Exhaust Help-I Know, Here We Go Again!
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Pro
Joined: Jan 2008
Posts: 657
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From: Sykesville Maryland
Exhaust Help-I Know, Here We Go Again!
I've been searching the forum and doing a lot of research about what I want and how much I want to spend. Every time I think I'm there, I get a little more confused.
I need to replace everything-currently have swiss cheese and muffler eliminators. Don't have to worry about emissions since it's tagged historic but I do want to maintain stock status but willing to compromise a bit on the exhaust.
I'm looking at a 2.5" front Y (O2 bung with no pre cats) High flow cat and either a Magnaflow cat back or B & B cat back system.
Will eliminating the pre cats mess with the ECM? Will the larger front Y create more heat since I'm tucking more pipe in there or will the added flow rate keep it cooler? Are there noticeable advantages to going 2.5".
Any opinions on cat back systems? I want it toned down from what I have now with the eliminators and still maintain a nice growl. Any resonance issues? Will there be any performance gains in this set up?
I did have a guy tell me that if I go with true dual exhaust and eliminate the cat I'll lose torque on my '86. Can that be true?
I need to replace everything-currently have swiss cheese and muffler eliminators. Don't have to worry about emissions since it's tagged historic but I do want to maintain stock status but willing to compromise a bit on the exhaust.
I'm looking at a 2.5" front Y (O2 bung with no pre cats) High flow cat and either a Magnaflow cat back or B & B cat back system.
Will eliminating the pre cats mess with the ECM? Will the larger front Y create more heat since I'm tucking more pipe in there or will the added flow rate keep it cooler? Are there noticeable advantages to going 2.5".
Any opinions on cat back systems? I want it toned down from what I have now with the eliminators and still maintain a nice growl. Any resonance issues? Will there be any performance gains in this set up?
I did have a guy tell me that if I go with true dual exhaust and eliminate the cat I'll lose torque on my '86. Can that be true?
Melting Slicks
Joined: Jan 2008
Posts: 2,065
Likes: 1
From: Jasper Texas
Yes, you will lose a little low end torque by going to a true dual setup, but not enough to worry about, especially with a tpi setup. Alot of people don't support the true dual setup here, but I went ahead and did it.
Here is a vid clip of headers straight back to flowmasters for you, with a little engine work.
http://s273.photobucket.com/albums/j...t=100_0621.flv
It is also very quiet in the car while at highway speeds.
Here is a vid clip of headers straight back to flowmasters for you, with a little engine work.
http://s273.photobucket.com/albums/j...t=100_0621.flv
It is also very quiet in the car while at highway speeds.
Last edited by cwyates4; Jul 25, 2008 at 11:50 PM.
Advanced
Joined: Feb 2005
Posts: 77
Likes: 0
From: N. Tonawanda NY
I replaced my front Y pipe with a 2 1/2" with no precats and a new high flow main cat. Works great! It runs with less heat because of the front cats being gone. I had a Flow Master cat back system on the car before I replaced the front Y, it sounded better and louder with the new Y. No issues with the ECU and it runs better. With just the exhaust and a new tranny rebuild I had it dynoed, it pulled 236hp at the rear wheels. Factory rates the 90 L98 @ 245 hp. So I would say it helps.
Team Owner
Joined: Jul 2004
Posts: 28,459
Likes: 3,288
From: Hartford WI
I would think that in true duals you will lose some scavenging unless you add some sort of crossover pipe. In any case, why bother? True duals have not shown to be helpful in street applications. Maybe a race application and the ricer effect but I have yet to see a test that proves true duals are better.
Tech Contributor
Joined: Jun 2004
Posts: 20,894
Likes: 962
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Think about how an engine makes power (horsepower or torque, take your pick). It takes cylinder pressure. How do you maximize cylinder pressure? Maximize the amount of fresh air getting into the cylinders, and maximize the amount of exhaust gas you remove from the cylinders. A restrictive single exhaust and cat are not the way to go, as it increases the amount of residual exhaust gas in the cylinder, and thereby reduces the space available in the cylinder to induct more fresh air. To promote increased airflow (and cylinder VE), reduce the exhaust restriction as much as your ears (and community sensibilities) allow.
