custom exhaust question
#1
Registered User
Thread Starter
Join Date: Jun 2004
Location: Bucks County, PA
Posts: 79
Likes: 0
Received 0 Likes
on
0 Posts
custom exhaust question
here is what im thinking...
as exhaust gasses get further from the headers, it cools and needs less pipe diameter to flow at the same rate, therefore wouldnt i experience better performance if i did 2.5 from headers to the cat and then 2.25 the rest of the way? and what if i did a flowmaster with single in and 2 out. (in that case, 40 or 50 series?) and for headers i am debating nwor, downey, and doug thorley
i have a 3.0
anyone have any experience with any of this and sound clips would be great for any of the headers and flowmasters
thanks ahead of time
as exhaust gasses get further from the headers, it cools and needs less pipe diameter to flow at the same rate, therefore wouldnt i experience better performance if i did 2.5 from headers to the cat and then 2.25 the rest of the way? and what if i did a flowmaster with single in and 2 out. (in that case, 40 or 50 series?) and for headers i am debating nwor, downey, and doug thorley
i have a 3.0
anyone have any experience with any of this and sound clips would be great for any of the headers and flowmasters
thanks ahead of time
#2
your logic sounds correct, but in real world, the temp at teh tailpipe is still pretty hot.... 2.25 all the way through sounds fine... be warned though, if you go with dual outs, you may lose backpressure as dual 2.25 outs is a lot more flow than a single 2.25
#3
Registered User
Thread Starter
Join Date: Jun 2004
Location: Bucks County, PA
Posts: 79
Likes: 0
Received 0 Likes
on
0 Posts
yes but is dual 2.25 out of a single muffler much more than 2.5?
what if i tapered the exhaust from 2.25 out of the muffler to 2.0 and then put on nice looking tips?
what if i tapered the exhaust from 2.25 out of the muffler to 2.0 and then put on nice looking tips?
Last edited by gtm130; 07-05-2004 at 08:25 PM.
#4
Contributing Member
Join Date: Feb 2003
Location: Kansas City, KS
Posts: 586
Likes: 0
Received 0 Likes
on
0 Posts
Your really set on gettin this 3.0 pepped up. Good luck man. As for the exhaust I would just go with a single pipe. Seems like dual would be just for looks.
#6
Registered User
Thread Starter
Join Date: Jun 2004
Location: Bucks County, PA
Posts: 79
Likes: 0
Received 0 Likes
on
0 Posts
i think im gonna stay away from dual. so....
2.5 from headers back
2.25 from headers back
2.5 to cat, 2.25 cat back
2.25 to cat, 2.0 cat back?
also... do i run it in the stock location or run it out the back next to the hitch? i dont do serious wheeling so is there any performance for strait as opposed to bent out the side?
2.5 from headers back
2.25 from headers back
2.5 to cat, 2.25 cat back
2.25 to cat, 2.0 cat back?
also... do i run it in the stock location or run it out the back next to the hitch? i dont do serious wheeling so is there any performance for strait as opposed to bent out the side?
Last edited by gtm130; 07-05-2004 at 08:29 PM.
#7
i would do 2.5 to cat then 2.25 out.... single pipe.. there is not real performance gains for duals on a v6
and as far as duals go.. exiting duals with 2,25" will try and flow a lot more air than a single 2.5" will provide, thus losing backpressure... especially with a high performance exhuast which is designed to scavenge gasses
and as far as duals go.. exiting duals with 2,25" will try and flow a lot more air than a single 2.5" will provide, thus losing backpressure... especially with a high performance exhuast which is designed to scavenge gasses
Trending Topics
#8
Registered User
Thread Starter
Join Date: Jun 2004
Location: Bucks County, PA
Posts: 79
Likes: 0
Received 0 Likes
on
0 Posts
thats what i was thinking, but the nwor header's y pipe is 2.25 so it would be 2.25 all the way through if i went with that.
still waiting to see if anyone has used these headers other than downey.
still waiting to see if anyone has used these headers other than downey.
#10
Registered User
Thread Starter
Join Date: Jun 2004
Location: Bucks County, PA
Posts: 79
Likes: 0
Received 0 Likes
on
0 Posts
that looks nice but you have forced induction and no backpressure problems, i need the backpressure. you could run 3" without a problem where i would loose power there.
also, in the winter, one pipe will have have "smoke" coming out and the other wont so your little secret is given away. id rather not pay for something not functional as well.
also, in the winter, one pipe will have have "smoke" coming out and the other wont so your little secret is given away. id rather not pay for something not functional as well.
Last edited by gtm130; 07-06-2004 at 05:52 AM.
#11
Contributing Member
Originally Posted by gtm130
here is what im thinking...
as exhaust gasses get further from the headers, it cools and needs less pipe diameter to flow at the same rate
as exhaust gasses get further from the headers, it cools and needs less pipe diameter to flow at the same rate
I'm going to go ahead and say a full 2.5" system would be awesome, and sound really good too. 2.25" is also good as long as you have a good cat and muffler, but if your header has a 2.5" collector, why not just stay there?
