Optimal exhaust pipe diameter - JeepForum.com
Search  
Sign Up   Today's Posts
User: Pass: Remember?
Advertise Here
Jeep Home Jeep Forum Jeep Classifieds Jeep Registry JeepSpace Jeep Reviews Jeep Gallery Jeep Clubs Jeep Groups Jeep Videos Jeep Events Jeep Articles
Go Back JeepForum.com > Models > Jeep Cherokee & Comanche Forums > XJ Cherokee Technical Forum > Optimal exhaust pipe diameter

ROCK BOTTOM prices on LIFT KITS at Rockridge4wd!! WANT TO Savvy FREE SHIPPING!Year End Clearance Sale! Save 20%

Reply
Unread 03-26-2013, 02:26 PM   #1
Mizzil-XJ
Registered User
 
Join Date: Mar 2013
Location: Coon Rapids, MN
Posts: 2
Optimal exhaust pipe diameter

I have a 97 XJ 4.0L that is at the moment fully stock. I have heard a lot of talk about the 4.0l engine loosing power with bigger high flowing pipes. I would still like to increase my HP and torque. with the mods listed below, does anyone have any info/experience with choosing the correct pipe diameter to take advantage of the increased airflow without loosing torque?


I will be installing a hiflow CAI-Mounted in the cowl, a 2001 intake manifold possibly a 62mm bored TB, 1" TB spacer, Banks headers, hiflow cat, and flowmaster super 40 muf.

any input is welcomed thanks!

Mizzil-XJ is offline   Reply With Quote Quick reply to this message
Unread 03-26-2013, 02:32 PM   #2
sjones26573
Au revoir, gopher.
 
sjones26573's Avatar
2004 TJ Wrangler 
 
Join Date: Aug 2011
Location: Concord/Harmony/Raleigh, NC
Posts: 9,563
A CAI and TB spacer is a waste of money. Stock 2.25" is going to be the best. But you won't see any significant gains out of a 4.0 without forced induction or stroking it.
__________________
The Yellowtail Build

Quote:
Originally Posted by Jeremy Clarkson - Top Gear Botswana Special
Why don't all cars have no doors? When I come to power I'm going to make it a rule because this is just better.
sjones26573 is offline   Reply With Quote Quick reply to this message
Unread 03-26-2013, 02:56 PM   #3
demonoid369
Registered User
1997 XJ Cherokee 
 
Join Date: Oct 2012
Location: salem, oregon
Posts: 79
everything but the spacer will do a positive increase in torque and horsepower, will it be a big improvement? not really. you'll gain 1-2mpg more, 5-15lbs of torque. best diameter is 2.5 tubing, but you'll want to get rid of the crushed pipe below the header.

and a cai does do some good. its not a waste of money, by itself it can be but with all the other mods listed, it does do what it suppose to do.
demonoid369 is offline   Reply With Quote Quick reply to this message
Unread 03-26-2013, 03:12 PM   #4
mschi772
Registered User
1997 XJ Cherokee 
 
Join Date: Apr 2012
Location: Racine, WI
Posts: 2,365
High flow cats don't exist, or I should say that all cats are high flow. The "high flow" label is a myth/gimmick to prey on consumers. Buy a cat based on construction quality, not flow, because they all have little to no restriction.

TB spacer does nothing.

If you're boring your TB to 62 mm, you better be boring your intake manifold too. If you don't want to bore the manifold, 60 mm is the limit for the TB and should be plenty unless you're really dumping a ton of money into a stroker/forced induction build.

Banks headers are nice, but really not an ideal setup (no one makes a very ideal header for 4.0 performance) and as such aren't worth the money over something less expensive such as APN imo. I'd love a header with equal-length, narrow primaries that collect 6 into 3 pairing cylinders 1+6, 2+5, and 3+4, but no one makes anything like this to my knowledge.

Like the poster above said, you can throw a bunch of money at your 4.0, but you won't get ton out of it. The 4.0 is pretty well tapped for power from the factory. Stroking it gets good gains, but then again, once it's stroked, it's not a 4.0 anymore (it's a 4.5 or 4.7 or 4.9 or whatever) and is still maxed-out for whatever its new displacement is. Forced induction provides gains but is super expensive.


