Which exhaust for your f.i app?
 

Hey everyone, which exhausts are you running in your cars for your f.i applications and why? I am about to (Monday), pickup a Tomei 60r for the unbelievable weight savings, sound, straightness of the exhaust and the fact that I love single exits. I know the Tomei type 80 is a more free flowing exhaust for our cars with any type of f.i, but does anybody know what kind of power we can make before we actually max out the flow of a 2.35" exhaust?


The exhaust is in stock and I wouldn't have time to wait for a type 80 to come in before my time attack season opener.

Fyi, Stock op, and front pipe are being used for my setup but will eventually be upgraded.

IMO if you want some noise for your time attack session, get a cheap single exit track pipe till you can get the Type 80. Most recommend a full 3 inch header back system. Don't settle if you really want the type 80. Nameless has a decent trackpipe.

Cool thanks man that's a good idea. I really don't care what I get as long as it works and its a single exit. If I do buy the 60R, any idea what kind of hp it would support?

Not sure. The 60 is 2.5inch right? Unless your going crazy on the turbo build, should support most people's target goals.

It will only be for between 300-425rwhp for a few years, so not too crazy. I think 60mm is about 2.4", seems pretty standard for all catbacks for our vehicles.

You're limiting yourself if you have a 2.5" making over 300. There is a lot of power/spool be picked up even before 300 when you are FI. Definitely replace your front and overpipe if you're getting a catback.

I'm currently running perrin overpipe to 3" maperformance front / midpipe to a custom muffler.

Anything over 300hp will be limited by exhuast under 3"

well most turbo kits have a 2.5 outlet unless you're running a gtx30. I know my GTX2867r is 2.5 but feeds into a 3 inch DP then has a 2.5 flange on the bottom like most kits. But what everyone seems to forget is even though most kits have a 3 inch DP they have 2.5 inch flanges on to mate with just about every overpipe on the market. Fullblown made 605whp on a factory overpipe! (I think that's 2.2), and I made 461whp with a 2.5 perrin op matted to a 3 inch fullblown exhaust. Now exhaust gasses slow down as they cool down so a 2.5 op matted to a 3 inch exhaust can make a great difference in spool. This is also why stepped headers work. Which is probably why fullblown was able to make good power on the factory OP with a 3 inch exhaust. As the exhaust pulse moves away from the turbo it cools and effectively expands as it slows. So fatory OP to 2.5 works, or 2.5op to 3 inch exhaust works. Will you be limited on power? A little with the 60r. I think king tut made 280wtq on a 2.5 perrin exhaust but you'd have to ask him yourself. Will it hurt spool? Yes but you may not notice it until you put a bigger exhaust on later. Over 350whp the turbo will work a little harder to make the same power as something with a 3 inch exhaust. For reference fullblown made 300whp on a factory exhaust on 93. swapped it all out and made I think 320whp+.


in short, the 60r is small but the 80r is pretty damn big for the street and very loud. fullblown and perrin make some nice 3 inch exhausts but they have zero ground clearance. Perrin, nameless and abunch others make nice 2.5's. if you want next weekend I can have video of the fullblown dual 3 inch.

Exhaust gases expand as they heat and contract as they cool. Gases contracting during travel through a constant piping size is what will cause a decrease in velocity, and is why stepped headers/exhaust components are effective in maintaining velocity.

yes they contract as they cool but the exhaust pulse slows down further down the exhaust stream which has a greater effect. That's why I wrote "effectively" I was trying to make it easier to understand. So I didn't have to explain how a cooling contracting exhaust gas slows down and creates back pressure.

I understood the use of 'effectively', just that the use of 'expands' is completely wrong. I don't think or mean to imply that your understanding of this aspect of fluid dynamics is lacking. And disclaimer: I am no expert myself. I only think it was your explanation that was incorrect.

As the decrease in exhaust gas velocity is, at least in part, due to its contraction, using the term "expands" in the explanation is counter-intuitive when introducing these concepts to someone unfamiliar.

Nice write up thanks very much. So if I'm going to be sticking to my factory overpipe and my factory front pipe 60r is fine if I'm only shooting for 300whp, and if I want more then I should consider a complete exhaust setup using a 3" "catback" minimum. This is the first time I've turbocharged a car so all this information is excellent.

Thanks a lot guys!

You're likely going to learn that 'fine tuning' your exhaust to be 100% optimal for FI costs more than its worth (especially with modest goals), unless you absolutely need to squeeze every ft/lb of output (and every 50rpm of boost threshold/response) from the engine.

You're not going to have a problem reaching a goal of 300whp with any of the aftermarket exhausts that are currently popular and circulating (as most if not all are at least 2.5" diameter), assuming all other supporting mods and turbo selected are up to the task.

IMHO, Just pick a system that appeals to your tastes for design, aesthetics and tone and call it a day.

That said, FYI, incrementally stepping diameter sizes up (2.2" OP, 2.5" FP, 3" CatBack) is exactly backwards in regards to exhaust design with regards to fluid dynamics. That is not to say or imply that swapping to a larger cat back has a negative effect on performance. The internet has plenty of evidence of the contrary. This leads me back to the first line of this post...

Thanks! I really appreciate you guys taking the time to write this up for me. Hopefully I will be able to pass this information and experience down to other people if they need the help!

Rob.