2.5" exhaust on a stock port?
04-28-10, 01:14 PM
#1
2.5" exhaust on a stock port?
Baja needs a new exhaust. Figured I'd ask in here because we tend to use 2", 2.25" and 2.5".
Is 2.5" too big on a carbed stock port 13B? I want some opinions before I piece together my next exhaust system.
My current system is really loud and doesn't flow worth anything because it is 2" and only two mufflers with a supertrapp tip. The supertrapp is killing flow and HP above 4k. Without the supertrapp, it is too loud for the street. I'd like to stop using the supertrapp. Only two mufflers will fit.
Is 2.5" too big on a carbed stock port 13B? I want some opinions before I piece together my next exhaust system.
My current system is really loud and doesn't flow worth anything because it is 2" and only two mufflers with a supertrapp tip. The supertrapp is killing flow and HP above 4k. Without the supertrapp, it is too loud for the street. I'd like to stop using the supertrapp. Only two mufflers will fit.
04-28-10, 01:16 PM
#2
Oh yeah it has a short primary header, collected into a single 2" RB thickwall pipe and on to the two 2" ID mufflers.
If I went with 2.25", I'd get more muffling potential than 2.5", but also more restrictions.
If I went with 2.5", I'd have less muffling potential but also less restrictions.
I feel I could probably get by with 2.25" if I left the ports alone. Remember this is for a 13B, not a 12A. 2.25 is probably just about right for a stock 13B, maybe. I've already driven it with stock ports on the current tiny 2" exhaust, and it had almost too much low end and tip in but nothing past about 3 or 4k. I need more rev range and maybe a little less low end.
By the way last year I temporarily tested an FC NA engine with an adapted Nikki manifold and carb. This thing had no low end at all but flowed up to about 7k with very little power. The reasons are boring and numerous which I could explain in another post if anyone is curious how it was set up.
Suffice it to say I want something in between these two engines. I feel 74 ports are the way to go. But to get the flow I need to make 74 ports worth using, I'd probably have to go with 2.5" exhaust, wouldn't I?
If I went with 2.25", I'd get more muffling potential than 2.5", but also more restrictions.
If I went with 2.5", I'd have less muffling potential but also less restrictions.
I feel I could probably get by with 2.25" if I left the ports alone. Remember this is for a 13B, not a 12A. 2.25 is probably just about right for a stock 13B, maybe. I've already driven it with stock ports on the current tiny 2" exhaust, and it had almost too much low end and tip in but nothing past about 3 or 4k. I need more rev range and maybe a little less low end.
By the way last year I temporarily tested an FC NA engine with an adapted Nikki manifold and carb. This thing had no low end at all but flowed up to about 7k with very little power. The reasons are boring and numerous which I could explain in another post if anyone is curious how it was set up.
Suffice it to say I want something in between these two engines. I feel 74 ports are the way to go. But to get the flow I need to make 74 ports worth using, I'd probably have to go with 2.5" exhaust, wouldn't I?
04-28-10, 01:29 PM
#4
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baja = need for low and midrange power?
i think provided you get the right mufflers, either 2.25 or 2.5" pipe is fine, noise shouldn't be terrible either way either.
AND AND AND there is no reason you couldn't run 2.5" mufflers on a 2.25 pipe either.
i like big pipes, i think i'd do 2.5" if it was mine, although i doubt 2.25 would be a big difference, its more like i can screw up the 2.5 and it'll work like a well constructed 2.25...
i think provided you get the right mufflers, either 2.25 or 2.5" pipe is fine, noise shouldn't be terrible either way either.
AND AND AND there is no reason you couldn't run 2.5" mufflers on a 2.25 pipe either.
i like big pipes, i think i'd do 2.5" if it was mine, although i doubt 2.25 would be a big difference, its more like i can screw up the 2.5 and it'll work like a well constructed 2.25...
04-28-10, 03:19 PM
#5
Jeezus, I couldn't find any thickwall 2.25". I didn't look very hard, but that's the reason I've never used 2.25" on any of my projects. The most I've found so far is 14 gauge which is more like a medium wall.
Mike, I like the thought that a less than ideal 2.5" system will flow more like an ok 2.25" system, which, as you can see, those 180° u-bends are, yeah.
