Does anyone know where I can get torque curve data for a 1988 Jeep
Wrangler 4.2 L with a manual transmission?
My interest stems from the apparent loss of power when I recently
up-sized my tires from 205/75R15s to 30x9.50R15s. I knew that I would
lose some power with this change, but I'm now finding that I can't
even maintain 70mph going up some of the hills on the way to work even
when I downshift. Before, I could easily have maintained speed even in
5th gear. Right now, when I do get to 70 on flat terrain, I'm at
about 2200 RPMs in 5th or 2850 in 4th. At 60mph I'm at somewhere
around 1800 and 2300 RPMs, respectively.
So I am wondering where the peak torque is for this engine. Is this
power loss just something to be expected, or is there more that I
should be able to get more out of my engine?

 

Welcome to the wild world of larger tires.

You need to regear now to return the torque curve to its original location.
I suggest 4.10s because this ratio will work well up to 32" tires before you
start to see this problem again.



<howard.phelan@us.army.mil> wrote in message
news:1102609511.587782.112030@z14g2000cwz.googlegr oups.com...
> Does anyone know where I can get torque curve data for a 1988 Jeep
> Wrangler 4.2 L with a manual transmission?
> My interest stems from the apparent loss of power when I recently
> up-sized my tires from 205/75R15s to 30x9.50R15s. I knew that I would
> lose some power with this change, but I'm now finding that I can't
> even maintain 70mph going up some of the hills on the way to work even
> when I downshift. Before, I could easily have maintained speed even in
> 5th gear. Right now, when I do get to 70 on flat terrain, I'm at
> about 2200 RPMs in 5th or 2850 in 4th. At 60mph I'm at somewhere
> around 1800 and 2300 RPMs, respectively.
> So I am wondering where the peak torque is for this engine. Is this
> power loss just something to be expected, or is there more that I
> should be able to get more out of my engine?
>

 

Welcome to the wild world of larger tires.

You need to regear now to return the torque curve to its original location.
I suggest 4.10s because this ratio will work well up to 32" tires before you
start to see this problem again.



<howard.phelan@us.army.mil> wrote in message
news:1102609511.587782.112030@z14g2000cwz.googlegr oups.com...
> Does anyone know where I can get torque curve data for a 1988 Jeep
> Wrangler 4.2 L with a manual transmission?
> My interest stems from the apparent loss of power when I recently
> up-sized my tires from 205/75R15s to 30x9.50R15s. I knew that I would
> lose some power with this change, but I'm now finding that I can't
> even maintain 70mph going up some of the hills on the way to work even
> when I downshift. Before, I could easily have maintained speed even in
> 5th gear. Right now, when I do get to 70 on flat terrain, I'm at
> about 2200 RPMs in 5th or 2850 in 4th. At 60mph I'm at somewhere
> around 1800 and 2300 RPMs, respectively.
> So I am wondering where the peak torque is for this engine. Is this
> power loss just something to be expected, or is there more that I
> should be able to get more out of my engine?
>

 

Welcome to the wild world of larger tires.

You need to regear now to return the torque curve to its original location.
I suggest 4.10s because this ratio will work well up to 32" tires before you
start to see this problem again.



<howard.phelan@us.army.mil> wrote in message
news:1102609511.587782.112030@z14g2000cwz.googlegr oups.com...
> Does anyone know where I can get torque curve data for a 1988 Jeep
> Wrangler 4.2 L with a manual transmission?
> My interest stems from the apparent loss of power when I recently
> up-sized my tires from 205/75R15s to 30x9.50R15s. I knew that I would
> lose some power with this change, but I'm now finding that I can't
> even maintain 70mph going up some of the hills on the way to work even
> when I downshift. Before, I could easily have maintained speed even in
> 5th gear. Right now, when I do get to 70 on flat terrain, I'm at
> about 2200 RPMs in 5th or 2850 in 4th. At 60mph I'm at somewhere
> around 1800 and 2300 RPMs, respectively.
> So I am wondering where the peak torque is for this engine. Is this
> power loss just something to be expected, or is there more that I
> should be able to get more out of my engine?
>

 

Wow, you sound like you have some power or tune up issues.

I have been told that the engine peaks the timing advance around 2300
rpm and 2300 seems to be a real 'sweet spot' for my engine.

It will just haul out fast from 2300 and hold almost any hill at that
rpm. It drops off power real fast at lower rpm under load though unless
I am down in the hundreds, it pulls at 400 rpm on pit walls just fine.

