International Full Size Jeep Association
Home Forums Reader's Rigs Tech Library Trail Stories FSJ-List
International Full Size Jeep Association  

Go Back   International Full Size Jeep Association > Tire Kickin' > General FSJ Tech

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 08-04-2010, 05:51 PM
Emupickle's Avatar
Emupickle Emupickle is offline
Member
 
Join Date: Feb 16, 2009
Location: Lemon Grove CA
Posts: 67
Question 258 swap, would it be worth it?

So, I pose this question, hp and torque aside, what kind of fuel economy boost would I get if I swapped in a strong 258 and manual transmission. I have a relatively new 360, 35,000 miles and a brand new 727 in my jeep, but no matter what i do, I never see any more than 13mpg, even with a feather foot. I don't drive fast, and I don't do any hardcore wheeling in my wag, so I feel as though a sluggish six might fit my current purposes more than my 360. Plus I have an irrational love of straight sixes. If I had funds to allocate towards my jeep I'd swap in a modern drive train any day a 4.0 perhaps, but I'm feeling a lot more like pulling the 360 and swapping in a six to use the wag as a daily driver, and saving the v8 for a trail rig that will be acquired somewhere down the line. If I could squeeze ~20mpg out of a 258 I'd consider the effort worth it in the long run, but anything less seems pointless except possibly for reliability sake. Any Ideas? How much $ does a 258 even go for? I'm not even sure if I can find a post 85 258 out here to put in it. I know california wont allow motors older than the model year to pass smog. At least thats what the smog tech told me. Opinions?
__________________
Brendan

Jeepless for the moment.

'85 Grand Wagoneer...Sold
stock and saggy suspension
360/727/np229

'00 Mustang 5spd, DD...Dirty and Fast
'71 Beetle -resto- project...Sold
~'96 2276cc vw powered sand car...Sold
'92 Ford Ranger 4.0...Sold
Reply With Quote
  #2  
Old 08-04-2010, 06:00 PM
1983 j10's Avatar
1983 j10 1983 j10 is offline
327 Rambler
 
Join Date: Apr 13, 2008
Location: ohio
Posts: 728
your best bet for swaping in a I6 would be to go with a 4.0HO out of a 91-96 xj and even use the fuel injection from it.
__________________
1983 j10 lwb soon to be a 4.5l stroker AMC 20 rear 44 front 4spd manual in the process of restoring

01 xj 3" and 31's
Reply With Quote
  #3  
Old 08-04-2010, 07:59 PM
del's Avatar
del del is offline
327 Rambler
 
Join Date: Apr 13, 2006
Location: ofallon,il
Posts: 538
keep the 8

Although the 6 may seem appealing, it's alot of work for minimal gain in mpgs. Not to mention, the loss of HP. If you're really wanting MPGs, try swapping to numerically lower gears. Axles shouldn't be hard to find since that gear ratio (lower) is not desirable. They will kill you're off-line acceleration tho.
If you do decide to go 6, get better technology. The 4.0 is a great motor, and it can get good MPGs and decent power if you throw a little $$$ at it. A FI and computer managed engine would make a pleasant daily driver. It will also meet any smog regulations you have to pass....Del
Reply With Quote
  #4  
Old 08-04-2010, 08:15 PM
seventynine's Avatar
seventynine seventynine is offline
350 Buick
 
Join Date: Apr 13, 2003
Location: Marshall, VA
Posts: 1,183
There have been some recent thread discussing this. I think the 258 guys are getting somewhere in the upper teens for MPG...maybe 20 on a good day.

Do the math on how many miles you will have to drive to make up for the expense of doing the swap...probably more than you think...especially if you want a rebuilt or newly rebuilt motor.

