2.5" vs 3" exhaust
11-13-2007, 11:42 PM
#16
Three Wheelin'
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You would need a muffler guy to hook them up. Carl at 928MS has nice X-Pipes that bolt right up but they are much more $$ and arguably of better design.
With MSDS headers, every set is slightly different so no stock X-pipe is made, you have to use a universal and bridge the difference.
As for the generic X, I see no difference in the Magnaflow other than price. In fact the generic is much shinier making your car faster. Chrome any where, even unseen makes your car faster. Every hot rod at the dairy queen knows that.
With MSDS headers, every set is slightly different so no stock X-pipe is made, you have to use a universal and bridge the difference.
As for the generic X, I see no difference in the Magnaflow other than price. In fact the generic is much shinier making your car faster. Chrome any where, even unseen makes your car faster. Every hot rod at the dairy queen knows that.
11-14-2007, 08:19 PM
#17
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Although I may track the car in the next couple years, for the short term it is my daily rice killer, light to light and some highway driving. Also 3" in/out mufflers are hard to find locally, and usualy bigger as well. With two mufflers to tuck in next to the tranny, I want to keep them lower profile. 2.5" may give me more options, though I think I will be staying with the Flowmaster models. I already have one 3" Flowmaster, so I'd save 100 beans re-using it. But it is pretty large and it has dual 2.5" outs so I'd have 2 tips on each side...
11-15-2007, 01:37 AM
#18
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Sterling---
we ran twin 2.5 on a 340 ci smallblock Plymouth Duster, then changed to 3 inches and checked the ET (1/4 mile dragstrip at Orlando Speed World, back in the late '70s).
no changes in ET between the small or big pipes, but......
There was no loss of power (affecting the ET) with the stock bore/stroke 340, but there was a big improvement with a stroker engine (about one tenth of a second, if memory serves me correctly) between the two pipe sizes.
We did a similar test using a 440 big block Dodge super stocker, and there was an improvement in ET with the bigger pipes.
The loss of low end power has more to do with the header configuration, than anything downstream of the header collector.
That's why you see most muscle cars using modern day 3 inch exhaust systems for maximum performance on street or strip. some have even gone to 4 inch systems for big inch strokers (600 inches and more) and blown motors.....
If you look at my recently ported and polished Euro heads, you will see that the ports are a sane 25/26mm (in/ex). Much bigger than the US version, but not sewer pipe sized limiting low end power.
when choosing headers though, we are quite limited to our selection.
the MSDS units are 1.75 inches on the primaries, not 2 inch. A 2 inch primary tube is where mild street engines get into trouble. Similarly, a 4 inch collector is not recommended, as this will harm low end power as well.
My exception to this is my (eventual) set up, which will have header primary tubes fully connected to the sidepipe collector, but keeping in mind that my primaries will be extremely long, negating the low end loss effect of the 4 inch collector.
the one thing that does improve performance beyond the header is an x-pipe of some sort---there are some good and then there are better ones. this has more to do with scavenging than low end power loss/gain, just as long as the tube diameter is the same as the header collector.
-Russ
we ran twin 2.5 on a 340 ci smallblock Plymouth Duster, then changed to 3 inches and checked the ET (1/4 mile dragstrip at Orlando Speed World, back in the late '70s).
no changes in ET between the small or big pipes, but......
There was no loss of power (affecting the ET) with the stock bore/stroke 340, but there was a big improvement with a stroker engine (about one tenth of a second, if memory serves me correctly) between the two pipe sizes.
We did a similar test using a 440 big block Dodge super stocker, and there was an improvement in ET with the bigger pipes.
The loss of low end power has more to do with the header configuration, than anything downstream of the header collector.
That's why you see most muscle cars using modern day 3 inch exhaust systems for maximum performance on street or strip. some have even gone to 4 inch systems for big inch strokers (600 inches and more) and blown motors.....
If you look at my recently ported and polished Euro heads, you will see that the ports are a sane 25/26mm (in/ex). Much bigger than the US version, but not sewer pipe sized limiting low end power.
when choosing headers though, we are quite limited to our selection.
the MSDS units are 1.75 inches on the primaries, not 2 inch. A 2 inch primary tube is where mild street engines get into trouble. Similarly, a 4 inch collector is not recommended, as this will harm low end power as well.
