3" or 2.5" duel exhaust (what's better?) and X-pipe
11-09-2010, 01:07 PM
#1
Race Director
Thread Starter
3" or 2.5" duel exhaust (what's better?) and X-pipe
currently I have a 2 1/2" duel exhaust on Baby..... dyno numbers at the rear wheels are ~440tq and ~440hp ... this is a 383 stroker...
I was on the phone with Borla, working on ordering a new set of 3" Borla's to replace my 2.5" Borla's since I was going to go to a 3" duel mandrel bend exhaust. they ask me what my set up was and what hp i was at... they then informed me that a 3" exhaust would in fact DECREASE HP because of lack of scavenging, and to stay with the 2.5" .... They said they have run many Dyno's on all there systems and have found that engines producing less than 600 crank HP actually looses power going from a 2.5 to a 3" ..... So they recommend staying with 2.5"............ Opinions?
Also, on a side note i ask them about the X-pipe, and told them it would be mounted about 3' behind the headers....(under the rear end) they informed me that it would do nothing for the power that far back, but would mellow the sound.... Opinions?
I was on the phone with Borla, working on ordering a new set of 3" Borla's to replace my 2.5" Borla's since I was going to go to a 3" duel mandrel bend exhaust. they ask me what my set up was and what hp i was at... they then informed me that a 3" exhaust would in fact DECREASE HP because of lack of scavenging, and to stay with the 2.5" .... They said they have run many Dyno's on all there systems and have found that engines producing less than 600 crank HP actually looses power going from a 2.5 to a 3" ..... So they recommend staying with 2.5"............ Opinions?
Also, on a side note i ask them about the X-pipe, and told them it would be mounted about 3' behind the headers....(under the rear end) they informed me that it would do nothing for the power that far back, but would mellow the sound.... Opinions?
11-09-2010, 01:31 PM
#2
Race Director
Do you plan on doing anything to increase the power in the future ? 440HP at the wheels is getting up there in the HP range to around 550HP on an engine dyno 
11-09-2010, 01:39 PM
#3
Le Mans Master
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So if the 2.5 inch system makes more power than a 3 inch system would, why not switch to a 2 inch system and make even more power? That Borla guy doesn't know what he's talking about.
What kind of exhaust do you see on engine dynos? The biggest pipes and mufflers possible.
What kind of exhaust do you see on engine dynos? The biggest pipes and mufflers possible.
11-09-2010, 02:06 PM
#4
I have heard of this before and the Borla guy is correct. It is all about air movement and physics. Some engines need back pressure on the exhaust side to make power. Ever driven a stock car with no muffler? Runs like crap and sounds like a crap. I have always run 2.5" exhaust my muscle cars, all making 300hp - 400hp it was perfect. Never tried 3" as all of the exhaust shops even said it was over kill and would hurt the performance than help it.
11-09-2010, 02:09 PM
#5
Race Director
Thread Starter
Can't believe i am going to say this....but no...... the engine is done, other than maintenance. It is the quickest and fastest engine I have ever built. it SMOKES my C5, and will keep up with many of the C6Z06 cars to ~140... run out of RPM...
no, my new $$$ is going to go to a new Richmond 4+1 transmission (overdrive!!!)... running down the freeways at 3-4Krpm has got to stop...about the only thing left to do to this engine is put a bigger one in.... and that is not going to happen. (wife would have a hart attack!!)
so, 2.5" or 3"
11-09-2010, 02:26 PM
#7
Race Director
Thread Starter
a story about a 2 stroke dirt bike..... have been racing and riding dirt bikes since i was 5, and I had this one bike about 10 years ago and it normally ran great!.... one day i took it out and while I was ridding I noticed the power was way way down... i though maybe i scored the piston... took it back home and started troubleshooting the problem... there was a small bend in the pipe, did not think much of it as it was very small.... took the head off and piston and wall looked fine... hmmmmmm... got the torch out and pulled the dent out.... BAMMM... all the power can back... all over a little bend....
the exhaust system is more than a large port to funnel gasses, and there is a lot of engineering behind its construction... if it were just a matter of increasing size I think we all would be looking at 4"..... and there is a reason that so many manufactures, Borla, Magnaflow, and others that do not make a 3" exhaust for our cars and many others. They all want to be the best, offer the best, and if a great increase in hp would always come from bigger pipes, then we would see a lot available... just my thoughts, nothing else...