Team Owner
Joined: Jul 2004
Posts: 28,459
Likes: 3,288
From: Hartford WI
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I'm looking at a 2.5" front Y (O2 bung with no pre cats) High flow cat and either a Magnaflow cat back or B & B cat back system.
Will eliminating the pre cats mess with the ECM?
No.
Will the larger front Y create more heat since I'm tucking more pipe in there or will the added flow rate keep it cooler?
Likely cooler.
Are there noticeable advantages to going 2.5".
Yes, over stock.
Any opinions on cat back systems?
Based on personal preference alone, you must hear them yourself.
Any resonance issues?
Possibly, depends on what catback you run.
Will there be any performance gains in this set up?
Yes, roughly 10-15hp, depending on what you do exactly, maybe a little more.
I did have a guy tell me that if I go with true dual exhaust and eliminate the cat I'll lose torque on my '86. Can that be true?
You dont lose it, you just move it up in the powerband and you end up with more at peak.
Will eliminating the pre cats mess with the ECM?
No.
Will the larger front Y create more heat since I'm tucking more pipe in there or will the added flow rate keep it cooler?
Likely cooler.
Are there noticeable advantages to going 2.5".
Yes, over stock.
Any opinions on cat back systems?
Based on personal preference alone, you must hear them yourself.
Any resonance issues?
Possibly, depends on what catback you run.
Will there be any performance gains in this set up?
Yes, roughly 10-15hp, depending on what you do exactly, maybe a little more.
I did have a guy tell me that if I go with true dual exhaust and eliminate the cat I'll lose torque on my '86. Can that be true?
You dont lose it, you just move it up in the powerband and you end up with more at peak.
Tech Contributor
Joined: Jun 2004
Posts: 20,894
Likes: 962
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Remember, it's all about pumping air.
Intermediate
Joined: Jun 2008
Posts: 43
Likes: 0
From: Franklin TN
When he says you'll lose torque, I'll bet he means low end torque. Personally, I don't care much about the low end. In a racing application, I get out of the low end during 1st gear, then never see it again. I want horsepower in the 4-6k rpm range. Also, he's probably referring to the tuning of your exhaust's pressure waves. These waves are complicated, so unless you have your entire system tuned with a specific goal in mind, I expect you won't get much out of these anyway (I'm not saying its not worth it, just that you'll have to really put some thought into it).
Heel & Toe
Joined: Aug 2007
Posts: 15
Likes: 0
I replaced my front Y pipe with a 2 1/2" with no precats and a new high flow main cat. Works great! It runs with less heat because of the front cats being gone. I had a Flow Master cat back system on the car before I replaced the front Y, it sounded better and louder with the new Y. No issues with the ECU and it runs better. With just the exhaust and a new tranny rebuild I had it dynoed, it pulled 236hp at the rear wheels. Factory rates the 90 L98 @ 245 hp. So I would say it helps.
This sounds like one of the best conservative mods there is for the exhaust system.
BTW: Japicella, ALL exhaust threads are interesting!
Racer
Joined: Apr 2007
Posts: 305
Likes: 0
I wish there were two dyno sheets we could compare for the true duals vs the 2 /1/ 2 exhaust. I'm really stuck in the same mind torture chamber right now. On my mustangs and every other car in the history of the world true duals with an h-pipe or an x-pipe is the way to go. My hot-rodding experience is leaning me this way. BUT......it seems the majority of forum members like the 2 /1/ 2 exhaust. Plus I have never had a car that only likes to rev to 5000 rpms either.....
Intermediate
Joined: Jun 2008
Posts: 43
Likes: 0
From: Franklin TN
I would assume the duals would win out on most setups. I believe that Vader was just saying that the 2.5 Y would be better than stock. That doesn't mean it is best. That is a small pipe for a vette, even stock.
So, x-pipe is best, but a y is at least better than what you've got.
So, x-pipe is best, but a y is at least better than what you've got.
Team Owner
Joined: Jul 2004
Posts: 28,459
Likes: 3,288
From: Hartford WI
I wish there were two dyno sheets we could compare for the true duals vs the 2 /1/ 2 exhaust. I'm really stuck in the same mind torture chamber right now. On my mustangs and every other car in the history of the world true duals with an h-pipe or an x-pipe is the way to go. My hot-rodding experience is leaning me this way. BUT......it seems the majority of forum members like the 2 /1/ 2 exhaust. Plus I have never had a car that only likes to rev to 5000 rpms either.....
