BMW M3 Forum
BMW M3 Forum BMW M3 Gallery BMW M3 Reviews BMW M3 Social Groups BMW M3 Chat M3Forum Sponsors >>
Loading


Mobile M3forum
Go Back   BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X) > BMW M3 Discussions > M3 Frequently Asked Questions
Tire Rack Buy Winter Tires Now!
Not a member? Register Now!
Register Gallery All Albums Garage Search Today's Posts Mark Forums Read Calendar FAQ

M3 Frequently Asked Questions First place to check if you've got a question about your BMW M3. UNDER CONSTRUCTION


Closed Thread
 
Thread Tools Display Modes
Old Fri, Feb-11-2005, 12:10:01 AM   #1
Divexxtreme
On Leave
 
Divexxtreme's Avatar
 
Join Date: Jan 2003
Posts: 13,479
Reputation: 0 Divexxtreme has disabled reputation
Location: Virginia, USA





Default PRIMER: Relationship of air and fuel in an internal combustion engine

Originally posted by NIXLIMITED, 2-10-2005:

"Air and fuel burn at a ratio of 14.7 parts to 1, or 14.7:1. This is called stoichiometric ratio. However, on most cars, this ratio will cause detonation and or overheating since it produces so much heat (read: bunson burner example), therefore most cars are tuned to run at richer conditions (i.e. more fuel) because the added fuel helps cool the cylinder walls as it vaporizes. This is the same idea as water/ethanol injection - cool the combustion chamber. Now, when talking about intakes, it is possible that the cars fuel maps will not be immediately optimized for the new intake which is letting in more air than expected thus your OEM ratio at some load might be 11.x:1 and all the sudden it has leaned out to 12.x:1, thus producing a hotter combustion, and as we know from the pv=nrt gas equation, that means more pressure and more pressure on the piston means more power at the wheels. Likewise, if the fuel map is causing the opposite problem, making the mix too rich, you could loose power at the wheels. This is what some of us speculate the Dinan software might be doing.

In reference to my prior argument that lean will produce more power than rich, that's because a N/A engine has a set amount of air in each cylinder, and that is based on the cylinder's displacement and the density of the outside air. Simply dumping more fuel into the cylinder will NOT produce more power because there isn't enough time or air to combust it. It will, as I have said, help to regulate the combustion chamber temp since the liquid gas will evaporate and draw heat out of the cylinder.

This is why A/F ratios are so important when tuning because it helps you to understand what is going on in the combustion chamber."
__________________
Current:
'14 Viper TA, 8/33
'15 Macan TT
'07 997TT 6-MT, 1054whp

Past:
'14 Stingray Z51 Coupe 7-MT, '13 Cayenne GTS / '13 GT-R - 1136whp on E85 / '12 GT-R - 927whp on 93 / '10 GT-R - 1248whp / '03 996 GT2 - 712whp on 93 / '10 GT-R - Bolt-ons / '01 996TT, 889whp / '06 Z06, 722whp / '98 Supra, 711whp / '03 M3, 416whp / '05 M3 ZCP / '01 M5

Last edited by Divexxtreme; Fri, Feb-11-2005 at 12:15:33 AM.
Jump to top Divexxtreme is offline  
Sponsored Links
Register now and remove these ads
Old Fri, Feb-11-2005, 12:11:26 AM   #2
Divexxtreme
On Leave
 
Divexxtreme's Avatar
 
Join Date: Jan 2003
Posts: 13,479
Reputation: 0 Divexxtreme has disabled reputation
Location: Virginia, USA





Default

Question:

"It seems like the more air you push into the engine, the more fuel it will consume, because it will need to adapt a richer fuel to air ratio in order to keep the combustion champer temps steady."


Answer, by NIXLIMITED:

"Well, it depends what you mean by that. The more air you "push" into the engine the more fuel you could consume, to a point. If you push more than 14.7 parts of air in per part of fuel, it will make no difference. Remember, though, that we don't "push" air into our engines, we draw it in like a pump. Thus, the gains we get from intakes have nothing to do with more air, just getting the air in easier. There are factors which slightly complicate that assumption, however, like the velocity of air coming down the intake tract, which is why on some cars you see adjustable length runners leading into the cylinder. This is also why we have a plenum that has a minumum volume of all of our engine's total displacement (I think).