My 5th at 65 mph is only 1750 rpm and it runs like a pig there. 4th is
2300 rpm. So basically I forget about 5th or overdrive all together and
get great mileage. 11L/100km or 23 mpg.

I am running 33's with 3.31 gears in my 86. I don't have the emissions
computer in the loop though and my CJ didn't need a CAT when new so I
have a straight pipe back to a Dynomax turbo muffler. I also have an
Accel SuperCoil in there for a hotter spark. The rest is stock on a
light 'glass CJ7.

It sounds like you are in a strange limbo for gear ratios at regular
speeds, but dropping down when in 4th at 2850 rpm means tune up issues
to me.

Could you have a partially blocked air or gas filter? Is your gas
filter in right side up? That filter has two outlets, the center one
goes to the carb and the top one goes to the return line. If the return
line isn't at the top gas can syphon back to the tank when it sits
making it a bugger to cold start and at high speed the gas pump pretty
much matches the engine needs so if some is going back to the tank it
can starve the engine.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

howard.phelan@us.army.mil wrote:
>
> Does anyone know where I can get torque curve data for a 1988 Jeep
> Wrangler 4.2 L with a manual transmission?
> My interest stems from the apparent loss of power when I recently
> up-sized my tires from 205/75R15s to 30x9.50R15s. I knew that I would
> lose some power with this change, but I'm now finding that I can't
> even maintain 70mph going up some of the hills on the way to work even
> when I downshift. Before, I could easily have maintained speed even in
> 5th gear. Right now, when I do get to 70 on flat terrain, I'm at
> about 2200 RPMs in 5th or 2850 in 4th. At 60mph I'm at somewhere
> around 1800 and 2300 RPMs, respectively.
> So I am wondering where the peak torque is for this engine. Is this
> power loss just something to be expected, or is there more that I
> should be able to get more out of my engine?

 

Wow, you sound like you have some power or tune up issues.

I have been told that the engine peaks the timing advance around 2300
rpm and 2300 seems to be a real 'sweet spot' for my engine.

It will just haul out fast from 2300 and hold almost any hill at that
rpm. It drops off power real fast at lower rpm under load though unless
I am down in the hundreds, it pulls at 400 rpm on pit walls just fine.

My 5th at 65 mph is only 1750 rpm and it runs like a pig there. 4th is
2300 rpm. So basically I forget about 5th or overdrive all together and
get great mileage. 11L/100km or 23 mpg.

I am running 33's with 3.31 gears in my 86. I don't have the emissions
computer in the loop though and my CJ didn't need a CAT when new so I
have a straight pipe back to a Dynomax turbo muffler. I also have an
Accel SuperCoil in there for a hotter spark. The rest is stock on a
light 'glass CJ7.

It sounds like you are in a strange limbo for gear ratios at regular
speeds, but dropping down when in 4th at 2850 rpm means tune up issues
to me.

Could you have a partially blocked air or gas filter? Is your gas
filter in right side up? That filter has two outlets, the center one
goes to the carb and the top one goes to the return line. If the return
line isn't at the top gas can syphon back to the tank when it sits
making it a bugger to cold start and at high speed the gas pump pretty
much matches the engine needs so if some is going back to the tank it
can starve the engine.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

howard.phelan@us.army.mil wrote:
>
> Does anyone know where I can get torque curve data for a 1988 Jeep
> Wrangler 4.2 L with a manual transmission?
> My interest stems from the apparent loss of power when I recently
> up-sized my tires from 205/75R15s to 30x9.50R15s. I knew that I would
> lose some power with this change, but I'm now finding that I can't
> even maintain 70mph going up some of the hills on the way to work even
> when I downshift. Before, I could easily have maintained speed even in
> 5th gear. Right now, when I do get to 70 on flat terrain, I'm at
> about 2200 RPMs in 5th or 2850 in 4th. At 60mph I'm at somewhere
> around 1800 and 2300 RPMs, respectively.
> So I am wondering where the peak torque is for this engine. Is this
> power loss just something to be expected, or is there more that I
> should be able to get more out of my engine?

 

Wow, you sound like you have some power or tune up issues.

I have been told that the engine peaks the timing advance around 2300
rpm and 2300 seems to be a real 'sweet spot' for my engine.

It will just haul out fast from 2300 and hold almost any hill at that
rpm. It drops off power real fast at lower rpm under load though unless
I am down in the hundreds, it pulls at 400 rpm on pit walls just fine.

My 5th at 65 mph is only 1750 rpm and it runs like a pig there. 4th is
2300 rpm. So basically I forget about 5th or overdrive all together and
get great mileage. 11L/100km or 23 mpg.

