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FWIW, a 2.5L engine at ~14PSI will put out the same amount of exhaust as a 5.0L engine. I was under the impression the Bosal exhaust was 2.5" ID pipes, then split to two 2.25" ID pipes. Plus, they are straight-through design mufflers/resonator. If a 5.7L engine is fine with a single 3" (Camaro, Firebird, Corvette), why can't a roughly 3.7L engine be fine with a 2.5" ? You also have to look at the exhaust components in front of the cat. Is the smallest piece equivelant to a 3" ID pipe? Still keep in mind the velocity factor. Oh, and the stock Y-pipe sucks 
-Auto Mak or-
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SuperChipFOR SALE
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Joined: Sep 2000
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Hard-core CEG'er
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Because a 5.7L engine is NOT fine with a single 3" exhaust. The F-bodies are just hosed by poor underbody design (ring a bell  )
Also there are companies that make larger exhausts (3.5" & IIRC even 4") for the F-bodies that show power improvements over the 3" systems.
There are even people that feel 2" duals are too small for a really hot 3L and too small for any S/C SVT's.
2.5" single is only ~75% of 2" duals (like I mentioned) Plus all the other drawbacks of having one larger pipe! (like I mentioned)
If one was going to still use this "sucky" (as you mentioned ) Y-pipe design and has a moderately modified SVT (~175FWHP) or below then 2.5" O.D. piping would be plenty for them. Not ideal or the best, but definitely would work well.
I'd highly recommend an aftermarket Y-pipe to get the most gains. (which is basically 2" duals Y'd into one 2.5" pipe!)
2000 SVT #674
13.47 @ 102 - All Motor!
It was not broke; Yet I fixed it anyway.
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Joined: Jun 2001
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Hard-core CEG\'er
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for all you out there who may think that larger diameter will produce more power- I have an idea- go listen to the tape on headers by Headers by Mike IIRC- this will astound you- he has been makeing custom headerand exhaust comboes since the 60's. He really knows his stuff- and the funny thing is that he is all about flow rates, and velocity- not diameter- so usually a single step smaller will provide more horsepower! I dont remember the exact example he uses on the tape - but he states that when he went from a IIRC 2inch header to a 1 and 7/8 he gained almost a half second on his E/T. This theory of his is amazing and will change how you look at exhausts! A MUSTread!
PS- for what its worth a 427 Cobra loses about 100hp through its exhaust. Yes those Fabulous 2" tube headers into a 4" exhaust coming out the sides(usually with a glasspack or similar) LOSES CLOSE TO 100HP
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Joined: May 2002
Posts: 388
CEG\'er
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so with all this talk about doing 3'' exhaust on the street flight setup would be a bad ideah????????
2000 t-red SVT
****too quick for civics****
i have a few tricks up my sleeve
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Joined: Dec 2001
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Hard-core CEG'er
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you have to remember, if this guy is working with NA applications, it's a lot different. . .
FI is forcing air in, you don't even really have to change headers out on an FI s/c since the flow is that much the better, so I think this dude's theory may stand on certain NA app's, but as far as tc, the wider the better since it RUNS on exhaust gases velocity exiting in order to turn the turbine to pump the air in. . ., it'll exit faster if it's BIGGER. OF course headers come with most tc app's, but I'm sure DemonSVT or someone else mentioned you really don't need headers with a sc. . .
just my .02, I may be wrong, everybody has their theories, hell we could banter about this for 200+ posts. . .
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Joined: Apr 2002
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Originally posted by DemonSVT:
There are even people that feel 2" duals are too small for a really hot 3L and too small for any S/C SVT's.
If I was running almost any FI setup I would be using 3" single or 2.25" duals.
But I still do not see how 2" duals on a N/A setup can even be remotely considered too restrictive! I certainly would not consider 2.5" single the perfect race diameter, but even it is only flowing 78% of 2" duals, it is still not holding the car down by any means.
-Giovanni
One turbocharger. Two intercoolers. All love.
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Joined: Aug 2001
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Hard-core CEG'er
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Originally posted by ssmumich00:
you have to remember, if this guy is working with NA applications, it's a lot different. . .
