Air Fuel Ratio?
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Pro
Joined: Nov 2004
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From: Frisco TX
Air Fuel Ratio?
Yesterday was my first time on the Dyno. Turned a measley 232 RWHP with a whopping 309.7 Max Torque (I am happy with the Torque). I was expecting more but this post is not about that.
The Dyno included a reading on the Air Fuel Ratio (AFR) at the exhaust. It started out at 65 MPH on the scale (First scale is Speed, second pull was printed with RPM) and the AFR was setting at about 13.7. He stomps on it and at 70Mph it droppped to 12.0 and stayed there until he let off the gas.
On the second run it started out at 16 at 2600 RPM and then at went this way
3100 \ 12.9
3400 \ 12.2
4000 \ 12.9
4400 \ 12.4
4600 \ 12.1
4800 \ 12.0
then he let off.
So, my question is... Is this a normal AFR? Should I try and get this up or down or keep it at this rate? Is this rating a %?
12% fuel to 88% air?
Here are the details on the car.
89 L98
A4
3.07
Headman LT Headers
3" RT Cats
3" Dual all the way back
Cutouts open at the back of the car
K&N w\cut lid
MSD
Frisbee Removed
New Plugs, Wires, Cap, Roter
The Dyno included a reading on the Air Fuel Ratio (AFR) at the exhaust. It started out at 65 MPH on the scale (First scale is Speed, second pull was printed with RPM) and the AFR was setting at about 13.7. He stomps on it and at 70Mph it droppped to 12.0 and stayed there until he let off the gas.
On the second run it started out at 16 at 2600 RPM and then at went this way
3100 \ 12.9
3400 \ 12.2
4000 \ 12.9
4400 \ 12.4
4600 \ 12.1
4800 \ 12.0
then he let off.
So, my question is... Is this a normal AFR? Should I try and get this up or down or keep it at this rate? Is this rating a %?
12% fuel to 88% air?
Here are the details on the car.
89 L98
A4
3.07
Headman LT Headers
3" RT Cats
3" Dual all the way back
Cutouts open at the back of the car
K&N w\cut lid
MSD
Frisbee Removed
New Plugs, Wires, Cap, Roter
Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
I'm curious exactly what type of numbers you were hoping for. Sure there's a little to be found by tweaking the tune a little but don't expect a lot. You've improved the ability for your car to get rid of exhaust but without doing anything significant to help get more air in, the gain is minimal.
Ditch the TPI, put a cam in it and throw on some new heads and you'll see much better horsepower numbers. I'm not trying ot burst your bubble, but a lot of these bolt ons and freebies such as the K&N, open lid, frisbee, etc all amount to maybe 1 HP at the end of the day. The exhaust can be a restriction once you start doing other mods, but in stock form it isn't really holding you back much.
The key to making big horsepower is the proper combination of parts. You've free'd up your exhaust which certainly won't hurt anything. It didn't really give you much now, but it will open the doors for you to make bigger power down the road when you start working on other mods. The funny thing about cars is that the horsepower gained from a proper combination of parts is greater than the sum total of all the parts if they were installed individually.
Ditch the TPI, put a cam in it and throw on some new heads and you'll see much better horsepower numbers. I'm not trying ot burst your bubble, but a lot of these bolt ons and freebies such as the K&N, open lid, frisbee, etc all amount to maybe 1 HP at the end of the day. The exhaust can be a restriction once you start doing other mods, but in stock form it isn't really holding you back much.
The key to making big horsepower is the proper combination of parts. You've free'd up your exhaust which certainly won't hurt anything. It didn't really give you much now, but it will open the doors for you to make bigger power down the road when you start working on other mods. The funny thing about cars is that the horsepower gained from a proper combination of parts is greater than the sum total of all the parts if they were installed individually.
Thread Starter
Pro
Joined: Nov 2004
Posts: 677
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From: Frisco TX
Originally Posted by Nathan Plemons
I'm curious exactly what type of numbers you were hoping for. Sure there's a little to be found by tweaking the tune a little but don't expect a lot. You've improved the ability for your car to get rid of exhaust but without doing anything significant to help get more air in, the gain is minimal.