Dean
__________________
Dean

'79 J10
'77 Cherokee Chief
'79 CJ-7
'79 CJ-5
'46 CJ-2A
'93 ZJ Limted
'79 Cherokee Chief (traded for the J10)
'79 Wagoneer (RIP)
'13 FLSTN Softail Deluxe
Reply With Quote
  #5  
Old 08-04-2010, 08:33 PM
smogdredd's Avatar
smogdredd smogdredd is offline
Grease Monkey
 
Join Date: Jul 19, 2010
Location: Apple Valley Ca.
Posts: 464
Gears

Almost every vehicle made in the mid to late 80s was horribly over geared. The Waggy was no exeption. The problem is You can't stay out of the second stage of the power valve. I was shocked to see the gear ratio jn my waggy. If You put a 258 in place of a 360 wthout adressing the gear ratio it won't get out of it;s own way! I put 356s in mine to get some snap out of it and to stay in the first stage of the power valve more. One thing to keep in mind is that vehicles from this era were designed to be driven at 55 mph. They were also designed around the EPA fuel economy test, not the real world!
Reply With Quote
  #6  
Old 08-04-2010, 09:29 PM
tazzerzz's Avatar
tazzerzz tazzerzz is offline
Gear Head
 
Join Date: Jan 31, 2007
Location: Flagstaff, AZ
Posts: 685
my 2 cents on this
I have owned both and both have their good and bad points
The 360 = better power and bad mileage, 12-13 mpg
The 258 = less power, better reliability, Better mileage 14-18 mpg

I can tell you. this, With the 258 it's a love hate relationship
The 258 seems to be less problematic, Then again climbing a grade on the freeway in second gear is no fun.

If it were my decision I would keep what I had, If you have a fresh 360 keep it, It's really not worth the expense for a few more mpg.

If you have a good running 258 as well keep it, it will run forever properly maintained
__________________
1980 j10 w/Brow and a nice fresh dent on the bed
Reply With Quote
  #7  
Old 08-05-2010, 01:13 PM
Emupickle's Avatar
Emupickle Emupickle is offline
Member
 
Join Date: Feb 16, 2009
Location: Lemon Grove CA
Posts: 67
Quote:
Originally Posted by smogdredd
Almost every vehicle made in the mid to late 80s was horribly over geared. The Waggy was no exeption. The problem is You can't stay out of the second stage of the power valve. I was shocked to see the gear ratio jn my waggy. If You put a 258 in place of a 360 wthout adressing the gear ratio it won't get out of it;s own way! I put 356s in mine to get some snap out of it and to stay in the first stage of the power valve more. One thing to keep in mind is that vehicles from this era were designed to be driven at 55 mph. They were also designed around the EPA fuel economy test, not the real world!
I am well aware its meant to be driven at 55, i seldom push it past sixty. I have other cars to go fast in, my wag is for cruising. But how difficult is it to switch gear ratios? Can i pull the gears out of the diffs and switch them or do I need new axels? I know little to nothing about gearing.
__________________
Brendan

Jeepless for the moment.

'85 Grand Wagoneer...Sold
stock and saggy suspension
360/727/np229

'00 Mustang 5spd, DD...Dirty and Fast
'71 Beetle -resto- project...Sold
~'96 2276cc vw powered sand car...Sold
'92 Ford Ranger 4.0...Sold
Reply With Quote
  #8  
Old 08-05-2010, 02:03 PM
seventynine's Avatar
seventynine seventynine is offline
350 Buick
 
Join Date: Apr 13, 2003
Location: Marshall, VA
Posts: 1,183
Quote:
Originally Posted by Emupickle
I am well aware its meant to be driven at 55, i seldom push it past sixty. I have other cars to go fast in, my wag is for cruising. But how difficult is it to switch gear ratios? Can i pull the gears out of the diffs and switch them or do I need new axels? I know little to nothing about gearing.

You can just swap out the gears but it's not a trivial task. You will have to remove all four axle shafts and you will need some specific tools to set the new gears up such as a press and a dial gauge set up.

Setting up gears is not rocket surgery but it will take some research if you have never done it before....and you still might screw it up.

New gears and install kits for two axles will cost you around $500 maybe a bit more.

Depending on what ratio you have now and what you want to go to you may need to change out the carrier too which would add cost...but it's always an opportunity to add a locker though it sounds like you don't need one for what you use the rig for.

I'm guessing your '85 has 3.07 gears or maybe 2.73s....and you can't really go lower than 2.73. It's already likely geared for mileage.

If you are getting 13mpg that about as good as it gets with a 360. I don't think re-gearing is going to help you. If you go to a 258 and then re-gear to try an make up for the power loss you'll be eating away at the mileage you just gained and you'll spend more money to save pennies at the pump.

