Jeep Wrangler Forum banner
  • Hey everyone! Enter your ride HERE to be a part of JUNE's Ride of the Month Challenge!

1 - 19 of 19 Posts

·
Registered
Joined
·
55 Posts
Discussion Starter · #1 ·
Greetings all. It turns out my old jeep frame took a massive **** on me and PO did a good job covering up rust with a paint job.... so after snapping a suspension mount and a leaf spring recommendations were for me to replace the whole frame. Nonetheless in the midst of difficulty lies great opportunity.

So that said I was playing with a couple of ideas for my jeep. Im going to get a frame from a 2.5 and just re-weld the motor mounts- cheap. Probably like $1000 for all of that from my local jeep guy. I was playing with the idea of an engine swap but realized theres so much that would have to be modded that cost would add up quickly- at least $4k on top of what I already have to get fixed. I lost interest in that. Thought about a stroker engine since I could just drop it in, but $8k for a stroker engine is pretty obscene.

So that said, primary reasons for wanting to do the above is MILEAGE. Right now that's my primary concern (after getting the jeep repaired of course). A larger, more capable engine will get more MPG than this gutless 112 horses will. I don't mind so little power, but Im only getting about 9-10 MPG at the moment.

Now I've got what appears to be a 4 inch lift and 33" tires on this. I love carbs- the simplicity of them and the lack of CPU's. What mods can I do that would improve the MPG on this thing? Im hoping I could get 14-15 MPG out of this thing. The next question is: is it possible? I've heard of several mods, such as a headers, holly or motorcraft carbs, etc. Shes being rebuilt from the ground up so this is the time to do it. I have a spare set of 4 cylinder axles with 4.10 gearing that Im thinking of swapping in (to replace the 3.07). The catch is, they have 200k+ miles on them. Intelligent swap or no?

Any help and suggestions are appreciated, Thank you
 

·
Premium Member
'89 YJ 4.2 with MC-2150 Carb & HEI, 2-1/2" Ex. AX-15, NP231 SYE, Adams shafts, F&R ARB, 3
Joined
·
3,909 Posts
The best I have ever got in mileage was 16 mpg, on flat freeway, not going over 65 with 31's and 4.10's. That being said, Major mileage improvement will never be a key result of any Mods improvement. A little more throttle response, yes. More power, debatable.

These 4.2's are what they are, and you get what they got. I recently ran 140 miles of desert at 15mph avg. speed with about 2hrs of idle time and a 25 mi freeway run at the end. 11.5 mpg for the trip. My regular weekly daily driving nets me 14 mpg.

If your looking for mileage improvement I'd look at Smaller Tires (We both know that's not gonna happen with a 4" lift), Regear for the 33's, (We both know that's needed) Or start looking for a good 4.0 or LS swap.

Maybe a Honda or a daily driver and split the difference on the mileage.

Tough Decision, let us know what you decide.
 
  • Like
Reactions: Instructor9

·
Registered
Joined
·
9,000 Posts
Absolutely swap the 4.10's in but don't get hung up on mileage....
 

·
Registered
Joined
·
55 Posts
Discussion Starter · #4 ·
The best I have ever got in mileage was 16 mpg, on flat freeway, not going over 65 with 31's and 4.10's. That being said, Major mileage improvement will never be a key result of any Mods improvement. A little more throttle response, yes. More power, debatable.

These 4.2's are what they are, and you get what they got. I recently ran 140 miles of desert at 15mph avg. speed with about 2hrs of idle time and a 25 mi freeway run at the end. 11.5 mpg for the trip. My regular weekly daily driving nets me 14 mpg.

If your looking for mileage improvement I'd look at Smaller Tires (We both know that's not gonna happen with a 4" lift), Regear for the 33's, (We both know that's needed) Or start looking for a good 4.0 or LS swap.

Maybe a Honda or a daily driver and split the difference on the mileage.

Tough Decision, let us know what you decide.
Fair enough. I've been spitballing with my mechanic (who'll be doing all the work...) and I've decided to merely rebuild it as is when I (hopefully) get the new frame.