See those u-bends? They're restrictive, right? If I used 2.5" u-bends they'd probably flow like a straight 2.25.
Those mufflers you see there are actually glasspacks. The little one is a 3" outer shell about 12" or 13" long. The upper one is an old RE glasspack about 20" long and 4" outer shell. Both have a 2" core though I think the hotdog has louvers which effectively make the core more like 1 7/8 or 1 3/4.
I have my eye on a Magnaflow 5" round at 14" long to replace the 3" hotdog and 22" long 4" round Magnaflow for the upper. As you'll notice on the upper glasspack, it has a length of straight pipe in front of it. The long Magnaflow will easily fit here. The lower glasspack is about 14" long give or take, so the 5" round could fit down there pretty well.
The nice part is if I go with 2.5", I can chop the collector quite a ways closer to the engine due to how wide the pipe is when you smash it down to 2".
This will create room for the slighter wider u-bends in 2.5"
The radius bend of my curent u-bends is the 3" version sold by RB, not the 4" version. I looked around and Columbia River Mandrel Bends sells 2.25" u-bends with the 3" radius I'd need. However the tightest 2.5" u-bend they sell is 3.75", and RB's thickwall u-bends in 2.5" are 4" radius. What this means for my baja install if I use CR's 3.75" radius u-bends is, I'll loose a little ground clearance, which is ok, but it may push the whole contraption further forward into the CV joint, which would be very bad for clearance and especially heat. However there may be a silver lining thanks to having to chop up the collector closer to the engine, as this will move the lower muffler further rearward and keep the u-bend away from the CV joint. It may just wind up keeping the u-bend int he same place. If you didn't follow any of that, don't worry about it, it was just me thinking out loud. 
Mike, I like the thought that a less than ideal 2.5" system will flow more like an ok 2.25" system, which, as you can see, those 180° u-bends are, yeah.
See those u-bends? They're restrictive, right? If I used 2.5" u-bends they'd probably flow like a straight 2.25.
Those mufflers you see there are actually glasspacks. The little one is a 3" outer shell about 12" or 13" long. The upper one is an old RE glasspack about 20" long and 4" outer shell. Both have a 2" core though I think the hotdog has louvers which effectively make the core more like 1 7/8 or 1 3/4.
I have my eye on a Magnaflow 5" round at 14" long to replace the 3" hotdog and 22" long 4" round Magnaflow for the upper. As you'll notice on the upper glasspack, it has a length of straight pipe in front of it. The long Magnaflow will easily fit here. The lower glasspack is about 14" long give or take, so the 5" round could fit down there pretty well.
The nice part is if I go with 2.5", I can chop the collector quite a ways closer to the engine due to how wide the pipe is when you smash it down to 2".
This will create room for the slighter wider u-bends in 2.5"The radius bend of my curent u-bends is the 3" version sold by RB, not the 4" version. I looked around and Columbia River Mandrel Bends sells 2.25" u-bends with the 3" radius I'd need. However the tightest 2.5" u-bend they sell is 3.75", and RB's thickwall u-bends in 2.5" are 4" radius. What this means for my baja install if I use CR's 3.75" radius u-bends is, I'll loose a little ground clearance, which is ok, but it may push the whole contraption further forward into the CV joint, which would be very bad for clearance and especially heat. However there may be a silver lining thanks to having to chop up the collector closer to the engine, as this will move the lower muffler further rearward and keep the u-bend away from the CV joint. It may just wind up keeping the u-bend int he same place.
If you didn't follow any of that, don't worry about it, it was just me thinking out loud.
04-28-10, 04:19 PM
#7
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picture is helpful!
i think i'd run a bullet/round can off the header in 2.5" the second one also 2.5" but maybe i'd run a small tailpipe, or a Y tailpipe tip or something
i think i'd run a bullet/round can off the header in 2.5" the second one also 2.5" but maybe i'd run a small tailpipe, or a Y tailpipe tip or something
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04-28-10, 08:07 PM
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my friend had an N1 dual on his FC, and the car was totally quiet unless one of those cannons were pointed at you, then it was incredibly loud...