You're better off not checking your mileage;-> In the same way that you're better off not adding up what you spend on your Jeep;-)

Dean
__________________
Dean

'79 J10
'77 Cherokee Chief
'79 CJ-7
'79 CJ-5
'46 CJ-2A
'93 ZJ Limted
'79 Cherokee Chief (traded for the J10)
'79 Wagoneer (RIP)
'13 FLSTN Softail Deluxe

Last edited by seventynine : 08-05-2010 at 08:00 PM.
Reply With Quote
  #9  
Old 08-05-2010, 02:39 PM
tgreese's Avatar
tgreese tgreese is offline
 
Join Date: May 29, 2003
Location: Medford MA USA
Posts: 11,209
The 258 is not a drop in replacement for the 360. It bolts up, but a lot of other stuff has to change to make it work. Search old posts - lots of discussion previously about 258 to V8, and vice-versa.

IMO you'd be vastly better off with the Mopar MPI and 4.0L. The 258 is not a very efficient (or powerful) design compared to the 4.0L HO. A more efficient automatic transmission would also be helpful - the 727 is strong but wastes a lot of power.

Search old posts about fuel economy ... this topic has been done to death here.
__________________
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination ATs, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
ECO Green: '15 FCA Jeep Cherokee KL Trailhawk
Reply With Quote
  #10  
Old 08-05-2010, 02:55 PM
Emupickle's Avatar
Emupickle Emupickle is offline
Member
 
Join Date: Feb 16, 2009
Location: Lemon Grove CA
Posts: 67
Quote:
You're better off not checking your mileage;-> In the same way that you're better off not adding up what you spend on your Jeep;-)

Sadly I think I may have to take that advice. =/ I dont understand how a smogged down chevy 350 bolted to a slushbox would get such better mileage than a smogged down amc 360 bolted to a slushbox. Ive seen guys with 80 something suburbans with tired small blocks getting high teens, and I think those burbs weigh even more than How in-efficient are amc v8s...
__________________
Brendan

Jeepless for the moment.

'85 Grand Wagoneer...Sold
stock and saggy suspension
360/727/np229

'00 Mustang 5spd, DD...Dirty and Fast
'71 Beetle -resto- project...Sold
~'96 2276cc vw powered sand car...Sold
'92 Ford Ranger 4.0...Sold
Reply With Quote
  #11  
Old 08-05-2010, 03:21 PM
Emupickle's Avatar
Emupickle Emupickle is offline
Member
 
Join Date: Feb 16, 2009
Location: Lemon Grove CA
Posts: 67
Quote:
I'm guessing your '85 has 3.07 gears or maybe 2.73s....and you can't really go lower than 2.73. It's already likely geared for mileage.

Well, it has a factory/dealer tow package, amc and jeep labels all over it. Would that pinpoint what my gearing is?
__________________
Brendan

Jeepless for the moment.

'85 Grand Wagoneer...Sold
stock and saggy suspension
360/727/np229

'00 Mustang 5spd, DD...Dirty and Fast
'71 Beetle -resto- project...Sold
~'96 2276cc vw powered sand car...Sold
'92 Ford Ranger 4.0...Sold
Reply With Quote
  #12  
Old 08-05-2010, 04:12 PM
seventynine's Avatar
seventynine seventynine is offline
350 Buick
 
Join Date: Apr 13, 2003
Location: Marshall, VA
Posts: 1,183
Quote:
Originally Posted by Emupickle
Ive seen guys with 80 something suburbans with tired small blocks getting high teens,

Well...I'd be skeptical. There are folks here who claim the same thing for AMC V8s.

Here are the facts though. fueleconomy.gov shows an '85 K10 Suburban getting 11mpg on in town and 14mpg on the highway...which is one mile mpg better than a GW for the same year:

http://www.fueleconomy.gov/feg/calcu...mn=1&id=1 645

Dean
__________________
Dean

'79 J10
'77 Cherokee Chief
'79 CJ-7
'79 CJ-5
'46 CJ-2A
'93 ZJ Limted
'79 Cherokee Chief (traded for the J10)
'79 Wagoneer (RIP)
'13 FLSTN Softail Deluxe
Reply With Quote
  #13  
Old 08-05-2010, 04:18 PM
seventynine's Avatar
seventynine seventynine is offline
350 Buick
 
Join Date: Apr 13, 2003
Location: Marshall, VA
Posts: 1,183
Quote:
Originally Posted by Emupickle
Well, it has a factory/dealer tow package, amc and jeep labels all over it. Would that pinpoint what my gearing is?

