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914World.com _ 914World Garage _ V8 conversion exhaust question
Posted by: ringerdc Jan 15 2015, 11:10 PM
What are the "pros and cons" of routing the exhaust pipes over or under the axles in a V8 setup? I see that most V8 conversions choose the "over" configuration using an "s" pipe. However, the "under" route is more of a straight path. In both the 4 and 6 factory setups the pipes are routed under the axle as well. Hmmmm..
Inquiring minds want to know
Posted by: matthepcat Jan 15 2015, 11:30 PM
I would suggest routing to one side where both sides combine. This will greatly reduce drone. I have run over with dual exhaust, and under where they combine on one side. Better ground clearance going over.
Posted by: mgp4591 Jan 15 2015, 11:35 PM
I can't speak from experience in having a v8 (mine is a 6 in progress) but having built many systems I would be in favor of over the axle for clearance issues. The run of pipe isn't that long and with the correct sized pipe and mandrel bends, I wouldn't think you'd lose any flow speed especially running low restriction mufflers. Now, if our exhaust runs were over 10 ft long there would be more considerations but we're short enough not to worry. Manifolds keep the start height of the pipe high enough that you shouldn't dip down too far and keep it up high for easy clearance over the axles. IMO. 
Posted by: shoguneagle Jan 16 2015, 05:15 AM
Very simple - clearance and half-shaft maintenance along with all the reasoning mentioned in the foregoing comments.
Posted by: chads74 Jan 16 2015, 06:53 AM
Clearance, exactly why I decided to run over the axle. I under you would still have the clearance needed, I think its more of a personal preference than anything.
Posted by: sb914 Jan 16 2015, 09:53 AM
You should think about heat shields if you plan on using your trunk,it's gets extremely hot and I've heard of a fire starting in a guys trunk.
Posted by: Bruce Hinds Jan 16 2015, 10:19 AM
My selection was due to the headers I wanted to run. It seems most of the V8s I've seen use the very short "Hugger" header. Those will give you choice to go over or under.
I was told that longer tube headers are better for power at mid-higher RPM. I was looking to "Kill" some of the low-end torque since that's a killer for the CVs and 901. This option put the collector just ahead and slightly below the CV, under was my only option.
This makes it difficult to have a crossover unless you use a can style muffler in the rear. The cross over is necessary to eliminate the "drone" mentioned earlier which can be a real annoyance.
Posted by: Andyrew Jan 16 2015, 11:17 AM
I've always thought the over solution was the best due to ground clearance and bottoming out.
The issue typically is with the exhaust manifolds and therefore exhaust collector being really close to the shift linkage, throttle cable, and clutch cable. I've burned more than one cable..
Shorty headers and a nice custom job on the manifolds is what does it. I used to have a nice set of long tube headers I was going to cut down but never did. I think the S10 has a nice header system (Vs towards the block)that goes straight down and gives you lots of clearance to run the accessory lines.
Posted by: mgp4591 Jan 16 2015, 12:34 PM
It is possible to build a good breathing Y-pipe to join the two sides together, then pipe it through a single in- dual out low restriction muffler for the dual exhaust look without the drone. There's also ways to knock the droning down by kinking the pipes (small kinks, carefully measured) along the resonating spots in the piping but it takes awhile, looks REALLY goofy but it doesn't affect the flow that much. I've put together systems that have NO mufflers and don't get those audible peaks and valleys but it's laborious and once you do it wrong it can't be undone without redoing the system. Paying attention to the merge collector on a Y pipe system is the key to keeping flow rates high and increasing your power.
Posted by: Mike Bellis Jan 16 2015, 04:27 PM
Here is my old setup. Over the axle.
Posted by: computers4kids Jan 16 2015, 07:15 PM
I would suggest routing to one side where both sides combine. This will greatly reduce drone.
Combining both sides greatly reduces drone. Here's how I did mine.
Posted by: messix Jan 16 2015, 07:20 PM
good reasonable 2-1 merge collector http://www.jegs.com/i/Magnaflow/642/10778/10002/-1
Posted by: mgp4591 Jan 16 2015, 07:50 PM
Here is my old setup. Over the axle.
Very cool setup- did that kill alot of the droning sound because it looks like it could! I'd be interested to see dyno results on these various systems too- probably unrealistic but again, with the overall length of these systems I doubt if backpressure is a big issue.
Posted by: matthepcat Jan 16 2015, 07:57 PM
Mike traded this system pictured on to me. I ran it like that for a while, but it was kinda restrictive with those mufflers. I stupidly upgraded to some magnaflo muffler in their place and the drone returned. Run the quiet more restrictive exhaust to avoid drone.
