sp2 and downpipe

[Swerny]

My hypothesis is that 3 inches does make a difference. The ion tb exhaust made 22 whp overall and is 3 inches all around. Other exhaust systems arent that big and dont make that much power. The extra money part of the equation is damn near negligible when you go to a custom exhaust shop anywayz.

Let's remember to compare apples to apples here.
The Ion and GHL are 3 inches, and they replace the entire exhaust. They are turbobacks and replace the stock S-pipe, which is why they make the most power.
I have yet to see a dyno for a 2.5 inch turboback basically because they haven't existed until recently, when CS and MAM released replacemnt S-pipes.
I remember reading the CS exhaust made 13 HP, with the stock S & J Pipe.
If you have the $, by all means, go with GHL or Ion.
Frankly, i'd buy the CS turboback at this point for under $600,keep the change, and probbaly make 5 HP less than Ion or GHL.
Unless youre planning for massive boost, building your motor, or going with a bigger turbo, the 2.5 (or 2.4 if it really matters) will be plenty.
I actually measure the stock piping last night, and the resonator section tapers to 1.8 inches at the ends. At its biggest, it doesnt get bigger than 2 inches.
That being said, If you can get the Thermal for a good price, go for it. It can't hurt to have bigger for down the road.

 

[Titanium]

^^^Like he said^^^ This has gotten way off topic. We started talking about the difference in 2.5" apex j-pipe or 3" j-pipe to go with a greddy sp catback. This in my mind is a great combo from someone that is looking for something alittle different than stock with some power gains from deleting the cats or replacing with one high flow cat and a great sound to boot! At no time should we compare this to a full turbo back exh.

My hypothesis is that 3 inches does make a difference. The ion tb exhaust made 22 whp overall and is 3 inches all around. Other exhaust systems arent that big and dont make that much power. The extra money part of the equation is damn near negligible when you go to a custom exhaust shop anywayz.

The key to that quote is "hypothesis". Not trying to start a flame war anything. Just putting out info for others. Hopefully people will do some research and see what the thing is best for them and there application as to not waste money on something. The key to any modding is to set a goal. First define your goal and then look what it will take to get to that goal. Research anything that has to go into meating that goal.

 

[AutoBox]

GRAB corky bells book on FI and shut up about "BIGGER IS BETTER" when delain with exhuast...its proven and engineered for years.....so on the actual topic at hand....i would run the same piping thru out the exhuast....even with a 3" dp you still have the restriction when u collect at the 2.5" cat back.....on a turbo setup you have to think of lag also....with a 2.5" system you have slight backpressure at the turbo for the sake of spool up.....with a striaght 3" you sacrifce some response instead gettin massive flow at high rpms.....again it depends on the application and power you are puttin down...to compare...when i had my msp...i replaced the j-pipe-catback with a full 3" system.....on stock boost it was non-responsive below 4k....it just felt more sluggish then stock exhuast...after 4k it was like a bat out of hell......pulled like no other......if thats what u want...get the 3" dp...if you want linear reposive power.....get the 2.5"

 

[speedmo21]

so your sayin i shouldnt go 3" to 2.5? go eiher 3 or 2.5 the whole way? also any dynos on the sp2??

 

[Striker187]

haven't seen any dynos.....i wouldn't worry about it though. there's maybe a 2-5 hp difference range in the catbacks out there.

and yes, you don't want to go big to small. either same size through or small to big. and fyi, straight from corky bell's book, the best exhaust is no exhaust. but seriously, 2.5" will support ~475 bhp (i'm staring straight at fig. 11-4 from the book). i went with 3" to keep the same size throughout and to give me a little more on top end (whenever i get around to turning up the boost)

 

[CasopoliS]

haven't seen any dynos.....i wouldn't worry about it though. there's maybe a 2-5 hp difference range in the catbacks out there.

and yes, you don't want to go big to small. either same size through or small to big. and fyi, straight from corky bell's book, the best exhaust is no exhaust. but seriously, 2.5" will support ~475 bhp (i'm staring straight at fig. 11-4 from the book). i went with 3" to keep the same size throughout and to give me a little more on top end (whenever i get around to turning up the boost)

What is the book's title, where can I get it?

Thanks.

 

[AutoBox]

you'll have to tell me what page in his book he states that no exhuast is the best route......exhast tuning is a freakin art....ppl dont realize the amount of R&D f1 teams put into the layout of the exhast system......of course for maximum power no restriction is best...thats common sense....what im sayin is that for a specific purpose....the right diameter is key.....and corky does state that...also states that many ppl assume that the bigger the diameter the better and that isnt so......and if you want ill point out the pages he states this in...s*** he has one chapter just on exhuast layout......like i said...if you want max power and the most top end...then get the 3"...cus thats what its good for....the 2.5" allows better torque and mid-range in general.....i lost torque when i had my 3" on and i could feel it...of course i would of got some back with more boost but then ur gettin more into the flow characteristcs of the 3" and even then a 2.5" is gonna still provide better mid-range then a 3" at the same boost level....only when u maximize the 2.5" piping is when u truely

 

[AutoBox]

What is the book's title, where can I get it?