According to the '82 TSM on oljeep.com it shows 2.73 being standard and 3.31 being an option. The gearing is likely the same for '85. The tow package would probably have had the 3.31 gears.

Take a look at the diff covers and see if the metal tag is still on them...if so it will tell you the gearing.

Dean
__________________
Dean

'79 J10
'77 Cherokee Chief
'79 CJ-7
'79 CJ-5
'46 CJ-2A
'93 ZJ Limted
'79 Cherokee Chief (traded for the J10)
'79 Wagoneer (RIP)
'13 FLSTN Softail Deluxe

Last edited by seventynine : 08-05-2010 at 04:35 PM.
Reply With Quote
  #14  
Old 08-05-2010, 04:28 PM
tgreese's Avatar
tgreese tgreese is offline
 
Join Date: May 29, 2003
Location: Medford MA USA
Posts: 11,209
I don't think the gearing is as much of a problem as the aerodynamics. With a 29" tire and a 1:1 final drive ratio, 3.31s would put you at 2492 RPM at 65 mph, which should be fine.

In the 4 decades since the FSJs were introduced, the car manufacturers have put a lot of effort into making the wind profile a lot smoother for all cars and trucks. Wind resistance is a mighty barrier that goes like the square of velocity, so for every 40% increase in speed, you double the wind resistance. Your greatest return will likely come from reducing your cruising speed by 10% or 20% or whatever you can stand.

That's not to say that you cannot do better by upgrading the drivetrain, but it will be a battle with diminishing returns ... and will likely be economically unrewarding. You can't squeeze blood from a stone.
__________________
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination ATs, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
ECO Green: '15 FCA Jeep Cherokee KL Trailhawk

Last edited by tgreese : 08-05-2010 at 04:31 PM.
Reply With Quote
  #15  
Old 08-05-2010, 06:02 PM
grimgaunt grimgaunt is offline
Master Mechanic
 
Join Date: Aug 06, 2002
Location: close enuff to Denver, but far enuff from the people
Posts: 929
so, a different statistical point that may change your opinion. My neighbour has a 1988 MJ (Jeep Commanche truck) that has one of my Mercedes diesels in it. The engine specs are startlingly similar to the 258, 120 hp/185 TQ @ 4200 and 2400 rpm peak respectively (although the torque curve is FLAT from 2200 - 4200).

That thing has waggy axles under it and is fairly heavy but probably a couple of hundred lbs less than a stock waggy. It is running 5.38's w/35" tires.

It has a Chevy T-5 behind the mercedes diesel (homebrew adapter) and gets mid 30's for mileage.

The key is gearing to the engine. Do the math with the online calculators and you'll find that Aaron calculated what it would do for 80% of its life (regular driving) and figured out the optimum rpm that the engine would have to turn for that function. The rest is easy.

Let me know if you need more details
Reply With Quote
  #16  
Old 08-06-2010, 02:36 PM
Emupickle's Avatar
Emupickle Emupickle is offline
Member
 
Join Date: Feb 16, 2009
Location: Lemon Grove CA
Posts: 67
Quote:
My neighbour has a 1988 MJ (Jeep Commanche truck) that has one of my Mercedes diesels in it. The engine specs are startlingly similar to the 258, 120 hp/185 TQ @ 4200 and 2400 rpm peak respectively (although the torque curve is FLAT from 2200 - 4200).

What kind of Mercedes diesels? I would love to go diesel but its such an expensive build.
__________________
Brendan

Jeepless for the moment.