A nice 2.25" or maybe 2.5" exhaust with a header is the best bang-for-buck you can do imo. CAI can contribute a little after that. Replace your mechanical fan with electric to free some power. If you want to throw even more money at it, stroke it and/or consider port/polishing the head and shop around for a cam that will give you the kind of power curve you want.
__________________
Might trade rebuilt 231 for new/rebuilt 242. Contact me.

New sig rules suck.
mschi772 is offline   Reply With Quote Quick reply to this message
Unread 03-26-2013, 03:58 PM   #5
Azzy
Web Wheeler
 
Azzy's Avatar
1996 XJ Cherokee 
 
Join Date: Sep 2010
Location: Finleyville
Posts: 3,238
Quote:
Originally Posted by mschi772 View Post
High flow cats don't exist, or I should say that all cats are high flow. The "high flow" label is a myth/gimmick to prey on consumers. Buy a cat based on construction quality, not flow, because they all have little to no restriction.

TB spacer does nothing.

If you're boring your TB to 62 mm, you better be boring your intake manifold too. If you don't want to bore the manifold, 60 mm is the limit for the TB and should be plenty unless you're really dumping a ton of money into a stroker/forced induction build.

Banks headers are nice, but really not an ideal setup (no one makes a very ideal header for 4.0 performance) and as such aren't worth the money over something less expensive such as APN imo. I'd love a header with equal-length, narrow primaries that collect 6 into 3 pairing cylinders 1+6, 2+5, and 3+4, but no one makes anything like this to my knowledge.

Like the poster above said, you can throw a bunch of money at your 4.0, but you won't get ton out of it. The 4.0 is pretty well tapped for power from the factory. Stroking it gets good gains, but then again, once it's stroked, it's not a 4.0 anymore (it's a 4.5 or 4.7 or 4.9 or whatever) and is still maxed-out for whatever its new displacement is. Forced induction provides gains but is super expensive.


A nice 2.25" or maybe 2.5" exhaust with a header is the best bang-for-buck you can do imo. CAI can contribute a little after that. Replace your mechanical fan with electric to free some power. If you want to throw even more money at it, stroke it and/or consider port/polishing the head and shop around for a cam that will give you the kind of power curve you want.
TL;DR: Cant just bolt on more power from ebay in an afternoon.

__________________
Raising money for charity with Jeep-mas ornaments, get yours here in time for Christmas!
Azzy is offline   Reply With Quote Quick reply to this message
Unread 03-26-2013, 03:59 PM   #6
djb383
Registered User
1998 XJ Cherokee 
 
Join Date: Jan 2010
Location: The Republic of TEXAS
Posts: 2,201
Here's good read with some dyno facts/results vs opinion.

http://www.jpmagazine.com/techarticl...s/viewall.html
__________________
Man Law - hoods should be raised at least once a week.....have a look see.
djb383 is offline   Reply With Quote Quick reply to this message
Unread 03-26-2013, 04:53 PM   #7
Motorcharge
I know more than you.
 
Motorcharge's Avatar
1991 MJ Comanche 
 
Join Date: Oct 2008
Location: Richmond, Virginia
Posts: 12,116
Quote:
Originally Posted by sjones26573 View Post
A CAI and TB spacer is a waste of money. Stock 2.25" is going to be the best. But you won't see any significant gains out of a 4.0 without forced induction or stroking it.
Cold intake is only as waste of money if you leave the damn thing in the engine bay to suck up hot air. Relocating it to the cowl produces noticeable changes, plus you have the benefit of significantly raising the height of your intake.
__________________

Quote:
Originally Posted by Ron Swanson
There is no such thing as bad weather. Only inadequate clothing and transportation.
Motorcharge is offline   Reply With Quote Quick reply to this message
Unread 03-28-2013, 02:15 AM   #8
Mizzil-XJ
Registered User
 