Here is my old setup. Over the axle.
Very cool setup- did that kill alot of the droning sound because it looks like it could! I'd be interested to see dyno results on these various systems too- probably unrealistic but again, with the overall length of these systems I doubt if backpressure is a big issue.
Posted by: bobo914 Jan 17 2015, 11:56 AM
"180 degree" exhaust. The sound is correct for V8 in 914. Long tube headers help kill low end power and increase mid and upper range which helps save drivetrain. Over axle is nice for cv service and ground clearance.
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Posted by: Mueller Jan 17 2015, 11:59 AM
"180 degree" exhaust. The sound is correct for V8 in 914. Long tube headers help kill low end power and increase mid and upper range which helps save drivetrain. Over axle is nice for cv service and ground clearance.
How dare you not include a sound clip!
Wow, that looks cool, will have to hunt down your build thread later on if you have one.
Didn't Chris Julian up here in Nor-Cal do the 180° exhaust also?
Posted by: messix Jan 17 2015, 01:03 PM
"180 degree" exhaust. The sound is correct for V8 in 914. Long tube headers help kill low end power and increase mid and upper range which helps save drivetrain. Over axle is nice for cv service and ground clearance.
long tube headers do NOT kill low rpm power. the design and engineering of headers and exhaust is much more than a blanket statement like that.
primary tube diameter, length, collector size and length, all are part of where the power balance will be. stating that, longer primary tubes will optimize the lower rpm torque.
the reality between long tube header and "shortys" is that the long tube will have less compromises than the short tube header will and will make better power across the board.
Posted by: bobo914 Jan 17 2015, 02:14 PM
Sorry for the blanket statement. I had "shorty" headers with S pipes over the axles on the same motor. When I went to the 180 system low end power decreased while mid and upper range increased. Probably do to my specific engine combo.
Posted by: messix Jan 17 2015, 02:31 PM
more than likely you maximized the exhaust when you used the 180 long tubes and it just "felt" like you lost some low end when in effect you gained across the board but more so in the higher end.
or you went too big on pipe size for the engine, that would have dumped the low end.
dyno results from both set ups would have been the real tell tale.
Posted by: bobo914 Jan 17 2015, 02:54 PM
Had two goals with the exhaust change. 1 lose some low end power. 2 change sound. I increased the primary tube size for goal 1. And went 180 for goal 2.
Posted by: Maltese Falcon Jan 17 2015, 03:27 PM
Here is my old setup. Over the axle.
Try to keep Square Joints out of the equation (like at these muffler discharges) Realizing space requirements and sharp turns , square bends =power loss, almost like Press-bending Vs. Mandrel bending.
If your muffler shop is building a system for you and does not understand exhaust flow, nor have tight radius bends, I'll be happy to send you some random mandrel bends no cost (you pay shipping). I usually recycle remnants every week, but available if on hand
Marty
Posted by: andys Jan 17 2015, 04:07 PM
I went over the axles for most of the reasons many have already stated. Notice the heat shielding. The muffler shields are available from Flowmaster. I get a drone at 2000RPM. Perhaps the next time I drop the motor/trans, I may add Helmholtz chambers to cancel out the drone. Granted a cross-over would reduce some of the noise, but a lack of a tidy solution will probably keep me from doing it. BTW, those Flowmaster's are three chambered, and according to the literature, they greatly reduce interior noise.
Andys
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Posted by: Bruce Hinds Jan 17 2015, 04:19 PM
I went over the axles for most of the reasons many have already stated. Notice the heat shielding. The muffler shields are available from Flowmaster. I get a drone at 2000RPM. Perhaps the next time I drop the motor/trans, I may add Helmholtz chambers to cancel out the drone. Granted a cross-over would reduce some of the noise, but a lack of a tidy solution will probably keep me from doing it. BTW, those Flowmaster's are three chambered, and according to the literature, they greatly reduce interior noise.
Andys
Andys - what kind of gearbox is that?
Posted by: andys Jan 17 2015, 04:21 PM
Andys - what kind of gearbox is that?
Audi 01E 6 speed.
Andys
Posted by: Mike Bellis Jan 17 2015, 05:18 PM
I went over the axles for most of the reasons many have already stated. Notice the heat shielding. The muffler shields are available from Flowmaster. I get a drone at 2000RPM. Perhaps the next time I drop the motor/trans, I may add Helmholtz chambers to cancel out the drone. Granted a cross-over would reduce some of the noise, but a lack of a tidy solution will probably keep me from doing it. BTW, those Flowmaster's are three chambered, and according to the literature, they greatly reduce interior noise.
