AHU exhaust: 2.5" or 3"

[hopcarolina]

Hello all,
Wanted to maybe get some input from everyone on this. I am building a TDI Corrado. 98 AHU engine. I am not going for a hypermileage car or SCCA racer but a little doesn't hurt...a good daily driver for a mid forties old guy!

Currently it has a 130 hp BEW intake with EGR delete and 2" boost lines on a stock G60 intercooler. The stock turbo. I am in the process of building the exhaust. The flex line was broke so I replaced it with a 2.5" line. I can either stay with that 2.5" stainless out the back or up it to 3". I haven't decided if I should add a resonator or muffler. Probably run the straight pipe to hear it then if too loud add something to calm it down.

I am wondering if there will be much power increase from the intake to the straight pipe to the different sizes. 3" over 2.5" will not be much extra I would think. How much would a flowmaster kill it? Maybe just a single resonator? How much will mileage be affected?

Any help or comments will be much appreciated!

 

[bturpin]

I don't think it really matters on size. However get rid of the cat if you haven't already. That is if you can in your state. And a Flowmaster wouldn't make any difference in flow. The cat is the bottleneck of the exhaust system.

 

[turbobrick240]

I don't think a free flowing 3" exhaust begins to add any real power vs. a free flowing 2.5" exhaust until over 250 hp or so.

 

[Exenos]

I agree with turbobrick that 3" is not needed until higher power levels, however personally I'd be going 3" around 200hp. Until then it is really just noise. The 3 inch will be louder than the 2.5. You would most likely be able to get away without a muffler on the 2.5.

 

[LNXGUY]

3in @ 200hp is still a waste. 2.5in is more then enough.

 

[Exenos]

3in @ 200hp is still a waste. 2.5in is more then enough.

That's why I said personally. Certainly not needed but sounds better.

 

[hopcarolina]

Well, I'll go with 2.5". Hope that will work. Thanks ya'll

Appreciate it!

 

[Gotrek]

I have a 3" Buzzken but only because it came up for sale cheap Still a waste but it saved me money It does sound awesome though.

 

[mrchill]

Depends on ones taste. All my cars are 3 inch...thats what I prefer. 2.5 is fine...but then so are stock turbos. I like upgrades...even if you done "need" them......

 

[[486]]

I don't think a free flowing 3" exhaust begins to add any real power vs. a free flowing 2.5" exhaust until over 250 hp or so.

this

if you're running a stock turbo (or similarly sized) you're not going to gain anything going from a 2" straight pipe all the way to the extreme example of just running without any downpipe at all

ETA: go with aluminum if you can weld it, no reason not to on a diesel

 

[To87]

My old cordoba vario did have 3" downpipe and the straight section under car was 3" rest was 2.5". For the 3" dp there is not so much room. Easier to make full 2.5" pipe. Power from wheels 178hp/380nm. Injectors 0.216x6 holes nozzles, self made manifold and td04-14t turbo from volvo, IC on the front, tuning box was v-tech. 416000km on it when i sell it.