performance mods "maybe"

[dogwater]

Using a cooler thermostat, instead of a 180 or 190 try using a 170
Using slightly thicker shims under the came lobs. This makes the valve open wider, but their is danger in doing this. You really need to know the distance between the top of the piston an the valve when open. Don't know if its better to do the intake or exhausts. Most of the time the exhaust side is better because if the exhaust valve can open wider, which means its also open slightly longer it helps to pull in the air/fuel mixture. Depending on the cam when the exhaust valve is just starting to close the intake valve is starting to open. When the exhaust gases are leaving the cylinder an going down the exhaust pipe it create a vacuum an draws in the fuel/air charge quicker. This is why headers work so well.
Another thing that aids performance is making you car weight less, the rule of thumb is for every 100 lbs. Less in weight you gain 10 to 15 HP.
I'm not sure on this but I've read that using a fuel regulator with a higher pressure will be able to make fuel injectors squirt harder.
Almost all of the horse power an engine makes is in the cylinder head. Big gains can be had by head porting. If your valve springs are old they can rob HP.
Doing these things an having the ECU reflashed would be a good thing. I'm going to add this in, the ECU is a limiting factor when doing mods, such as 2 yrs. ago I rebuilt a 1500 ZD engine, it had a knocking rod. So since I had the head off I went ahead an did some porting to it, mainly just cleaning up some casting flash an smoothing out the runners. I expected a little bit more power but that didn't happen. I did get a jump in torque but that was about it. Why I didn't get any more HP was because of the ECU. The ECU was still programed for a normal flowing. So if big changes are made like different cam shafts an a header the ECU is a must to be reflashed or an after market ECU.

 

[kamesama980]

Just discovered the internet didja?(yippy)

-cooler thermostat makes more of a difference in old muscle car V8s with the intake in the valley. it'll help a little on a modern I4, but not enough to measure on a dyno. Go too far and you'll piss off the ECM by not reaching expected operating temps, on some cars (ECM throws a code for thermostat performance/failed thermostat).
-proper valve clearance will help if they're out but going less than spec will hold the valves open. That means compression bleeds through the valve (less torque)and eventually you burn a valve. I just did the valves on my bike (first time on this bike and it's a PITA) and got them a little on the tight side and it's a turd (meaning significant power loss across the board) set up like that. specs .003"-.005" cold and I used a .003" gauge.
-losing weight: works 100%. 100lb=10hp is a super rough rule of thumb.
-increasing fuel pressure will cause the injectors to inject more fuel for a given pulsewidth but this isn't the limiting factor of a stock engine since they're designed around a 70-80% duty cycle.
-headwork, yes, will help. anythign that increases airflow will increase power and in some cases, economy.
-weaker valve springs will free up HP from less friction on the cam. up to the point where they start floating. then things get ugly. at the same time, overly strong valve springs cause increased friction and therefore more drag.
-ECU tuning: depends. it's adaptable to a point to changes in airflow and fueling. big changes will take engine operation beyond it's capability and require tuning/flashing.

If you got more torque, you got more HP. Torque, HP, and RPM are 3 points of the same equation. Look it up, there are whole books on the subject. I suspect you got more bottom end torque while you were expecting top end torque. It's kind of a hard concept for most people to grasp completely. The easiest way to summarize it without being grossly inaccurate is that torque is the force doing the moving. HP is the relationship between how much and how fast it's moving. same torque at diferent speeds is different HP. different torque at different speeds could be the same HP (100 hp at 2626 rpm is 200 ftlb. 100 hp at 5252rpm is 100 ftlb.