cold air intakes work: although they really only do about 8hp
cat backs, headers and high flow cats work: back to gaining only a few hp
bored throttle bodies work: only a few more hp
external engine mods will net a few hp, your not going to be laying down serious rubber when you stomp on your skinny pedal but you will feel a difference and all together add up to a smoother running motor maybe a little gas mileage bump (or larger if your replaced parts were in a very sorry condition)
Like previously posted external mods compliment internal mods.
what does NOT work on late model 4.0l are throttle body spacers you might as well send your money to me and ill send you a BFH to smash your head in.
and JET chips dont work; all the do is take the governor off. and whens the last time you pushed 105mph in your jeep?
injectors with a 4 hole pattern as opposed to 1 will give a better atomization of the fuel. basically 4 holes instead on 1 squirtin gas.... tenths of a mpg, but it is more efficient. headers are also more efficient than stock manifold but again tenths of a mpg and 2-5 horsies real world. CAI again more efficient burn due to more air being available fr the intake pulse, giving you maybe 1mpg but in real world driving again tenths of a mpg. bored tb is again good for a few ponies at the crank but nothing you will see at the wheels, better throttle response is all you will actually feel. high flow cat is in my opinion one of the best things you can do. factry cats are honey combs and that = RESTRICTION! spiral cores are more efficient and still will pass emissions maybe 1-1.5 mpg. cat back is also good for a few ponies everyone claims 3-5-15 but 1-3 is more likely in real world. a 99+ manifold is more efficient and will actually yeild about 10 ponies cuz of smoother runners. Port and polish is always good for a couple ponies and also 1-1.5 mpg. All and all breathing is the most important thing for this engine (without doing any internal modifications). Intake and exhaust but if you do everything listed above your into the engine $3-4k, but with an engine that routinely runs up to 200k without any major issues it should be seen as an investment. if everything is compounded and i mean EVERYTHNG! you would probably see a 3-5 mpg increase as well as about 15-30 horsies. IMO power is great, but if thats all youre looking for you may as well invest your $4k in a supercharger or turbo. but if longevity and efficiency are the goal the above in combination will net you some appreciable power and gas mileage. as an after thought cams should also be mentioned but again maybe 3-10 horsies... but it will lope at idle and that sounds pretty cool maybe 1 mpg, probably less but is should be considered.
99' WJ... tank raise mesh grill homebrew cai
magnaflow 11226, banks header, bb sittin on 31s
Most aftermarket addons will increase HP and Fuel economy but some things (TB spacer, cold air intake, Larger TB) will not work as well if the exhaust system has not been upgraded as well...
The best upgrades you can make are:
- Electric Fan Conversion
- High flow Cat and Muffler with 2.5" tubing
- 99+ Intake manifold
- Proper Header to replace the crap Exhaust manifold
- Cold air intake
- Larger injectors to match the Estimated HP increase
Big Money Upgrades
- Adding a Turbo or Supercharger
- The ultimate is building a Stroker engine
From my experience and I have alot of it, Most people do not see the increases because they usually only upgrade the intake flow and not the exhaust flow...
Also the Factory injectors are undersized from the get go, so once you add more HP you need to upsize the inectors to compensate for the increase in fuel demand otherwise you will not notice the HP gains...
Black 89/98 MJ Eliminator, 1997 HO 4.0L, AW4, 31x10.5x15" MT's, 4.5" Lift ZJ Rear D44A W/Alloy USA shafts and Spartan Locker
There's cams, rollor rockers, bigger tb, engine programer, stroker kits, the list goes on. On my 87 4.2 I installed a holley 470 4 barrel, offy intake, comp cam, rollor rockers, ported head, header, hipo pistons, HEI distributor, and MSD, THE THING SCREAMS!!!
1987 wrangler, 258 I-6, 5-speed.
2007 liberty sport 4X4, automatic
2009 ford ranger 4x4 FX4 OFF/ROAD, 5-speed