Mass confusion surrounding my YJ. - Page 2 - JeepForum.com
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post #16 of 32 Old 04-04-2019, 05:55 AM
fishadventure
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I remember a thread from the nineties about aerodynamics of a VW Bus and the coefficient of drag of them and various other fractional subsonic moving objects. Aerodynamics of a tirewell 10.5 VS 12.5 is like arguing XJ passenger shaft VS cad on the basis of fuel mileage.
A tire’s rotating mass I’d take a wild guess is 20 times more important to power/mileage concerns. But I’m not interested in driving a prius or having the payment on one.

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[size=“3”]Shackles & D-rings are different things.
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post #17 of 32 Old 04-04-2019, 12:04 PM
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Originally Posted by Msmith5425 View Post
All of the information in both of the reply’s on this thread is extremely helpful and I can’t express how much I appreciate it.
I’m probably just gonna stick with the 4.10s. Gearing up to 3.73s isn’t worth the power trade off for 8mph on top end (according to the chart).
You guys are arguing about aerodynamics and here I am stuck back on this comment. Msmith, you are looking at this all wrong. You are going to want to go the other direction with your gearing to compensate for those larger tires. Propably to a 4.56.
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post #18 of 32 Old 04-04-2019, 04:25 PM
1project2many
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Quote:
There are intense studies for instance of the disturbance of air at the tire/wheel/ wheel well combo causing a race car body to lift at higher speeds and oppose the effects of downforce.
It's often called the Magnus Effect and it is worth considering. Spinning cylinders can create significant changes in air pressure around the wheel. They do consume power in the process.
https://www.youtube.com/watch?v=hlmvHfIAszo&list=PLq1e8D3Q-o-VXvYg20qiizrDeMkpy4H2W&index=3

Quote:
You guys are arguing about aerodynamics and here I am stuck back on this comment. Msmith, you are looking at this all wrong. You are going to want to go the other direction with your gearing to compensate for those larger tires. Propably to a 4.56.
Seems like the best way to determine this is to use the RPM at a given speed to figure out where in the power curve the engine is at and what gears are currently installed.

Last edited by 1project2many; 04-04-2019 at 08:22 PM. Reason: Changed video link to better example
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post #19 of 32 Old 04-04-2019, 04:53 PM Thread Starter
Msmith5425
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Quote:
Originally Posted by daddyjeep87 View Post
Quote:
Originally Posted by Msmith5425 View Post
All of the information in both of the reply’s on this thread is extremely helpful and I can’t express how much I appreciate it.
I’m probably just gonna stick with the 4.10s. Gearing up to 3.73s isn’t worth the power trade off for 8mph on top end (according to the chart).

You guys are arguing about aerodynamics and here I am stuck back on this comment. Msmith, you are looking at this all wrong. You are going to want to go the other direction with your gearing to compensate for those larger tires. Propably to a 4.56.
Yeah this thread got way off subject but there still a lot of intelligence and good information in the conversations.

I asked earlier in this thread or in my other thread about going up to 4.56 or 4.88s. Seems like 4.56s would be a happy medium between low gear pull and top end speed. Considering my commute to work is only 14 miles one way and I only drive the Jeep about once or twice a month it’s really not that big of a deal. This whole thread really stemmed from my wife asking why it’ll only 60mph down hill in 5th hahaha.

As for the RPM at a certain speed, I got to test that today.
In 5th on a very flat stretch of highway I was maintaining 66mph at 3000 rpm and that was pretty much petal to the metal to maintain it.
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post #20 of 32 Old 04-04-2019, 05:57 PM
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The springs I have are OME 36R on each corner with Skyjacker Hydro 7000 shocks. A smooth combination.
The springs I put on my kid's Jeep are OME 37R's. It's a little smoother than the 36R's. Same shocks.

The higher the Jeep goes (lift) the more air it's gonna catch. It's not just the frontal area that pushes the wind, the rear causes a low pressure vacuum. Air must rush in to fill the low pressure zone behind. Tractor trailers are starting to address this with those odd-looking rear flaps.

Jeeps are not shaped for efficient freeway use. Not much can be done to change that.

