2.5" DP, too small for my setup?

[Prodigyman]

I've updated my car quite a lot since I installed my custom 2.5" DP and 3" high Flow Cat and 3" Cat back exhaust so I am just wondering if my 2.5" DP is too small for the setup with FP Green? Because i really don't want any back pressure and I am getting electric cut out valvue too right after the bent where I am welding the Tail WG return pipe, even with cutout open wouldn't it cause some back pressure problems or when it is closed?

Check my car profile for full list of mods

You suggestions are appreciated

 

[hopwoodp]

Well, like RRE says its better to have a 2.5" on the first bend then 3" after that to keep the exhaust velocity right. Unless your O2 housing is larger than 2.5" then, your fine esp. if you have a cut-out after the bend. So, in other words - your fine if your cutout is after your 1st downpipe bend, you have no worries.

 

[Prodigyman]

Well, like RRE says its better to have a 2.5" on the first bend then 3" after that to keep the exhaust velocity right. Unless your O2 housing is larger than 2.5" then, your fine esp. if you have a cut-out after the bend. So, in other words - your fine if your cutout is after your 1st downpipe bend, you have no worries.

Yeah that O2H is 2.5" Hybrid Connection old school one.. from SBR. Well that puts this problem at rest

Thx for the info

 

[pboglio]

The first bend in the downpipe IS one of the most restrictive portions of the exhaust system due to the high exhaust gas temps and the resulting high exhaust velocity. Bumping up to a 3" downpipe would definitely help.

I thought about running ATP Turbo's pneumatic cutout, sortof like an external wastegate for the main exhaust. However, I planned on doing a Y off the downpipe so the cutout takes a straight shot straight down to the ground without having to turn at all after the 02 housing.

 

[hopwoodp]

From Road Race Engineering: 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. From there they are a full 3" back to the Apex 3" flange with 14 gauge aluminized steel piping.