4.2 or small block ford

BDCCLARK

Member
LIFETIME
City
gravois mills
State
MO
#1
I am looking for some perspective please. My scrambler is a 4.2 jeep currently. I have a 4.2 with gm hei and howell fi with 10,000 miles in another jeep that I am parting out. I also have a gt40 302 small block ford. I know the v8 will have way more power, but I don't have enough personal experience with the 4.2 to know if it will really have enough punch to hold speed for highway travel. The transmission will be an ax15 regardless of engine choice. I will run a 35 inch tire with the new drivetrain swap. I am looking to hear from those of you that run 4.2s on the highways at 65-80. Chris
 

Rosco1974

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
West Haven
State
UT
#2
A 4.2L will hold 65. Need that V8 for 80mph. Appropriate gears needed for both.
 

BDCCLARK

Member
LIFETIME
City
gravois mills
State
MO
#3
I don't need 80. It would be nice to have enough left in the tank to do it. I'm either running 4.10s or 4.56s. Can you hold speed climbing hills out there in Utah?
 

barrys

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
East Norriton
State
PA
#4
Years ago I was driving my brothers CJ7. 4.2 with Weber carb, auto(no overdrive), 4.10's, and 35". I could do 65 on the highway. That was about it. With overdrive, I think I could have done 70+.
My current 7 with a stock 4.2, t-176, unknown gears, and 31's will do 70.

I have a worked 302 (stock bottom end and iron heads, expect cam amd roller rockers)in my '90 LX Mustang. Heaven forbid, if that car gets wrecked, the engine and tranny are going into a CJ and will will be VERY fun(car went 11.44@119mph 20 years ago). 45,000 HARD miles later, it would be slower at the track but still very fun and fast.

I would hold onto the 5.0. Install the FI 4.2 and see how it is. If you don't like it, sell it and use the money for adapters to install the 5.0.
 

BDCCLARK

Member
LIFETIME
City
gravois mills
State
MO
#5
I feel your point. It's so much easier to drop in the injected 4.2, but I feel like the 302 will yield so much higher on the over all smile meter. Chris
 

barrys

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
East Norriton
State
PA
#6
The 302 will be SO much higher on the smile meter. And with the right exhaust, it will sound like a muscle car if you want it to. I have 2 chamber flowmasters and didn't have a radio in the car for 5 years because I loved the sound .
 

Spieg

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
Aurora
State
CO
#8
I'm probably a little biased, but I'd take a 5.0 over a 4.2 any day... particularly if you plan to run 35s (4.10-4.56 gears with the AX15 should work out about perfect for highway cruising). Both are good engines (and weigh about the same) but the V8 will have a wider power band, and should yield similar gas mileage if you're not too heavy on the go pedal.
 

John N

Addicted....Ex-SOA VP
LIFETIME
CJ-8.com Member
SOA Member
City
Rockville
State
VA
#9
You might as well just go straight to the V-8. The questions you’re asking make it obvious. From my experience, you’ll want the 4.56 gears to get it off the line better.
 

barrys

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
East Norriton
State
PA
#10
Did you run the stock efi with the 90 lx?
It has
Gt40 intake, 65mm throttle body, 77mm pro-m mass air meter, 19lb injectors, msd ignition, 110lph fuel pump, auxillary NOS fuel pump, NOS 2 stage, MSD 6al w/ multi step retard, MAC full length headers. KIMG0038.jpg
 

spankrjs

Scrambler Junkie
LIFETIME
CJ-8.com Member
SOA Member
City
Biloxi
State
MS
#11
I have drove my Red Scrambler, 4.2 with Mopar MPI, 33" tires, AX15, 4.10 axle gears, cross country numerous times. We are talking two days straight driving. I run 75-80 mph NO problem at all :thumbsup:

The tan Scrambler I sold, had a TBI 350, 4L60, 33" tires, 4,10 axle gears, cross country numerous times. We are talking two days straight driving. It ran 75-80 mph NO problem at all :thumbsup:

The V8 will hold the hills better, and fight the strong head winds better. But, I get better MPG with the 6, and less interior heat with 6/standard transmission :twocents:

The V8's are fun, but I prefer the inline 6's. Fuel injection, and proper gears, goes a long way :twocents:
 

Rosco1974

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
West Haven
State
UT
#12
A 4.2L will hold 65. Need that V8 for 80mph. Appropriate gears needed for both.
My 8 has 4.0L/AX15/4.88's/33"s so its a bit over geared to hold 80mph, but fun in-town and I dont worry about hills. Currently have a few projects in my shop that I am thinking of swapping parts around. My 8 will likely go down to 31-32" with 3.73 or 4.10.
 

BDCCLARK

Member
LIFETIME
City
gravois mills
State
MO
#13
I have drove my Red Scrambler, 4.2 with Mopar MPI, 33" tires, AX15, 4.10 axle gears, cross country numerous times. We are talking two days straight driving. I run 75-80 mph NO problem at all :thumbsup:

The tan Scrambler I sold, had a TBI 350, 4L60, 33" tires, 4,10 axle gears, cross country numerous times. We are talking two days straight driving. It ran 75-80 mph NO problem at all :thumbsup:

The V8 will hold the hills better, and fight the strong head winds better. But, I get better MPG with the 6, and less interior heat with 6/standard transmission :twocents:

The V8's are fun, but I prefer the inline 6's. Fuel injection, and proper gears, goes a long way :twocents:
You make a strong point. Mine would be 4.2 with howell and hei, ax15, 4.56s, and 35s.
 

BDCCLARK

Member
LIFETIME
City
gravois mills
State
MO
#14
My 8 has 4.0L/AX15/4.88's/33"s so its a bit over geared to hold 80mph, but fun in-town and I dont worry about hills. Currently have a few projects in my shop that I am thinking of swapping parts around. My 8 will likely go down to 31-32" with 3.73 or 4.10.
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.
 

Spieg

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
Aurora
State
CO
#15
Being in Colorado, most of my trips involve at least one high altitude mountain pass. My old 4.2 with 32s sucked balls trying to climb up to Eisenhower tunnel in 3rd gear and getting passed by everyone except big rigs (add a trailer or strong head wind, and it was 2nd gear and even the big rigs would pass me). With the 5.0 I can hold 65-70 all the way and can actually accelerate again if I get slowed down by traffic.
 
Last edited:

BDCCLARK

Member
LIFETIME
City
gravois mills
State
MO
#16
Being in Colorado, most of my trips involve at least one high altitude mountain pass. My old 4.2 with 32s sucked balls trying to climb up to Eisenhower tunnel in 3rd gear and getting passed by everyone except big rigs (add a trailer or strong head wind, and it was 2nd gear and even the big rigs would pass me). With the 5.0 I can hold 65-70 all the way and can actually accelerate again if I get slowed down by traffic.
That is the unfortunate truth I was looking to hear from a first hand experience. Thank you. What is your exact setup now?
 

Spieg

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
Aurora
State
CO
#17
5.0 with a T18/D300 with 4.10 gears and 35" BFG KM2. I lack the gears to cruise at 75-80 for long periods but I don't have overdrive (yet). Have an AX15 in the garage that will cure that problem one of these days...
 

BDCCLARK

Member
LIFETIME
City
gravois mills
State
MO
#18
5.0 with a T18/D300 with 4.10 gears and 35" BFG KM2. I lack the gears to cruise at 75-80 for long periods but I don't have overdrive (yet). Have an AX15 in the garage that will cure that problem one of these days...
What is your 5.0 from? Are you on the scrambler facebook page too?
 
Top