4.2 or small block ford

Rosco1974

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
West Haven
State
UT
#21
When you say you don't worry about hills, do you mean they aren't a problem or you avoid them?

I had a stock 4.0, 5speed, 97 tj, and the hills ate it's lunch. Gears would have changed that I believe.
I go right up, but on a long grade I may have to go to 4th and spin the motor a bit. Some people get nervous about these straight 6's @ 3500rpm but that's where they produce max torque.

My 2003 Rubicon (4.10/5 speed/33") hated long uphill grades like I-70 east out of Utah @ 65-70. Needed 4.56 gears.

Realistically, mild built older V8 or LS solves this.
 

spankrjs

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
Biloxi
State
MS
#22
I have crossed southern Colorado, twice, on 160, the infamous "Wolf Creek Pass", 7% grades, high elevation. On the steepest parts, I would drop to third gear, never dropped below 50 mph, the only thing passing me were the TURBO diesel pick ups and sports cars. The 2 door JK Rubicon that was with me, 35's and 4.88's, could not keep up :shrug:

Granted, a V8 would have given me a bit more, but I thought my 6's did fine. The first time I went this route was with the 4.2. The second time, the 4.0. The 4.0 seemed to have a bit more at higher RPM's, breathed a bit easier :twocents:

If I drove those conditions more regularly, I would swap in 4.56 gears, and/or seriously look at forced induction, i.e. turbo or super charging. At the higher altitudes, forced induction seems to be the key :twocents:

I actually thought the drive/climb on Utah 89A up to Jacob Lake was more brutal then Wolf Creek Pass. The 89A was shorter, steeper, and more curvy, very hard to maintain speed. On some of those grades I could only maintain 45 mph MAX :eek: It was a fun, scenic drive, but I would not want to be driving an RV or pulling a trailer on this road :fingerscrossed:

I think the V8 has an advantage here over the sixes, BUT the benefits of the V8's do not outweigh the pitfalls, in my opinion/uses :twocents:
 

BDCCLARK

Member
LIFETIME
City
gravois mills
State
MO
#23
I go right up, but on a long grade I may have to go to 4th and spin the motor a bit. Some people get nervous about these straight 6's @ 3500rpm but that's where they produce max torque.

My 2003 Rubicon (4.10/5 speed/33") hated long uphill grades like I-70 east out of Utah @ 65-70. Needed 4.56 gears.

Realistically, mild built older V8 or LS solves this.
Thank you. That's good information. I know the 4.0 is a higher revving engine, but I thought the 4.2s made max torque closer to 2000-2300?
 

BDCCLARK

Member
LIFETIME
City
gravois mills
State
MO
#24
I have crossed southern Colorado, twice, on 160, the infamous "Wolf Creek Pass", 7% grades, high elevation. On the steepest parts, I would drop to third gear, never dropped below 50 mph, the only thing passing me were the TURBO diesel pick ups and sports cars. The 2 door JK Rubicon that was with me, 35's and 4.88's, could not keep up :shrug:

Granted, a V8 would have given me a bit more, but I thought my 6's did fine. The first time I went this route was with the 4.2. The second time, the 4.0. The 4.0 seemed to have a bit more at higher RPM's, breathed a bit easier :twocents:

If I drove those conditions more regularly, I would swap in 4.56 gears, and/or seriously look at forced induction, i.e. turbo or super charging. At the higher altitudes, forced induction seems to be the key :twocents:

I actually thought the drive/climb on Utah 89A up to Jacob Lake was more brutal then Wolf Creek Pass. The 89A was shorter, steeper, and more curvy, very hard to maintain speed. On some of those grades I could only maintain 45 mph MAX :eek: It was a fun, scenic drive, but I would not want to be driving an RV or pulling a trailer on this road :fingerscrossed:

I think the V8 has an advantage here over the sixes, BUT the benefits of the V8's do not outweigh the pitfalls, in my opinion/uses :twocents:
That's some good first hand perspective. Thank you. What are the v8 pitfalls from your eyes?