This is how I address the Jeep freeway travel issue. I tow it!
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post #21 of 32 Old 04-04-2019, 06:32 PM
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Quote:
Originally Posted by daddyjeep87 View Post
You guys are arguing about aerodynamics and here I am stuck back on this comment. Msmith, you are looking at this all wrong. You are going to want to go the other direction with your gearing to compensate for those larger tires. Propably to a 4.56.
4.56 + 33x12.5s + 4banger here.

I like it just fine

Stop whining about the 'ride' - If your YJ ain't wrangling your soul free, then might I suggest you buy a stationwagon... at least you can fit all your bull**** in the back.
~YJOTM MAY '16~
~YJOTM JULY '19~
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post #22 of 32 Old 04-04-2019, 08:07 PM
1project2many
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The 2.5 has a fairly broad torque curve but it peaks around 3000 RPM. Torque peak is where maximum engine efficiency occurs so most engineers today try to design a vehicle to operate most often in a range just below the torque peak. But in your case the engine just can't apply enough torque to the wheels to maintain speed. Changing to a numerically higher gear ratio increases the torque applied to the wheels but shifts the engine away from torque peak. Luckily the torque curve shows the engine should still be able to move the vehicle and will likely operate even better.

At 3000 RPM in 5th doing 66 with 32" tires the math shows 4.10 gears. The difference between 4.10 gears and 4.88 gears is like the difference between 5th and 4th. If you drop the trans into 4th and you are ok with the acceleration, speed, and engine rpm on the highway then you know how 4.88's will perform. This should be about 3500 rpm. Using 4.56 gears instead will put you at 3300 rpm.

Quote:
This whole thread really stemmed from my wife asking why it’ll only 60mph down hill in 5th hahaha.
That's funny. My wife drives by the speedometer. I could adjust it to show 70 at 55 and she'd happily cruise along with everyone passing her.
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post #23 of 32 Old 04-06-2019, 08:04 AM Thread Starter
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Alright guys. I've got a new inquiry about the Jeep upgrades. I've done a little, very little, research on an engine swap. I was looking at a possible 4.0 swap but I've seen where the 5.3 small block chevy V8 is a pretty popular swap.

Would anybody be able to fill me in on some of the details of this process. The good, the bad and the ugly haha.
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post #24 of 32 Old 04-06-2019, 10:24 AM
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I haven’t done a V8 swap and likely will not. I have swapped 2.5 > 4.0 however and I liked it, still do.

I’m jaded because i have been fascinated since I stole my dad’s copy of Petersen’s “Six In A Row Can Go” when I was about 13 years old... My dad didn’t miss it but I still have it LOL

Anyway, at 195HP the Jeep 4.0 has 45-50 HP over what the 2.5 needs to excel. At 125HP the 2.5 does quite well as an off-road powerplant but lacks the 20-30HP needed to make a dual-duty jeep “acceptable” once rpm horsepower needs to be available. One could argue as well that 195HP isn’t ‘enough’ but the six cylinder is as innately long-lasting as a 2.5, maybe more so, is very smooth on power delivery over a significantly broader RPM range, and best of all has a surprising amount of available torque from a very, very low RPM.

The 5.3 LS swap is quite popular because the source engines are moderately inexpensive, a proven design, and plentiful in supply. Overall horsepower is also well beyond what the jeep requires to excel.

I don’t know what kind of offroading you plan to do. Outside of sand drags, huge tires, rock-bouncing, or mud-bogging even the 5.3 fans who have installed it will readily admit that the added 5.3 horsepower is desirable, fun, and dependable- but not required.

I would recommend the 4.0.
However, I know what everyone wants or expects is different. So I would recommend that you decide which direction based on only two criteria: 1) is the NEED for power for mud drags/competition-type performance or huge tires something that exists (and you have the big dollars to include the other huge mods those criteria require); 2) do you just want a bedrock-dependable jeep with more available power?
If #1 there’s a lot to learn but that’s available in this forum - others have done it
If #2 the info is available here and there’s nothing wrong with a 4.0
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[size=“3”]Shackles & D-rings are different things.
Cranking IS turning over
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post #25 of 32 Old 04-07-2019, 11:01 AM
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Quote:
Originally Posted by Chrisnvegas View Post
The springs I have are OME 36R on each corner with Skyjacker Hydro 7000 shocks. A smooth combination.
The springs I put on my kid's Jeep are OME 37R's. It's a little smoother than the 36R's. Same shocks.