I am running 33's with 3.31 gears in my 86. I don't have the emissions
computer in the loop though and my CJ didn't need a CAT when new so I
have a straight pipe back to a Dynomax turbo muffler. I also have an
Accel SuperCoil in there for a hotter spark. The rest is stock on a
light 'glass CJ7.

It sounds like you are in a strange limbo for gear ratios at regular
speeds, but dropping down when in 4th at 2850 rpm means tune up issues
to me.

Could you have a partially blocked air or gas filter? Is your gas
filter in right side up? That filter has two outlets, the center one
goes to the carb and the top one goes to the return line. If the return
line isn't at the top gas can syphon back to the tank when it sits
making it a bugger to cold start and at high speed the gas pump pretty
much matches the engine needs so if some is going back to the tank it
can starve the engine.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

howard.phelan@us.army.mil wrote:
>
> Does anyone know where I can get torque curve data for a 1988 Jeep
> Wrangler 4.2 L with a manual transmission?
> My interest stems from the apparent loss of power when I recently
> up-sized my tires from 205/75R15s to 30x9.50R15s. I knew that I would
> lose some power with this change, but I'm now finding that I can't
> even maintain 70mph going up some of the hills on the way to work even
> when I downshift. Before, I could easily have maintained speed even in
> 5th gear. Right now, when I do get to 70 on flat terrain, I'm at
> about 2200 RPMs in 5th or 2850 in 4th. At 60mph I'm at somewhere
> around 1800 and 2300 RPMs, respectively.
> So I am wondering where the peak torque is for this engine. Is this
> power loss just something to be expected, or is there more that I
> should be able to get more out of my engine?

 

Well this morning, after driving to work, I checked under the hood
because I had heard an fairly loud hissing noise when I applied gas.
Looking in the air cleaner I discovered a lot of oil that had come in
the backside of the air cleaner. In fact the brand new air cleaner on
that side was soaked and the oil was puddled about 1/4 inch deep in the
back. Some was even dripping out the air intake of the air cleaner.
I had just had the engine tuned with new plugs, wires, dist. cap, fuel
filter, and PCV valve. When I showed it to the mechanic that did the
work, he checked out the catalytic converter and discovered that it was
quite damaged, as he could hear the ceramic inside rattling around when
he shook it. His theory is that the converter is restricting airflow
and therefore I guess causing back pressure which is causing the oil to
come in from the backside of the air cleaner.
I guess this sounds reasonable and could result in lack of power, and
besides that, he recommeded a place other than his to do the converter
work since they could do it cheaper than he could.
Any thoughts? Maybe he owns the other shop, too!

 

Well this morning, after driving to work, I checked under the hood
because I had heard an fairly loud hissing noise when I applied gas.
Looking in the air cleaner I discovered a lot of oil that had come in
the backside of the air cleaner. In fact the brand new air cleaner on
that side was soaked and the oil was puddled about 1/4 inch deep in the
back. Some was even dripping out the air intake of the air cleaner.
I had just had the engine tuned with new plugs, wires, dist. cap, fuel
filter, and PCV valve. When I showed it to the mechanic that did the
work, he checked out the catalytic converter and discovered that it was
quite damaged, as he could hear the ceramic inside rattling around when
he shook it. His theory is that the converter is restricting airflow
and therefore I guess causing back pressure which is causing the oil to
come in from the backside of the air cleaner.
I guess this sounds reasonable and could result in lack of power, and
besides that, he recommeded a place other than his to do the converter
work since they could do it cheaper than he could.
Any thoughts? Maybe he owns the other shop, too!

 

Well this morning, after driving to work, I checked under the hood
because I had heard an fairly loud hissing noise when I applied gas.
Looking in the air cleaner I discovered a lot of oil that had come in
the backside of the air cleaner. In fact the brand new air cleaner on
that side was soaked and the oil was puddled about 1/4 inch deep in the
back. Some was even dripping out the air intake of the air cleaner.
I had just had the engine tuned with new plugs, wires, dist. cap, fuel
filter, and PCV valve. When I showed it to the mechanic that did the
work, he checked out the catalytic converter and discovered that it was
quite damaged, as he could hear the ceramic inside rattling around when
he shook it. His theory is that the converter is restricting airflow
and therefore I guess causing back pressure which is causing the oil to
come in from the backside of the air cleaner.
I guess this sounds reasonable and could result in lack of power, and
besides that, he recommeded a place other than his to do the converter
work since they could do it cheaper than he could.
Any thoughts? Maybe he owns the other shop, too!