My exception to this is my (eventual) set up, which will have header primary tubes fully connected to the sidepipe collector, but keeping in mind that my primaries will be extremely long, negating the low end loss effect of the 4 inch collector.
the one thing that does improve performance beyond the header is an x-pipe of some sort---there are some good and then there are better ones. this has more to do with scavenging than low end power loss/gain, just as long as the tube diameter is the same as the header collector.
-Russ
11-15-2007, 01:49 AM
#19
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one further note: I believe that if you consult with Martin, he'll probably tell you the unequal length primaries are to aid in scavenging due to 2 cylinders on each bank firing together.
as for the short collector, I suspect it is a space issue under the car.....
the 928 engine may react differently than the old muscle cars we tested 20 years ago, but until I see either some dyno or ET numbers to verify changes....?
---Russ
--Russ
as for the short collector, I suspect it is a space issue under the car.....
the 928 engine may react differently than the old muscle cars we tested 20 years ago, but until I see either some dyno or ET numbers to verify changes....?
---Russ
--Russ
11-15-2007, 02:16 AM
#20
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the 928 engine may react differently than the old muscle cars we tested 20 years ago, but until I see either some dyno or ET numbers to verify changes....?
I think I may be able to provide this proof. We had a local 32v-S owner put a whole bunch of money into rebuild which include big valve heads, porting, etc., from a well known engine builder, and it wasn't putting out very good numbers. It had headers into a single exhaust. He took it to a local high end wrench who suggested exactly what you did, dual 3's with a flowmaster and was told he should get to 300 rwhp. I'll have to check the facts again, but I think he lost ground.
We've had a few 32v-S motors locally here that kept the stock exhaust systems with the only mod being replacing the stock cat with an Ott X (can't recall if an RMB was involved) and they have produced power well into S4 territory. I don't know that I've seen a 32V-S motor put out better numbers with an aftermarket (larger diameter) exhaust.
The 32v motors aren't typical in how they respond to exhaust mods. I think this may have to do with how little overlap they have, but I'm not a cam expert.
I'll see if I can get the dynosheets for you on the pre/post dual 3 w/magnaflow set up.
11-15-2007, 02:19 AM
#21
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Also, I think Dave Lomas at Motorsport SLC did a bunch of testing with different exhausts and mufflers, and lost ground with the flowmaster. Dave, you out there to confirm?
11-15-2007, 03:25 AM
#22
Three Wheelin'
About 9 mos ago, I put a set of high end headers on a GT. It had the stock manifolds and one of my X pipes with 2.5" duals all the way back. Power was good at around 325 rwhp. After the headers and tapered transition from the 3" collectors to 2.5" and a new X pipe section connecting to the same rear exhaust it lost 4 hp. I Sharktuned until I was exhausted and that's all it would do. Dyno testing X pipes without a rear exhaust at all will show a mid range increase when a 2.5" rear dual exhaust connected. A 3.5" single loses mid range and I suppose dual 3" would be similar to no rear exhaust. That's on a 5.0L 32v. I wouldn't use a Flowmaster muffler either, but that's only because of the poor flow tests with them. I don't know about the sound of them. Too much turbulatin' goin' on in there for good flow. Just my personal opinion. Use whatever you like.
Edit to change "A 3" single" to "A 3.5" single".
Edit to change "A 3" single" to "A 3.5" single".
Hi Russ,
I think I may be able to provide this proof. We had a local 32v-S owner put a whole bunch of money into rebuild which include big valve heads, porting, etc., from a well known engine builder, and it wasn't putting out very good numbers. It had headers into a single exhaust. He took it to a local high end wrench who suggested exactly what you did, dual 3's with a flowmaster and was told he should get to 300 rwhp. I'll have to check the facts again, but I think he lost ground.
We've had a few 32v-S motors locally here that kept the stock exhaust systems with the only mod being replacing the stock cat with an Ott X (can't recall if an RMB was involved) and they have produced power well into S4 territory. I don't know that I've seen a 32V-S motor put out better numbers with an aftermarket (larger diameter) exhaust.