FI is forcing air in, you don't even really have to change headers out on an FI s/c since the flow is that much the better, so I think this dude's theory may stand on certain NA app's, but as far as tc, the wider the better since it RUNS on exhaust gases velocity exiting in order to turn the turbine to pump the air in. . ., it'll exit faster if it's BIGGER. OF course headers come with most tc app's, but I'm sure DemonSVT or someone else mentioned you really don't need headers with a sc. . .
just my .02, I may be wrong, everybody has their theories, hell we could banter about this for 200+ posts. . .
I mentioned before that you don't need headers with FI. However that isn't entirely true. The cost/performance ratio is not good enough for most people to justify it and there are other factors that make header design with turbos a very complicated process.
The part about what you said bigger = faster, is not really true as well as it may not be the whole story. Think of an analogy where you are washing your car on a concrete driveway. You want to push some dirt off the drive with the hose and put your thumb over the end. The water shoots further now than it did before....What's changed? It has a higher velocity now, but the opening is smaller because your thumb is pressed over it. Well, that is the first rule, smaller diameter hole = higher velocity, and also allows the jet of water to shoot further than it normally would. The next factor is volume. If you hold your thumb over the end you are restricting the flow and reducing the volume. Now you may be shooting out a jet of water real far, but you aren't letting out enough water volume to push the dirt off the driveway now. The result is you are letting off the pressure at the thumb and allowing a little more water to come out and provide enough force to push the dirt the rest of the way off the driveway.
This analogy makes sense to me, but then it is friday night and I am buzzing off of a good French wine! 
The moral of the story is that you must restrict the flow to speed up velocity, but you also need to compromise between velocity and volume. There is a 'sweet spot' for exhaust in either turbo or Forced induction where the diameter and the length of the pipes come together to provide the right combination to yield the best power...AT A SPECIFIC RPM! It doesn't apply to the whole rpm range either. Sometimes big power numbers don't tell the whole story. Just compare the vortech kits with 275HP to the streetflight kit at similar HP measurements, 240-290 depending on state of tune, the average being 265HP. The area under the torque curve is hugely in the turbo kits favor and the car should out-accelerate the average vortech kit significantly. (I say average because some people out there have above average kits!!).
warmonger
Former owner of '99 CSVT - Silver #222/2760
356/334 wHP/TQ at 10psi on pump gas!
See My Mods
'05 Volvo S40 Turbo 5 AWD with 6spd, Passion Red
'06 Mazda5 Touring, 5spd,MTX, Black
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If I was running almost any FI setup I would be using 3" single or 2.25" duals.
But I still do not see how 2" duals on a N/A setup can even
so when i put on the street flight kit should i do a single 3'' or could i just have the 3 in the middle and still have it branch off to two pipes in the rear. b/c to be honest i dont want to have just one pipe coming out in the back, i like having dual tips, looks clean.
2000 t-red SVT
****too quick for civics****
i have a few tricks up my sleeve
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Joined: Feb 2001
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Another good analogy from a while ago is the straw analogy: try drinking a coke through a 1/2" straw and a 3" straw. Although the 3" straw has the ability for more volume, most people can't suck hard enough to see the gain. (No jokes guys) This makes sense to me because I've been drinking microbrew. Anyway, I am vorteching my car and keeping the stock exhaust. If you look at the y-pipe, it is rediculously restrictive compared to any cat-back so I put on a shoshop pipe and am calling it good.
95 SE Modded - Gone
98 E0 Black SVT - Gone
98 se sport - Broken
00 T-Red SVT - Nice
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Joined: Jun 2001
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LMAO- you think you know more about exhaust than a man who has been doing it for 40 years? 
RIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIGHT!!
Quote:
[it'll exit faster if it's BIGGER./color]
LOL- again- WHATEVER- FASTER is by a restriced area- ever heard of a venturi?? thats the principle that a carburator works on- narrow the area and the speed through which it flows will increase!
Lets just say you werent yourself when you typed that last post ok? someone stole your log in and posted without your approval!
(FYI- FI or N/A doesnt mean a thing - all it ammounts to is more air entering the system- all an internal combution engine is, is an air pump- wether you pressureize the system or not- its just an airpump- so you just need to design the entire system to be as efficient as possible- you CAN have a N/A system with more than 100% efficiency, and FA systems with less. There are even theoretical systems (Idont remember the designation) were exen the exhaust is supercharged to maintain a pressurized enviroment, so in closeing - remember when you dont know - dont argue!)
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