Running Lean

[REDSLED]

Just dynoed my VRL car today on a Dyno Jet and was told that the car was running lean. The air/fuel mixture measured 13.9. The car pulled 461 RWHP and 483 Tq. The car has no engine mods, no headers, no cats but does have K & N filters and small race mufflers with 3" straight pipes. Is this too lean for road racing? I would rather sacrifice a little HP to keep the motor safe. How do I get the motor to run richer? What would a safe air/fuel ratio be for road racing? Any constructive thoughts would be greatly appreciated.

 

[Bad_Byte]

Call John H. at WCV they put a fuel boost pump on mine and brought the A/F down to around a steady 13:1

I actually picked up a little hp.

 

[REDSLED]

Thanks for the tip Art.

 

[REDSLED]

Any more suggestions?

 

[PRVT JET]

13.9 is not that lean at all, your car is tuned for full power. How did they read the a/f?

 

[Bill B]

That's pretty good for a N/A car.
If the car isn't running hot I don't think I would change it.

 

[Larry Macedo]

Ideal would be 13 - 13.5 depending on the mods. Some of the newer imports are rumored to be higher than 14.

 

[REDSLED]

There are no mods to the engine. Still the stock 98 manifolds with the K & N filter set up (cone style) small race muffler and 3" straight exhaust. I have some 1.7 roller rockers coming as well as some headers. These mods should put me pretty close to 500 RWHP you think? I want the car to run safe as I'm not too keen on a rebuild every year. Like I said , I'd rather run the car a little rich and be safe then have the motor grenade on me. Thanks for your replies. The comments are very helpful. Keep em' coming. Would replacing the 02 sensors help out? The prior owner ran race gas in the car and perhaps it had an impact on the sensors?

 

[Bill B]

If he ran leaded gas it will ruin the o2's

 

[REDSLED]

If he ran leaded gas it will ruin the o2's

That's what I'm thinking. I guess I will be ordering 02's from the Wizard on Monday.

 

[Bad_Byte]

Hey J., If you're going to put on headers, I would think about having bungs welded in place for O2 sensor(s) (I'd put on on each side, IMO), for monitoring the A/F once in a while when running around the track. The only tricky part is knowing exactly where to put them so they are easy to get to so you can install/remove them.

Just a thought.

 

[REDSLED]

Good idea Art. I will be calling Horton on Monday.

 

[Jack B]

RedSled:

A boost-a-pump is not the answer. Here is some insight into your post. The dyno has issues, no stock viper does 460 hp. Secondly, most stock vipers do run approx 13.9 in the 2500-3500 rpm region and then start to get rich above 4000.

 

[Jack B]

Redsled:

I should have given some back-up to my comment on the boost-a-pump (BAP). Our cars have a regulator that maintains 55 psi at idle and approx 50 psi at 5200 rpm and wot. The a/f ratio during wot is directly related to this pressure. On a stock or slightly modded car if the pressure drops below the stated pressure there is a problem with the fuel delivery system.

The BAP cannot change the pressure if it is within tolerance and if the pressure is low you first have to fix the problem. Where the BAP is valuable is on high hp cars where the pump cannot keep up with the demand and the pressure drops. In this case the BAP will increase your volume, it still it won't increase the pressure above the 50-55 psi value. The whole idea on a non-fuel return system is to maintain the volume at the oem regulator value (psi).

In summary, the BAP won't affect a/f on a car where the fuel system maintains the oem pressure, in addition, if the the fuel pressure is low that requires correction prior to any other changes.

 

[Bad_Byte]

With all that said Jack, I certainly respect your opinion. However, I can only go by what the dyno says. The first dyno showed my A/F consistantly in the range of 14.5 to 1 all the way up to about 5800rpm.

After the installation of the boost pump I get a consistent A/F of 13:1

I hear what you're saying and certainly understand the issue of fuel pressure and volume. However, I have to go with the dyno.

Perhaps your the system you're thinking of isn't the same system I have.

 

[REDSLED]

Jack B, I read my dyno sheet wrong. It wasn't 461.8 RWHP it was only 451.8 RWHP / 473.2 Tq Oops I have spoken to several respected tuners from this board and they all asked if race gas had been run through the engine. Yes, the previous owner ran race gas and hence they believe the 02 sensors are now junk. They all advised replacing the 02 sensors and to then check the A/F ratio again. I have a fuel cell in the car that has (2) Aeromotive fuel pumps. I checked the pressures and they are both operating normal.
I will return to the dyno after I install the 1.7 Rockers, new 02 sensors & Headers later next week and I will see how what the A/F ratio is as well as how much RWHP & Torque I've picked up with the new goodies. Thanks for your reples.

