258 2bbl acceleration

[MDJEEPER]

I took my project vehicle out for a test drive last night. It was the first time I really tired to get into the throttle. I was pretty surprised by the lack of acceleration from that V6 when I went WOT in fourth gear. However, I did get some light knocking/pinging.

I should note that my last experience with a carb vehicle was an 85 Bronco with a 351 V8 & 4 bbl carb. Going WOT in that would push you back into the seat and there would be a big engine roar when those secondaries opened. We won't even go into the modern FI vehicles as a comparison.

What kind of acceleration should I expect from the AMC 258 i6 / 4.2l ?? How do I know what is normal vs. some sort of engine problem?

 

[Old Dog]

I was pretty surprised by the lack of acceleration from that V6 when I went WOT in fourth gear. However, I did get some light knocking/pinging

What kind of acceleration should I expect from the AMC 258 i6 / 4.2l ?? How do I know what is normal vs. some sort of engine problem?

Your profile doesn't say what gears you have or what size tires you have
so I have no idea if it's normal or not. More info please.
One thing for sure you don't want pinging. That could either be low grade gas, or to much timing. You need to fix that.
One more thing do you have a V6 or the AMC 258 i6 / 4.2l ? You say both in your question.

 

[MDJEEPER]

Ooops! Sorry, I mean straight 6!

The rear axle is the standard 2.73...and it's got 31" (by 10.50) tires.

 

[Old Dog]

2;73 = no power. I'm surprised it has any acceleration in forth.
AMC was trying to get MPG's in the 80's,they forgot about performance.
Best idea is to regear.

 

[LongHorn]

2;73 = no power. I'm surprised it has any acceleration in forth.
AMC was trying to get MPG's in the 80's,they forgot about performance.
Best idea is to regear.

X2 on that!

 

[Canadian CJ 7]

I have the exact same set up in my Jeep and same problem. I am going to one piece axle and 355 gears this year. Next year I am going to be swapping in a AMC 304 and a T-176 and tossing out that T-5 .

 

[MDJEEPER]

So, more mystery...I took it out on the highway...when I tried to climb a hill (NOT a really steep one -- just a normal highway grade) it could not hold 60 mph in 4th, but slipped down to about 54 by the crest.

Is that normal with the 2.73 gears!!!??

 

[LongHorn]

I took my project vehicle out for a test drive last night. It was the first time I really tired to get into the throttle. I was pretty surprised by the lack of acceleration from that V6 when I went WOT in fourth gear. However, I did get some light knocking/pinging.

I should note that my last experience with a carb vehicle was an 85 Bronco with a 351 V8 & 4 bbl carb. Going WOT in that would push you back into the seat and there would be a big engine roar when those secondaries opened. We won't even go into the modern FI vehicles as a comparison.

What kind of acceleration should I expect from the AMC 258 i6 / 4.2l ?? How do I know what is normal vs. some sort of engine problem?

Granted the bronco's heavier, but that's a V8 with probably a 3.55 gear 4 barrel & 4 speed auto.

My wifes YJeep has a AMC 258 i6 / 4.2l 4 speed with a Offenhauser 4 barrel intake, Holley 4barrel, Hotter cam 6 to 2 headers, 3.92 gears & 33"X 12.50" tires. It will smoke the tires off the line & rip second. Top end 95mph.

 

[LongHorn]

So, more mystery...I took it out on the highway...when I tried to climb a hill (NOT a really steep one -- just a normal highway grade) it could not hold 60 mph in 4th, but slipped down to about 54 by the crest.

Is that normal with the 2.73 gears!!!??

How many miles on the engine?
How long since last tuneup?
Stone stock?
Head wind or tailwind?

 

[IOPort51]

I think you have a problem. You have pretty close to the same drive line as muy truck and it will pull a 16 foot trailer with a ford 2000 tractor on it at 70 up a hill.
I never expect to set a land speed record but even with the 2.73's you should be able to hold highway speed.