wish i could see a dyno run between the both.... but i do know that scavenging is important...
the exhaust system is more than a large port to funnel gasses, and there is a lot of engineering behind its construction... if it were just a matter of increasing size I think we all would be looking at 4"..... and there is a reason that so many manufactures, Borla, Magnaflow, and others that do not make a 3" exhaust for our cars and many others. They all want to be the best, offer the best, and if a great increase in hp would always come from bigger pipes, then we would see a lot available... just my thoughts, nothing else...
wish i could see a dyno run between the both.... but i do know that scavenging is important...
11-09-2010, 03:50 PM
#9
Team Owner
The truth is there are lots of so call experts out there with a whole following of stupid sheep and bubba mechanics. You also have the morons and bull Shi***ers.
Like a few Sundays ago when that NASCAR car landed upside down at Talledega. That was the biggest X box and pipe system I've seen and that is on the lower hp restrictor plate motors.
Ever ask your self why uncapped headers with 8 - 14 inch collector extensions make the most power. Surely a million racers can't be all wrong when BUBBA says it makes more power with a 2.5 inch exhaust.
I will say this. Without proper tuning you can actually loose power going to a nonrestrictive exhaust. Nonrestrictive exhaust systems use less timing because of less burnt gas dilution which slows flame travel. You also require larger jets to get the new cleaner mixture in the cylinders, air fuel ratio right.
Like a few Sundays ago when that NASCAR car landed upside down at Talledega. That was the biggest X box and pipe system I've seen and that is on the lower hp restrictor plate motors.
Ever ask your self why uncapped headers with 8 - 14 inch collector extensions make the most power. Surely a million racers can't be all wrong when BUBBA says it makes more power with a 2.5 inch exhaust.
I will say this. Without proper tuning you can actually loose power going to a nonrestrictive exhaust. Nonrestrictive exhaust systems use less timing because of less burnt gas dilution which slows flame travel. You also require larger jets to get the new cleaner mixture in the cylinders, air fuel ratio right.
Last edited by gkull; 11-09-2010 at 05:40 PM.
11-09-2010, 05:08 PM
#11
Race Director
MagaFlow and Borla don't make exhaust systems for our C3's because they are rated at 200HP and have a hard time getting out of there own way.
Put a 600HP mill in a C3 and ask them what size pipe they would they would recommend. gkull is right you have to tune the motor properly for the pipe size.
My 406ci was on a engine dyno with 2 inch primary headers and it makes the most power that way. You have to jet up for bigger pipes as I had to jet down when I put it back in my Vette with 1 3/4 " primary headers and 2 1/2" exhaust.
These guys on the tech lines know nothing, 10 bucks an hour if they knew anything they wouldn't be answering a phone for peanuts
Put a 600HP mill in a C3 and ask them what size pipe they would they would recommend. gkull is right you have to tune the motor properly for the pipe size.
My 406ci was on a engine dyno with 2 inch primary headers and it makes the most power that way. You have to jet up for bigger pipes as I had to jet down when I put it back in my Vette with 1 3/4 " primary headers and 2 1/2" exhaust.
These guys on the tech lines know nothing, 10 bucks an hour if they knew anything they wouldn't be answering a phone for peanuts
11-09-2010, 05:41 PM
#12
Burning Brakes
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Your engine doesn't pump enough air to justify larger pipes. If you think you need larger pipes to get that extra .5 HP, just install a set of electrically operated exhaust cutouts and open them up when you want to make it 'really' go.
11-09-2010, 05:56 PM
#13
Le Mans Master
The truth is there are lots of so call experts out there with a whole following of stupid sheep and bubba mechanics. You also have the morons and bull Shi***ers.
Like a few Sundays ago when that NASCAR car landed upside down at Talledega. That was the biggest X box and pipe system I've seen and that is on the lower hp restrictor plate motors.
Ever ask your self why uncapped headers with 8 - 14 inch collector extensions make the most power. Surely a million racers can't be all wrong when BUBBA says it makes more power with a 2.5 inch exhaust.