My question was not about the HP results though...
Tim
Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
Nope, that's just what the TPI cars make, sorry. You'll always be glad that you made the baseline though, it'll really let you see how the mods help out.
For your A/F question it is the ratio, not the percentage. You read it as say 12.9:1 or 12.9 to 1. This means there are 12.9 parts air for every one part fuel, which doesn't fall directly into a percentage. Imagine you had 1 pound of fuel, to obtain a 12.9:1 ratio of air to fuel, you would need to mix it with 12.9 pounds of air.
If you want the percentage you would have to look at the total. Since you have 1 pound of fuel and 12.9 pounds of air, that's a total of 13.9 pounds of material. 1 pound of fuel out of 13.9 pounds total would give you approximately 7% fuel and 93% air. Make sense?
Also as far as what air / fuel ratio is "perfect" for your car, well that depends on your car, the dyno, etc. For example one car with one wide band may make the most power at 12.5:1 while on another dyno with another A/F gauge it may read 13:1. The car is still running at the same real ratio, but other factors may be affecting the reading, such as exhaust leaks, placement of the sensor, etc. 12.9 is very much "in the ballpark" but you'd really have to just play with the tune to figure out exactly what your car likes the best.
For your A/F question it is the ratio, not the percentage. You read it as say 12.9:1 or 12.9 to 1. This means there are 12.9 parts air for every one part fuel, which doesn't fall directly into a percentage. Imagine you had 1 pound of fuel, to obtain a 12.9:1 ratio of air to fuel, you would need to mix it with 12.9 pounds of air.
If you want the percentage you would have to look at the total. Since you have 1 pound of fuel and 12.9 pounds of air, that's a total of 13.9 pounds of material. 1 pound of fuel out of 13.9 pounds total would give you approximately 7% fuel and 93% air. Make sense?
Also as far as what air / fuel ratio is "perfect" for your car, well that depends on your car, the dyno, etc. For example one car with one wide band may make the most power at 12.5:1 while on another dyno with another A/F gauge it may read 13:1. The car is still running at the same real ratio, but other factors may be affecting the reading, such as exhaust leaks, placement of the sensor, etc. 12.9 is very much "in the ballpark" but you'd really have to just play with the tune to figure out exactly what your car likes the best.
Le Mans Master
Joined: Apr 2000
Posts: 6,341
Likes: 1
From: Shelton CT
Lower Your Fuel Pressure if you have an AFPR, or tune it via a chip for lower FP. Make sure your timing is at 6-8degrees advanced, get soem GOOD gas. Otherwise with yoru mods, your #'s are pretty much dead on..
Looks like you've picked up around 35hp from your mods. I'd say thats close to what you should be at.. With the above tuning of the A/F ration you might see another 10-20.
Heck when I dynoed the car (before my major mods, only bolt ons), I went from 228RWHP to 251RWHP by lowering the FP to 38psi from 43psi...
Looks like you've picked up around 35hp from your mods. I'd say thats close to what you should be at.. With the above tuning of the A/F ration you might see another 10-20.
Heck when I dynoed the car (before my major mods, only bolt ons), I went from 228RWHP to 251RWHP by lowering the FP to 38psi from 43psi...
Safety Car
Joined: Dec 2004
Posts: 4,088
Likes: 0
From: Poop land
For some reason, my TPI had about the same numbers but because of the SuperRam, the numbers occur at higher rpms. Dunno if that sounds good but my torque curve flatter than it was with the stock "spider" intake.
Le Mans Master
Joined: Apr 2005
Posts: 8,077
Likes: 4
From: Scarborough ONTARIO
Nathan and Alvin is right, here is a live example for u, check my sig for mods and i got 277 Rwhp and 398 Rwt, Ditch the Tpi slam some nice 21x/22x Cam and not more than 200cc heads u will see a big huge diff at horse power. Try not to make PEAK HP instead let power came early in the curve, to achieve this slam some mild Cam not more than 220 intake duration.
