I need your input here , is the havey duty injectors and upgrade fuel pump will improve the performance interm of Torque and HP?
Look man, not to be an ass here, but I see all of your posts about forced induction, heat issues and power upgrades. I get it, you want more HP. Don't we all? Instead of throwing things like high flow injectors and forced induction into your X, try doing the basics first.
Increased airflow (both into and out of your engine) will improve performance. It takes less work to move air that is less restricted. Start by throwing a cold air intake on it and some exhaust. If you want to maximize your potential with regards to exhaust, start at the heads and go all new... Headers, high flow, performance catalytic converters, larger diameter piping and a less restrictive muffler. All of this will improve performance, but at a price. Improved airflow shows results at the high end of the engine RPM range.
I'm not sure what you mean by "uprev", but I'm assuming it means the speed at which the engine increases its RPMs. If you want it to rev faster, reduce the unladen, rotational mass. Lightweight flywheel, underdrive pulleys, reduce the amount of things that the engine is turning (power steering, A/C, etc). Replace the belt driven accessories with electric motor driven units. A big one would be to remove the belt driven water pump and replace it with an electric unit. Replace the driveshaft with a lightweight aluminum shaft. Reduction of rotational mass results in more power delivered to the wheels. for example, let's say the engine currently uses 26 hp to turn all of the heavy components it is turning. If you reduce that rotational mass by 50%, you now have 13 more usable hp at the wheel. This is where you'll feel your biggest gains using a butt-dyno.
If low-end torque is what you're after, then you need to break into the internals of your engine. longer throw crankshaft, pistons, cam-shafts, roller-rockers. That's when things like bigger injectors are needed. Since the amount of air being sucked into the engine has increased, so must the amount of fuel. None of these should be done without also improving airflow (Intake and exhaust).
If you want a well-balanced machine that has better performance at the high end, mid-range and low end, then you'll want to do things like bigger cams, Intake, exhaust and some reduction of rotational mass.
Basically it's like this:
Easier airflow = hp increases at higher RPMs
More airflow (Increased Displacement) = Increased low end hp and torque
Less rotational Mass = more usable hp and torque at all engine speed ranges.
Honestly, if I was in the Middle East and building a good, solid rig, I wouldn't even mess with gasoline engines. I'd rip it all out and throw a Compound Turbo Diesel engine in it with massive intercoolers and radiator. You'd be able to get insane amounts of torque and horsepower out of it, but you wouldn't be running high RPMs and generating a ton of heat. Diesels just run well in the desert. Paired with the right transmission and drivetrain and you'd have a monster of an Xterra.
Just my 2 cents.