Originally Posted by hustler316

Let me see if I can simplify this and try to explain the problem with the lean issue a lot of people seem to have. This car in the stock form has near perfect ARF's, this is because for the amount of boost (forced air) the engine is getting, the injectors and the pump are sufficient in both flow and volume. The stock fuel filter regulates the pressure to the rail, we need around 54 to 60 psi at the rail. The stock pump is also capable of handling the pressure and the flow at stock settings.

Once we starting adding things like pulleys to increase boost this is where we run into trouble. As we add more forced air into the system we then need to add more fuel to the system in order to equalize the equation. You can't add one without the other. What most people do is add a pulley then get a tune to try to add more fuel. This combination will usually work if you are only adding only 1 or 2 more lbs of boost. In this scenario the stock fuel system is sufficient, but if you want more than 2 lbs of boost you start to ask a fuel system to do things it doesn't have the ability to do.

Lets start by looking at the fuel pump, the fuel pump on these cars are quite simple, they are either on of off, they are not regulated by voltage therefore the flow is constant. The problem with the stock pump is it can not keep up with the volume of fuel we are asking it to. When this happens we experience a drop in pressure at the rail at WOT. The numbers we were seeing were 54 psi at the rail during idle and 42 psi at the rail at WOT. At that point it became pretty apparent we needed a new pump. When you replace the pump it has to be replaced with a HIGH flow pump, it is important that it is able flow enough volume to keep up with the demands. Keep in mind the stock fuel filter is still being used, it has sufficient fuel flow characteristics to feed the system.

Next issue to address is the injectors. Remember as we add more air, we need to add more fuel. Since we just added a new high flow pump we now know we have sufficient fuel flow and pressure to the rail. Now how do we get the fuel into the engine, obviously it's via the injectors, so naturally we tell the computer to increase fuel flow through the injectors. The computer in return says "ok" and presto changeo problem solved, right? The answer is maybe...if you are running low to mild boost pressure you may be ok, but if you are running over 16 lbs ish you are probably running out of injector as well. This is why no matter what tune you throw at it it doesn't solve the problem. Although the computer is telling the injectors to add more fuel, they physically are not capable of keeping up with the demands that we are asking them to do. Even if they are able to "just" keep up, the duty cycle at which we are asking them to operate at significantly decreases their life span. So the solution as you may have guessed is bigger injectors, ones that can not only handle the volume but can also do it at a significantly lower duty cycle. This allows you some wiggle room with your tune to add more fuel if needed in the future. It also allows the injector to operate at a much more efficient rate and increases the life span of the injectors.

Moral of the story is, bigger pump, and bigger injectors are needed. Now you may be saying "in theory you may be right, but I think our cars have plenty of injectors and plenty of pump, the pressure is the problem. I think I'll just turn up the pressure to solve the problem". I will tell you with 100% certainty that that is not a solution to the problem, that is a band aid fix for a wound that needs a tourniquet. A lot of information that we have learned about this car has come not only from our race program but also from the SRT division of dodge/chrysler. I have talked extensively with a lot of the people who were involved with the development of this car. SRT is at our track quite frequently testing the Viper and I have the advantage of picking their brains while they are there.

Any question? Class dismissed!

Originally Posted by SRT6 Gang Member

1. Fuel pressure
2. Boost
3. Injectors

You have to address one of the three to prevent leaning.

1. Increase fuel pressure to counteract elevated boost on the injectors.
2. Reduce boost levels so you don’t need additional fuel pressure to counteract the effects elevated boost has on our injectors.
3. Get larger injectors to offset the elevated boost seen by the injectors.

The SL55 fuel pump does not increase fuel pressure enough to counteract elevated boost on the injectors because it is still governed by our filter/regulator setup.