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I am correcting an exhaust leak in my exhaust manifold (lose head bolt). Anyway, I wanted to take advantage and port my manifold while it's off. Is it worth my effort to port the manifold without porting the turbo exhaust housing or O2 sensor? What gains if any can I expect from just porting the manifold?
 

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Well yes and no to be short abou it =-)

The 95 manf stock flows more then the 90-94 units do and they dont crack like the 1G's units do.

porting the manf alone will help some but the real gains are in all 3 parts matched togeather. just doing one means that it will get through that part faster but then have to slow as it is choked down in the next part ( turbo in your case ) it is always best to work back to front, this is why a Cat back system comes before a Down pipe. Think of it like this. if I put a huge 3 inch DP on the car but it still had stock cat and cat back the DP would flow great but still back up going in to the cat and the rest of the system. trus this is better then it was but not worth the gains that could have been made with a cat back.

So folowing that thinking porting the manf with out the turbo yes will make some gains but not nearly as much as if all parts were done togeather. Having a manf, turbo and 02 all ported at 1 time helps a lot as the person who is doing the porting work will work the mating surfaces to match up and not have flow restrictions.

A quick word about porting. Porting is a art form. MANY VENDORS miss that fact big time and even more of the end users have no idea about this. people say "ya I hade BLANK port my stuff. But what does that really mean? ya anybody can get in the parts and hog out the turbo and ring on the manf but there is MUCH MUCH MORE to it then that. porting work has to be done based on the mods the car has and the future of the car. A VERY GOOD porting job WILL NOT hold boost with the stock W/G and only limited control with all the larger flappers that are out there. this means that people must get a limited amount of porting work to keep the car driveable. There are a lot of factors that control this. full 3 inch is one of them. car with that have to be limited in the totoal size as boost spike will be uncontroable b/c of the huge drop in back pressure on the turbine.

A GREAT site that helps is www.vfaq.com it shows the BASIC IDEA of porting. some parts I personally don't agree with but you will get the basic idea.

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Bill Marino
NYC DSM
[email protected]
 

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Yes porting is an art but it is also a science. The larger valve does hold boost. I think you meant to say that the larger valve has more surface area and this will cause exhaust pressure to force the valve open at a lower boost. This is true. I have found that the a 16g with TRE MODS will run about 10 psi when plumbing the hose from the wastegate actuator straight to the intake manifold without any boost controller but it will hold close to 25 psi with a boost controller if the driver dares to turn it up that much. This is true for the Frankenstein turbos as well.
 
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