Re: Crank sensor position?
Good explanations - especially about the intake "shockwaves" as you call them. Essentially that's the same principle as the exhaust.
So far - on mine:
I put on a less restrictive muffler - not because of this, but the main reason was to get more room under it (04 Rubicon 4.0) for the suspension and mods. It eliminated probably 50 pounds too! The stock one is really big and heavy.
Performance increase was very slight, if any.
Throttle body spacer: About the same change in performance as changing the color of my shirt. Took it off.
Ditching the stock air box has made a significant difference. So far it's the only thing that's really been noticeable. At low R's and up to lower mid range no change, but around 2000 RPM under load it did. At WOT under hard load it's definitely better. Try it - just take a ride around the block with it disconnected - you'll see if it will help yours or not.
Variable MAP sensor - I used a switch to increase the signal voltage to the ECM. I could toggle it in and out.
On normal loads it made 0 difference. Increasing voltage simulates that it's under a heavier load than it really is.
Yes, the O2 sensor will counteract it, but it takes a reaction time to do it. First it has to richen the mixture before the O2 drops (but the richer mix has already passed through the engine,) then the ECM has to react and shorten the pulse widths to the injectors.
That all takes a second or two. But - during that second or two, if the limiting power factor (choke effect as it's being called here) there would have been a noticeable increase in power, even if only temporary. None noticed.
But - I know it did have an effect and how long it takes to react - when toggling back to normal voltage, after the O2 had told the ECM it was too rich and compensated for my false input - now it goes too lean for a moment. It would almost stall during the second or so recovery time.
So I know it was richening it.
In WOT up a steep hill it made 0 difference. Yes, the O2 normally would compensate for the false signal, but at WOT throttle (told to the ECM by the TPS) it ignores O2 readings - it's in open loop for that time.
No noticeable increase in power.
Mid range under load it reacts like at idle - including the "recovery" stall like at idle.
Still, the false signal did not increase power enough to notice, but toggling back to normal made it try to stall from going lean an instant was just like before.
There was a possible reason why the variable MAP showed no effect, that would have been if the ECM just did not have the capability of lengthening the pulse length, or the fuel system was not capable of giving more fuel. So the possibility exists it's a lack of fuel delivery problem. Higher volume pump, larger injectors etc would help in that case. But there is a way to verify it's a lack of fuel too:. Propane.
As you all know, propane is a hydrocarbon fuel - it can be added to the system easily with a hose and a valve. Running a hose to the front, right into the intake airstream - the PVC breather - is easy.
I could add fuel, as much as I wanted. As more propane is added, the O2 sensor commands the ECM to shorten the pulse widths, eventually the system runs on the propane, gasoline provided by the normal system becomes minimal. This can be done at idle or whatever speed desired.
Mid range - richening it - if it really was too lean - it would give an increase in power - even though temporary. No effect.
WOT - same thing - no effect.
At WOT under heavy load it's in open loop, so the O2 sensor has 0 influence. So adding the propane only serves to increase the richness. Propane could be added until a noticeable DECREASE in power existed - indicating lack of available fuel has has not been the ”choke.”
In fact, it reacted just like the variable MAP did.
Increasing the bore on the throttle body would help only at WOT where the added area would be used. The ECM and fuel system can most likely provide enough fuel to feed the extra air. But, I'd rather have an increase in mid range, that would make 0 difference at that speed.
So - that leaves either the intake - such as manifold, or the exhaust system. Being in California I cannot do much that can be seen. Increasing power and efficiency should not drive emissions up, but since laws say modifications cannot be done - even if they make it cleaner, it's a problem.
The next step would be camming - changing cam timing does not actually increase or decrease power very much per se. What it does is move the peak of the torque curve up or down RPM wise. It can make a significant difference if the rest of the system has a different peak (breathing, ignition timing etc) - getting all the peaks together really makes a big difference.
But - recamming can increase breathing - if that's the limiting factor now. Increasing duration or overlap can, and will have a profound effect (negative) on emissions. So that's out. Plus the fact that the system is using a MAP causes problems too. Much increase on duration or overlap really gets the intake pulsing - drives the poor MAP crazy!
But, more lift can be added as long as it's kept within reason. More mixture can be ingested. The simple and easy way for that is increasing the rocker ratios. Even that causes more pulsing, but not near as much as the other way.
So far I haven't found ratio rockers for the 4.0 - but I haven't really tried either - yet.
I was hoping there would be a little “trick” that could be done to increase drivability power. It seems like the engineers have done a great job optimizing it as it is, leaving not much more room for improvement. Especially considering the fact they have to keep emissions down and satisfy all the greenies in their VW busses!