The higher the Jeep goes (lift) the more air it's gonna catch. It's not just the frontal area that pushes the wind, the rear causes a low pressure vacuum. Air must rush in to fill the low pressure zone behind. Tractor trailers are starting to address this with those odd-looking rear flaps.

Jeeps are not shaped for efficient freeway use. Not much can be done to change that.

This is how I address the Jeep freeway travel issue. I tow it!
.
.
.
Airflow under a vehicle is very turbulent and disruptive also. Lifts also increase this.
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If you cannot fix it with a hammer then it has to be an electrical problem.
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post #26 of 32 Old 04-07-2019, 11:06 AM
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Quote:
Originally Posted by Msmith5425 View Post
Alright guys. I've got a new inquiry about the Jeep upgrades. I've done a little, very little, research on an engine swap. I was looking at a possible 4.0 swap but I've seen where the 5.3 small block chevy V8 is a pretty popular swap.

Would anybody be able to fill me in on some of the details of this process. The good, the bad and the ugly haha.
The good, the bad and the ugly are more determined by your skills and resources than anything else.
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If you cannot fix it with a hammer then it has to be an electrical problem.
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post #27 of 32 Old 04-07-2019, 03:06 PM
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For the original topic, I've rolled my 95 4-banger on all versions of tires, wheels, and lifts over the last 20 years...the two biggest impacts to speed/power were: gearing and wheel type. Gearing was the biggest, but you're going to see the RPMs go up and fuel needle go down quick (currently running 4.88s behind an automatic). Ran steel wheels for a while, then eventually picked up a set of 17" alloys, and believe it or not that was a very noticeable difference (in a good way).

The YJ is no longer my DD. I have sacrificed all future retirement plans for jeep parts. I'm depending on social security!
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post #28 of 32 Old 04-07-2019, 04:35 PM
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Quote:
Originally Posted by Msmith5425 View Post
Alright guys. I've got a new inquiry about the Jeep upgrades. I've done a little, very little, research on an engine swap. I was looking at a possible 4.0 swap but I've seen where the 5.3 small block chevy V8 is a pretty popular swap.

Would anybody be able to fill me in on some of the details of this process. The good, the bad and the ugly haha.
Lot's of useful info in here... https://www.jeepforum.com/forum/f22/...-name-1484933/

FWIW, if I were doing a swap and lived where it wasn't such a PITA to make it legal I'd do the 5.3 all day over the 4.0.

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post #29 of 32 Old 04-07-2019, 04:50 PM Thread Starter
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Originally Posted by timatoe View Post
Lot's of useful info in here... https://www.jeepforum.com/forum/f22/...-name-1484933/

FWIW, if I were doing a swap and lived where it wasn't such a PITA to make it legal I'd do the 5.3 all day over the 4.0.
As far as I know as long as there isn't any fuel pouring straight on the ground it's pretty much legal here haha. I'm sure there is some kind of emissions controls in place but no one ever enforces them in MS. Everywhere you look there's a Z71 with straight dual exhaust driving by.

The 5.3 swap peaked my interest because I am possibly about to be i a situation where I can get a 5.3 engine for basically free.
I wouldn't be about to actually do the swap for quite a while given all the other components that have to be replaced or upgraded to stand up to the Torque and HP increases but at least I might have a very critical component considering you can't do a 2.5 to 5.3 swap without a 5.3 to swap it with haha.

Another question I do have is, which vehicle would I need to get an 8.8 rear axle from to best match up with my current wheel base? Or should I just forget my current Wheel Base and go with what i can find?
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post #30 of 32 Old 04-07-2019, 05:25 PM
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You should spend a little time in the FAQ and stickies! There’s a lot of what you’re looking for there https://www.jeepforum.com/forum/f12/#/topics/2414825
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[size=“3”]Shackles & D-rings are different things.
Cranking IS turning over
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