Also, it depends on how the car manages itself. Most cars manage a/f by using maps which are adaptive + an adjustment factor based on active sensors. In some cars the maps are treated as first priority while in others the sensors (like 02) take priority. This makes it a ***** for tuners to tune properly.

Edit: I just realized I didn't really answer your question. Yes, if you start to lean out/detonate, adding fuel is one way to regulate temps, so is timing, and a variety of other things. The utter complexity of the modern engine is pretty amazing."
__________________
Current:
'14 Viper TA, 8/33
'15 Macan TT
'07 997TT 6-MT, 1054whp

Past:
'14 Stingray Z51 Coupe 7-MT, '13 Cayenne GTS / '13 GT-R - 1136whp on E85 / '12 GT-R - 927whp on 93 / '10 GT-R - 1248whp / '03 996 GT2 - 712whp on 93 / '10 GT-R - Bolt-ons / '01 996TT, 889whp / '06 Z06, 722whp / '98 Supra, 711whp / '03 M3, 416whp / '05 M3 ZCP / '01 M5
Jump to top Divexxtreme is offline  
Old Fri, Feb-11-2005, 12:13:10 AM   #3
Divexxtreme
On Leave
 
Divexxtreme's Avatar
 
Join Date: Jan 2003
Posts: 13,479
Reputation: 0 Divexxtreme has disabled reputation
Location: Virginia, USA





Default

Originally posted by NOSOUP4U, 2-10-2005.

"The only problem with learning more, is that you begin to doubt and question "everything" anyone claims ... hehhe I'll try to give a quick synopsis of things which most everyone should understand.

Quick acronym breakdown:

lambda = stoichiometric as Nix explained it
s/w = software
14.7/1 = lambda = stoichiometric
LTFT = long term fuel trim (IIRC, also known as closed loop operation -- but, I forget, day is long)
STFT = short term fuel trim (see caveat above, I believe it is open loop mode).
a/f = air/fuel ratio's or (also known as AFR's)

closed loop = in this situation, the computer measures the a/f ratio and tries to maintain a constant a/f ratio. This is deemed closed loop. Typically, feedback is given from 02 (oxygen) sensors. In all cars, this is also termed stoichiometric or 14.7. The reason 14.7 is maintained is for catalytic converters -- it helps reduce emissions the best at this level. Plus, most O2 sensors function well at this level. Closed loop is basically the car at normal conditions, e.g., at any times other than WOT. Because of closed loop -- engines can last a long time. The fuel system compensates for any changes as the engines get older. This is also the reason why at LOWER rpm's, a dyno can indicate that a modification has made power!!!

Does it make sense? I think NIX will agree with me here, 14.7 we know is NOT optimal for making power. BUT, if we richen it up "slightly" at this point, what do we get? More power. IF the s/w company already is richer than 14.7 in closed loop though ... then, you can conceivably LOSE power b/c now you are TOO rich.

open loop= this is different from closed loop, obviously . The reason it differs is that in this mode, the O2 sensors are IGNORED. There is no feedback on whether the injectors programmed to deliver a certain amount, actually has yielded that in the engine. E.g., now the car can run different afr's, typically, richer than 14.7. Open loop typically occurs when you start the engine from cold. 02 sensors are not warmed up at this point. You adjust this as well to match engine load. Open loop can also be used at idle in some cases b/c sometimes cars run better when richer.

There are a few more modes I believe and I forget what they are called. One of them is when you are at 50% and higher in throttle application (it could be 70% or something like that, I forget). In this mode, the throttle position sensor governs. Again, the 02 sensor is ignored and a richer afr results. This is the area of particular importance to tuners.

Thus, you have to keep in mind that whatever the car does in closed loop, it will do in open loop. A properly tuned car, should not adapt greatly (make richer/leaner the afr's). If IT DOES, then that typically means that closed loop is too rich.

