wheelieking
Novice Class
Posts: 41
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posted October 30, 2007 07:11 PM
BMC Air Fuel Ratio Question
Fellow Tuning Experts
Can some one give me some direction on this. I am looking at my last dyno run in combination with another 5 months prior. Horsepower numbers differ greatly due to the correction factor going from SAE .98 to 1.18. The 1.18 was on a cool day with 0 humidity... the reading was way off (like 201hp with a akro pc3r yea right). Question one... the AF ratio looks similar for both runs at different times even thought the hp numbers differ greatly. Is it safe to assume that even thought the dyno was messed up the AF should stay somewhat similar. That answer provides credibility to the next question. My AF ratio is around 12 from 2k to 5k rpm. Then it hovers around 12.5 until 8500 rpm. Then it starts to slowly rise up to 13.5 and carries 13.5 from 10k to 11k rpms. I have stock filters with a race akropovic. My logic was the BMC race filter would cure my richness down low and make it run better from 2-9k rpm.. more power I think.?. But I am alittle scared thinking that my AF ratio might go up from the 13.5 in the upper rpms.. that is if the AF is correct. I think this would result in more top end horse power but should I be worried about this AF ratio up top? And What kind of difference would I expect to see in the AF ratio by adding the BMC race. I would like to avoid dyno tuning. I do not have anyone close that I trust. I am using the dyno jet akropovic map with stock filter with some timing advance added in. I have not found an akropovic map with the bmc race filters yet.
Vince? Doug? Phantom? Ice man? Shiphteey? Mad Mike? Gadsen? Muzzy? Supra? Ridge?
Thanks
  
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MadMike
Moderator
FEAR THE BLACK FLAG!!!!!!!!
Posts: 6579
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posted October 30, 2007 08:14 PM
I think you are good up top... your A/F will be adjusted by the sensor's so Ideally it should be the same any time of the year... or close to... my personal opinion I think you are way to fat down low... I believe we have shot for 13.5 all the way across on my stuff...
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wheelieking
Novice Class
Posts: 41
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posted October 30, 2007 08:26 PM
quote:
I think you are good up top... your A/F will be adjusted by the sensor's so Ideally it should be the same any time of the year... or close to... my personal opinion I think you are way to fat down low... I believe we have shot for 13.5 all the way across on my stuff...
but will it go to 14 or so with the filter?.. or just a couple decimal points
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rgeorge
Expert Class
Posts: 220
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posted October 31, 2007 03:04 AM
 Edited By: rgeorge on 31 Oct 2007 04:09
quote:
...your A/F will be adjusted by the sensor's so Ideally it should be the same ...
+1
The ECU calculates the amount of fuel added based on (among other things) the inlet air pressure sensor reading. If you use a more free flowing filter, the manifold absolute air pressure will be higher for a given TPS and RPM. The ECU will add more fuel accordingly. IMHO the ECU does a very good job of this. I have done back to back runs with dirty/clean K&Ns, my datalogs show the same AFR for both runs but the inlet pressure was higher with clean filters (and I had more power).
If you are worried about not being rich enough at upper rpms, edit your PC map. While you are at it, you can remove fuel on the lower end.
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entropy
Moderator
Posts: 8671
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posted October 31, 2007 03:17 AM
quote:
Fellow Tuning Experts
Horsepower numbers differ greatly due to the correction factor going from SAE .98 to 1.18.
I'll say the hp numbers would "differ greatly"... 
1.18!!!!!????????
what altitude was the dyno at??
a cool day w/0 humidity should give a correction factor close to 1.0 unless you are at WAY high altitude, and then the .98 doesn't make sense.
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wheelieking
Novice Class
Posts: 41
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posted October 31, 2007 10:26 AM
should I be worried about this AF ratio with a bmc race filter... or is it considered acceptable?
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VincentHill
Needs a life
Posts: 6520
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posted October 31, 2007 12:18 PM
The Race Filter WILL Lean it out some more! Also under a Load that will lean it out More Yet! The "Adjustments" everyone is talking about that the System will do (as far as I am concerned) adjust for the "Extra" incomming Air. I do not think it will add fuel to give you a Richer Mixture because without an O-2 Sensor it does not know if your are lean or rich!!
The PC3r can Flip Flop on Timing like the Republicans on the Treatment of War Veterans! Ask me about the Mapping changes that come out of No where (20 to 30 are the real numbers in the timing maps!) Look there first! All you should see is somewhere between 0 to 7 which is a lot of additional Timing!
