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Discussion Starter · #1 ·
I've had an M&S 3" DP/Cat/Ubend with 2.5" out on my car for a little while now, but having just seen a picture of the stock exhaust manifolds, it seems like that might be too big for me. Am I losing power with the 3" DP, or is the increased Cat flow area making up for it?

Those with experience: should I sell my 3" DP/Cat/Ubend to someone and then buy another 2.5" DP/Cat/Ubend, or should I keep what I have?

I have PEMs on the way, and I have Borla exhaust on right now. I plan on getting rocker arms or a cam soon. Let me know your thoughts.
 

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Here's my experiance

L36 Style--- Open Cone intake and a T stat
* Ubend/Resonator Delete - Seemed to help a little... results seemed negliable
* 3" Downpipe, 3" High Flow cat, coupled with 2.5" to stock Y.... Now... this is what I call gains I noticed a very large increase in top end, with a very negligable loss in low end torque.
* Pulled 3" setup in favor for a 2.5" setup. Lost some top end, gained all of bottom end back... didn't like it, put 3" back on. I like my top end better, 3800s are notorious for low end power, so why not take some low end, make it easier to launch and put it back in the top end.
Took car to track with above exhaust setup and some smallish 2.25" Turbo mufflers and some tips.
15.098 @91.18 MPH, best trap speed was 91.78 MPH


Later on in preperation for Project Boost-A-Slut I removed my stock Y and put in a 2.5" wye. I lost out bad on low end.... scrap the 2.5" wye pipe,

Now...moving on to more present day information
L67 Style.... whole bunch of mods to it starting off with TOG headers.

This is going to deal strictly with the Y pipe and I'm not going to say much more than this, I saw absolutly NO losses going from a IMO crap designed 2.5" wye pipe to a much better designed 2.25" wye pipe. Now on the flip side, I saw no gains either, except for a little less drone.

So I guess my point is in all this...

for L36s
3" Downpipe, (optional Cat) 2.5" pipe to 2" wye pipe

for L67
3" Everything to the 2.25" wye pipe

For Retarded L67 - Open TOGs
 

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I would stay with what you got,I have a Random Technology 3" HFC and Borla exhaust and love it. Add some headers and your golden.
 

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I can't say as I agree. I custom fabbed a 3" DP, and found it to be too free flowing. I experimented with inserts right behind the manifold, and found the most all-around power by using a 3" to 2 1/2" reducer inside the pipe. It's not a matter of too much flow, it's poor velocity. It dumps out of the manifold quick and comes to a stop, causing a bunch of reversion. The factory flex (even though it's a big restriction) plays an important role in combatting reversion. Try playing with different inserts like I have, and you'll see what I mean. There aren't any inserts like I suggest on the market, they have to be cusom made, but it's not too hard if you get one of the reducer cones and experiment.
 

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Discussion Starter · #5 ·
Here's why I started thinking about changing it out for a 2.5"... I saw a picture of the stock exhaust manifold outlet and saw that it was a good bit smaller than 3" in there... seems like going from way smaller than 3" to 3" would be a huge hit on velocity. I have some PEMs on the way, and that should help out on the manifold problem a little bit, but I'm not sure how much because I doubt the manifold can be ported much right there. Anyway- I don't have a supercharger/turbo, and I plan on staying N/A... I do plan on rockers or a cam in the near future. I'd love some more opinions... Thanks for the help guys! Good stuff
 

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If you weld the outer circumferance you can open the inside to 3",if your planning on a cam the 3"dp is a good choice,I noticed a lot smoother tourqe curve with pems and a 3"dp.
 

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Discussion Starter · #7 ·
I emailed Zooomer about it and he said I should probably keep the 3" DP...... and that I might be better off upgrading my Borla exhaust system! That took me as a total shock because I always thought of Zooomer as a promoter of smaller exhausts to get better velocity...... but on with my questions...

What do y'all think of Zooomer suggesting I upgrade my Borla? Wow, really shocked by that suggestion... How big is the Borla? I always thought it was 2.5" into 2x2.25", but Zooomer says it's smaller.... I'd love some opinions on this!
 
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