The 32v motors aren't typical in how they respond to exhaust mods. I think this may have to do with how little overlap they have, but I'm not a cam expert.
I'll see if I can get the dynosheets for you on the pre/post dual 3 w/magnaflow set up.
I think I may be able to provide this proof. We had a local 32v-S owner put a whole bunch of money into rebuild which include big valve heads, porting, etc., from a well known engine builder, and it wasn't putting out very good numbers. It had headers into a single exhaust. He took it to a local high end wrench who suggested exactly what you did, dual 3's with a flowmaster and was told he should get to 300 rwhp. I'll have to check the facts again, but I think he lost ground.
We've had a few 32v-S motors locally here that kept the stock exhaust systems with the only mod being replacing the stock cat with an Ott X (can't recall if an RMB was involved) and they have produced power well into S4 territory. I don't know that I've seen a 32V-S motor put out better numbers with an aftermarket (larger diameter) exhaust.
The 32v motors aren't typical in how they respond to exhaust mods. I think this may have to do with how little overlap they have, but I'm not a cam expert.
I'll see if I can get the dynosheets for you on the pre/post dual 3 w/magnaflow set up.
Last edited by Louie928; 11-15-2007 at 01:00 PM.
11-15-2007, 08:54 AM
#23
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My old hybrid had dual 2.25 (maybe be was 2.5?) into a 3.5" single exhaust w/ spintech muffler. Made 305rwhp.
Stroker uses dual 3" into a flowmaster Y to a single 4" with a spintech muffler. Good for 551rwhp.
My opinion is that a dual 3" is overkill for a 5.0L "stockish" 928 motor.
Stroker uses dual 3" into a flowmaster Y to a single 4" with a spintech muffler. Good for 551rwhp.
My opinion is that a dual 3" is overkill for a 5.0L "stockish" 928 motor.
11-15-2007, 04:34 PM
#24
Nordschleife Master
My set up.
I have MSDS headers and I went with a frugal approach. I bypassed the cats with straights pipes into the OEM pipes. From the OEM pipes the shop placed a 2 into 1 merge collector into a 3" pipe, From the 3" pipe, I have a 3" In/Out 2 chamber flowmaster. IMO and under WOT, she's brutal and sounds friggin awesome!!
No problems with low end trq.
No problems with low end trq.
Last edited by Drewster67; 12-30-2012 at 11:14 AM.
11-15-2007, 05:25 PM
#25
Well I don't know exactly how much I can add here, hopefully it wont just be confusion. I do have a duel 3" system on my 5.0 litre Euro, it makes 305 hp on a Dyno Dynamics dyno, these dynos read lower than Dynojets, now this exhaust does have a number of special features.
One the pipes are equal length within 1/2" max two they do have proper merge collectors, three it has a variable pressure bypass valve. I don't have dyno testing before and after just for the exhaust, but the engine does have more power at the wheels than a GTS has at the flywheel EXCEPT after 5000 rpm where I am fixing it's breathing problem.
So how was it done, well after the headers like what Louie has it coned down to 2.5" and then into a 2.5" X pipe that I made myself, they are not hard to make, also I used stainless steel and ceramic coated the front section of the xhaust. This was to keep the velocities up. The exhaust after the X pipe expands to duel 3". I see that expansion as a bit of anti reversion too. After the X I didn't want any pressure, it has already had the area that needed the velocity and now I want it gone.
My friend with a very similar engine, that is new and similar capacity but standard exhaust it only made 227 rwhp he is today dyno testing his 86.5 manifolds and larger rear exhaust. He tells me that the car is much faster and has more low end torque. So it will be interesting to hear the results.
Good luck with your choice
Greg
One the pipes are equal length within 1/2" max two they do have proper merge collectors, three it has a variable pressure bypass valve. I don't have dyno testing before and after just for the exhaust, but the engine does have more power at the wheels than a GTS has at the flywheel EXCEPT after 5000 rpm where I am fixing it's breathing problem.
So how was it done, well after the headers like what Louie has it coned down to 2.5" and then into a 2.5" X pipe that I made myself, they are not hard to make, also I used stainless steel and ceramic coated the front section of the xhaust. This was to keep the velocities up. The exhaust after the X pipe expands to duel 3". I see that expansion as a bit of anti reversion too. After the X I didn't want any pressure, it has already had the area that needed the velocity and now I want it gone.