Join Date: Mar 2013
Location: Coon Rapids, MN
Posts: 2
Quote:
Originally Posted by sjones26573 View Post
A CAI and TB spacer is a waste of money. Stock 2.25" is going to be the best. But you won't see any significant gains out of a 4.0 without forced induction or stroking it.
I am mostly adding the CAI in the cowl for the ability to allow my xj to handle having a good portion of the hood submerged without having to mount a snorkel. Im going the cheap route and fabricating my own with universal parts. The extra power with the other upgrades is more of a bonus. My main problem i have is deciding if the stock exhaust pipe will be the best choice or if i should go bigger to handle the increased airflow created as a result of the increased airflow after adding a complete airflow upgrade listed in my first post.
Mizzil-XJ is offline   Reply With Quote Quick reply to this message
Unread 03-28-2013, 05:08 AM   #9
LimeLJ
Senior Member
2004 LJ Wrangler 
 
Join Date: Dec 2010
Location: Location, AL
Posts: 834
Quote:
Originally Posted by mschi772 View Post
If you're boring your TB to 62 mm, you better be boring your intake manifold too. If you don't want to bore the manifold, 60 mm is the limit for the TB and should be plenty unless you're really dumping a ton of money into a stroker/forced induction build.
The 1999+ horseshoe style manifolds have a 62mm opening and the provided gasket is 62mm.

Do not worry about the difference between 62mm, 63mm, and 64mm bored throttle bodies. 63mm+ throttle bodies are pushing into the dangerous area of thin walls of the bore.

A stock throttle body even works well on a 4.7L stroker setup. On a stock engine what a bored throttle body really does it just increase the throttle response per the amount of pedal travel.
LimeLJ is offline   Reply With Quote Quick reply to this message
Unread 03-28-2013, 12:04 PM   #10
mschi772
Registered User
1997 XJ Cherokee 
 
Join Date: Apr 2012
Location: Racine, WI
Posts: 2,365
Quote:
Originally Posted by LimeLJ View Post
The 1999+ horseshoe style manifolds have a 62mm opening and the provided gasket is 62mm.

Do not worry about the difference between 62mm, 63mm, and 64mm bored throttle bodies. 63mm+ throttle bodies are pushing into the dangerous area of thin walls of the bore.

A stock throttle body even works well on a 4.7L stroker setup. On a stock engine what a bored throttle body really does it just increase the throttle response per the amount of pedal travel.
You're right, I had completely forgotten about that. I appreciate the correction.

FWIW, Dino Savva has that page on his site about using a 65 mm 86-93 Mustang throttle body, but like some of the other stuff on Dino's site I don't think that one was really thought-out very well; I highly doubt that he achieved anything that a 62mm bore wouldn't have especially since he didn't bore his intake manifold. Heck, he uses a TB spacer (useless) and even that is only 62 mm. F&B also makes a 68 mm throttle bodies for stroker builds, but again, they are useless as a stand-alone mod (F&B even state specifically that the manifold should be bored/ported).
__________________
Might trade rebuilt 231 for new/rebuilt 242. Contact me.

New sig rules suck.
mschi772 is offline   Reply With Quote Quick reply to this message
Unread 03-28-2013, 06:32 PM   #11
LimeLJ
Senior Member
2004 LJ Wrangler 
 
Join Date: Dec 2010
Location: Location, AL
Posts: 834
Quote:
Originally Posted by mschi772 View Post
You're right, I had completely forgotten about that. I appreciate the correction.

FWIW, Dino Savva has that page on his site about using a 65 mm 86-93 Mustang throttle body, but like some of the other stuff on Dino's site I don't think that one was really thought-out very well; I highly doubt that he achieved anything that a 62mm bore wouldn't have especially since he didn't bore his intake manifold. Heck, he uses a TB spacer (useless) and even that is only 62 mm. F&B also makes a 68 mm throttle bodies for stroker builds, but again, they are useless as a stand-alone mod (F&B even state specifically that the manifold should be bored/ported).
Even then the restriction is the intake runners. While the 1999+ intake is better overall cylinders one and six still have to fight the most to get air. If you are trying to squeeze every last bit of power out of the engine going to multiple smaller size throttle bodies space evenly on a custom manifold will be a better setup.

