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Topic Review (Newest First)
08-18-2011 06:40 PM
NCJeepin
Quote:
Originally Posted by InvertChaos View Post
Ha it's worth it of you plan on sticking to a certain tore size! Lots of people spend the same amount of cash on programmers and CAIs and snake oil add ons to improve their butt dyno but never address the main issue.
Haha the PO put a CAI and throttle body spacer on my Jeep. But, at least it makes a cool whistling noise under hard acceleration..

But yea, I don't think I'll ever go above 35s on my Jeep. Because then, that's where the big $$$ mods come into play.
08-18-2011 06:28 PM
InvertChaos
Quote:
Originally Posted by danieldlg_13
Duly noted. Thank you for the explanation. With cars that are more aerodynamic it makes since but I guess not the Jeep.
Oh most definitely. That's why that Corvette idles down the highway at 70mph and gets 35mpg lol.

Quote:
Originally Posted by NCJeepin
Dang it Invert!!!! You're making me really wanna regear now!!! My wallet is starting to hate you, btw.

Well, maybe I will regear one of these days...
Ha it's worth it of you plan on sticking to a certain tore size! Lots of people spend the same amount of cash on programmers and CAIs and snake oil add ons to improve their butt dyno but never address the main issue.
08-18-2011 06:24 PM
fire239 Well said chaos, just glad I didn't have to type it on my phone....lol
08-18-2011 06:22 PM
Kevinm2467 I have 33's and 4.10 gears on my 97 tj, 4.0 and a 6 inch susp lift and I run right at 3K rpms at 70 mph. And I'm only MAYBE at half throttle... There is plenty of skinny pedal left :-)... And she drives close to stock... Well alot better then most tj's I have ridden in :-)))
08-18-2011 06:05 PM
NCJeepin Dang it Invert!!!! You're making me really wanna regear now!!! My wallet is starting to hate you, btw.

Well, maybe I will regear one of these days...
08-18-2011 06:01 PM
danieldlg_13 Duly noted. Thank you for the explanation. With cars that are more aerodynamic it makes since but I guess not the Jeep.
08-18-2011 05:41 PM
InvertChaos
Quote:
Originally Posted by danieldlg_13
Do tell
I'm on my phone so I'm not going to type a book but here it goes as explained to me by Jerry Bransford.

Here we go. So the Jeep is shaped like a brick right? Not very aerodynamic, and it just gets worse once there is a lift added on. At highway speed its pushing through a LOT of air with all of its flat surfaces (grill, windshield, bumper, drag from the soft top, etc), and in order to so so, it needs power. More power than say, a Corvette, to push it through the same space. The Corvette has the nice sloped front end and is very streamlined so that it has very little air resistance comparitively. Okay so say at 60mph with 33" tires and 3.73s in 5th gear (how mine used to be set up) I'm sitting at 1800rpm. That's pretty low right? Low=less engine revolutions=less gas burned right? Wrong. Because of wind resistance, I have to put the accelerator on the floor to keep speed. Even though my rpms are low, I am dumping gasoline into the engine, using more gas than I would in 4th at 2700rpm. Okay so I swapped in 4.56. Same tires in 5th my rpm sits at 2100. Higher, but producing more power. Now my foot is lightly resting on the accelerator and I'm not dumping gas into the engine. I'm using less gas at a higher rpm to produce more power to push me through the air. Next, it gives the engine a mechanical advantage. When you jump from 3.73s and 30" tires to 3.73s and 33" tires, you're making the engine work harder. It has less leverage to use to spin the tire. Its like using a 3ft shovel to dig up 2ft rocks all day, the suddenly having to use the same shovel to dig up 4ft rocks. Wow that was a terrible analogy. Anyways, regearing gives you a 6ft shovel so you have more leverage to move those "rocks". Finally, those larger tires weigh more and require more energy to spin them (inertia and all) so you also use that power boost to move them.

In my personal experience I was getting 12-14mpg with the 4.0L, 5 speed, 3.73s, and 33" tires. When I switched to 4.56 I now get 16-19mpg depending on how I drive.

Also if I've made any mistakes someone with more experience please correct me

Edit: I forgot to add that apparently the 4.0L runs most efficiently at 2500-2700rpm
08-18-2011 05:25 PM
danieldlg_13 Do tell
08-18-2011 05:19 PM
InvertChaos
Quote:
Originally Posted by danieldlg_13
Lower RPMs means less gas. But I guess if you need to go faster then it would be easier at higher RPMs.
Not necessarily.
08-18-2011 05:12 PM
danieldlg_13 Lower RPMs means less gas. But I guess if you need to go faster then it would be easier at higher RPMs.
08-18-2011 05:08 PM
fire239 I would like to turn 28-29 hundred at 75 instead of 2500
08-18-2011 05:05 PM
danieldlg_13 Ugh, my Jeep is dusty. I think 4.11 would be the best gears. I don't want to get in the 3ks for that speed.
08-18-2011 04:59 PM
danieldlg_13 I like my RPM's being low at that speed. As for power in the city, even with those tires my 4.0 is good on pick up.
08-18-2011 04:47 PM
fire239 Probably 3.07, that's what I have and looks like my tach and speedo at that speed. That's my dilemma between 373 and 410 gears. Seems to be a dine line for the correct highway powerband there.
08-18-2011 04:40 PM
danieldlg_13 I think they are stock 3.07, but who knows what the PO put in.
08-18-2011 04:37 PM
Jerry Bransford Those rpms are a little lower than I'd like, what ratio and transmission are you running?
08-18-2011 04:25 PM
danieldlg_13 Attachment 63447

