Modded Mustang Forums banner
1 - 13 of 13 Posts

·
Registered
Joined
·
776 Posts
Discussion Starter · #1 · (Edited)
So I dropped my car over to the only custom exhaust shop in my area today to have some work done. We ended up having a 20 min conversation about what I'm doing to my car and he told me some things that I never heard about on any mustang forums. While he is the owner of a custom exhaust shop he is not a mustang specialist at all so I just wanted to get some mustang people to give me their take on two of his claims and whether he is correct...

This is what I asked him to do today. I brought him an o/r h pipe, a pair of high flow cats, and a new axle back. Asked him to weld the high flows into the o/r h and install it, and to replace my current axle back with the new one. As a related piece of information, I mentioned how I would be installing a set of short tubes that are currently sitting in my garage in the next week or two. Btw, I ended up not getting any work done today, based on his advice that I will now share...

First statement - He told me I really, really, really, should install the headers FIRST, before he chops up the midpipe and welds it all back together. His reasoning was that one of the most common cause of header leaks was an ill fitting midpipe to collector attachment. He said that if the midpipe puts any pressure (pulling, pushing, etc) on the headers, it will most likely eventually cause a leak at the header gaskets. He said do the headers first, and then let him fabricate the new midpipe to line up perfectly with the new header collectors when he welds the new cats in. I told him that shorties on mustangs were supposed to be a matching fit with the stock manifolds so if he did the midpipe now to my stock manifolds, it should fit the new headers later on. He said "well yeah the company always says direct replacement, same fit but that's a joke". What he is telling me makes sense but I've never heard this logic before. Is he correct?

Statement 2 - He recommended that I relocate the new cats to a different location than where the stock cats are located because he said the headers would overheat and fry the new cats. Never heard this one before. And I really don't want them moved lower on the midpipe where they can get damaged due to low ground clearance. Also, I'd have to get 02 extensions. Once again, is this guy right??

Please hold the "short tubes suck, LT's FTW comments" I understand the superiority of LT's but I want to stay legal and the shorties were given to me for free.

BTW my new setup once the parts are all on will be... BBK ceramic coated tuned length shorty headers, H pipe with Pypes high flow cats, MAC boom tubes.

Thanks
 

·
Your Resident Badass
Joined
·
4,199 Posts
First one is plausible.. 2nd one im not too sure about. They do always say the fit, but theres many times where you gotta do a little messing with it but usually they do.
 

·
Registered
Joined
·
890 Posts
Well I think that the new headers would actually lower the temp of the underhood ambient. So how does that affect the cats...... But then again you can also go catless lol
 

·
Tini Tini Bo Bini
Joined
·
9,029 Posts
If youve got cats then why not get lts. You will still be "legal"
 

·
Registered
Joined
·
1,427 Posts
Dont go back, or go to a shop that will do what you want.

I would keep the cats in the stock location and the headers should hurt anything. You can do the axleback by yourself in ten minutes though.
 

·
2011 September ROTM
Joined
·
1,868 Posts
i agree with your exhaust guy on the first one. the second one is probably a good idea as well. and headers will not reduce under hood temps unless the are coated or wrapped
 

·
Registered
Joined
·
1,930 Posts
why not get a catted midpipe?
 

·
Registered
Joined
·
185 Posts
Well gotta say from experiance on my old 6 I had shorty headers and they were cheep and the chrome flaked off first time they got hot. I got the whole systme done and got some cheap metal cats and they melted (the insides) and I was told because they were too close to the headers in the pipe and I needed to move them down the pipe to prevent it in the future. As fas as the mid pipe causing the headers to leak I've heard that before too! Never had it happen to me but I guess it could happen.
 

·
Registered
Joined
·
176 Posts
I think the guy is steering you strait. Just bolt the headers up and get the o2 extensions. That way if you have any leaks you can make him fix it since you did it his way. What he says though, sounds like he does know what he's doing.
 

·
Registered
Joined
·
13,629 Posts
All of what he said was true and kudos for him to steer you in the right direction. I'm not sure how much better the shorties flow better than the stock exhaust but it has to be a slight improvement. Anyways, headers are designed to remove the heat by extracting the exhaust faster. Well when you do that the heat energy is still there, it doesn't disappear, it just moves out of the engine bay and down the exhaust. Thus heating up the softer precious metals in your cats. It's not like the inside is stainless like the casing.

And that is good advise as far as making sure stuff lines up. Even though they all say direct fitment, there are manufacturing tolerances and other factors involved. Even a fraction of an inch can cause enough stress on an exhaust to crack welds and stuff. Your exhaust should fit and hang freely without any clamps tightened on there. If you have to line up something by forcing it over to line up and clamping it, you will have issues down the road. Though you can usually get **** to line up by heating and bending the exhaust hangers, he is telling you to do it in the right order to avoid the most possible issues.
 

·
Registered
Joined
·
776 Posts
Discussion Starter · #11 ·
Wow, thanks everyone. All these comments are really helpful. I'm going to follow his advice. I'll be doing the headers hopefully next weekend. Then I'll pass my car on to him to fab the midpipe to line up directly to the new collectors without putting any strain on them in order to prevent future head gasket leaks. I'll probably just let him finish the job and put the axleback on just so I know the tips are aligned perfectly and that I don't have any noisy hangers. Just like 07Boss stated.... If everything is hanging freely in place without any force, the seal at the headers should go undisturbed. I'm using Percy's split lock header bolts and percy's aluminum gaskets so I hopefully all this leak prevention will pay off in the end.

Kind of a dumb question but... since I don't want to put any strain on the headers, I hesitate to even put my midpipe back on temporarily to drive it to the exhaust shop. It wouldn't hurt anything (besides my ears) to drive it to the exhaust shop without the midpipe on right?

Thanks again everyone.
 

·
Registered
Joined
·
2,043 Posts
I'd put it back on. That short time through one heat cycle would never cause a problem. The headers will probably fit fine, but there are times they do not. That's not uncommon.
 

·
Premium Member
Joined
·
4,253 Posts
He is pretty accurate.

Where do I start? On his first point, I agree 100%. Nothing will line up perfectly unless you mock up the whole thing - especially since you are talking welding and not clamps.

Secondly, it will be extremely difficult to get high flow aftermarket cats in the stock location. This is something that is hard to explain, but I've been there, done that, and fabricated my own cats into a Mac setup...the OEM cats have a "bent" inlet and outlet so they follow the contour for the underbelly; an aftermarket cat can't be shaped that way, plus the left and right are asymmetrical.

Your cats are going to have to go under the car just aft of where the piping goes parallel to the ground.

In short, he is giving you great advice.

Oh yeah, shorties suck and long tubes FTW! Shorties are not worth the effort unless you are running a turbo, or have to have them because you live in the Peoples Rupublik of Kalifornia. They offer almost no gain.
 
1 - 13 of 13 Posts
Top