The only other thing I'd change is throwing the 410 axles on there. Hes of the opinion my MPG will be worse. He grew up with Jeeps (had a CJ) and I don't want to argue with the guy, but maybe hes mistaken? Maybe hes not taking my tire size into account? Im not positive. But to double check those 410 are almost perfect (3.73 would be ideal I suppose) for 33's that's almost all highway commute. Even if its not perfect it'd be an improvement either way yes?
 

·
Premium Member
'89 YJ 4.2 with MC-2150 Carb & HEI, 2-1/2" Ex. AX-15, NP231 SYE, Adams shafts, F&R ARB, 3
Joined
·
3,909 Posts
To be fair, I did have 33's on mine at purchase, After a new exhaust incl. Cat It would do the freeway and 70-75mph with a little patience, But I had to get into the pedal pretty heavy to get that last 10mph, with the 4.10 gearing in the back. (PO only got as far as the rear) I finally got the front done earlier this year. Once I went to the 31's I picked up a couple mpg, also got a lot more zing on freeway onramps, and can get er up to 80-85 if needed... You have enough low end torque to get off the line with those gears, but the top end just doesn't and won't have the horses.

All just my personal experience, YMMV. Again, Good Luck making the call...
 

·
Super Moderator
Joined
·
12,662 Posts
Looking at the tire/gear ratio charts, 4:10 gears with 31" tires will put a 6 cyl right back to the performance end of the ratio curve. With 33s a guy will be more to the mileage end of the curve. I'm thinking you might see a bit of improvement in mileage, especially since the 4:10s will be easier on your clutch. You shouldn't have to rev the engine as much when starting out in first gear.
31" tires with stock gears (3:07) is harder on the clutch than stock sized tires. I've noticed recently that my clutch is engaging higher than it used to. I have a set of 4:10 axles that I'll install as soon as the doc gives me the OK to move heavy assemblies. Hopefully that will stretch the clutch out until I get a '94-'95 bell housing for an external clutch slave cylinder.

How bad is your frame rust? There's repair sections available for the most common areas that rust out. You might see what a body shop would charge (way expensive) or perhaps you can enlist a journeyman welder that does side work. Ask around. It might be a lot less expensive than paying someone to change a frame.

Keep us posted on how it goes for you.

Good Luck, L.M.
 

·
Super Moderator
Joined
·
12,662 Posts
BTW, if you don't have to pass emissions, you might consider a HEI distributor. Got it at last has one, and I do too. He went with a Motocraft carb and I stayed with a non-stepper Carter BBD. The HEI was probably the biggest bang for the buck as far as ease of maintenance and reliability that I did. If you have to pass emissions, talk to your mechanic.

Good Luck, L.M.
 

·
Registered
Joined
·
1,154 Posts
Since your main question seems to be about MPG, are you factoring in the large tires into the equation? Larger tires on the same gears will throw off the MPG. This website can help you determine how much you are off. Plug in stock numbers on the left chart and current ones on the right. Then play around with different ratios to find what works best for you.

http://www.grimmjeeper.com/gears.html
 

·
Premium Member
'89 YJ 4.2 with MC-2150 Carb & HEI, 2-1/2" Ex. AX-15, NP231 SYE, Adams shafts, F&R ARB, 3
Joined
·
3,909 Posts
^ assuming you have not changed your speedo gear
 

·
Registered
Joined
·
945 Posts
What about an HEI distributor, 4.0 HO head swap and mild cam like one of the 4x4 pro comps. Then add a Howell fuel injection kit to top it all off.

A coworker friend of mine did this setup on his 84 CJ and hole [email protected]*t did it make a huge improvement. Both to power and fuel economy.
 

·
Registered
Joined
·
9,000 Posts
Would probably pay for itself in 70 to 80 years too....
 

·
Registered
Joined
·
55 Posts
Discussion Starter · #12 ·
Thank you for the replies and the insight.

