Intake, Header, HFC, CBE = Too Lean?

Red370 · 03-24-2010, 08:05 AM

Self admittedly, I know jack squat about A/F ratios, but i'm curious... my AP says that i'm running an avg. of 14.2-14.4 at idle, is that a normal idle ratio? is it only considered running lean at a specific RPM?

F.I. Inc. · 03-24-2010, 09:48 AM

Quote:

Originally Posted by Red370

Self admittedly, I know jack squat about A/F ratios, but i'm curious... my AP says that i'm running an avg. of 14.2-14.4 at idle, is that a normal idle ratio? is it only considered running lean at a specific RPM?

You are fine! Optimum A/F ratio at idol is 14:7! Now WOT (Wide Open Throttle) You reallly want to be in the high to mid 12 range once you get above 4-5000 RPM. At the lower RPM's the A/F being leaner will not be catastrophic to the engine. However if you run it the high 13's low 14's in the upper RPM range you can cause serious damage to the engine. Detonation will occur inside of the engine and you can actually hear it if it is real bad. Bottom line, it is not enough fuel.

Thanks, Tony

Modshack · 03-24-2010, 09:57 AM

Quote:

Originally Posted by Red370

Self admittedly, I know jack squat about A/F ratios, but i'm curious... my AP says that i'm running an avg. of 14.2-14.4 at idle, is that a normal idle ratio? is it only considered running lean at a specific RPM?

There are 2 fuel control systems. The first, when at idle or partial throttle, is controlled by the MAF and 02 sensors who are constantly sending readings back to the ECU to maintain ideal Stociometric ratios (14.7:1). This is called closed loop. An A/F gauge will bounce around a lot as the mix is read and constant corrections are sent to the ECU. When you go wide open throttle (open loop), the fueling defaults to some pre-built fuel maps in the ECU. These are usually slightly modified by the Long term fuel trims (correction factors) that are determined over time by the adjustments the 02 sensor Has been making. Typically the Z corrects from a slightly rich tune.
As Parts are added (Exhaust, Intake, HFC's), the rich correction is reduced as the Fuel trims approach Zero. Add Zero to the pre-built map and you'll have a bit more power due to the leaner mix.. (richer is slower). To truly see how closely you are to optimum, read the A/F ratio at WOT as is the case with all dyno plots.

In this picture, Additive is the short term fuel trims, Multiplicative is the long term trims:

Red370 · 03-24-2010, 10:02 AM

Quote:

Originally Posted by Modshack

There are 2 fuel control systems. The first, when at idle or partial throttle, is controlled by the MAF and 02 sensors who are constantly sending readings back to the ECU to maintain ideal Stociometric ratios (14.7:1). This is called closed loop. An A/F gauge will bounce around a lot as the mix is read and constant corrections are sent to the ECU. When you go wide open throttle (open loop), the fueling defaults to some pre-built fuel maps in the ECU. These are usually slightly modified by the Long term fuel trims (correction factors) that are determined over time by the adjustments the 02 sensor Has been making. Typically the Z corrects from a slightly rich tune.
As Parts are added (Exhaust, Intake, HFC's), the rich correction is reduced as the Fuel trims approach Zero. Add Zero to the pre-built map and you'll have a bit more power due to the leaner mix.. (richer is slower). To truly see how closely you are to optimum, read the A/F ratio at WOT as is the case with all dyno plots.

In this picture, Additive is the short term fuel trims, Multiplicative is the long term trims:

Tis why I love this forum, lots more people smarter than I, learn somethin new every day, thanks, +1 rep to you sir.

Zsteve · 03-24-2010, 09:26 PM

Quote:

Originally Posted by Red370

Self admittedly, I know jack squat about A/F ratios, but i'm curious... my AP says that i'm running an avg. of 14.2-14.4 at idle, is that a normal idle ratio? is it only considered running lean at a specific RPM?

And you read me at the same point too and I dont have a tune and only had the CBE and K&Ns drop ins.

mrdino77 · 03-25-2010, 09:38 AM

Wow I just learned a lot by reading up on this thread. I have a question then, since I will be running FI CBE w/test pipes and might do a K&N Drop in would I need a retune for that as well? I plan on most likely getting a tune anyway but I was just curious if this would also present a case to retune seeing im not actually switching the CAI.

semtex · 03-25-2010, 09:48 AM

Quote:

Originally Posted by mrdino77

Wow I just learned a lot by reading up on this thread. I have a question then, since I will be running FI CBE w/test pipes and might do a K&N Drop in would I need a retune for that as well? I plan on most likely getting a tune anyway but I was just curious if this would also present a case to retune seeing im not actually switching the CAI.

Just dyno your car after you get all your mods in. As part of the dynoing process, they measure your AFR. (Not all places do it automatically, so you might have to ask for it.) If your AFR is in the acceptable range, then you're good to go. If it's out of whack, then you know you need a tune. There's no sense in guessing on whether or not you'll need a tune when you can actually go get your AFR measured and find out for sure. It's like trying to figure out if you need blood pressure medication without getting your BP reading checked first.

F.I. Inc. · 03-25-2010, 09:58 AM

Quote:

Originally Posted by semtex

Just dyno your car after you get all your mods in. As part of the dynoing process, they measure your AFR. (Not all places do it automatically, so you might have to ask for it.) If your AFR is in the acceptable range, then you're good to go. If it's out of whack, then you know you need a tune. There's no sense in guessing on whether or not you'll need a tune when you can actually go get your AFR measured and find out for sure. It's like trying to figure out if you need blood pressure medication without getting your BP reading checked first.

Good analogy about the blood pressure medication!

Tony

Zsteve · 03-25-2010, 10:43 AM

Quote:

Originally Posted by mrdino77

Wow I just learned a lot by reading up on this thread. I have a question then, since I will be running FI CBE w/test pipes and might do a K&N Drop in would I need a retune for that as well? I plan on most likely getting a tune anyway but I was just curious if this would also present a case to retune seeing im not actually switching the CAI.

Im not sure if this means I am running lean but again when I did the K&N drop ins and the CBE my tail pipes went from having black junk on them(before the mods), to not having any black junk on them after the mods. But something changed. Im getting my Cobb today so I will do a AF reading before and after to see the changes and where Im at when at higher rpms then idle before I put the new map in. I think I went leaner than I was but thats not to say that Im too lean to hurt anything, Im sure the tune will get me some extra gains.

03-24-2010, 08:05 AM	#1 (permalink)
Red370 A True Z Fanatic Join Date: Jul 2009 Location: Kaiserslautern, Germany Posts: 4,391 Drives: your mom to church Rep Power: 297	Self admittedly, I know jack squat about A/F ratios, but i'm curious... my AP says that i'm running an avg. of 14.2-14.4 at idle, is that a normal idle ratio? is it only considered running lean at a specific RPM? __________________ 2011 Mustang 5.0 \| 3.55's \| Lethal Performance off road H-Pipe \| Magnaflow Muffler Delete \| JLT CAI/Bama tuned 417whp/ 404 ft/lbs

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03-25-2010, 09:38 AM	#6 (permalink)
mrdino77 Base Member Join Date: Jan 2010 Location: Tampa FL Posts: 52 Drives: 2009 370z Rep Power: 17	Wow I just learned a lot by reading up on this thread. I have a question then, since I will be running FI CBE w/test pipes and might do a K&N Drop in would I need a retune for that as well? I plan on most likely getting a tune anyway but I was just curious if this would also present a case to retune seeing im not actually switching the CAI.