My car currently has an aftermarket exhaust manifold that was installed by the previous owner. However, a few weeks ago I had my car tuned and the guys at the shop reccomended that I go back to the stock manifold because they said that the aftermarket manifolds tend to crack and they provide very little in terms of performance gains. Is there anyone out there that can either agree or disagree with my tuners opinion and back it up with some dyno numbers? I'm in the process of changing out the studs and the gaskets on the manifold and am trying to decide on which manifold to put back on the car? Unfortunately, I don't know who the aftermarket manifold was made by.

 

mine had one on it too when i bought it, one of the first things i did was buy a stock one and put it back on. they crack like its going out of style.

 

Depends on who made it. Shearer/JMFab/ETS/Full Race (and the newone from jesseB/4WS, remains to be seen how it holds up) all are great quality and the Shearer in particular was dyno'd against a Buschur ported stocker and it made 20 hp more (something to that fact) on stock frame turbo. Shearer and JMFab offer life time warranty as well.

megan's or cheaper exhaust manifolds do crack (mine came with a megan and it cracked).

 

ya interesting thread I have heard the same thing about them cracking because i was thinking of upgrading to something different from stock, but then i was told the same thing and decided against it for now

 

I would go with a stocker.Most if not all tubular manifold will crack on daily drivers.Even the higher end ones if they are daily driven can crack.For 20hp not worth the headache if manifold cracks.

 

Thanks everyone for the input!

 

Just like Green Meanie said, it's going to depend on the brand of exhaust manifold. If you purchase one of the eBay style manifolds no telling what you will get. If it's a name brand manifold with some R&D like our manifold there is some power to be had.

Good Luck!

Michael

 

I personally contemplated this myself. Get yourself a ported / coated stock manifold if you're going to be under 600AWHP.

 

Any other thoughts on this??

 

Manifolds will crack for several reasons. Most manifolds on the market today are not constructed from materials that are suitable for the application. I know that many vendors on the forum run the thick walled 304SS jobbers, but those lower grades of SS are not rated for the temperatures seen on turbocharged applications. With that said they do work well because they use such thick walled material. Regardless of this fact they have no way to absorb the thermal expansion because of their compact design.

I haven't logged EGT's 2" of the head, but on my old Z EGTs in the 1600F were very common. The only materials rated for such use are 321SS and inconel.

Other issues are a result of a lack of expansion points within the manifold that allow for safe thermal expansion without cracks. This coupled with the manifolds requirement to support the weight of the turbo as well as the vibration will lead to cracking.

I have made several manifolds from 321SS that utilized slip joints in the design and properly supported the turbo. These manifolds have been in use for 5+ years on street cars with no issues.

I think for the EVO a 321SS top mount turbo would allow for the use of slip joints and bends within the header to absorb the thermal expansion of the pipes without stressing the welds. This would also allow you to support the turbo to the block and head to isolate vibration and support the weight of the turbo. I will show a few headers below that were fabricated from 321SS for street use and had no issues.

My point is that if you design a manifold properly it will survive no problem on a daily driver for many years with no issues.

 

Thanks everyone for your input! You definitely made my decision a lot easier. My car is definitely a daily driver so it sounds like it'll be best for me if I stick with the stock manifold.

 

what kind of gains can be expected from porting the stock exhaust manifold using a stock turbo?

 

Def get a ported stocker.....

 

a ported stocker is the cheaper route for sure but again dont get caught up in the bs that a tubular manifold will not net power because it will and been proven to make more power. Anything has the potential to crack its what kind of warranty you have that makes the difference. on the full race shearer mona lisa and i think ets you have a lifetime warranty. if it cracks guess what unbolt it send it back in get it repaired or anew one and your back in action. I understand the ported stocker route but in my engine bay as well as many others im trying to make the most power as well as add looks and flare to the bay. Go with what you want but only the Cheaper megan manifolds etc crack all the time not quality products

shearers 1196
full race 827
ets 869
mona lisa 750

those are the only brand tubulars i would consider putting on my car and not worry about a thing happening. Anything else is a choice you make

 

A stock manifold; ported, polished and coated is pretty much all you need for the majority of motor build-ups out there. The stocker already flows pretty good as it sits. I agree that once you get over a certain power level you will need to look into one of the better made, higher quality pieces.