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The early 00s were the gas guzzler era; think Hummer, Ford Excusion, etc. Gas was cheap so there was not a big emphasis on gas mileage when producing vehicles. Now there’s a much bigger emphasis on gas mileage. Aerodynamics are improved, smaller and more efficient engines are used, tech such as active fuel management and auto stop/start exist. With almost any 20 year old vehicle your expectations for gas mileage and performance have to match that of that time, not the present.
 
Discussion starter · #5 ·
Are there "headers" made for the 4.0l engine in my '03 Grand Cherokee? I understand there are standard exhaust manifold mufflers addons to be had but they are mainly for power or sound changes.

Would headers help/increase gas mileage?

Expensive?

pclaptop

P.S. Any other mileage improving addons?
 
Once upon time there was a popular swap mod replacing the stock 4.0L single hole injectors with Dodge Neon 2.0L four hole injectors.
Supposedly the better fuel atomization made for a smoother idle and slightly improved gas milage.
IDK if the information still out there but you might want to look at what's involved.
 
Once upon time there was a popular swap mod replacing the stock 4.0L single hole injectors with Dodge Neon 2.0L four hole injectors.
Supposedly the better fuel atomization made for a smoother idle and slightly improved gas milage.
IDK if the information still out there but you might want to look at what's involved.
I have some bosch 4-hole in my 4.0L, (do not know their original application), but idle is butter smooth. I have made some other modifications including a larger throttle body, 1.7:1 roller rockers, free-flow exhaust, 4.11 gears & 20" TrackHawk rims. I put my foot in it & still avg. 19mpg.
 
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