I know the 302 will bring more smiles, but I will be running 4.56s with my 35s and the ax15 and I wonder how much that gearing will really help.
 

spankrjs

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
Biloxi
State
MS
#25
In my experience, pitfalls of a V8:

1) increased interior heat from the larger displacement/power output/exhaust system (especially on long interstate drives)
2) harder to keep the engine cool when working it hard (I've yet to get a 258/4.0 to run Hot)
3) the fun/expense of swapping a V8 in (all the little details)
4) less MPG (I would "think" the newer generation GM V8's would get same/better then a MPI 4.2/4.0, depending on pedal usage)
5) running the exhaust, single or dual (clearance at ground/transmission/front driveshaft/transfer case/cross members/ rear shackles/etc.)
6) easier to break drive train components (depending on skinny pedal usage)

Obviously, lots of benefits to a V8 swap, too :thumbsup:

I've had two Jeeps with V8's, a 304 and a TBI 350. Both were fine/fun to drive, I just prefer my inline 6's :twocents:

As far as gearing goes, 4.10's and 33's with a 6 cylinder is good. BUT, depending on conditions, i.e. lots of mountain driving or driving across the great plains with strong head winds, 4.56 might be better. I ran 35's with 4.10's and a T176 behind a 6 cylinder. It was barely "OK".

IMO, 35's and a 6 cylinder, minimum of 4.56, I would probably go 4.88's :twocents:

With a V8 you can be a hair less aggressive with the gearing, BUT keeping any engine in it's powerband is critical for peak performance:twocents:
 
Last edited:

BDCCLARK

Member
LIFETIME
City
gravois mills
State
MO
#26
In my experience, pitfalls of a V8:

1) increased interior heat from the larger displacement/power output/exhaust system (especially on long interstate drives)
2) harder to keep the engine cool when working it hard (I've yet to get a 258/4.0 to run Hot)
3) the fun/expense of swapping a V8 in (all the little details)
4) less MPG (I would "think" the newer generation GM V8's would get same/better then a MPI 4.2/4.0, depending on pedal usage)
5) running the exhaust, single or dual (clearance at ground/transmission/front driveshaft/transfer case/cross members/ rear shackles/etc.)
6) easier to break drive train components (depending on skinny pedal usage)

Obviously, lots of benefits to a V8 swap, too :thumbsup:

I've had two Jeeps with V8's, a 304 and a TBI 350. Both were fine/fun to drive, I just prefer my inline 6's :twocents:

As far as gearing goes, 4.10's and 33's with a 6 cylinder is good. BUT, depending on conditions, i.e. lots of mountain driving or driving across the great plains with strong head winds, 4.56 might be better. I ran 35's with 4.10's and a T176 behind a 6 cylinder. It was barely "OK".

IMO, 35's and a 6 cylinder, minimum of 4.56, I would probably go 4.88's :twocents:

With a V8 you can be a hair less aggressive with the gearing, BUT keeping any engine in it's powerband is critical for peak performance:twocents:
Thank you for that. I appreciate your thoughts. Chris
 

Spieg

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
Aurora
State
CO
#27
I understand on the facebook thing. Stock mustang motor, stock cam, and injection?
Stock engine, header exhaust (routed to single cat and muffler), throttle body from (IIRC) a 93 or 94 Mustang, and some aftermarket heads (they made not much difference in performance from original, just needed to either rebuild or replace so opted to replace).
 

BDCCLARK

Member
LIFETIME
City
gravois mills
State
MO
#28
Stock engine, header exhaust (routed to single cat and muffler), throttle body from (IIRC) a 93 or 94 Mustang, and some aftermarket heads (they made not much difference in performance from original, just needed to either rebuild or replace so opted to replace).
Thank you Spieg. A truck or explorer cam would make a nice difference for you I'll bet. Lower power band for torque.
 

Rosco1974

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
West Haven
State
UT
#29
Thank you. That's good information. I know the 4.0 is a higher revving engine, but I thought the 4.2s made max torque closer to 2000-2300?
Spec sheets vary by source but I have a 1991 4.0L and these are the calculations @ 70mph Screenshot_20200114-204909_Chrome.jpg

Screenshot_20200114-204436_Drive.jpg
 
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