Thanks.

maximum boost by corky bell...B&N has them

 

[speedmo21]

so if i go w/the sp2 which i prob will.. will the 2.5 downpipes not be a direct fit seein the sp2 is slightly smaller than 2.5? also which 2.5 dp should i got with? think i saw the wagner catless for 190$

 

[AutoBox]

so if i go w/the sp2 which i prob will.. will the 2.5 downpipes not be a direct fit seein the sp2 is slightly smaller than 2.5? also which 2.5 dp should i got with? think i saw the wagner catless for 190$

60 mm is exactly 2.362198"......so 2.5"-2.362198"=.137803" or 3.5 mm/2 = .0689015 or 1.75 mm of different between the two diameters

1.75mm of thickness isnt exactly a restriction in terms of street use......but if ur relaly anal then i would get a 60mm dp or a 2.5" exhast to match perfectly

 

[speedmo21]

so im gonna need alittle piece made to connect the dp to the sp2 right?

 

[AutoBox]

so im gonna need alittle piece made to connect the dp to the sp2 right?

no..ur just gonna have about 1.75mm of the greddy exhuast overlapin inside the 2.5" dp

so lookin down the 2.5" dp ur gonna have 1.75mm of "lip" from the 2.5" dp's ID pipe to the sp2 ID pipe size.....

 

[Titanium]

It'll be so small of difference that you will not probably be able to even tell by looking at it. Plus this measurement is for the out diameter of the piping.

 

[AutoBox]

ahh good point...exhuast size isnt measured at ID on aftermarket cat-backs.....gotta factor in piping thickness etc......but if we say they have the same grade/thickness piping there is gonna be less then 2mm difference.....grab a ruler and look at 2mm and see if you think thats gonna affect ur street driving

 

[speedmo21]

ya i figured it wasnt big enuff to matter.. i just gotta figure out what dp i want...any of them have better fittings than the other? also should i get the kartboy exhaust hangers and the apexi DP gasket?

 

[Titanium]

get this set up and you'll be happy, apex pipe w/ or w/o highflow cat with the greddy sp. and add the kartboys to cut down on the vibration that could end up breaking welding on the exhaust. You'll love the sound and the look and the quality is top nonch! Note if you get the catless pipe you will either have to get the mil elminator or search this forum of other stricks.

 

[daedalus]

Yea, the apex dp and sp2 are very nice. Though, consider the JIC Magic SUS catback as well. Even nicer sounding than the SP2 (if thats possible) and its sexy as hell.

 

[msp35]

GRAB corky bells book on FI and shut up about "BIGGER IS BETTER" when delain with exhuast...its proven and engineered for years.....so on the actual topic at hand....i would run the same piping thru out the exhuast....even with a 3" dp you still have the restriction when u collect at the 2.5" cat back.....on a turbo setup you have to think of lag also....with a 2.5" system you have slight backpressure at the turbo for the sake of spool up.....with a striaght 3" you sacrifce some response instead gettin massive flow at high rpms.....again it depends on the application and power you are puttin down...to compare...when i had my msp...i replaced the j-pipe-catback with a full 3" system.....on stock boost it was non-responsive below 4k....it just felt more sluggish then stock exhuast...after 4k it was like a bat out of hell......pulled like no other......if thats what u want...get the 3" dp...if you want linear reposive power.....get the 2.5"

Lag?....no our turbos?...Sure some, but MINUTE! Once I had the GHL installed I was at full spool ~3-500RPM's sooner than with stock.
Then, suppose you are blowing into various size straws. As size increaces exhaling is much much easier. With that said, how can ANY backpressure be good and (beneficial) to a turbo, as you describe?
I will agree size does matter on N/A. What does F1 run? isn't it N/A

 

[Titanium]

What does F1 run? isn't it N/A

umm, I reach full boost on stock around the 3500k. Yes F1 does run N/A. So lets look at it from your side. If bigger is better then why not have a 4" exh if it could fit. Exhaust tuning still applies to your application. You dont have a hugh turbo and you dont have loads of power. As it has been stated there is no data to support that a full 3" exh is better for a stock application when compaired to a 2.5" exh. cause there is no complete 2.5" turbo back exh on the market.

 

[Swerny]

there is no complete 2.5" turbo back exh on the market.

There is now the Corksport turboback, but it's 2.4.
No dyno's as of yet.