So I’ve managed to score a frame from my local Jeep guy- he’s a good guy I’ve done business with and I like giving him my money so it works out. I will be doing a frame swap with the same engine, but then do the axle swap with the 4.10.

Just to clarify- the 4.10 axles I’ve got have a little over 200k miles on them compared to the 125k on my stock 3.07s. Would there be any cause for concern that they’re near the end of their life and may need to be changed soon and therefore not be a smart swap? Lmk your thoughts.

Now back t the engine. I do like the carburetor- I’m not keen on going to fuel injection. I’ve heard a lot abou Weber and motor craft carbs and HEI distributor upgrades. Are these worth it on a stock engine. I’m in the process of dong my research to see if these are desirable only after the engine has been worked/ cammed. I’m not opposed to doing that if needed, but given that I’m doing none of the work I’m trying to figure what the budget will be for all of this. I won’t spend $8k on a new engine but I will spend $1k is upgrades and cams and all for the smiles.

Thanks again for your help
 

·
Registered
Joined
·
9,000 Posts
My 95 yj has 270k on it and my 04 has 210k on it.... I don't consider either one to be near the end of anything...
No problem driving either one on a 1000 mile trip tomorrow except for the having to drive 1000 miles...
 

·
Super Moderator
Joined
·
12,662 Posts
The Weber carbs are reputed to be difficult to keep in tune. The Motocraft (MC 2100 & MC 2150) are pretty much bulletproof once properly set up.
I went with a non-stepper Carted BBD because it was about half the price of a MC2100 conversion. It's been trouble free for around 4 years.

As far as mileage, get an app for your phone that will track your miles driven and speed. Fill your tank, and start the app. Don't forget to turn the app off once you shut the Jeep off and turn it back on whenever you drive the Jeep.
Once you've gone through a couple tankfulls of gas, you'll have a pretty good idea of your MPG.
Then, once you do your gears, have your HEI and whatever carb you go with, you can let us all know how much your mileage has (hopefully) improved.

Good Luck, L.M.
 
  • Like
Reactions: SlyJJ

·
Registered
Joined
·
44 Posts
I have the Weber on my 89, it does need to be adjusted here and there but it does suck some fuel into the 4.2. It’s a auto so getting up the inclined roads here in NEPA,requires some patience for sure, also no matter how I adjust it always seems to burn rich, lucky if I get 10 mpg
 

·
Registered
Joined
·
15 Posts
best mileage I ever got with a 4.2 was a bone stock '89, in 1989. 17 mpg on the highway. My "new" '89 gets about 13.9 mpg with the slush box running 31's I'm ditching the 31's and going to a 235 ( about 2" shorter} that will pull things back down where they need to be though it's still taller than stock.I don't have a clue which carb is on my current one, haven't looked at it yet to determine which one it is. I'm suspecting its the fomoco carb from the look of it. My plan is to add a holley fuel injection kit to it after the first of they year, better mileage, better drivability, no issues climbing steep hills. Whats not to love.
 

·
Registered
Joined
·
55 Posts
Discussion Starter · #18 ·
So it would seem that it is what it is- an old carbureted jeep with an engine pulling 112 HP it being pushed to its limits when lifted with 33" tires, so 9-10 MPG is what you get.

That said, anything worth doing is worth doing properly. The frame I got is in incredible shape. Im going to invest in a proper prepping and undercoat. The axle swap is "free" since the tub and all have to be swapped from the old one.

Im hopefully budgeting around $4k max for this project. $1000 for the frame, 100 for the uhaul pickup, 1400 was the quote to swap everything over. Just spent $250 on POR15 products for the frame and tub underside so I guess Im up to 2750 atm. I think I'll need new steering column bearings as well.....

We'll make it nice and neat and properly rebuilt, since Im assuredly fond of this vehicle. With only 125k on the engine, I figure its engine life ought to give it 250k ballpark. I'll save up for the next couple of years and contemplate doing an engine swap at that point, most likely a stroker at that point.
 

