4.0 engine mods?

Jay P

Jay P

TJ Enthusiast
Joined
Nov 6, 2017
Messages
609
Location
West Jordan, UT
Just a quick question, do you guys suggest any upgrades that actually work or would changing gears be the best option? We have a 2000 TJ Sport with 31x10.50s and 3.07 gears. It runs great but of course it’s sucks gas and it’s tapping my 19 yr olds bank account. Or just refer me to a thread that this has been discussed before. Thanks!


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Firstly, what kind of mileage is it getting? Remember, it is a Jeep so anything in the mid to upper teens is about all you can expect. If it is significantly lower than that, a gear swap may help. If on a budget try to find some complete axles with 3.73 or 4.10 and swap them out.
 
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Rob5589 said:
Firstly, what kind of mileage is it getting? Remember, it is a Jeep so anything in the mid to upper teens is about all you can expect. If it is significantly lower than that, a gear swap may help. If on a budget try to find some complete axles with 3.73 or 4.10 and swap them out.
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It’s about 200 to 220 miles per tank. This is my 4th jeep and 2nd TJ but my others were all manual. I was much younger then and dumped tons of cash on gears and axles. Maybe I’m just older and the automatic is throwing me off. We are doing a slow build with it and gears are on the list. I just thought I’d ask since the only think I’ve ever done to my others was a K&N filter. Thanks for the info!


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glwood said:
None of the 'performance' mods do anything but lighten your wallet. Gears are your best course of action to regain stock performance with larger tires.
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X2, this is solid advice. Your best bet if you want performance is to re-gear it or slap on a supercharger (or just put in a V8).

You will gain little to nothing from mods like air intake, headers (if you can even call them that), etc. It's a very widely documented fact that the 4.0 won't gain anything from bolt-on mods. A stroker will make some serious power, but again, that's lots of money.
 
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Chris said:
X2, this is solid advice. Your best bet if you want performance is to re-gear it or slap on a supercharger (or just put in a V8).

You will gain little to nothing from mods like air intake, headers (if you can even call them that), etc. It's a very widely documented fact that the 4.0 won't gain anything from bolt-on mods. A stroker will make some serious power, but again, that's lots of money.
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Just looking at this rusty exhaust system wondering what to do with it. It’s fine but it bothers me


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Jay P said:
Just looking at this rusty exhaust system wondering what to do with it. It’s fine but it bothers me


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I'd replace it for sure. I just bought a Magnaflow muffler and then went to my local exhaust shop and had them make me an exhaust using that muffler. Cost me less than $200 and saved way more money than one of those $500 complete Magnaflow or Borla catback exhausts (which are a waste of money). I wouldn't say I gained anymore power, but it sounds better and looks better.
 
Chris said:
I'd replace it for sure. I just bought a Magnaflow muffler and then went to my local exhaust shop and had them make me an exhaust using that muffler. Cost me less than $200 and saved way more money than one of those $500 complete Magnaflow or Borla catback exhausts (which are a waste of money). I wouldn't say I gained anymore power, but it sounds better and looks better.
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Ahh very nice. I’m going to call on that on Monday.


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Jay P said:
Ahh very nice. I’m going to call on that on Monday.


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Good idea. Any local exhaust shop can do it. The TJ exhaust is a really easy one for them to do as well.
 
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Jay P said:
It’s about 200 to 220 miles per tank. This is my 4th jeep and 2nd TJ but my others were all manual. I was much younger then and dumped tons of cash on gears and axles. Maybe I’m just older and the automatic is throwing me off. We are doing a slow build with it and gears are on the list. I just thought I’d ask since the only think I’ve ever done to my others was a K&N filter. Thanks for the info!


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If you haven’t changed your speedo to accommodate the 31’s, your getting more mpg than you think. I’m on 31’s too and it always comes back with ~13mpg. According to my calculations I’m actually getting ~14mpg.
 
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At a minimum make sure it is running as well as possible. Fresh plugs, wires, air filter, etc. Check for any codes that may be stored due to exhaust/sensor issues. Then see where you are.
 
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