#12
Contributing Member
Originally Posted by gtm130
yes but is dual 2.25 out of a single muffler much more than 2.5?
3.141 * (2.5/2)^2 = 4.908 in^2 area for single 2.5"
3.141 * (3.0/2)^2 = 7.06 in^2 area for single 3"
In essence, to get flow <similar> to a dual 2.25", you would need something like 3.125".
#13
Registered User
Thread Starter
Join Date: Jun 2004
Location: Bucks County, PA
Posts: 79
Likes: 0
Received 0 Likes
on
0 Posts
thanks for that technical data.
but i was under the impression from my chem classes in highschool way back when tha the hotter the gas, the less dense, meaning more volume, cooler gasses = more dense and less volume? correct me if im wrong but i think thats right.
heres the problem. nwor headers have a 2.25 y pipe. downeys i think is 2.5 and thorley i dont know anything about.
but i was under the impression from my chem classes in highschool way back when tha the hotter the gas, the less dense, meaning more volume, cooler gasses = more dense and less volume? correct me if im wrong but i think thats right.
heres the problem. nwor headers have a 2.25 y pipe. downeys i think is 2.5 and thorley i dont know anything about.
#14
Contributing Member
Originally Posted by gtm130
but i was under the impression from my chem classes in highschool way back when tha the hotter the gas, the less dense, meaning more volume, cooler gasses = more dense and less volume? correct me if im wrong but i think thats right.
That being said, I would go for the downey (2.5" collector) and keep 2.5" all the way back. This will be especially beneficial for mid to top end gain (about 2500 to 5500), but you may lose a tiny bit in low end (under about 1500 rpms), probably not noticeable.
The 2.5" will be a good choice for exhaust size IMO.
#17
Contributing Member
Originally Posted by gtm130
thanks, i see you have a flowmaster as well, how does it sound? and do you have the headers as well?
The flowmaster is a good choice, it sounds deep and powerful, with little to no interior reverb (I feel like it has less obnoxious backfiring or high pitch noise, better than a magnaflow or the like IMO). I got center in/offset out and it fit quite well.
#18
Registered User
First off, you should be talking about cross sectional area, not surface area when dealing with flowrates. (flow rate, or M-dot as we call it, is the densityXvelocityX cross-sect area)
The amount of gasses as far as number of molecules going into the pipe equal that going out. As the gasses cool, and they DO cool, they will take up less space and cause less pressure. (pv=nrt) The pressure will affect scavenging. Whether or not it's in a good or bad way is another story.
Unless you want to get on a dyno and try some different sizes, you are probably fine just sticking with the 2.25" all the way out.
Another thing to consider, since you are modding in stages, what might be the optimum diameters now, might not be after say some intake work. Since the exhaust is probably the largest bottle neck, it's a good way to start. After all is said and done, if you are curious and can find some shop to accomodate you, maybe you can run the truck ona dyno with the cat back, off, a 2" mock up, and your existing set up. Then you'll know for sure.
Frank
The amount of gasses as far as number of molecules going into the pipe equal that going out. As the gasses cool, and they DO cool, they will take up less space and cause less pressure. (pv=nrt) The pressure will affect scavenging. Whether or not it's in a good or bad way is another story.
Unless you want to get on a dyno and try some different sizes, you are probably fine just sticking with the 2.25" all the way out.
Another thing to consider, since you are modding in stages, what might be the optimum diameters now, might not be after say some intake work. Since the exhaust is probably the largest bottle neck, it's a good way to start. After all is said and done, if you are curious and can find some shop to accomodate you, maybe you can run the truck ona dyno with the cat back, off, a 2" mock up, and your existing set up. Then you'll know for sure.
Frank
#19
Contributing Member
Originally Posted by elripster
First off, you should be talking about cross sectional area, not surface area when dealing with flowrates. (flow rate, or M-dot as we call it, is the densityXvelocityX cross-sect area)
I stand with 2.5"...
#20
Registered User
Join Date: May 2004
Location: 100 miles offshore as much as possible, & Springfield Oregon USA
Posts: 3,291
Likes: 0
Received 0 Likes
on
0 Posts
gtm130, the reduction in pipe size over distance would be correct if you were building a fireplace flue, where you need to accellerate the flow over distance and at the same time compensate for the gas cooling (othewise smoke up the house...) But here the gasses are being pumped out, and only a little backpressure is needed. I would guess that if stepping down the pipe size worked better in a car, all the aftemarket systems (Borlas etc) would come that way...
jason B - that looks cool with those big tips, but I'd smash em to pulp in minutes the first trail I hit... <grin>
jason B - that looks cool with those big tips, but I'd smash em to pulp in minutes the first trail I hit... <grin>