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Discussion Starter · #1 ·
Just curious, what is considered bad in regards to A/F? ANything over 14? 15? Does it matter if it is N/A? Say for example you have a car with a NOS shot making 800 RWHP, but the A/F is 16, is this bad and if so what can happen long term?
 

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No, I'm not claiming to be smart, but 800hp on nitrous @ 16:1 a/f and "long" do not belong in the same sentence unless the long is referring to the trail of oil /images/graemlins/smiles

N/a can go leaner than s/c applications. I was reading some surprising stuff about nitrous pro mod cars the other week......they are running very rich...something in the 9:1 ?? area.
 

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16:1 and that engine is not long for this world.

Optimum a/f ratios will vary depending on the engine. Many variables with the engine will determine just what is optimum.

Lets look at one IIRC one ULEV Honda engine. These things run at around 17:1 and I have heard also as lean 19:1

It all depends........

If memory serves me, what about Tuners who set up the Vipers a/f rich saying that under speed the added air fed in thru the NACA duct will lean out the a/f ratio? Yet many say the NACA duct adds Zero extra forced air?


Riddle me this Batman, just what is optimum and what is not? No one correct answer for this question.



 

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Discussion Starter · #4 ·
Jerome said:
16:1 and that engine is not long for this world.

Optimum a/f ratios will vary depending on the engine. Many variables with the engine will determine just what is optimum.

Lets look at one IIRC one ULEV Honda engine. These things run at around 17:1 and I have heard also as lean 19:1

It all depends........

If memory serves me, what about Tuners who set up the Vipers a/f rich saying that under speed the added air fed in thru the NACA duct will lean out the a/f ratio? Yet many say the NACA duct adds Zero extra forced air?


Riddle me this Batman, just what is optimum and what is not? No one correct answer for this question.
Well let's just talk about the V-10 since that is what this board is all about. If you're running 12-13, I would think you're safe and making that power with a bit of safety built in for any given changes, but at 16-1 I would think it is on the edge of destruction, am I wrong? /images/graemlins/confused /images/graemlins/confused
 

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An optimum A/F ratio at least for a supercharged motor generally is in the neighborhood of 13:1 to 14:1 at idle, and then it tapers off (along with the timing) as the RPM and Boost increase. I have seen motors at 3 bar in the 11.5 to 12 range, obviously the leaner you go the closer you are dancing with the devil. Every motor is different and the only good way to skate close to the edge is do some full throttle runs and immediately check your plugs. Look for aluminum specks (of your pistons), etc.
 

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Under WOT, you are asking for it at 16:1, especially with a power adder. Although under part throttle conditions, lean can be safe and offer much better mileage. Same goes for timing, you can run nearly twice the timing advance at part throttle aiding in throttle tip-in and again, mileage.

Viper tuners seem to be extremely conservative in their tunes, never crossing the 12:1 threshold, at least to the public.
 

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ive been told that 12.9-13.1 is optimum for NA. mid to high 11s for nitrous
 

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Discussion Starter · #8 ·
V10 MOJO said:
ive been told that 12.9-13.1 is optimum for NA. mid to high 11s for nitrous
What is your A/F there MOJO? And call me back, check your voice mail! :nod:
 

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my AF, after last dyno tune in, was a steady 12.8-13.1 across the board. I then got it to mid/high elevens on the juice which is safe for that application. now this was all dyno work so no true tuning was done, however it seems to be running just fine since then.

i am wanting to purchase one of those devices to more accurately measure the AF while driving, just waiting to learn a bit more so as to get the best product out there and to use it to the best of its capability.

I have to go retune the car this week since ive made some "changes" since columbus V10 nats /images/graemlins/toothy
 

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In closed loop and light throttle, the oem pcm keeps the car in a 14-15 range. When tuning with a device such as a VEC2, optimum hp on a NA car is approx 13:1.

Nitrous imposes many vaiables, therefore, you need a margin for error. The leanest you want to go is 11.5-12 and that is cutting it close. By going richer you can soften the nitrous blow or reduce the torque at turn-on and still get max hp at higher rpm's.
 

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Viper Spray,

I have one of the AEMs on my car. Works great!

As to the question of AF ratios, I think that under cruise, 14-15 is desirable for most cars. Under load or under open loop conditions (such as WOT) the desired AF ratio is a function of many things (like Jack B said).

NA ... target 13.0 - 12.5

SC/NX/Turbos increase cylinder pressure. To avoid detonation, tuners increase the amount of fuel in the mix (decrease the AF ratio). The extra fuel actually cools the mixture in the cylinder before ignition which helps prevent detonation. For these cars the target is generally 10.5 - 11.5. Hope this helps.
 
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