05-05-10, 01:15 PM
#11
Ok, I'm getting a Magnaflow 12216 5x8 oval 14" long with a 2.5" core as the lower muffler. Having the u-bends here to test fit things is really helpfull. A 5x8 will actually fit where a 3" used to be!
The upper muffler will be a Magnaflow 10436 4" round (Mangapack) 22" long with a 2.5" core. I have one of these and it muffles suprisingly well for a Magnapack. That means it only contains a coarse stainless steel wool. There is no accoustical sound absorbtion fiber stuff. That is why it is called a "Magnapack". You yell through it and it really dumbs down the noise.
I'm glad a 5x8 oval will fit. I've got an 18" long one sitting here that I used to test fit stuff together. It really quiets things down too. The 14" version I need for the baja should still do a pretty good job. It does contain that acoustical absorbtion stuff. Is it rock wool? Some people say it is.
Here is an interesting trend I've noticed in my own exhaust systems. It seems the 2" systems I've put together over the years have all been way too loud. The one I just removed from my '81 FB was too loud and awful sounding. It had an RB road race header, 2" collector, RB 2" presilencer, stock over the axle pipe, and a center/offset Borla ProXS. Now the 3" system I just installed is probably just as loud, but it doesn't sound awful so it actually sounds quieter. It sounds so good you might actually want it a little louder.
It's perfect for me, though.
The one in the baja, as described in this thread is too loud for the street. Two 180° u-bends and 2" pipe apparently weren't enough to quiet this beast down so I had to get a supertrapp, which killed any and all flow. Bitch gotta go. It sounded good, but I bet the new 2.5" system will be a lot quieter and still sound good.
The GLC had a 2" system with a header, an old resonator off of an RX-4, and two RE glasspacks. I swapped out the rearmost glasspack because it was empty to a repacked RB presilencer. This helped a little, but it was still too loud for comfortable driving. The resonator leaked lots of noise up into the passenger's legs. It gives you a headache. The plan is to replace the header with an exhaust manifold, install a 6 port 12A (how cool is that) to take advantage of the manifold and its aux port opening feature, and change out the RB presilencer in the rear to the Borla ProXS mentioned above. If it's still too loud I'll wrap the resonator in a sleeve of 14 gauge steel tube and some coarse stainless steel wool like a Magnapack. If it's still too loud, I'll throw on the supertrapp. This is the only car that's staying 2" for now. I may some day do a turbo 13B and a short 3" system ending in front of the rear tire like the drag racers do. It's a GLC so it's only good as a grocery getter or a drag racer (or both?).
The REPU is getting a 2.5" system that will probably be quieter than your mom's SUV, maybe. The Cosmo is also getting a 2.5" system that needs to be very quiet because it's like a luxury car.
Just kind of interesting how hard it's been to muffle 2" compared to anything bigger.
A 5x8 will actually fit where a 3" used to be!The upper muffler will be a Magnaflow 10436 4" round (Mangapack) 22" long with a 2.5" core. I have one of these and it muffles suprisingly well for a Magnapack. That means it only contains a coarse stainless steel wool. There is no accoustical sound absorbtion fiber stuff. That is why it is called a "Magnapack". You yell through it and it really dumbs down the noise.
I'm glad a 5x8 oval will fit. I've got an 18" long one sitting here that I used to test fit stuff together. It really quiets things down too. The 14" version I need for the baja should still do a pretty good job. It does contain that acoustical absorbtion stuff. Is it rock wool? Some people say it is.
Here is an interesting trend I've noticed in my own exhaust systems. It seems the 2" systems I've put together over the years have all been way too loud. The one I just removed from my '81 FB was too loud and awful sounding. It had an RB road race header, 2" collector, RB 2" presilencer, stock over the axle pipe, and a center/offset Borla ProXS. Now the 3" system I just installed is probably just as loud, but it doesn't sound awful so it actually sounds quieter. It sounds so good you might actually want it a little louder.
It's perfect for me, though.The one in the baja, as described in this thread is too loud for the street. Two 180° u-bends and 2" pipe apparently weren't enough to quiet this beast down so I had to get a supertrapp, which killed any and all flow. Bitch gotta go. It sounded good, but I bet the new 2.5" system will be a lot quieter and still sound good.