·
Registered
Joined
·
9,000 Posts
Por15 is decent stuff... I would advise against any sort of rubber or asphault or gooey undercoating.... if you desire anything more than the por15 I would go with a semi gloss or flat black epoxy paint...

I would suggest against a stroker too... for tha same money you can have a v8 that makes the same or more power on 87 octane and will be MUCH more durable...

This is an excerpt I posted in another thread...
I had linked the source but I guess wranglerforum didn't want links to other forums posted...

Here's the main post from the thread I linked above...

Quote:
Originally Posted by wendell
JP mag says they haven't seen a stroker get over 20,000 miles on them.
Sometimes stroker's aren't as durable. Now, that's not to say, "Oh my God! A stroker will wear down after 10,000 miles." Let me explain. (Hmmmm, let me do some Googling here.)

Its mostly about rod ratio (rod to stroke ratio). Rod Ratio = (rod length / stroke) This little calculation tells you the motor's rod angularity. A LOW rod ratio means a HIGH rod angle. A high rod angle creates a greater potential for accelerated wear to cylinder walls, pistons, and piston rings (picture an extremely low rod ratio that is driving the piston into the side of the cylinder wall). For example, a motor with a 5.400" rod length and a 3.000" stroke yields a rod ratio of 1.8:1. If we maintain the same stroke and shorten the rod length to 5.000" we get a 1.7:1 rod ratio. The rod angle has increased.

The picture on the left is Low Rod Angle (or High Rod Ratio) and the picture on the right is High Rod Angle (or Low Rod Ratio). The bottom picture is just there as an extra visual aid.
View attachment 4187819
View attachment 4187821
By lengthening the rod (as stroke is increased) you can offset the increased rod angle. But this requires further shortening of the piston. The further the piston is shortened the more likely the piston pin will intersect the oil ring groove, creating a potential for increased oil consumption.

Basically, there comes a point when you cannot shorten the piston any further before dependability is compromised.

The consensus, from what I've read, among engine manufacturers is that a ratio of 1.50" is the lowest acceptable rod ratio for a street motor. Realistically, rod ratios between 1.65 - 1.80 are ideal. (Maybe this has a lot to do why the 4.0L engines are so long lasting. Their rod ratio is 1.794)

When I was originally researching this topic, it was for my 68 Mustang
I was considering stroking a 302 out to a 347. A stock 302 has a rod ratio of 1.696:1 ------- A 347 would put the block at a 1.588:1 ratio. So I actually decided against stroking out the engine because I was more concerned with durability than power. (Actually I went with a 289, but thats a different story. Long story short, I was "persuaded" by my parents to save money for college. And by "persuaded" I mean "Listen to me or else.") rotfl2.gif

So.....

A stock 4.0L (241.5 cubic inches; 3.875" bore) has a 6.123" rod and a stroke of 3.413" so its rod ratio is 1.794

A stock 4.2L (258 cubic inches, right?) has a 5.875" rod and a 3.895" stroke so its rod ratio is 1.508.

As you already know, most guys who build their own "poor man's" stroker out of the 4.0L get the 3.895" stroke crankshaft from the 4.2L engine. On a 4.0L engine with the stock 6.123" rods and 3.875" bore, the stroker crank increases displacement to 276ci (4.5L). This gives a rod ratio of (6.123 / 3.895) = 1.572.

There are many ways to get around a "bad" rod ratio, but with them comes increased cost. Here's some real good stroker information. Definitely Google around and read up:
Jeep Stroker Motor Information

Jeep Strokers • Dynamic\Static Compression Ratio Calculator

From Junker to Stroker”

Whats your buddies stroker putting to the wheels? Or even before drivetrain? The only stroker builds I have seen that don’t run a higher octane are the simplier built ones, not the ATK/Golen ones (Like the ones putting 270hp before flywheel). Don’t get me wrong, I am seriously considering a Golen stroker, but its not the same always hitting 200k tractor engine that came from the factory.
 
1 - 19 of 19 Posts
Top