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Running lean with speed density mods?

4K views 14 replies 8 participants last post by  jcmeci 
#1 ·
Being that the charger is a speed density system, are you afraid you are opening up the exhaust and intake and creating a lean condition? I think the Mass Air systems can adjust for this pretty well.. But the speed density systems have a pretty set fuel timing setup.. Thoughts?
 
#3 ·
From what I have seen these cars run too rich anyway.
Also, there is an open debate on how much the PCM can adjust closed loop programming.
We do know that some of the stored information while in closed loop "calibrates" the open loop programming. But it is still using the factory relations between the inputs to establish injector pulse length.
Closed loop programming is as adaptive as MAF systems. So cruising around the car will be fine.
 
#5 ·
I recall GoDaddy saying his exhaust got deeper and more blubbery when he installed the Jet Stg. 2 chip.. Which makes me think it was running a little lean before the install...
 
#6 ·
How would a better flowing intake make it richen the mixture? Because it is sampling more air? I figure more air in, more air in the mix, unless it can sample that and adjust accordingly.. :)

You know more about this than me and have done a lot more testing, I'm not contesting what you say, just trying to learn..


maneval69 said:
One more thing.
Headers should lean the mix and a freer flowing intake should make it run richer.
 
#7 ·
Considering that the Daytona has a freer flowing exhaust and Dodge sells a Mopar CAI, I don't think the car should be running dangerously lean. You can bet your bum Dodge tested the snot outta the CAI on the Daytona. Warranty claims cost them money, and they will do everything they can to avoid it.

To further my point...there are many other variables that could make your car run lean, but the programming and sensors take care of it. For example running the car at 10,000ft above sea level and then dropping the altitude to sea level, you have more oxygen available...in the winter time the air is denser and you have more air available.

Do you know why you see power gains when you add a CAI or it gets colder? It's not the air on it's own-since you have more air to play with you can add more fuel to maintain the correct A/F ratio and hence make more power.


I'm definitely not an expert on the electro-gizmos (I'm a mechanical engineer-give me gears and pistons baby!) but to a certain extent the ECM will adjust for changing environmental conditions (or mild mods).

Hope this helps somebody!!! :D
 
#8 ·
SmoothSL said:
How would a better flowing intake make it richen the mixture? Because it is sampling more air? I figure more air in, more air in the mix, unless it can sample that and adjust accordingly.. :)
I dont think it can, speed density works off of a fixed table.

rpm * displacement * known VE +- adjustments for density and MAP.
 
#9 ·
Even in Open loop the PCM uses manifold pressure, air inlet temp, rpm, and throttle position to plot a point on the fuel map. The fuel map is based on those inputs relationship to one another.
At a given rpm, throttle position and air temp, if you reduce the vacuum by reducing the restriction of flow into the engine (freer flowing intake) the PCM sees this as more air entering the engine and adjust the injector pulse to add more fuel. The problem is the PCM's fuel map is set to the stock volumetric efficiency and because the engine can not exhale any better than before the intake change the increase of incoming volume is less than the PCM can calculate.

This is all theory but my own dyno numbers with the A/F charted support this. We will see tomorrow if the headers lean the A/F mixture. (because this should increase vacuum)
 
#10 ·
Since adding my Zoomers and CAI I am definitely running richer. After only 1000 miles the carbon buildup in the Zoomers tips is incredible. I assume this is from a rich condition. Correct me if I am wrong.
 
#11 ·
jcmeci said:
Since adding my Zoomers and CAI I am definitely running richer. After only 1000 miles the carbon buildup in the Zoomers tips is incredible. I assume this is from a rich condition. Correct me if I am wrong.
All manufacturers program the computers to run rich during wide open throttle conditions. A rich running engine causes less damage than a lean running engine.

Stop flooring the car. :wink:

Dave
 
#12 ·
jcmeci said:
Since adding my Zoomers and CAI I am definitely running richer. After only 1000 miles the carbon buildup in the Zoomers tips is incredible. I assume this is from a rich condition. Correct me if I am wrong.
When you’re cruising the mixture will be 14.7:1, if it is not the computer will kick a code. The only time this ratio changes is when you accelerate more than a little and when you’re at WOT. (also when the car is not up to operating temperature)
 
#13 ·
How about if the exhaust system has a leak? Just got the shop to fix and tighten up the zoomers and a lot quieter. Wondering if I should clean the carbon from the tips and see if that was causing the problem.

I do like the sound and feel at WOT so I won't be backing off that at all!
 
#14 ·
All that carbon at the tips is from you opening up your exhaust and thusly it has become far less restrictive. Your HEMI is breathing...cleaning out it's lungs. More of the carbon that would have been in your exhaust is now making its way out into this wonderful world of ours. I love it when HEMI's breath! :rockon:
 
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