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Mizzil-XJ 03-26-2013 01:26 PM

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!

sjones26573 03-26-2013 01:32 PM

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.

demonoid369 03-26-2013 01:56 PM

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.

mschi772 03-26-2013 02:12 PM

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.

Azzy 03-26-2013 02:58 PM

Quote:

Originally Posted by mschi772 (Post 15197926)
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.

:2thumbsup:

djb383 03-26-2013 02:59 PM

Here's good read with some dyno facts/results vs opinion.

http://www.jpmagazine.com/techarticl...s/viewall.html

Motorcharge 03-26-2013 03:53 PM

Quote:

Originally Posted by sjones26573 (Post 15197664)
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.

Mizzil-XJ 03-28-2013 01:15 AM

Quote:

Originally Posted by sjones26573 (Post 15197664)
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.

LimeLJ 03-28-2013 04:08 AM

Quote:

Originally Posted by mschi772 (Post 15197926)
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.

mschi772 03-28-2013 11:04 AM

Quote:

Originally Posted by LimeLJ (Post 15206798)
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).

LimeLJ 03-28-2013 05:32 PM

Quote:

Originally Posted by mschi772 (Post 15208360)
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.

mschi772 03-28-2013 09:41 PM

Quote:

Originally Posted by LimeLJ (Post 15210363)
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
http://www.extrudabody.com/catalog/J...ject_1933c.jpg
http://www.cherokeeforum.com/attachm...oject_inta.jpg

cruiser54 03-29-2013 06:08 AM

I know Renix intake manifolds are at 60mm with a 52mm throttle body. HO throttle body is 58mm on a 62mm manifold IIRC.

LimeLJ 03-30-2013 08:10 PM

Quote:

Originally Posted by cruiser54 (Post 15212492)
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.

5-90 03-30-2013 10:23 PM

Quote:

Originally Posted by Mizzil-XJ (Post 15197633)
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.


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