Dyno pull (HP and TQ) and A/F tuned
Second picture: Header#1(RED) and Header#2(YELLOW) torque plots, Header#2 A/F untuned.