IF a company is willing to throw stoich out the window, then you CAN make more power (e.g., fool around with closed loop so it does not read 14.7 anymore). If a car maintains stoich as 13.0 now vs. 14.7 -- the 13.0 car will make more power. Adding a modification now, however, will cause the car to become TOO rich. So, now, new s/w is needed. However, this is screwing around with emissions. Your car now becomes a bigger polluter than before and will have a harder time passing emissions, even when using the stock cats.

You also have to be careful because the speed of the throttle opening can be changed in software. The drive by wire system will FEEL faster if someone fools around with this as well. Creating the sensation that you have gained significant HP.

On a dyno, since there is typically NOT ENOUGH air-flow, timing is retarded (pulled back) as a result of the s/w trying to establish a richer condition. Remember, that in open loop, some of the fuel maps are determined by the EGT (exhaust gas temperature) sensor and air intake temperature sensor, e.g., how hot and cold the combustion chamber is. On the dyno, you cannot get enough air flow for proper exchange to simulate the real world over the radiator. Thus, the s/w becomes richer at that point to REDUCE combustion temperatures b/c it senses high load but higher EGT's. Okay, now we have created a richer condition on the dyno ... which can yield higher numbers. BUT, remember this is ONLY on a dyno -- in the real world, it won't happen. You won't be making the claimed HP that the dyno world results in.

Conversely, the opposite can happen which can still yield higher numbers. Confused yet? You can put a large fan blowing on the engine and the intake (open hood, etc.) and you will have lower temperatures. Lower temperatures can result in a leaner afr. Now, timing will be advanced yielding more power. So, in some instances, you can get more power by advancing timing and sometimes by retarding it. It really depends on the dyno conditions. Some have criticized Steve Dinan for employing this tactic. He uses a super duper NASA designed space fan in his dyno's (no joke).

So, as I said, the more you learn about this stuff, the more you start to question everything, ehhe. Sometimes, ignorance can be bliss! But, in all honesty, you DO have to question gains from dyno's ... for at least the reasons I've given above. Hope this helps."
__________________
Current:
'14 Viper TA, 8/33
'15 Macan TT
'07 997TT 6-MT, 1054whp

Past:
'14 Stingray Z51 Coupe 7-MT, '13 Cayenne GTS / '13 GT-R - 1136whp on E85 / '12 GT-R - 927whp on 93 / '10 GT-R - 1248whp / '03 996 GT2 - 712whp on 93 / '10 GT-R - Bolt-ons / '01 996TT, 889whp / '06 Z06, 722whp / '98 Supra, 711whp / '03 M3, 416whp / '05 M3 ZCP / '01 M5
Jump to top Divexxtreme is offline  
Closed Thread

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Internal engine pictures Black02M3 E46 M3 (2001-2006) 15 Mon, Apr-07-2008 07:19:33 AM
Need quick help... what happens when you spray self-etch primer on exsisting primer? Brandon318 E36 M3 (1992-1999) 1 Sun, Aug-19-2007 04:29:00 PM
Where is our internal air inlet? SWOLE E46 M3 (2001-2006) 8 Tue, Jul-18-2006 03:13:09 AM
Air/Fuel problem causing engine bog - E30 M3 ethirty Faults, Fixes and DIY 2 Fri, May-13-2005 07:32:02 PM
BMW sets 9 records with Hydrogen Combustion Engine crystalq3 General BMW Discussion 9 Tue, Sep-21-2004 04:15:27 AM



All times are GMT. The time now is 10:52:23 PM.


Powered by vBulletin® Version 3.8.6
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
M3Forum.com and M3forum.net is in no way sponsored, endorsed or affiliated by or with BMW NA / BMW AG or any of it's subsidiaries or vendors.
BMW and M3 (E90 M3 | E92 M3 | E93 M3 | E46 M3 | E36 M3 | E30 M3) are registered trademarks of BMW AG.
M3Forum Terms of Service
Copyright 1999-2017 M3Forum.com
Discussing PRIMER: Relationship of air and fuel in an internal combustion engine in the M3 Frequently Asked Questions Forum - First place to check if you've got a question about your BMW M3. UNDER CONSTRUCTION at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)