 

[Jack B]

Redsled:

The O2 sensors may be bad, but, they are not your problem. They can not modify the a/f during wot (open loop). During wot the car runs on a fixed program contained in the PCM. In addition, the OEM sensors are not wide band and do not have the resolution or capability of the after market wideband units.

There is one case where the a/f could be driven by the O2 sensors during wot throttle. If during pre-wot the O2's sense one side is very lean and the subsequent O2 adjustment (short term fuel trim) does not bring it back into range, the PCM will throw a code and make the lean bank full rich to protect it. That is a hard code and would be seen as a "service engine" light.

 

[Russ M]

RedSled,

I would say go to another dyno, sounds like the a/f meter used at this one may be off. Not to even go into the hp produced, no gen 2 is going to pull that type of power with just an exhaust.

Were they using a tail pipe sniffer? If so that is your problem. Now the other thing it could be is that since you are not the original owner the car has more mods to it than you think. It is not uncomon for people to do a little port work here and there to bend the rules set for certain series. And this would also explain the high hp numbers, and the lean mixture.

 

[Russ M]

Almost forgot, have you checked you fuel filter?

 

[REDSLED]

RedSled,

I would say go to another dyno, sounds like the a/f meter used at this one may be off. Not to even go into the hp produced, no gen 2 is going to pull that type of power with just an exhaust.

What do you think a 98 engine should be putting down to the rear with a race exhaust? Just curious, as the numbers weren't that far off from what my 97 pulled at Cragin's a while ago? I will try another dyno and compare the numbers. Thanks for all the replies. I'm just looking to keep my engine from grenading on the track. I will inspect the fuel filters as well. Yes they sniffed from the driver side exhaust only.

Jonathan

 

[Russ M]

If you have no cats, it should pull about 430. This is when the car is warmed up not when its cold and makes the first pull, otherwise you could probably get 445-450 but its not real world numbers.

 

[Gavin]

Have to agree with Jacko - on the 'code to run the lean bank full rich' however my understanding and experience of that code is the following:
1. This code kicks in on a motor that reaches an overheated condition (translated - it gets into the red band on the water temp gauge) The code kicks in to cool the motor down.

2. If an engine is running lean, as Sleds is, it could burn a piston before water temps get to the redline

3. so the code is not designed to prevent piston burn in the event of a lean condition.

More data on Sled HP
This is what I know - I have a modified motor in my VRL car'. At Buttonwillow Sled car pulls equally down the straights as mine does - we have done this a bunch of times.

I have a dyno sheet (via Archer Racing) on my motor 496 RWHP

Sled did this on a cold day - ambiant about 65 Sled? And that was problably outside right? What was the temp in the shed?
Some motors just make more horsepower??
Sled has a fuel pressure problem??
Sled has a modified motor??

 

[viper spray]

The Mopar performance computer will make it run a bit richer and is a good add on for 96 to 99 cars with exhaust mods. yes , I have one for sale. $375 shipped

 

[Fast Viper Dan]

No cats and small mufflers = lean motor.
How much can the CPM adjust the fuel flow? Not a pro here! When changing pipes on a carburetor type motor jetting is a must. So what can be done to "fatten up" the mixture?
boost-a-pump (BAP) and or larger injectors?
Jonathan, too much fuel is better than not enough. IMO
Good Luck,
Dan

 

[Jack B]

Since you have a regulated fuel supply the only way in open loop to fatten up the a/f is with injector control such as the Vec2. The viper doesn't truly run lean. It runs lean in the middle hp range, typically, it runs rich in the max hp range, even with mods. Only as you approach the max injector output does the car start to lean out. This is typically at about 600 fwhp.

 

[REDSLED]

I certainly agree with you Dan. I'd much rather have my car running rich than lean. I put the Mopar race computer back on the car and took it to the track today. The car ran great and the pipes seemed to have more carbon on the tips than previous. Perhaps the car is running a little richer than before? I'm putting new 02 sensors on next week and then I will dyno and check the A/f mixture again. Thanks to everyone for the replies.