(Sorry I just watched Rudy a little while ago and had to vent)
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wheelieking
Novice Class
Posts: 41
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posted October 31, 2007 03:19 PM
quote:
The Race Filter WILL Lean it out some more! Also under a Load that will lean it out More Yet! The "Adjustments" everyone is talking about that the System will do (as far as I am concerned) adjust for the "Extra" incomming Air. I do not think it will add fuel to give you a Richer Mixture because without an O-2 Sensor it does not know if your are lean or rich!!
The PC3r can Flip Flop on Timing like the Republicans on the Treatment of War Veterans! Ask me about the Mapping changes that come out of No where (20 to 30 are the real numbers in the timing maps!) Look there first! All you should see is somewhere between 0 to 7 which is a lot of additional Timing!
(Sorry I just watched Rudy a little while ago and had to vent)
My timing figures are around 4. Are you saying that the pc3r can change from 4-20 with out touching it?.. Do you think that I am at risk with with my AF ratio?
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VincentHill
Needs a life
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posted October 31, 2007 03:27 PM
quote:
My timing figures are around 4. Are you saying that the pc3r can change from 4-20 with out touching it?.. Do you think that I am at risk with with my AF ratio?
YES!! My bike staarted to run differently and I checked my map and found the timing all over the place! It is just something you should look at because timing can burn more or less fuel! Late timing does not burn as much and makes it look rich because it is sending some unburned fuel out the exhaust. Early timing will do the oposite.
All I am saying is just make sure your Timing map is as you set it! Because of just these kinds of problems they stopped making the "r" Version of the PC3 . Most likely you are OK but you NEVER KNOW! I would add more fuel to bring it to 12.8 to 13.0 because during dyno runs the engine is not loaded enough to get the real readings. WHen they do the mapping and the engine is under a load, that is a LOT Closer!
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dougmeyer
Needs a job
moderated
Posts: 2713
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posted October 31, 2007 04:02 PM
Hold on, Vince is chasing Zebras.
Yes, the free-er flowing filters will allow more air to the engine and yes the ecu will compensate (slightly). Leaner is mo betta' the further you get from peak torque (like over 9)
I might like to see 13.2 or so but you aren't hurting anything.
Doug
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ridgeracer
Pro
Posts: 1309
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posted November 03, 2007 08:31 AM
Edited By: ridgeracer on 3 Nov 2007 09:36
First thanks for including me in a list of 'tuning experts' but while I'm a competent Electronics Engineer my tuning experience amounts to knowing a guy who had his bike on a dyno once
But maybe I can shed some light on the question of ECU compensation.
From the ECUs perspective the issue here is Volumetric Efficiency or VE. The volume is the difference between the piston at TDC and BDC. The efficiency has to do with how fast you can fill that volume. A cylinder with no head has a 100% VE. But soon as you start sucking air thru valves, throttle bodies, air boxes, FILTERS, the VE changes. Also how well the exhaust scavenges effects VE.
So why is VE important? Well for the bike to deliver the right ratio of fuel mass to air mass it needs to know what the air mass is. There are to ways to do this. Measure it with a Mass Air Flow sensor (MAF) or calculate it using Manifold Absolute Pressure (MAP) The zx-12 uses MAP. Now the air flow thru the engine changes at different engine speeds and throttle settings. It is to complex to describe with a single formula so the ECU has a VE map.
The VE map describes how much air the engine will flow when the manifold is at a given pressure and the engine at a given RPM. Add density to this calculation and you have your air mass. Understand however that this is basically an educated guess. The prototype engine at the factory flowed this much on the test stand at this rpm and manifold pressure so yours will too.
Guess what happens when you start changing parts on your engine, thats right, the VE map no longer accurately describes your bikes flow. Remember your MAP sensor is not measuring the flow its used to look up a map value that is the flow on a stock bike.
So back to the filter question. What happens when you put a less restrictive filter on an otherwise stock bike? Adding the filter increases the VE of the engine by providing more air pressure for a given condition. It also increase the MAP sensor number which moves the ECU up the VE map. Your increasing the VE but your also moving to an increased VE section of the map. Is it a perfect correlation? Probably not, but its in the right direction. The ECU will do a good job of compensating for a new filter on an otherwise stock bike. To the ECU it just 'feels' like more ram air.
Now what about a better scavenging pipe on a bike with a stock filter? This is also going to increase the actual VE of the engine but it is going to lower the MAP number and move the ECU into a lower VE region of the VE map. Here you have the engine flowing more than stock and the ECU thinking its less than stock. Less air, less fuel says the ECU as it leans out the fuel when it should increase it.
