You'd probably notice a significant power increase if you took those
three cylinders that have been twisted out of alignment and move them
back so your 4.0 is a straight six like it was intended.

The cat back does seem to help a bit with mileage. Crunched pipes are
never a good idea and should be replaced no matter how many myths there
are about "liking restrictions". If you go much beyond a simple cat
back conversion, say to headers, you might need to worry about improving
the fuel injectors to avoid running lean which can also cause nox
failures on smog tests. Not that headers are a bad idea, just that the
combo of header and cat back can improve air flow enough that now you
are looking at higher flow injectors and possibly a bored throttle body.
By that time, might as well consider stroking it.



abomb69 proclaimed:

> The 4.0 in my opinion has quite a bit of power for a V6. But I would also
> like to find out some little mods to get some edge
>
>
> <98XJ> wrote in message news:7le9u2tlu4gbsriefjcaf4kit0rj504b6p@4ax.com...
>
>>Hello, group -
>>While crawling under my XJ 4.0L, I have been amazed by the degree to
>>which the downpipe from the exhaust manifold is collapsed. It is 2/3
>>shut at the bend.
>>
>>I have mentioned this at both the local 4WD shop and at the dealership
>>parts counter, and the replies have been something to the effect that
>>"Those 4 Litres seem to like the restriction", to "That's normal.
>>They're all formed like that".
>>
>>When I read about modifications for power, those most popular seem to
>>be (not necessarily in their order):
>>1. Replace cat-back
>>2. Headers
>>3. Bored-out throttle body
>>4. low-restriction intake
>>
>>What do the experts on this board think? Does this engine really
>>benefit from headers,since it seems as though it was engineered for
>>significant back-pressure?
>>
>>Thanks.
>>
>>jim
>
>
>

 

It has more apparent power mostly because it has such a flat torque
curve and develops a real goodly amount of torque even at idle rpm.
Torque is what gives you the kick in the rear feeling and is what most
often wins the stoplight sprints to 30 over vehicles with far more
actual power but not nearly as good low end torque. It should be able
to climb gentle hills at idle rpm and on a flat surface with the auto,
it should be able to upshift still down at idle rpm. The other end of
the curve is that rpm much over about about 3500 is a waste of time and
a lot of noise for nothing.


abomb69 proclaimed:

> Thanks for correcting me...But either way the inline 6 has quite a bit more
> power than most V6s I've ever owned including the 4.3 GM
>
> "Jeff DeWitt" <JeffDeWitt@nc.rr.com> wrote in message
> news:45e4f31c$0$28138$4c368faf@roadrunner.com...
>
>>The XJ 4.0 IS the inline 6, not some weenie V6 <G>.
>>
>>Jeff DeWitt
>>
>
>
>

 

It has more apparent power mostly because it has such a flat torque
curve and develops a real goodly amount of torque even at idle rpm.
Torque is what gives you the kick in the rear feeling and is what most
often wins the stoplight sprints to 30 over vehicles with far more
actual power but not nearly as good low end torque. It should be able
to climb gentle hills at idle rpm and on a flat surface with the auto,
it should be able to upshift still down at idle rpm. The other end of
the curve is that rpm much over about about 3500 is a waste of time and
a lot of noise for nothing.


abomb69 proclaimed:

> Thanks for correcting me...But either way the inline 6 has quite a bit more
> power than most V6s I've ever owned including the 4.3 GM
>
> "Jeff DeWitt" <JeffDeWitt@nc.rr.com> wrote in message
> news:45e4f31c$0$28138$4c368faf@roadrunner.com...
>
>>The XJ 4.0 IS the inline 6, not some weenie V6 <G>.
>>
>>Jeff DeWitt
>>
>
>
>

 

It has more apparent power mostly because it has such a flat torque
curve and develops a real goodly amount of torque even at idle rpm.
Torque is what gives you the kick in the rear feeling and is what most
often wins the stoplight sprints to 30 over vehicles with far more
actual power but not nearly as good low end torque. It should be able
to climb gentle hills at idle rpm and on a flat surface with the auto,
it should be able to upshift still down at idle rpm. The other end of
the curve is that rpm much over about about 3500 is a waste of time and
a lot of noise for nothing.


