Dorman Manifold....Any good???

[CheekyMcgee]

My exhaust manifold has developed a crack. I was looking at some of the different options discussed here but, I didn't see anyone mention this one.

http://www.summitracing.com/parts/RNB-674-196/?rtype=10

I'm interested in this one because of the built-in flex sections on both the front and rear primaries. Also, I have a neighbor with a 4cyl Jeep who bought this one not realizing it was for the 4.0 and he's offering it to me for $150.

I also like this one but, I wonder if this one is prone to cracking due to the lack of flex in it.
http://www.ineedparts.com/index.php?target=products&product_id=15343

Any and all opinions would be appreciated. Thanks.

 

[Tim_MN]

#1 is an exhaust manifold of average quality.

#2 is the APN header. They are very quality for the price paid. There are plenty of APN threads but, you will have to use Google to find them the Naxja search doesn't like 3 letter word searches.

No exhaust manifold will hold up to excessive engine movement. Check or replace you engine mounts at the same time you install a new manifold.

 

[CheekyMcgee]

I'm replacing the mounts and a leaky freeze plug when I swap the manifold out. I thought #2 looked like a header but, I thought the price was too low. Thanks for the input.

 

[joe_peters]

They are both "headers" as is the OEM--a separate runner for each cylinder is the defining element of a header vs. an exhaust manifold.

Now, NEITHER of those headers is a "performance" header.

I honestly don't get the accordion sections on the two runners in the first header. While cracks at the runners are not unheard of, the majority of XJ 4.0 cracked headers I have seen are busted at the collector end.

As posted above--ENGINE MOUNTS, ENGINE MOUNT BRACKET TO ENGINE BLOCK BOLTS, AND TRANS MOUNT--an issue with any of those will get you a cracked header regardless of the design.

Also, as the exhaust mounting in the XJ is way to rigid for all of the unibody flex you can have perfect mounts and bracket bolts to the block and still crack a brand new header.

Because you have been good, I will share a secret with you: add a flexible section in the downpipe where it crosses from left to right, before the CAT. This flexible section will go a long way to preventing a cracked header. Sample flex section: http://www.cxracing.com/mm5/merchant.mvc?Screen=PROD&Store_Code=CXR&Product_Code=FLEXPIPE-250x8

 

[austinaubinoe]

^^^^^You sure do love those flex pipes!

 

[iwannadie]

I don't understand the flex sections either. I mean when it's mounted to the motor it becomes rigid and those 2 flex sections can't move unless the others flex. If you grab the flange and try to move it those flex sections can't allow movement because the other 4 are solid. Are they meant for heat expansion?

 

[Tim_MN]

The APN is a close copy of the Banks header. I would call it a performance header. It makes a different sound than the stock manifold in my 99 Cherokee.

 

[kastein]

I don't understand the flex sections either. I mean when it's mounted to the motor it becomes rigid and those 2 flex sections can't move unless the others flex. If you grab the flange and try to move it those flex sections can't allow movement because the other 4 are solid. Are they meant for heat expansion?

Yeah, they're for heat expansion.

I would really like to see a header with a flex section in one of the tubes going into the collector, since most of the cracked headers I see have the crack in the tube from the 4/5/6 runner right where it goes into the collector.

 

[CheekyMcgee]

Right on. Thanks for the input guys. Much appreciated.

 

[joe_peters]

The APN is a close copy of the Banks header. I would call it a performance header. It makes a different sound than the stock manifold in my 99 Cherokee.

Sounds good, and stronger yes, but if we apply the rule of performance headers having equal-length runners to balance the exhaust it doesn't fit the basic "performance" criteria.

 

[DieselSJ]

Sounds good, and stronger yes, but if we apply the rule of performance headers having equal-length runners to balance the exhaust it doesn't fit the basic "performance" criteria.

Not all "performance" headers have equal length tubes. I'm not arguing that equal length is better, I'm just saying that there are a lot of performance headers on the market for many different vehicles that do not have equal length tubes.

Will this one breathe better than a stock one and gain HP and torque? Yep.

 

[joe_peters]

Ideally, the primary pipe lengths should have the same lengths but can be within 2 inches of each other.

 

[s14unimog]

I like the flex sections but I've had larger flex sections develop leaks... I wonder why they don't just separate the flange. I see this a lot on turbo manifolds.