I am going INSANE trying to find this info using the so-called "search button". In fact I have been trying to independantly search using not only these forums, but also Google, etc. to find out what I want to know.

NO DICE.

Someone please help me out:

I have a plan for my car now. I am trying to make reasonable improvements to the stock system by replacing what I see is the most restrictive part of the exhaust, the OEM cats. I am most likely not going to change out the exhaust manifold simply because of its durability.

I want to get the crawford cats.

I currently plan to keep my stock exhaust as but will consider changing it out in the future.

Here are my questions.

1) Do the crawford cats have the same inlet and outlet diameters as stock? Will the crawford cats mate up with the OEM y-pipe nicely?

2) Is there a y-pipe that replaces OEM with the same diameters at inlet and outlet?

3) What are the inlet and outlet diameters to OEM y-pipe? How does this compare to a typical aftermarket y-pipe?

4) Let's say you go with a 2.5" inner diameter dual catback exhaust. How does this work ? Is there a dramatic step-change from the outlet of the cats to the main piping of the exhaust?


Thanks in advance to whomever takes the time to read and answer.

Mike

 

3a) What are the inlet and outlet diameters to OEM y-pipe?
Cat end 2" and Midpipe end 2.5"

3b) How does this compare to a typical aftermarket y-pipe?
Cat end 2.36" to 2.5" and Midpipe end 2.75" to 3"

 

1. I don't know but the Crawfords HFC are 2.25 on both ends.

2. No there is not a Y Pipe with the same inlet and outlet diameter.

3. g35strong man said 2" Inlets, 2.5" outlet.

4. I thought you didnt want to change the exhaust??

Since you want to use Crawford HFC's and keep the stock Exhaust. I would recommend going with a HKS Y Pipe.

The Crawford HFC's have a 2.25 Outlet diameter, that would bolt up to the 2.36 Inlets of the HKS Y Pipe, the 2.46 Inch outlet of the HKS Y PIpe would bolt up to the 2.5 inch oem exhaust.

So it would just gradually get bigger and bigger. There would be no restrictions that way.

 

So let me get this straight, if the inlet to the OEM y-pipe is 2", then the outlet of the stock cats must be 2" as well, right? So it seems great that the crawford cats are 2.25" but like you said, I would need a better y-pipe to avoid being restricted by the oem y-pipe.

I don't want to change out the stock exhaust to something bigger until I get a feel for the gains with HFC's. I plan to get HFC, E-manage ultimate, and get dyno tuned. Then if it seems that there are more gains to be had, I might consider an aftermarket exhaust and retune in the future.

Here's what I'm getting at:

Is there some way to make the entire exhaust system FLUSH at the flanges (to effectively keep exhaust gas velocity high as possible)... This is what I'm trying to do - avoid step-increases in diameter. But obviously step-increases in diameter are better then step-decreases.

My guess is this cannot be done with the stock exhaust ... right?

Thank you guys so far!! This has already been tremendous help.

 

If you go Crawford HFC, HKS Y Pipe, and stock exhaust. The increases in diameter at each flange is really minimal..

The Crawford HFC's are 57MM, the cats would dump into the 60mm inlets of the HKS Y Pipe, The HKS Y Pipe gradualley increases from 60MM inlets to a 62.5MM outlet.The 62.5 Inch outlet of the Y Pipe would dump into a 63.5 MM stock exhaust.

So its 57mm, 60mm, 62.5mm 63.5MM. Thats extremely minimal IMO

 

You have a good point and I strongly appreciate this info

Just when I thought my credit card was safe. Uh oh

 

Let me know how it goes. I might go the exact same route =)

 

I found a website that said the inlet to HKS y-pipe is 60mm = 2.36" and the outlet is 65mm = 2.56" ...

Not too bad but if the stock mid-pipe is indeed 2.50" then it will create a small step-decrease restriction.

I just can't figure out why it's SO DAMNED HARD for manufacturers/vendors to put inlet AND outlet diameter specifications on their websites.

What was your source for the HKS y-pipe diameter specs and where did you find it for a reasonable price?

 

Here is a example. Lets say that you go from headers to high-flow cats to cat-back exhaust. I know that you want a perfect inner diameter match, but the difference will be negligible.

 

I got the specs from here: http://www.*********.com/zwiki/Part:Y_Pipes

But that could be wrong. Now that im looking for prices the shops say 65mm outlet.

Hopupracing.com is the best price i have found for $469. =(

 

Actually upon further investigation, I am not sure I like the design of the HKS y-pipe.

Stock: 2 inlets, radius is 1", 2 * pi r² = 6.28 square inches
outlet: pi * 1.25² = 4.9 square inches

ratio: 1.28 reduction in cross sectional area


HKS: 2 inlets, radius is 1.18", 2*pi r² = 8.75 square inches
outlet: radius is 1.28", pi r² = 5.15 square inches

ratio: 1.7 reduction in cross sectional area

I don't like those numbers... I am going to keep looking.