I will say this. Without proper tuning you can actually loose power going to a nonrestrictive exhaust. Nonrestrictive exhaust systems use less timing because of less burnt gas dilution which slows flame travel. You also require larger jets to get the new cleaner mixture in the cylinders, air fuel ratio right.
Like a few Sundays ago when that NASCAR car landed upside down at Talledega. That was the biggest X box and pipe system I've seen and that is on the lower hp restrictor plate motors.
Ever ask your self why uncapped headers with 8 - 14 inch collector extensions make the most power. Surely a million racers can't be all wrong when BUBBA says it makes more power with a 2.5 inch exhaust.
I will say this. Without proper tuning you can actually loose power going to a nonrestrictive exhaust. Nonrestrictive exhaust systems use less timing because of less burnt gas dilution which slows flame travel. You also require larger jets to get the new cleaner mixture in the cylinders, air fuel ratio right.
100%
3" all the way if you make 500 crank HP or more...
11-09-2010, 06:32 PM
#14
Tech Contributor
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I have heard of this before and the Borla guy is correct. It is all about air movement and physics. Some engines need back pressure on the exhaust side to make power. Ever driven a stock car with no muffler? Runs like crap and sounds like a crap. I have always run 2.5" exhaust my muscle cars, all making 300hp - 400hp it was perfect. Never tried 3" as all of the exhaust shops even said it was over kill and would hurt the performance than help it.
11-09-2010, 06:36 PM
#15
Tech Contributor
Member Since: Jun 2004
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The truth is there are lots of so call experts out there with a whole following of stupid sheep and bubba mechanics. You also have the morons and bull Shi***ers.
Like a few Sundays ago when that NASCAR car landed upside down at Talledega. That was the biggest X box and pipe system I've seen and that is on the lower hp restrictor plate motors.
Ever ask your self why uncapped headers with 8 - 14 inch collector extensions make the most power. Surely a million racers can't be all wrong when BUBBA says it makes more power with a 2.5 inch exhaust.
I will say this. Without proper tuning you can actually loose power going to a nonrestrictive exhaust. Nonrestrictive exhaust systems use less timing because of less burnt gas dilution which slows flame travel. You also require larger jets to get the new cleaner mixture in the cylinders, air fuel ratio right.
Like a few Sundays ago when that NASCAR car landed upside down at Talledega. That was the biggest X box and pipe system I've seen and that is on the lower hp restrictor plate motors.
Ever ask your self why uncapped headers with 8 - 14 inch collector extensions make the most power. Surely a million racers can't be all wrong when BUBBA says it makes more power with a 2.5 inch exhaust.
I will say this. Without proper tuning you can actually loose power going to a nonrestrictive exhaust. Nonrestrictive exhaust systems use less timing because of less burnt gas dilution which slows flame travel. You also require larger jets to get the new cleaner mixture in the cylinders, air fuel ratio right.
Keep up the good work, George.
11-09-2010, 07:04 PM
#16
Le Mans Master
It all comes down to the venturi affect. Large pipes can cause the exhaust gas to slow down and cool off forcing the engine to work harder to push it out. Add a turn or two, shrink the diameter and the venturi affect causes the gas to speed back up allowing the gas to exit quick, the engine to not work as hard and hp to go. Some people attribute that to backpressure. At least thats the explanation my physics professor told me.
11-09-2010, 07:21 PM
#17
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It all comes down to the venturi affect. Large pipes can cause the exhaust gas to slow down and cool off forcing the engine to work harder to push it out. Add a turn or two, shrink the diameter and the venturi affect causes the gas to speed back up allowing the gas to exit quick, the engine to not work as hard and hp to go. Some people attribute that to backpressure. At least thats the explanation my physics professor told me.
11-09-2010, 07:35 PM
#18
Le Mans Master
11-09-2010, 07:39 PM
#19
Melting Slicks
In my opinion you will lose power w/ the 3" pipes. Borla makes some of the best pipes in the world and they know more then the rest of us. When the local Nascar track was forced to run mufflers they broke the track record in every class. You need the "right" back pressure and 3" won't work as well as your present setup.
Last edited by BPHORSEGUY; 11-09-2010 at 07:41 PM. Reason: sp