abomb69 proclaimed:

> Thanks for correcting me...But either way the inline 6 has quite a bit more
> power than most V6s I've ever owned including the 4.3 GM
>
> "Jeff DeWitt" <JeffDeWitt@nc.rr.com> wrote in message
> news:45e4f31c$0$28138$4c368faf@roadrunner.com...
>
>>The XJ 4.0 IS the inline 6, not some weenie V6 <G>.
>>
>>Jeff DeWitt
>>
>
>
>

 

OP here. Thanks, Lon for the on-topic reply. For the record, I am
aware that I have an I-6, that was someone else opining about hos V-6.

Since my first posting, I stopped by a muffler shop where I was told
tha all OEM tubes come with that formed indentation n in the down
pipe, and that I am one among many to have asked about that.

It bothers me enough that I may have that section replaced with a
fully-round piece - and consider a cat-back.

Thanks again

On Sat, 03 Mar 2007 11:24:55 -0800, Lon <lon.stowell@comcast.net>
wrote:

>
>You'd probably notice a significant power increase if you took those
>three cylinders that have been twisted out of alignment and move them
>back so your 4.0 is a straight six like it was intended.
>
>The cat back does seem to help a bit with mileage. Crunched pipes are
>never a good idea and should be replaced no matter how many myths there
>are about "liking restrictions". If you go much beyond a simple cat
>back conversion, say to headers, you might need to worry about improving
>the fuel injectors to avoid running lean which can also cause nox
>failures on smog tests. Not that headers are a bad idea, just that the
>combo of header and cat back can improve air flow enough that now you
>are looking at higher flow injectors and possibly a bored throttle body.
>By that time, might as well consider stroking it.
>
>
>
>abomb69 proclaimed:
>
>> The 4.0 in my opinion has quite a bit of power for a V6. But I would also
>> like to find out some little mods to get some edge
>>
>>
>> <98XJ> wrote in message news:7le9u2tlu4gbsriefjcaf4kit0rj504b6p@4ax.com...
>>
>>>Hello, group -
>>>While crawling under my XJ 4.0L, I have been amazed by the degree to
>>>which the downpipe from the exhaust manifold is collapsed. It is 2/3
>>>shut at the bend.
>>>
>>>I have mentioned this at both the local 4WD shop and at the dealership
>>>parts counter, and the replies have been something to the effect that
>>>"Those 4 Litres seem to like the restriction", to "That's normal.
>>>They're all formed like that".
>>>
>>>When I read about modifications for power, those most popular seem to
>>>be (not necessarily in their order):
>>>1. Replace cat-back
>>>2. Headers
>>>3. Bored-out throttle body
>>>4. low-restriction intake
>>>
>>>What do the experts on this board think? Does this engine really
>>>benefit from headers,since it seems as though it was engineered for
>>>significant back-pressure?
>>>
>>>Thanks.
>>>
>>>jim
>>
>>
>>

 

OP here. Thanks, Lon for the on-topic reply. For the record, I am
aware that I have an I-6, that was someone else opining about hos V-6.

Since my first posting, I stopped by a muffler shop where I was told
tha all OEM tubes come with that formed indentation n in the down
pipe, and that I am one among many to have asked about that.

It bothers me enough that I may have that section replaced with a
fully-round piece - and consider a cat-back.