Looks like I might end up with something like a full catback such as tanabe. I have been sold on the tanabe y-pipe and the medalion touring exhaust for a while now, but the y-pipe is a bit bigger inlets and outlets I believe. Also IMO it is a bit expensive (almost as much as the HKS) when you factor in the y-pipe.


Davidv: No offense but I don't see how your pictures really help. Plus at high velocities, a small step will make a big difference. Not so bad with a diameter-increase step, but a diameter-decrease step will be effectively an orifice which creates backpressure.

What really shocks me is the large number of people on these forums with exhaust mods and the few number of people who apparently researched the actual diameters of said exhaust mods.

 

Uhh, all that math makes no sense to me

Anyway, which Tanabe Exhaust are you talking about? The Dual Muffler+Dual Tip, or the Single Muffler+Dual Tip?

Im confused as to why the Dual Muffler+Dual Tip is listed as having 70-60MM piping. What does that mean?

For the record the Dual Muffler Dual Tip is called the Tanabe Super Medalion Racing Exhaust, and the Single Muffler Dual Tip is called the Tanbe Super Medalion Hyper Exhaust.

There is even the Tanabe Ultra Medalion which is Single muffler, single tip exhaust.

 

All I'm saying with the "math" is that for the STOCK y-pipe,

the total flow cross-sectional area at the inlet is 1.28 times bigger than at the outlet. This means the exhaust should accelerate through the y pipe's outlet.

The HKS y-pipe has a larger inlet and a smaller outlet. So it may form a restrictive nozzle-type of effect, which could increase backpressure.

The Tanabe exhaust I'm referring to is the Tanabe Medalion Touring exhaust. It is relatively new, I saw it at the performance nissan meet and I liked the sound a lot (Very quiet). It is listed on their website along with sound clips.

To be honest I forget how the medalion touring looks, but I think it is basically a midpipe that splits into two exit mufflers.

 

Also, i found great prices on Tanabe exhausts..

$360 for the Y Pipe, $610 for the Single Muffler Dual Tip, and $650 for the Dual Muffler Dual TIp exhaust.

PM me if ya want to know the site.

Right now, im kinda on the fence between the Tanabe Single Muffler Dual Tip, and a Fujitsubo Legalis R. With either of those exhaust i plan on using the Tanabe Y Pipe which is 60MM inlets and 70mm outlet.

The Tanabe exhaust is 70mm, and the Fujitsubo is 76mm, i would get the Tanabe if i knew it was nearly as quite as the Fujitsubo. But its hard to find any reviews on the Tanabe Single Muffler Dual Tip

 

yeah dude please pm me

 

Wired 24/7 - very interesting thread. However, 1 suggestion, you made your math a lil bit too much complicated. let's now worry about input and output area first, but just the diameter. Which is common and easy to understand. The diameter is what specified the rest.

So based on your research.

A. Stock Y-pipe has 2" OD (outer Diameter) input and 2.5" OD output. So is the Y-back exhaust 2.5" OD pipes?
B. Did you find out the diameters of the stock Catalytic input and output?
C. How about stock header's output - AKA collector output?

To make it simplier? Go with a header

 

I emailed crawford and they said that the crawford cats diameters are the same as stock (also confirmed that they are 2.25").

So that means stock cats are 2.25 as well? Then is the stock y-pipe REALLY 2" -> 2.5" ??

If the crawford cats are really the same size as stock cats I will probably get them by themselves.

 

For the record, Kinetix cats are 2.25" Outer Diameter and 2.13" Inner Diameter (direct email from kinetix.)

Looks like I might go with kinetix cats since they're much cheaper, not sure yet.

 

Thanks Wired 24/7 for the info.

so, if the information is right, according to Crawford, the stock cat is 2.25" in/out?? But g35strongman said that, stock Y pipe is started at 2". That doesn't make sense.

can someone please confirm this?

 

I talked to both kinetix and crawford via email.

They BOTH said that their cats were basically designed to mate up with the stock y-pipe. In other words, stock y-pipe would be about 2.25" inlet.

I am 99% sure I am going with JUST CATS, one brand or the other. I am very happy right now, because IMO catback exhausts are a big $$$$$ item and are mostly just for aesthetics (looks and sound) if you're N/A. This is just my opinion of course. Secondly, I happen to love the sound of stock exhaust, so I am ecstatic that I can just change the cats out to hopefully amplify the volume of the sound I love.

My idea from the beginning (and my reason for creating this thread) is just to eliminate the worst part of the exhaust i.e. the cats. This way I can make a small change rather than a big change. Then instead of spending $1k+ on a catback exhaust that won't do much, I will spend that $1k on engine management and tuning.

At first I was getting discouraged and I thought that I would need a catback exhaust to mate up with the aftermarket cats.

Now after doing my research I have come to the conclusion that this is not necessary. I would of course get a huge piping exhaust if I were going F/I which I may consider in the next couple of years, but it's simply not happening with my small researcher salary (pays for rent, insurance, gas, not much else hehe) anytime soon. I have already used up too much of my savings on mods lol.