What will a downpipe do for my setup?

[a1320eclipse]

Ok, its a 90 tsi. Mods so far are: K&N, Turbo XS hpmbc set at 17psi, Apex'i SAFC II, walbro 255, B&M fpr set at 41psi, 3" cat back. Stock downpipe. So im thinking bout the megan 2.5" inlet and 3" outlet downpipe welded completely up with my 3" exhaust, just with my car tuned at 17 right now, is just the downpipe goin to give me any real gains?

 

[1glaserturbo]

You'll notice it a little. Opening up the exhaust is one of the best things you can do for a turbo. Getting that hotgas out as fast as possible will increase spool and help with the top end a bit. So, yes. You will notice a bit

 

[UofACATS]

Yes.

Besides reducing backpressure from the stock downpipe, the Megan will eliminate the cat. This will give you slightly better spool, but you will feel the "real gains" at higher RPM, now that your car has less "restriction."

Get it. The best horsepower is that which is found.

 

[diablos991]

Get it. The best horsepower is that which is found.

Wow. Thats deep.

 

[GVR4592]

Make sure you port the wastegate passage in the turbine housing and O2 housing, while you have it apart, or you might get some boost creep.

 

[fourreGsixty3]

it will take the back pressure away, and give some Hp gains, go with the 3" because it doesnt matter how big the cat back is, because if the DP is 2.5" will restrict the 3".

 

[daren_p]

Will it be a massive gain, no probably not but for the cost, would defently be worth it. Your probably not seeing the full benefit of that 3" catback since the stock dp will be restricting you. You'll notice more power, boost won't drop off as much (if it currently does) and you will see quicker spool.

 

[eclipsh]

it will take the back pressure away, and give some Hp gains, go with the 3" because it doesnt matter how big the cat back is, because if the DP is 2.5" will restrict the 3".

I'm going to have to disagree with that. A 2.5" dp is not going to be a major restriction. In fact, I wish I had one instead of my 3" dp. The 3" DP is a VERY tight fit and requires a LOT of porting to get rid of boost creep. It also kills your engine power in the low end when the turbo isn't working. My car had better low end response with a STOCK exhaust than it does with a 3". The modest amount of back pressure a 2.5" dp will keep should help fight boost creep and keep a little bit of that pre-turbo torque.

Also, from RRE:

Our DPs have a 2 1/2" stainless steel first bend with a 2 1/2" stainless steel flex section. They then expand to 3"# right after the flex section right under the oil pan area. Why start out at 2 1/2"? If you are running on the stock O2 sensor housing, even ported it is 2 1/2" inside diameter. When the exhaust gasses are hot, they flow better, 2 1/2" is plenty for the first 12". As the gasses cool , bigger helps. By going to 3" after the flex section, we allow this expansion and also allow for better clearance at the front where room is tight.

They used to include a comment on how the 2.5" DP restricted you to ONLY 500whp or something rediculously high that most of us will never reach.

 

[daren_p]

^^^^

 

[heppm01]

You can also think of the 3" DP as an "enabler". It make not make a huge difference right now, but it will allow you to get the most from any upgrades you make in the future, such as bigger turbo, cams, etc.

Matt

 

[fourreGsixty3]

Also, from RRE:


Quote:
Our DPs have a 2 1/2" stainless steel first bend with a 2 1/2" stainless steel flex section. They then expand to 3"# right after the flex section right under the oil pan area. Why start out at 2 1/2"? If you are running on the stock O2 sensor housing, even ported it is 2 1/2" inside diameter. When the exhaust gasses are hot, they flow better, 2 1/2" is plenty for the first 12". As the gasses cool , bigger helps. By going to 3" after the flex section, we allow this expansion and also allow for better clearance at the front where room is tight.

They used to include a comment on how the 2.5" DP restricted you to ONLY 500whp or something rediculously high that most of us will never reach.

Oh wow I didn't know that, thats a good bit of info. I stand corrected.

But as for

A 2.5" dp is not going to be a major restriction

I never said how big of a restiction, just that it would be a restiction, but perhaps with that new info from RRE its a good one.

 

[gsxin]

They used to include a comment on how the 2.5" DP restricted you to ONLY 500whp or something rediculously high that most of us will never reach.[/QUOTE]

speek for your self

 

[daren_p]

They used to include a comment on how the 2.5" DP restricted you to ONLY 500whp or something rediculously high that most of us will never reach.

speek for your self

Hmm I think you have some pretty big dreams if you think your 500whp on a 14b @ 15 psi with intake and exhaust jokes

 

[unlmtdndeavor]

just a comment on how you are planning to build the exhaust, i would not get the dp welded to the catback. there is no reason to and this will just further complicate things if you ever decide to part things out or store the exhaust system.