The movement of air through the throttle body is a fluid dynamics science. It affects the velocity of the air moving through it and how that affects the RPM power band.
LimeLJ is offline   Reply With Quote Quick reply to this message
Unread 03-28-2013, 10:41 PM   #12
mschi772
Registered User
1997 XJ Cherokee 
 
Join Date: Apr 2012
Location: Racine, WI
Posts: 2,365
Quote:
Originally Posted by LimeLJ View Post
Even then the restriction is the intake runners. While the 1999+ intake is better overall cylinders one and six still have to fight the most to get air. If you are trying to squeeze every last bit of power out of the engine going to multiple smaller size throttle bodies space evenly on a custom manifold will be a better setup.

The movement of air through the throttle body is a fluid dynamics science. It affects the velocity of the air moving through it and how that affects the RPM power band.
Absolutely right. $2000 can buy you this:
http://www.extrudabody.com/servlet/t...ne-6%2C/Detail

__________________
Might trade rebuilt 231 for new/rebuilt 242. Contact me.

New sig rules suck.
mschi772 is offline   Reply With Quote Quick reply to this message
Unread 03-29-2013, 07:08 AM   #13
cruiser54
Web Wheeler
 
cruiser54's Avatar
1990 MJ Comanche 
 
Join Date: Oct 2009
Location: Prescott, Arizona
Posts: 10,323
I know Renix intake manifolds are at 60mm with a 52mm throttle body. HO throttle body is 58mm on a 62mm manifold IIRC.
__________________
Quote:
Originally Posted by chris87xj View Post
If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

Cruiser's Mostly Renix Tips
My Jeep Technical Photos

http://www.cherokeeforum.com/g/album/1725214
cruiser54 is offline   Reply With Quote Quick reply to this message
Unread 03-30-2013, 09:10 PM   #14
LimeLJ
Senior Member
2004 LJ Wrangler 
 
Join Date: Dec 2010
Location: Location, AL
Posts: 834
Quote:
Originally Posted by cruiser54 View Post
I know Renix intake manifolds are at 60mm with a 52mm throttle body. HO throttle body is 58mm on a 62mm manifold IIRC.
Yeah, I am fairly sure the 1992 to 1998 are 62mm as well, but I do not have my old style one available to measure right now.
LimeLJ is offline   Reply With Quote Quick reply to this message
Unread 03-30-2013, 11:23 PM   #15
5-90
Registered User
1988 XJ Cherokee 
 
Join Date: Sep 2006
Location: San Jose, CA, Hammerspace
Posts: 5,344
Quote:
Originally Posted by Mizzil-XJ View Post
I have a 97 XJ 4.0L that is at the moment fully stock. I have heard a lot of talk about the 4.0l engine loosing power with bigger high flowing pipes. I would still like to increase my HP and torque. with the mods listed below, does anyone have any info/experience with choosing the correct pipe diameter to take advantage of the increased airflow without loosing torque?


I will be installing a hiflow CAI-Mounted in the cowl, a 2001 intake manifold possibly a 62mm bored TB, 1" TB spacer, Banks headers, hiflow cat, and flowmaster super 40 muf.

any input is welcomed thanks!
You are correct - going overlarge with the exhaust pipe on a non-turbocharged engine (naturally-aspirated or supercharged) will cause trouble with scavenging, increasing pumping losses and reducing power output.

2.25" ID is the stable optimax for a stock 6-242 or a mild stroker build that doesn't cross 3800-4000rpm, 2.5" ID for larger strokers or high-rpm mild strokers.

If you're going to get silly past that, we'll talk.
__________________
"recon" (sic - reckon)(tm) "hihgly"(tm) "seceed"(tm)
"Outback AIDS - Alcohol-Induced Dizzy Spells"
5-90 is offline   Reply With Quote Quick reply to this message
Reply

Tags
exhaust , headers , intake manifold , Torque

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the JeepForum.com forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid e-mail address for yourself.
Note: All free e-mails have been banned due to mis-use. (Yahoo, Gmail, Hotmail, etc.)
Don't have a non-free e-mail address? Click here for a solution: Manual Account Creation
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.


Thread Tools






Jeep, Wrangler, Cherokee, Grand Cherokee, and other models are copyrighted and trademarked to Jeep/Chrysler Corporation. JeepForum.com is not in any way associated with Jeep or the Chrysler Corp.