My friend with a very similar engine, that is new and similar capacity but standard exhaust it only made 227 rwhp he is today dyno testing his 86.5 manifolds and larger rear exhaust. He tells me that the car is much faster and has more low end torque. So it will be interesting to hear the results.
Good luck with your choice
Greg
11-16-2007, 12:09 AM
#26
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Well now I'm completely confused.
Maybe a little more information would help.
I'm hoping to hit 350HP at the crank N/A
Heads have been polished and ported with new valves, guides, seals and valve job. Intakes and exhaust gasket matched. Intake runners extrude honed. ' 85 5.0L block. MSDS Headers, no cats and an X placed back at the end of the cat heat shield. Not sure after that.
I also have up to 300HP Nitrous on tap. Most I have gone so far before rebuild was 175hp. @175HP of giggle gas I saw 171 RWHP more on the Gtech. Which means it was more like 185RWHP more accounting for air resistance. I plan on running 250HP next which should give 265RWHP or so more. With stock 300RWHP+/- I should be at just above mid 500's RWHP, little over 600HP crank.
I need the exhaust to handle the N2O, but don't want to loose to much for the 99% of my driving which is with out the N2O.
Sounds like the 2.5 would be better for the N/A and may be the way to go. I may loose a bit under N2O but it sounds like I may loose more N/A on the 3". Both options will be better than what I was running, a Y-Pipe directly into a 3" Flowmaster and then dual 2.5 outs.
Maybe a little more information would help.
I'm hoping to hit 350HP at the crank N/A
Heads have been polished and ported with new valves, guides, seals and valve job. Intakes and exhaust gasket matched. Intake runners extrude honed. ' 85 5.0L block. MSDS Headers, no cats and an X placed back at the end of the cat heat shield. Not sure after that.
I also have up to 300HP Nitrous on tap. Most I have gone so far before rebuild was 175hp. @175HP of giggle gas I saw 171 RWHP more on the Gtech. Which means it was more like 185RWHP more accounting for air resistance. I plan on running 250HP next which should give 265RWHP or so more. With stock 300RWHP+/- I should be at just above mid 500's RWHP, little over 600HP crank.
I need the exhaust to handle the N2O, but don't want to loose to much for the 99% of my driving which is with out the N2O.
Sounds like the 2.5 would be better for the N/A and may be the way to go. I may loose a bit under N2O but it sounds like I may loose more N/A on the 3". Both options will be better than what I was running, a Y-Pipe directly into a 3" Flowmaster and then dual 2.5 outs.
11-16-2007, 12:58 AM
#28
Rennlist Member
JV wrote:
John, do you have any pics of this set up? Sounds similar to what I want to run on my big motor.
Stroker uses dual 3" into a flowmaster Y to a single 4" with a spintech muffler. Good for 551rwhp.
11-16-2007, 10:24 PM
#29
Instructor
Ive posted these before, but this is what I did. 2.25" pipe into a Magnaflow Y pipe (WITH O2 INSTALLED IN IT) out to 2.5" pipe to the stock rear box. I can feel a difference but I did remove a broken up Catalytic Converter so that could account for the power loss. My car is stock so I just kept it simple..
11-16-2007, 10:40 PM
#30
Can someone explain why the single exhausts lose power? I would think (look out) that a proper equal-length header feeding into a 4-1 collector, which in turn feeds into a 2-1 collector necked down to 2.5" and then out to a 3" single, would scavenge properly without the positioning problems if the x-pipe. The cylinder firing would naturally promote scavenging while reducing back pressure via the 3" single.
Even better, has anyone ever tried a tri-y setup on a 928? This is a 4-2-1 equal length setup, again merging into a single exhaust. If you look at a lot of race cars, they go to single exhausts, but I know they are usually going for top end power.
I'm planning on some exhaust work to my car, hence the questions.
Even better, has anyone ever tried a tri-y setup on a 928? This is a 4-2-1 equal length setup, again merging into a single exhaust. If you look at a lot of race cars, they go to single exhausts, but I know they are usually going for top end power.
I'm planning on some exhaust work to my car, hence the questions.
