What are some different, unorthodox ways of increasing an engines power. Except turbo of course, I've heard of turbo. But seriously, are there any odd or weird ways of freeing up some ponies?
A few I can think of, excluding forced induction...
Uncommon high-end mods:- Have the engine blueprinted and balanced. This will eliminate vibration in the engine so it'll run smoother and make more power. The engine will also be able to safely run higher RPM than stock.
- Have the head, intake, and throttle body ported and polished. This raises volumetric efficiency, and as such, power and gas mileage both go up a little.
- Have the cylinders bored .030" over and stroked (larger stroke.) Pistons, rods, rings, and all the other stuff to match. This raises CID while still maintaining the stroke-ratio. The compression ratio will go up as well, meaning you may need to run higher-grade pump gas or better cooling to avoid detonation/pre-ignition. If I remember correctly .030" is about as far as you can overbore on the 2.5L without cutting into the water jackets. Remember, there's no substitute for cubic inches!
- PCM performance re-flash, or a custom tuneable PCM like the Megasquirt. In the case of a tuneable PCM, you'd need to figure out the correct figures for the power curve with your current mods.
Each one of these options will be very expensive (some possibly in the thousands.) All of them together will probably cost you more than your Jeep is worth. You can port and polish the head/intake/throttle body yourself with a dremel tool, but be advised, it is VERY delicate work and VERY easy to screw up.
Somewhat Common mid-range mods:- Increase the distance between the throttle body and the cylinders. You can increase distance by extending the intake runners, and you can decrease distance by shortening the intake runners. Increasing distance will give you more low-end torque, while decreasing distance should give you a few more horsepower and quicker throttle response. The throttle body spacer is a cheaper way of increasing the distance.
- Bigger injectors and adjusted fuel rail pressure to match. Won't gain you much by itself but it always helps with other mods.
- Larger diameter performance exhaust with a custom-fabbed mandrel-bent 4-2-1 header. I wouldn't go over 1" header runners and 2" exhaust pipe unless you're running forced induction. If you go any larger you probably wouldn't have enough backpressure.
- Regrind performance cam.
- E-Fan swap w/ DC control box. This will free up a few ponies that were already being used.
All of these are good mid-range options. These mods should cost less than or just over $300 each if you do the installation work yourself. The exceptions might be modified intake runners and a custom header.
Very Common cheap/easy mods:- Swap to a larger throttle body. 4.0L OEM or bored out 62mm, it doesn't really matter. Either one is better than stock.
- Buy or build your own 3" intake (cold air or short ram, doesn't really matter) with a performance air filter.
- Upgrade the ignition system (coil, plugs, wires, distributor, battery.)
- Throttle body spacer -- the cheap way to increase distance between the cylinders and the throttle body.
All of these are relatively cheap and easy. These mods should cost less than or just over $175 each. If you swap to a 4.0L throttle body from a junkyard you can expect to spend $30 max. The PD Screamin' Demon Firepower Ignition kit for a 2.5L costs around $190. You can build a 3" intake with ports for the PCV and charcoal canister runners for around $60 including the filter, and you can buy a 3" intake for around $150 including the filter.
If you were to perform all of these mods, I'd bet you could squeeze 200-250 hp and 250-300 lb/torque out of the 2.5L. This is why it's not worth it. You could spend a fraction of the amount needed for all of those mods and swap in a bigger engine that already has more power to begin with.
