Boost...A/F....
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From: Colorado Springs
Boost...A/F.... setup
turbo car
race gas
12.5 psi
18 degrees timing @ wot
A/F ratio is 10:1 @ wot
---------------------------
question...without changing nothing to the tune but
a. add 1psi of boost so now 13.5psi
what will the A/F ratio read?
b. add 2psi of boost so now 14.5psi
what will the A/F ratio read?
c. add 3psi of boost so now 15.5psi
what will the A/F ratio read?
take into consideration that
1. car is intercooled and is more than sufficient
2. fuel system is adequate - no loose in pressure
3. engine is forged low comp
turbo car
race gas
12.5 psi
18 degrees timing @ wot
A/F ratio is 10:1 @ wot
---------------------------
question...without changing nothing to the tune but
a. add 1psi of boost so now 13.5psi
what will the A/F ratio read?
b. add 2psi of boost so now 14.5psi
what will the A/F ratio read?
c. add 3psi of boost so now 15.5psi
what will the A/F ratio read?
take into consideration that
1. car is intercooled and is more than sufficient
2. fuel system is adequate - no loose in pressure
3. engine is forged low comp
9 Second Club
Joined: Feb 2002
Posts: 985
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From: Lake Orion, MI
Are you doing this for driving around town or getting ready to run at the track?
You are still runing stock cubes, moto 60s with boost refrenced regulator right?
What pump are you running?
At the very least, get off the halvesies and go to .0s
As hawk said, keep an eye on the wideband and Go a 1lb at a time until A/F settles where you are comfortable or you get some knock. Then just turn it back down a 1lb.
On race gas you'll probably be able to run 14lbs easy enough and it will be a different car. There will probably be some fine tunning required at 15lbs but you might be able to squeeze it in without a problem. 
Rick
You are still runing stock cubes, moto 60s with boost refrenced regulator right?
What pump are you running?
At the very least, get off the halvesies and go to .0s
As hawk said, keep an eye on the wideband and Go a 1lb at a time until A/F settles where you are comfortable or you get some knock. Then just turn it back down a 1lb.
On race gas you'll probably be able to run 14lbs easy enough and it will be a different car.
There will probably be some fine tunning required at 15lbs but you might be able to squeeze it in without a problem. Rick
Thread Starter
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From: Colorado Springs
Originally Posted by 2001-WS6
Are you doing this for driving around town or getting ready to run at the track?
You are still runing stock cubes, moto 60s with boost refrenced regulator right?
What pump are you running?
You are still runing stock cubes, moto 60s with boost refrenced regulator right?
What pump are you running?
stock cubed iron block...i got the rest of my fuel system done. twin intank...-8 feed...60 motos....fpr....etc...etc...
I guess I am a little confused as to what A/F ratio is the measure of..and factors change it..or dont change it.
is A/F dependant upon the octane of the gas?
if i have an A/F of 11.5 with 91 octane...no changes to tune/same boost...put in race gas...will the A/F still read 11.5?
9 Second Club
Joined: Feb 2002
Posts: 985
Likes: 7
From: Lake Orion, MI
My simple summary would be:
A/F is the mix of air and fuel in the intake charge. It is not directly affected by the octane of the fuel. Each fuel has different specific gravity/weight characterists to it. So a gallon of your local 91 octane gas may have slightly more or less burnable fuel in it than a gallon of Turbo Blue, Torco 110 or C16. There will therefore be some slight changes in A/F between fuels when you run them. So there is some fine tuning required to keep each fuel at the same target A/F. Your fuel system is up to the challenges of moving the volume of any fuel that might be required.
Higher octane fuels do help resist detonation because the octane slows the burn rate and allows a more complete burn of the fuel charge. The higher octane may let you target a slightly more aggressive (leaner means hotter burning process, upping the risk of detonation) A/F ratio than you would normally. Or you could run more timing then you would on a lower octane fuel with a lower risk of detonation. The perfect tune is accomplished by a mix of these two options for a given boost level on a setup.
The stock PCM, in closed loop, will try to manage the A/F within the boundaries of your tune. It will learn to adjust somewhat for the differences in the fuel over time. The O2 sensors are going to start getting touchy after 5-10 tanks of race gas probably. The options are to get another set of O2 sensors to finish out the year or tune it for open loop and loose some of the PCM's brain power.
Rick
A/F is the mix of air and fuel in the intake charge. It is not directly affected by the octane of the fuel. Each fuel has different specific gravity/weight characterists to it. So a gallon of your local 91 octane gas may have slightly more or less burnable fuel in it than a gallon of Turbo Blue, Torco 110 or C16. There will therefore be some slight changes in A/F between fuels when you run them. So there is some fine tuning required to keep each fuel at the same target A/F. Your fuel system is up to the challenges of moving the volume of any fuel that might be required.
Higher octane fuels do help resist detonation because the octane slows the burn rate and allows a more complete burn of the fuel charge. The higher octane may let you target a slightly more aggressive (leaner means hotter burning process, upping the risk of detonation) A/F ratio than you would normally. Or you could run more timing then you would on a lower octane fuel with a lower risk of detonation. The perfect tune is accomplished by a mix of these two options for a given boost level on a setup.
The stock PCM, in closed loop, will try to manage the A/F within the boundaries of your tune. It will learn to adjust somewhat for the differences in the fuel over time. The O2 sensors are going to start getting touchy after 5-10 tanks of race gas probably. The options are to get another set of O2 sensors to finish out the year or tune it for open loop and loose some of the PCM's brain power.
Rick
The stock PCM, in closed loop, will try to manage the A/F within the boundaries of your tune.
Also the race gas will only start messing up the O2 sensor if you go leaded.
Jim
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9 Second Club
Joined: Feb 2002
Posts: 985
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From: Lake Orion, MI
Originally Posted by DeltaT
Doesn't the stock PCM go open loop after a certain TPS? I don't know your PCMs at all but most do this.
Also the race gas will only start messing up the O2 sensor if you go leaded.
Jim
Also the race gas will only start messing up the O2 sensor if you go leaded.
Jim
Most people won't stop at 100 or 104 octane unleaded when they are looking for race gas.
Rick
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Huh???? 
TECH Resident
Joined: Nov 2002
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Also are you running a 2 or 3 bar SD tune? Maybe the a/f will remain the same, but you really need to check with a wideband.
If running a MAF tune, it will definitely get leaner as you increase the boost because the computer will see no difference (IE. MAP sensore useless, and MAF maxed out...)
Tommy
If running a MAF tune, it will definitely get leaner as you increase the boost because the computer will see no difference (IE. MAP sensore useless, and MAF maxed out...)
Tommy