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phils89sc
09-16-2010, 11:03 PM
I have done some pretty extensive searching on the forums about this topic. I have my manifolds off right now and have already started porting. I have the lip at the collector gone on the passenger side, nice and smoothed out using my die grinder and stone bit. I have seen on here where people are opening the collectors up to two inches, Inside Diameter I guess. This is quite a bit of opening up. My question is, if I go ahead and do this, how will my stock downpipe fit? Will it be too small and leak? I cannot afford to by new downpipes (larger, if someone makes them). What should I do?

Regul8r
09-16-2010, 11:11 PM
I have done some pretty extensive searching on the forums about this topic. I have my manifolds off right now and have already started porting. I have the lip at the collector gone on the passenger side, nice and smoothed out using my die grinder and stone bit. I have seen on here where people are opening the collectors up to two inches, Inside Diameter I guess. This is quite a bit of opening up. My question is, if I go ahead and do this, how will my stock downpipe fit? Will it be too small and leak? I cannot afford to by new downpipes (larger, if someone makes them). What should I do?

Open to the 2" and your stock down pipe will bolt up and seal, no problem.
Clean the connection cone area on the manifold AND inside the down pipe.
Also don't be afraid to use a little exhaust sealer or extreme high heat rtv, it will help ensure a good seal.

phils89sc
09-16-2010, 11:55 PM
Open to the 2" and your stock down pipe will bolt up and seal, no problem.
Clean the connection cone area on the manifold AND inside the down pipe.
Also don't be afraid to use a little exhaust sealer or extreme high heat rtv, it will help ensure a good seal.

What kind of gains can be had by doing this mod? I already have a custom true dual exhaust (2.25" I think, no mufflers with Flowmaster dual in dual out muffler for resonator and high flow cats.)

thanks

the-big-e
09-17-2010, 08:12 AM
I usually port mine out to 1.8" and still have plenty of lip surface left over....

Regul8r
09-17-2010, 08:48 AM
What kind of gains can be had by doing this mod? I already have a custom true dual exhaust (2.25" I think, no mufflers with Flowmaster dual in dual out muffler for resonator and high flow cats.)

thanks

Well, let's just say that when you open up that lip, the stock manifolds will support around 350HP. This lip and the resonator are the 2 choke points on our cars. They provide enough restriction that this mod and replacing the stock resonator are the first 2 mods recommended by most of the SC guru's.
Before you do ANY other mods, these have to be done in order for the other mods to work and show true results.

phils89sc
09-18-2010, 03:00 PM
Well, let's just say that when you open up that lip, the stock manifolds will support around 350HP. This lip and the resonator are the 2 choke points on our cars. They provide enough restriction that this mod and replacing the stock resonator are the first 2 mods recommended by most of the SC guru's.
Before you do ANY other mods, these have to be done in order for the other mods to work and show true results.

I just finished porting the passenger side collector on my 89 SC exhaust manifold. Although not quite 2" I don't think, it now transitions very smoothly on the inside, no more ridge, and the collector itself is enlarged a bit. I guess I am worried I will open it up too much and not be able to put my exhaust back on without leaking.

What do you think thus far?

Regul8r
09-18-2010, 03:22 PM
I just finished porting the passenger side collector on my 89 SC exhaust manifold. Although not quite 2" I don't think, it now transitions very smoothly on the inside, no more ridge, and the collector itself is enlarged a bit. I guess I am worried I will open it up too much and not be able to put my exhaust back on without leaking.

What do you think thus far?

What did you use?

phils89sc
09-18-2010, 03:59 PM
What did you use?

I used a die grinder with a stone bit to grind away the lip and another finer bit to smooth it out... Tell me the truth, either way, how does it look?

Regul8r
09-18-2010, 04:29 PM
I used a die grinder with a stone bit to grind away the lip and another finer bit to smooth it out... Tell me the truth, either way, how does it look?

looks good.
would make sure you are round and straight.
use something 2inches round and slip it in the hole to see where you are high or low(out of round).
That will show if you are a true size all the way.

TinManSC92
09-18-2010, 04:38 PM
Mine are only at 1-7/8 as well. Work fine.

Regul8r
09-18-2010, 04:45 PM
Mine are only at 1-7/8 as well. Work fine.

Same concept, something 1 7/8 to check your work.
Thats what I would do to ensure I got it right.

Others have done the 1 7/8 and seems to work fine too!
The one's I have are opened to 2 1/8.

TinManSC92
09-18-2010, 04:52 PM
:eek: What!! Now that's what I call precision work. I was worried about leakage at 1-7/8 as well. - I don't think he has that much to worry about then. His do look good.

Regul8r
09-18-2010, 05:01 PM
:eek: What!! Now that's what I call precision work. I was worried about leakage at 1-7/8 as well. - I don't think he has that much to worry about then. His do look good.

Yup, thats why they are at the machine shop doing something different to see IF I can get a different way to seal up.

I am going to try an idea I have on one of the other sets I have to see just how big they can go and some sort of gasket/donut set up.

the-big-e
09-18-2010, 08:52 PM
Looks like you did an excellent job.....:cool:

I don't think I could have done any better and I've been die grinding parts for over 30 years....:p

phils89sc
09-18-2010, 09:34 PM
Looks like you did an excellent job.....:cool:

I don't think I could have done any better and I've been die grinding parts for over 30 years....:p

Thanks Eddie! I have pics of the other side, will post them later. Ending I.D. is 1 7/8". I will buy another set eventually to try to hog them out. Thanks again!

phils89sc
09-18-2010, 11:38 PM
Yup, thats why they are at the machine shop doing something different to see IF I can get a different way to seal up.

I am going to try an idea I have on one of the other sets I have to see just how big they can go and some sort of gasket/donut set up.

What can I expect in the boost dept, a slight drop? My exhaust after the downtubes is true dual and pretty free flowing.