I wish i had listen to Nathan before i did mod to get rid of TPI, still looking for some cheap used SR upper.
I wish i had listen to Nathan before i did mod to get rid of TPI, still looking for some cheap used SR upper.
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Drifting
Joined: May 2003
Posts: 1,730
Likes: 1
From: Charlotte NC
St. Jude Donor '05
Guys i've got simularly equipped MR and SR 90-91 Vettes in the dyno sheet section on our website. The mini ram lacks some torque but pulls past 5500 no sweat.. The SR makes more torque but falls off much past 5200 RPM.
Both cars had a really good set of heads (not exactly equal but very close) and both had a 219 L cam.
Both cars had a really good set of heads (not exactly equal but very close) and both had a 219 L cam.
8th Gear
Joined: Oct 2005
Posts: 8
Likes: 0
Form vajenson@aol.com, I ran my stock LT-1 on a dyno last week. I got 277 hp on the third run. It also showed 12%. I was told to get the download from a firm for $450.00 and they would change the shift points, lean to 11% and probably get close to 300 rwhp? Let me know what you think. Maybe they are BSn me? I have a 96 w/ 51k miles and automatic. He ran the dyno up to 135 mph in drive to get the #s. Bill
Race Director
Joined: Jan 2002
Posts: 12,261
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From: O'Fallon Missouri
Originally Posted by vajenson
Form vajenson@aol.com, I ran my stock LT-1 on a dyno last week. I got 277 hp on the third run. It also showed 12%. I was told to get the download from a firm for $450.00 and they would change the shift points, lean to 11% and probably get close to 300 rwhp? Let me know what you think. Maybe they are BSn me? I have a 96 w/ 51k miles and automatic. He ran the dyno up to 135 mph in drive to get the #s. Bill
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
The stoch A/F is about 14.7:1 so it looks like that gauge was reading a little low before going to WOT. That offset could account for the low WOT values.
The best way to determine best A/F would be to install an AFPR and get several pulls with various fuel pressures. Of course you would need to be sure that coolant temps were the same (or nearly so) on each comparitive pull.
The best way to determine best A/F would be to install an AFPR and get several pulls with various fuel pressures. Of course you would need to be sure that coolant temps were the same (or nearly so) on each comparitive pull.
8th Gear
Joined: Oct 2005
Posts: 8
Likes: 0
Dyno on 96 LT-1
I saw you numbers and was surprised at either mine are wrong or? Anyway I had 3 pulls and on the best and last I got 300 ft # @4550 rpms and 277hp @5050 rpms. I hope these are good #s as I only have 50k miles on the car and I only have changed the air cleaner to K&N. The next one I will copy an scan so I can send it. Bill
Thread Starter
Pro
Joined: Nov 2004
Posts: 677
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From: Frisco TX
Originally Posted by vajenson
I saw you numbers and was surprised at either mine are wrong or? Anyway I had 3 pulls and on the best and last I got 300 ft # @4550 rpms and 277hp @5050 rpms. I hope these are good #s as I only have 50k miles on the car and I only have changed the air cleaner to K&N. The next one I will copy an scan so I can send it. Bill
My car is an 89 and has an L98 motor in it. They are known for high torque. Your car might be right were it should be.
Tim
Melting Slicks
Joined: Dec 2000
Posts: 2,719
Likes: 60
From: Fremont Oh
Originally Posted by vajenson
I saw you numbers and was surprised at either mine are wrong or? Anyway I had 3 pulls and on the best and last I got 300 ft # @4550 rpms and 277hp @5050 rpms. I hope these are good #s as I only have 50k miles on the car and I only have changed the air cleaner to K&N. The next one I will copy an scan so I can send it. Bill
The stock spec for your LT1 is like 340 lbs@4600 and 300 HP @5000 I'd say your looking good was this on a Dyno jet dyno ? ~guessing so~
So the difference is the intake on an LT1 and the L98 the L98's have more low end torque and longer intake runners.
Mo