 

[MDJEEPER]

How many miles on the engine?
How long since last tuneup?
Stone stock?
Head wind or tailwind?

It has 110,000 miles according to the odometer. As best I can tell (having just started with this project), it is stone stock in terms of drivetrain components. It does have 31x10.50 tires.

Thus far, I have replaced the spark plugs and wires. No idea when other tune up activities may have occurred.

Beautiful day...No wind at all!

 

[MDJEEPER]

I think you have a problem. You have pretty close to the same drive line as muy truck and it will pull a 16 foot trailer with a ford 2000 tractor on it at 70 up a hill.
I never expect to set a land speed record but even with the 2.73's you should be able to hold highway speed.

Going 70 up hill pulling a trailer seems pretty extraordinary based on my current experience! My jeep seems to have very good low end acceleration, but I can't imagine holding 70 pulling a trailer on the top end in fourth gear...

 

[LongHorn]

It has 110,000 miles according to the odometer. As best I can tell (having just started with this project), it is stone stock in terms of drivetrain components. It does have 31x10.50 tires.

Thus far, I have replaced the spark plugs and wires. No idea when other tune up activities may have occurred.

Beautiful day...No wind at all!

110K isn't real bad , but you most likely don't have a good knowledge of it's history. I'd check the compression just to see what I was working with. I would also put a vacuum gage on it that will tell you about the engines health.
The factory Jeep carbs are known problems.
With the oversized tires you have an 2.43 effective rearend ratio.
Not exactly racecar stuff.

 

[LongHorn]

Also all factory Jeeps can benefit hugely from one of the many ignition upgrades available. If nothing else plugs, cap, rotor & wires. Also check the timing.

 

[Cheepjeep85]

I think you have a problem. You have pretty close to the same drive line as muy truck and it will pull a 16 foot trailer with a ford 2000 tractor on it at 70 up a hill.
I never expect to set a land speed record but even with the 2.73's you should be able to hold highway speed.

you do have a problem, i have the same setup as well, but with 33s i can run down the interstate 65-70 with little a very little drop in speed going up hills

 

[Sasquach]

Going 70 up hill pulling a trailer seems pretty extraordinary based on my current experience! My jeep seems to have very good low end acceleration, but I can't imagine holding 70 pulling a trailer on the top end in fourth gear...

I doubt mine will even go 70mph except maybe downhill. 3.54 and 31" tires powered by the Ca. AMC 258 i6 / 4.2l 1bbl.

 

[IOPort51]

I doubt mine will even go 70mph except maybe downhill. 3.54 and 31" tires powered by the Ca. AMC 258 i6 / 4.2l 1bbl.

A two barrel will make a huge difference for you Sasquach, a cam would be a good thing too but I think you would be really impressed even with the carter two barrel.

 

[LongHorn]

110K isn't real bad , but you most likely don't have a good knowledge of it's history. I'd check the compression just to see what I was working with. I would also put a vacuum gage on it that will tell you about the engines health.
The factory Jeep carbs are known problems.
With the oversized tires you have an 2.43 effective rearend ratio.
Not exactly racecar stuff.

So did you try checking the compression to see what you have & if it's even between the cylinders?
The vacuum gage test can tell you a lot about your engine too.

 

[MDJEEPER]

So did you try checking the compression to see what you have & if it's even between the cylinders?
The vacuum gage test can tell you a lot about your engine too.

Unfortunately, I need to get the right tools first before I can do either a compression or vacuum test...

I did discover that it's got some sort of replacement Holley 2 barrel carb, rather than the original...

 

[LongHorn]

Unfortunately, I need to get the right tools first before I can do either a compression or vacuum test...

I did discover that it's got some sort of replacement Holley 2 barrel carb, rather than the original...

IMHO a 350 CFM. Holley is a good workable carb for that engine.
Easy to adjust good size for the CI.