The GLC had a 2" system with a header, an old resonator off of an RX-4, and two RE glasspacks. I swapped out the rearmost glasspack because it was empty to a repacked RB presilencer. This helped a little, but it was still too loud for comfortable driving. The resonator leaked lots of noise up into the passenger's legs. It gives you a headache. The plan is to replace the header with an exhaust manifold, install a 6 port 12A (how cool is that) to take advantage of the manifold and its aux port opening feature, and change out the RB presilencer in the rear to the Borla ProXS mentioned above. If it's still too loud I'll wrap the resonator in a sleeve of 14 gauge steel tube and some coarse stainless steel wool like a Magnapack. If it's still too loud, I'll throw on the supertrapp. This is the only car that's staying 2" for now. I may some day do a turbo 13B and a short 3" system ending in front of the rear tire like the drag racers do. It's a GLC so it's only good as a grocery getter or a drag racer (or both?).
The REPU is getting a 2.5" system that will probably be quieter than your mom's SUV, maybe. The Cosmo is also getting a 2.5" system that needs to be very quiet because it's like a luxury car.
Just kind of interesting how hard it's been to muffle 2" compared to anything bigger.
05-05-10, 01:20 PM
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05-05-10, 01:33 PM
#13
Yeah, the over the axle pipe in the '81 was just a thinwall stock pipe with the stock muffler swapped to a Borla. The Borla shell and inlet/outlet pipes are thinwall too 
(it's Magnaflow or RB for me). The thinwall was allowing lots of noise to leak up through my missing storage bins. I will have to relocate the battery to one of them so it will always be loud there. I'm glad I skipped over the thinwall u-bend (16 gauge) I originally bought for the 3" job and instead got a couple of 14 gauge (medium wall) u-bends. When I briefly listened to the exhaust inside the car yesterday, I didn't notice any tinny or ratty sounds. Seem like the 14 gauge stuff is working!
When you mandrel bend tubing like this, it thins it out on the ouside and maybe thickens it up on the inside. That means 16 guage becomes more like 18 or 22 guage! 14 gauge drops down to around 16 gauge at its thinest. As I was welding PercentSevenC's fully 16 gauge system together, I had to switch to .030 welding wire and turn the speed way up because the .035 was contantly burning through. It was nuts welding on his u-bend pieces, having to constanlty refill in the 22 gauge sections lol. Fortunately his turbo already kills the tinny high pitched noises so his system wound up sounded excellent and only slightly quieter than my NA system.
(it's Magnaflow or RB for me). The thinwall was allowing lots of noise to leak up through my missing storage bins. I will have to relocate the battery to one of them so it will always be loud there. I'm glad I skipped over the thinwall u-bend (16 gauge) I originally bought for the 3" job and instead got a couple of 14 gauge (medium wall) u-bends. When I briefly listened to the exhaust inside the car yesterday, I didn't notice any tinny or ratty sounds. Seem like the 14 gauge stuff is working!When you mandrel bend tubing like this, it thins it out on the ouside and maybe thickens it up on the inside. That means 16 guage becomes more like 18 or 22 guage! 14 gauge drops down to around 16 gauge at its thinest. As I was welding PercentSevenC's fully 16 gauge system together, I had to switch to .030 welding wire and turn the speed way up because the .035 was contantly burning through. It was nuts welding on his u-bend pieces, having to constanlty refill in the 22 gauge sections lol. Fortunately his turbo already kills the tinny high pitched noises so his system wound up sounded excellent and only slightly quieter than my NA system.
05-05-10, 02:45 PM
#14
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I'd be very interested in seeing a video of that running. How loud is it? I'm working on a similar project with a 13b in a Karmann Ghia and haven't yet figured out how i'm going to route my exhaust.
05-06-10, 12:08 AM
#15
Maybe after the exhaust is redone. It is too loud and too restrictive right now. The temp engine I'm throwing in is ported to 74 spec so it will flow even more than the current engine. Gotta redo the exhaust very soon. If this level of porting works out ok, I'll port the baja's engine to 74 spec and break it in in something else while leaving the temp engine in to work out the bugs in the install like cooling and, well, exhaust.
10-05-10, 01:46 PM
#16
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