'85 Grand Wagoneer...Sold
stock and saggy suspension
360/727/np229

'00 Mustang 5spd, DD...Dirty and Fast
'71 Beetle -resto- project...Sold
~'96 2276cc vw powered sand car...Sold
'92 Ford Ranger 4.0...Sold
Reply With Quote
  #17  
Old 08-06-2010, 03:02 PM
3rdelement's Avatar
3rdelement 3rdelement is offline
350 Buick
 
Join Date: Nov 25, 2009
Location: Castle Rock, Colorado
Posts: 1,119
just remember."our jeeps are as aerodynamic as rosie odonnel on a skateboard." LOL! still my all time favorite quote from this forum!
__________________
Richard Ricketts
build thread: click HERE
1985 Jeep Grand Wagoneer {woodless}-Edelbrock 1406 carb, Edelbrock Sp2p Intake, Hella ecode headlights, bixenon HID 5000k headlights, mb quart 6.5" component speakers f&r, alpine cde-100 deck, final edition grill, Hella 550 fog lights, 1991 window regulators, cs144, aluminum coolant&washer tanks
Reply With Quote
  #18  
Old 08-06-2010, 03:03 PM
CJ the noisemaker's Avatar
CJ the noisemaker CJ the noisemaker is offline
Bleedin' Gasoline
 
Join Date: Nov 29, 2009
Location: Tempe, AZ
Posts: 2,348
I have an '85 that gets around 15-19 MPG. It has an AMC 258 with 3.54 axles running on 28" tires.
__________________
CJ
[/color][/size] -1985 Ford LTD Country Squire "Rarity" - 302/AOD
Reply With Quote
  #19  
Old 08-07-2010, 12:09 PM
joe joe is offline
 
Join Date: Apr 28, 2000
Location: PNWet, USA
Posts: 22,392
Quote:
Originally Posted by seventynine
There have been some recent thread discussing this. I think the 258 guys are getting somewhere in the upper teens for MPG...maybe 20 on a good day.


Dean
You can get upper teens on the hwy. To get 20 you'll need to desmog, swap carbs, upgrade ign sytem. plus te 258 needs a different radiator, specific bellhoisings short input trans shaft on a manual. By the time you buy the motor correct trans and do the needed upgrades you'll have at least a couple grand tied up in parts. My Cherokee w/258/T5/208 w/2.72 gears got mid teens rural driving, high teens hwy. That was on a fresh 6,000 mile motor and the carb and smog junk was brand new. If your 360 only has 35,000 on it I'd fine tune it and upgrade the ign to HEI or TFI. I love the 258 but wouldn't swap one in unless the motor I had was shot.
This ain't what ya want to hear...but if fuel consumption is a big concern maybe FSJ's just aren't for you? you're better off buying an econobox for a DD and using the Wag as a hobby car.
__________________
joe
"Don't mind me. I'm just here for the alibi"
Reply With Quote
  #20  
Old 08-07-2010, 12:48 PM
mdcptman's Avatar
mdcptman mdcptman is offline
Jeep Therapist
 
Join Date: Apr 09, 2010
Location: New Orleans, LA.
Posts: 1,287
Here's another thought, How bout a 700r4, or 60L, rigged to shift hydraulically instead of all the diff swapping? It has a very nice low gear for off the line starts, and a good overdrive. I've been looking into this, and you can get the adapters from advance adapters for about $900. If you use a good used 700r4 out of a 4x4, it will have the correct tailshaft to fit the adapter, otherwise you have to buy the tailshaft from advance, and have it installed in the tranny.

I spoke to a guy a few years ago who was running this with 2.73s and 33" tires. He claimed 18mpg in the city. He also had TBI fuel injection, but said he got the most mpg gain from the transmission swap.

This is definitely on my list of todos for my GW.
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
4.0 head on a 258 is it worth it. Tahoe100 General FSJ Tech 30 01-19-2010 09:56 AM
258 to 360 swap firemanseth3 General FSJ Tech 10 03-20-2009 02:11 PM
needed parts for a 360 to 258 swap? kingeno General FSJ Tech 2 12-10-2008 04:17 PM
258 to 360 engine swap jrlane General FSJ Tech 6 07-30-2008 11:17 PM
258 to V8 engine swap question caionneach General FSJ Tech 35 02-04-2004 03:05 PM


All times are GMT -6. The time now is 07:19 AM.


Powered by vBulletin Version 3.5.4
Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.
corner corner