What happens when you add a better filter to your better pipe? You will bring the MAP number back up and get in higher VE region of the VE map but you will also be increasing the actual VE with your less restrictive filter and your less restrictive pipe. The bike will still run lean especially in RPM ranges where the stock pipe and the aftermarket pipe differ the most.
So to summarize:
New filters, stock pipe ECU handles well
New pipe, stock filter ECU handles poorly
New pipe, new filter ECU better than above until the bike comes 'on the pipe'
This is the VE map of the 12. I hi-lited the boundary region so you could see the peaks and valleys.
http://www.bikeland.info/images/ecu/VE.JPG
Adam Wade, a guy who writes books on fuel injection, remarked to me that this pattern is caused by all the different components having peak efficiencies at different RPMs and the valleys occur when they are out of phase, peaks when they get in phase and all coming together at peak power. If your pipe peaks when the stock pipe peaked then the ECU will handle it better than if your pipe peaks at 8000.
This probably explains why some of you can't solve the Muzzy pipe dip with just a PCIII which only adjusts by throttle and rpm. The problem is the VE is going to be different at 5000 rpm at 50% throttle in first gear than 4th gear because of the ram air.
If only there were some way to get inside the ECU and adjust the VE map...... 
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wheelieking
Novice Class
Posts: 41
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posted November 03, 2007 01:29 PM
Thank you very much everyone. I feel mo educated now...
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KZScott
Needs a life
high on speed
Posts: 7235
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posted November 03, 2007 02:56 PM
quote:
If only there were some way to get inside the ECU and adjust the VE map......
i wonder who we could get to try that out? :P
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VincentHill
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posted November 03, 2007 06:33 PM
Neat Stuff RR! What I said about it still being lean if it started out lean! You mentioned the Muzz Man's pipe that has the problem between 2 to 3,000 RPMS! Let us go there for a moment! 90% of the time when this problems occurs, it occurs in 1st gear, between (My Guess 20 to 30 MPH, and at Partial throttle (Again my guess at about 10 to 25% throttle!
I would not think that "Ram AIr" WOuld have much off set at those speeds and since each gear is different, and most of the times this is in 1st gear different so the gear is not in play either.
My Question is, can you map out a cure that they could use in their PC3??
I spent a LOT of time tuning my 4-2-1 Hindle and when finished, from Idle up, the thing was touchy. It was light on the front and very agressive in power to throttle. Can this be done with the Muzz mans pipe?
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ridgeracer
Pro
Posts: 1309
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posted November 04, 2007 06:56 AM
quote:
Neat Stuff RR! What I said about it still being lean if it started out lean! You mentioned the Muzz Man's pipe that has the problem between 2 to 3,000 RPMS! Let us go there for a moment! 90% of the time when this problems occurs, it occurs in 1st gear, between (My Guess 20 to 30 MPH, and at Partial throttle (Again my guess at about 10 to 25% throttle!
Look at this map again...
http://www.bikeland.info/images/ecu/VE.JPG
...around 2000 rpm at lower pressure (the left third) the map is in a hole, the lowest part of the whole map. By mid map its 'average' for its region but by the last third its peaking. Remember this map describes how well the stock bike can move air which it obviously didn't do well at low pressure around 2000 rpm.
I think the Muzzy pipe fixes that problem but nobody bothered to tell the ecu.
quote:
My Question is, can you map out a cure that they could use in their PC3??
Not with the PC by itself. While the pressure does somewhat track with throttle I'm guessing its not close enough and lags the throttle. If it did track the PC3 would have solved this problem long ago. Any thing you do will be a compromise. That 2000 area is a bitch. Compare it to other rows.
Look at 4600 rpm. Its trending high at low-map, mid-map, and hi-map.
Look at 8000 rpm. Its trending low at low-map, mid-map, and hi-map.
Look again at 2000 rpm. Its low at low-map, trending average at mid-map, and trending high by hi-map.
That has got to be harder to compensate for than anywhere else on the map.
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VincentHill
Needs a life
Posts: 6520
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posted November 04, 2007 01:45 PM
What you said was the Best compliment ever given to the Muzz Man's pipe! It also explains why it is so hard to resolve! U da Man!! Thanks!
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supra5677
Pro
Posts: 1279
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posted November 08, 2007 08:49 AM
put in the bmc and you'll probably be at 13.0 to 13.2 to 1... good stuff
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VincentHill
Needs a life
Posts: 6520
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posted November 08, 2007 04:53 PM
quote:
put in the bmc and you'll probably be at 13.0 to 13.2 to 1... good stuff
??How will flowing MORE air "Richen" his A/F?? You have the right amount of change but it would be that much LEANER 13.6 to 13.8
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