I have 33x12.5x15. My speedo is off so here I'm going about 75-77 mph
08-17-2011 03:21 PM
Jersey Sahara
Quote:
Originally Posted by zzzpoohzzz
i use 3.07's and i dont really notice a difference... but then again i don't floor it when i'm coming out of a stop sign or red light... i dunno... maybe i'm crazy
I have 32s with steelies with 3.07s but I haven't noticed a difference at all either with a jump from my stock 225s
08-17-2011 03:17 PM
zzzpoohzzz i use 3.07's and i dont really notice a difference... but then again i don't floor it when i'm coming out of a stop sign or red light... i dunno... maybe i'm crazy
08-17-2011 07:42 AM
GreenJack
Quote:
Just so you aren't mislead, it is not a static number. The inaccuracy increases the faster you go.
Correct, it isn't a static mph number. It is a static ratio or percentage number. For example if it's 10% off it is always 10% no matter how fast you go. At 50 mph it would be off by 5 mph, at 70 mph it would be off by 7 mph.... etc...


...
08-17-2011 06:23 AM
ospreyguy
Quote:
Originally Posted by NCJeepin View Post
How so? I kind of know what you're talking about I think. And I have 3.73 with 33s and I use 5th on the interstate. Going up long hills you lose a lot of power and momentum but otherwise it seems to be alright.
I agree. I use 5th every time I get on the highway.
08-16-2011 12:29 AM
MikeMTJ
Quote:
Originally Posted by Diverdown87 View Post
Holy crap . Did you change your speedo gear????? My 98, 5sp, 6cyl, with stock 3.73's and same size tires as you only gives me a 4mph difference on the speedo. So when it shows me doing 65 I am actually doing 69 ( confirmed by the 74 in a 65 speeding ticket dropped down from 80 I got).

I am looking to go to 4.56's at tax time and will need to know which gear to buy to correct the issue.

As far as driving. I can hit a bridge here doing 70 and by the time I get to the top I got p!$$3d off people cussing me and am doing about 54. If I get a head wind I am screwed....
Just so you aren't mislead, it is not a static number. The inaccuracy increases the faster you go.
08-16-2011 12:12 AM
oIIIIIIo 33x15x12.5 wrangler mtr's.

Quote:
Originally Posted by fire239 View Post
What size tires?
08-15-2011 11:45 PM
fire239
Quote:
Originally Posted by oIIIIIIo View Post
I also have 2000 wrangler sport 3 speed auto with 4.10 gears. At 70mph my tach is around 3k-3.1k rpm. Is this rmp revving too high? Or my I should of gone with 4.56 gears to bring down the tach rmp? Im confused...
What size tires?
08-15-2011 10:27 PM
InvertChaos
Quote:
Originally Posted by oIIIIIIo
I also have 2000 wrangler sport 3 speed auto with 4.10 gears. At 70mph my tach is around 3k-3.1k rpm. Is this rmp revving too high? Or my I should of gone with 4.56 gears to bring down the tach rmp? Im confused...
4.56 will make the tach go up at speed compared to your 4.11s
08-15-2011 10:19 PM
oIIIIIIo I also have 2000 wrangler sport 3 speed auto with 4.10 gears. At 70mph my tach is around 3k-3.1k rpm. Is this rmp revving too high? Or my I should of gone with 4.56 gears to bring down the tach rmp? Im confused...
08-15-2011 01:44 PM
fire239
Quote:
Originally Posted by Jerry Bransford
Your 32RH changes the ratio recommedation, what size tires do you run?
Sorry, 33x12.5 ATs. Really just feels as if I need a little more stoplight to stoplight power in town.
08-15-2011 12:05 PM
InvertChaos
Quote:
Originally Posted by psycho

nope never changed the speedo (yet)...but that shouldnt effect the tach should it? BTW at 70mph i had a lot of power left..very impressed with this set up.
Nope your tack is dead on.
08-15-2011 11:08 AM
psycho
Quote:
Originally Posted by InvertChaos View Post
Wow that's crazy! Your speedo is off because I assume you never swapped put the speedo gear did you? Other wise that's exactly where my rpm sits at 70mph.
nope never changed the speedo (yet)...but that shouldnt effect the tach should it? BTW at 70mph i had a lot of power left..very impressed with this set up.
08-15-2011 10:08 AM
NCJeepin
Quote:
Originally Posted by InvertChaos View Post
I don't use the interstate too often and all of our highways are 55mph. It sucks lol. But even around town I felt like it was kind of struggling in 3rd to sustain 25mph. Idk I'm extreme happy with my 4.56 for the mountainous driving around here. The thing is especially torquey on take off if I want it to :P I squeaked the tires on a left hand turn into traffic lol. This weekend I hit 75mph on an interstate and it definitely had more go left. Also at Rausch is where my 4.56s really shone. I was just idling in 4lo and 1rst over EVERYTHING.
Yea I'm sooo jealous lol. It's 25 though town here too and I just normally use 2nd gear. I runs at about 2000-ish rpms and I think it's fine. In 3rd it feels like it's lugging. But yea, I ONLY use 5th at 65mph+. Other than that, I use 4th because there's no power in 5th. I really wanna regear, but dang it's expensive lol. :P
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