Thanks again

On Sat, 03 Mar 2007 11:24:55 -0800, Lon <lon.stowell@comcast.net>
wrote:

>
>You'd probably notice a significant power increase if you took those
>three cylinders that have been twisted out of alignment and move them
>back so your 4.0 is a straight six like it was intended.
>
>The cat back does seem to help a bit with mileage. Crunched pipes are
>never a good idea and should be replaced no matter how many myths there
>are about "liking restrictions". If you go much beyond a simple cat
>back conversion, say to headers, you might need to worry about improving
>the fuel injectors to avoid running lean which can also cause nox
>failures on smog tests. Not that headers are a bad idea, just that the
>combo of header and cat back can improve air flow enough that now you
>are looking at higher flow injectors and possibly a bored throttle body.
>By that time, might as well consider stroking it.
>
>
>
>abomb69 proclaimed:
>
>> The 4.0 in my opinion has quite a bit of power for a V6. But I would also
>> like to find out some little mods to get some edge
>>
>>
>> <98XJ> wrote in message news:7le9u2tlu4gbsriefjcaf4kit0rj504b6p@4ax.com...
>>
>>>Hello, group -
>>>While crawling under my XJ 4.0L, I have been amazed by the degree to
>>>which the downpipe from the exhaust manifold is collapsed. It is 2/3
>>>shut at the bend.
>>>
>>>I have mentioned this at both the local 4WD shop and at the dealership
>>>parts counter, and the replies have been something to the effect that
>>>"Those 4 Litres seem to like the restriction", to "That's normal.
>>>They're all formed like that".
>>>
>>>When I read about modifications for power, those most popular seem to
>>>be (not necessarily in their order):
>>>1. Replace cat-back
>>>2. Headers
>>>3. Bored-out throttle body
>>>4. low-restriction intake
>>>
>>>What do the experts on this board think? Does this engine really
>>>benefit from headers,since it seems as though it was engineered for
>>>significant back-pressure?
>>>
>>>Thanks.
>>>
>>>jim
>>
>>
>>

 

OP here. Thanks, Lon for the on-topic reply. For the record, I am
aware that I have an I-6, that was someone else opining about hos V-6.

Since my first posting, I stopped by a muffler shop where I was told
tha all OEM tubes come with that formed indentation n in the down
pipe, and that I am one among many to have asked about that.

It bothers me enough that I may have that section replaced with a
fully-round piece - and consider a cat-back.

Thanks again

On Sat, 03 Mar 2007 11:24:55 -0800, Lon <lon.stowell@comcast.net>
wrote:

>
>You'd probably notice a significant power increase if you took those
>three cylinders that have been twisted out of alignment and move them
>back so your 4.0 is a straight six like it was intended.
>
>The cat back does seem to help a bit with mileage. Crunched pipes are
>never a good idea and should be replaced no matter how many myths there
>are about "liking restrictions". If you go much beyond a simple cat
>back conversion, say to headers, you might need to worry about improving
>the fuel injectors to avoid running lean which can also cause nox
>failures on smog tests. Not that headers are a bad idea, just that the
>combo of header and cat back can improve air flow enough that now you
>are looking at higher flow injectors and possibly a bored throttle body.
>By that time, might as well consider stroking it.
>
>
>
>abomb69 proclaimed:
>
>> The 4.0 in my opinion has quite a bit of power for a V6. But I would also
>> like to find out some little mods to get some edge
>>
>>
>> <98XJ> wrote in message news:7le9u2tlu4gbsriefjcaf4kit0rj504b6p@4ax.com...
>>
>>>Hello, group -
>>>While crawling under my XJ 4.0L, I have been amazed by the degree to
>>>which the downpipe from the exhaust manifold is collapsed. It is 2/3
>>>shut at the bend.
>>>
>>>I have mentioned this at both the local 4WD shop and at the dealership
>>>parts counter, and the replies have been something to the effect that
>>>"Those 4 Litres seem to like the restriction", to "That's normal.
>>>They're all formed like that".
>>>
>>>When I read about modifications for power, those most popular seem to
>>>be (not necessarily in their order):
>>>1. Replace cat-back
>>>2. Headers
>>>3. Bored-out throttle body
>>>4. low-restriction intake
>>>
>>>What do the experts on this board think? Does this engine really
>>>benefit from headers,since it seems as though it was engineered for
>>>significant back-pressure?
>>>
>>>Thanks.
>>>
>>>jim
>>
>>
>>