Racer
Joined: Apr 2007
Posts: 305
Likes: 0
I would assume the duals would win out on most setups. I believe that Vader was just saying that the 2.5 Y would be better than stock. That doesn't mean it is best. That is a small pipe for a vette, even stock.
So, x-pipe is best, but a y is at least better than what you've got.
So, x-pipe is best, but a y is at least better than what you've got.
Tech Contributor
Joined: Jun 2004
Posts: 20,894
Likes: 962
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Yeah, I mean above all it is still a small block chevy. Every hot chevy since 1955 ran a true dual exhaust. The only thing that has me guessing hot-rodding logic is that the powerband on this car really goes no where. A free flowing exhaust is great for the car that can rev up to 6000-6500 rpms. This car in 90% stock form still only revs to 4800-5000 rpms.
Team Owner
Joined: Jul 2004
Posts: 28,459
Likes: 3,288
From: Hartford WI
The benefits of a free flowing exhaust do not magically appear at 6000 RPM. You benefit at all loads and RPMs with a low backpressure exhaust. Other than a reduction of NOx, there's no real performance benefit to having residual exhaust gas remaining in the cylinder, not to mention having the engine work harder to push out the burned exhaust gas against the restriction of a small exhaust pipe.
Drifting
Joined: Sep 2002
Posts: 1,642
Likes: 0
From: Suwanee,Ga
I've been searching the forum and doing a lot of research about what I want and how much I want to spend. Every time I think I'm there, I get a little more confused.
I need to replace everything-currently have swiss cheese and muffler eliminators. Don't have to worry about emissions since it's tagged historic but I do want to maintain stock status but willing to compromise a bit on the exhaust.
I'm looking at a 2.5" front Y (O2 bung with no pre cats) High flow cat and either a Magnaflow cat back or B & B cat back system.
Will eliminating the pre cats mess with the ECM? Will the larger front Y create more heat since I'm tucking more pipe in there or will the added flow rate keep it cooler? Are there noticeable advantages to going 2.5".
Any opinions on cat back systems? I want it toned down from what I have now with the eliminators and still maintain a nice growl. Any resonance issues? Will there be any performance gains in this set up?
I did have a guy tell me that if I go with true dual exhaust and eliminate the cat I'll lose torque on my '86. Can that be true?
I need to replace everything-currently have swiss cheese and muffler eliminators. Don't have to worry about emissions since it's tagged historic but I do want to maintain stock status but willing to compromise a bit on the exhaust.
I'm looking at a 2.5" front Y (O2 bung with no pre cats) High flow cat and either a Magnaflow cat back or B & B cat back system.
Will eliminating the pre cats mess with the ECM? Will the larger front Y create more heat since I'm tucking more pipe in there or will the added flow rate keep it cooler? Are there noticeable advantages to going 2.5".
Any opinions on cat back systems? I want it toned down from what I have now with the eliminators and still maintain a nice growl. Any resonance issues? Will there be any performance gains in this set up?
I did have a guy tell me that if I go with true dual exhaust and eliminate the cat I'll lose torque on my '86. Can that be true?
I replaced the 2-1/4" [w/ pre-cats] on my '89 years ago and went with a Hi Flow cat. My emission numbers IMPROVED!!!
[ added a chip and they improved again, go figure?].
I didn't measure heat but the pre-cats are assumed to add more under hood heat [ their intended function results in just that].
The tone was lower and more mellow, as well.
I would say it is an overall positive thing.
TJM
Racer
Joined: Feb 2008
Posts: 435
Likes: 0
From: Bulverde TX
All sounds pretty good but lets take a look at the pros do to get max power. Largest pipe that you can use without losing to back pressure and an "X" pipe with free flow exhaust after the X pipe if your are the law following type a good free flowing muffler is in order. If the laws do not apply to you forget the muffler.
Oh yea I have 2.5 from front to back with x pipe and cheap mufflers sound pretty good NO CATS
Oh yea I have 2.5 from front to back with x pipe and cheap mufflers sound pretty good NO CATS
Last edited by pearlvett; Aug 5, 2008 at 02:55 PM.