honesT

Hi I`m new here & to the Jeep world and need some help.


I own a 1996 XJ and have bought a used highflow exhaust system from bottom of manifold flange to tail pipe off a 91 xj that had a stroker engine...

My question is can I just bolt this on to my stock manifold or is the 2.5 pipe to wide to give proper back pressure. My stock front pipe is 2 inches outside diameter for the 1st 20 inches then expandes to 2.5 inches outside diameter for the rest of the length.

4.0L I6 MPI "Power Tech HO" (High Output) - 190 hp @ 4750 rpm, 220 ft lb @ 4,000 rpm - used in 91-95 and updated in 96-01 to 225 ft lb torque @ 3000 rpm

Thanks in advance for your time.

djb383

Lots of myths out there about exhaust back pressure. I say open it up....we went with 2.5" exhaust all the way back.

http://www.google.com/#hl=en&expIds=...68904dd3283f54

honesT

QUOTE Lots of myths out there about exhaust back pressure. I say open it up....we went with 2.5" exhaust all the way back.

Did you install headers or start at the stock manifold or at the cat for the high flow?

honesT

This is reply I got from another forum : Any changes in exhaust size will affect torque/horsepower regardless of stock manifold or header. A larger free flowing exhaust will give you more top end horsepower while a smaller restrictive exhaust increase the torque on the low end of the RPM range. The question really is how do you drive it? If it is a trail beast then stay with the smaller one, if it is a highway cruiser go with the larger one. If it pulls dual duty and you're not out rock crawling the larger one will probably work for you just fine. It's all about what you need it to do.

1991Jeep_Man

This is false. Back-pressure in no real way effects torque in a positive fashion, unless you go rediculously open (like 3.5-4" or something), even then I am not for sure. Back pressure was important on old carb systems because the carb couldn't adjust the air/fuel mixture to compensate for a sudden rush of air, meaning a lean burn would be persistant and screw up valves. All of our XJ's, or the majority, have either TBI or MPFI with computers that can re-calibrate the fuel/air mixture should any lean burn happen.

odgreen

open it up and let that baby breathe!

honesT

Well here is my update:

I up graded to a high flow exhaust system after reading how it improves gas mileage due to the trans shifting into OD sooner. MY jeep is still STOCK with stock sized tires & I’m at 1250/1300 RPMS at 71 Km per hr. I will post on another thread what hwy RPMS are later.

I kept the stock down pipe (from manifold to cat) due to many conflicts stating that I would lose low end torque, I’m still on the table with this but why take any chances...It seems swapping the header sounds like the culprit for losing low end torque, not to rule out the stock pipe. I`m happy enough with the results of the high flow cat & muffler so I`ll save my $$$


I don`t know what the gas mileage was before but with city stop & go traffic & putting the pedal down a few times I`m at 315km with 1/4 tank left, so it looks like 400-450 km per 75 litres (FULL TANK) of gas in city driving. With stock sized tires

trans_am7935

as long as your exhaust is right for the application, then there is no reason not to have a high flow exhaust. when i went from stock cat back, to a borla header, stock down pipe, borla cat and flomaster cat back, i got 2mpg better (in stock tire size) and the thing ran a whole lot better. now an aftermarket down pipe would be nige but i have no idea where to get one.

retread

changes to the exhaust will be minimal unless the intake(TB, injector) is also improved//inhaling corresponds to exhausting