Andys
Awesome craftsmanship!
Posted by: speed metal army Jan 17 2015, 08:05 PM
I went over.
Posted by: bulitt Jan 17 2015, 08:45 PM
I went over the axles for most of the reasons many have already stated. Notice the heat shielding. The muffler shields are available from Flowmaster. I get a drone at 2000RPM. Perhaps the next time I drop the motor/trans, I may add Helmholtz chambers to cancel out the drone. Granted a cross-over would reduce some of the noise, but a lack of a tidy solution will probably keep me from doing it. BTW, those Flowmaster's are three chambered, and according to the literature, they greatly reduce interior noise.
Andys
Fmasters= drone city.
Posted by: andys Jan 17 2015, 09:29 PM
I went over the axles for most of the reasons many have already stated. Notice the heat shielding. The muffler shields are available from Flowmaster. I get a drone at 2000RPM. Perhaps the next time I drop the motor/trans, I may add Helmholtz chambers to cancel out the drone. Granted a cross-over would reduce some of the noise, but a lack of a tidy solution will probably keep me from doing it. BTW, those Flowmaster's are three chambered, and according to the literature, they greatly reduce interior noise.
Andys
Fmasters= drone city.
It only drones in about a 200RPM range, so I wouldn't categorize that as "drone city." I can easily drive around it. Any pieced together exhaust has the likelihood for droning, but it can be cancelled out. Production car systems are engineered and developed and tested to avoid/cancel drone. Much of the time, they can design chambers within the muffler that can cancel the drone of a specific engine configuration; one size does not fit all! In my case, knowing the RPM range of the drone, I can now configure a 1/4 wave drone cancelling chamber. To help soften the exhaust note, I can also cut the exhaust tips at an angle, but I don't think I'd like the look in my particular case.
Andys
Posted by: messix Jan 17 2015, 09:39 PM
I was just thinking [I know... dangerous] an easy way to build a "anti-drone" exhaust, use 2 1 in 2 out mufflers like these http://www.summitracing.com/parts/mpe-13288?seid=srese1&gclid=CKmthLLPnMMCFVJhfgod6RkAoQ and use one of the outlets on each to use as a cross over where the stock muffler would be.
I would draw up a picture but crayons don't upload
Posted by: mgp4591 Jan 17 2015, 10:53 PM
I went over the axles for most of the reasons many have already stated. Notice the heat shielding. The muffler shields are available from Flowmaster. I get a drone at 2000RPM. Perhaps the next time I drop the motor/trans, I may add Helmholtz chambers to cancel out the drone. Granted a cross-over would reduce some of the noise, but a lack of a tidy solution will probably keep me from doing it. BTW, those Flowmaster's are three chambered, and according to the literature, they greatly reduce interior noise.
Andys
I really like this setup- compact and well done. Do you have any sideshots of this or is it in a link for your build?
Posted by: rick 918-S Jan 18 2015, 07:51 AM
Under, tuck them in slightly as they pass the axle to clear the axle swing path. Never had an issue with the ground in 10's of thousands of miles. I installed a balance pipe between the mufflers just above the exhaust outlet. Simple. 
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Posted by: v82go Jan 18 2015, 08:18 AM
I too went under on both of mine (one sbc and a LS6),
On my first one I tried the dual flowmasters and grew
tired of the drone, after building 3 or 4 more exhaust
systems, I ended up with a good sounding Porsche GT3
muffler (ebay), not too loud and no drone.
On my LS I have 2 Corvette C5 mufflers, I gutted and
shortened and tied together. These have 2 hidden outlets
and a exposed center outlet. No drone, but rather loud
and rowdy sounding. I have had no issues by going
under the axles.
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Posted by: Amenson Jan 18 2015, 08:24 AM
How dare you not include a sound clip!
I agree, we must have a sound clip!
Cheers,
Scott
Posted by: bulitt Jan 18 2015, 08:52 AM
I went over the axles for most of the reasons many have already stated. Notice the heat shielding. The muffler shields are available from Flowmaster. I get a drone at 2000RPM. Perhaps the next time I drop the motor/trans, I may add Helmholtz chambers to cancel out the drone. Granted a cross-over would reduce some of the noise, but a lack of a tidy solution will probably keep me from doing it. BTW, those Flowmaster's are three chambered, and according to the literature, they greatly reduce interior noise.
Andys
Fmasters= drone city.
It only drones in about a 200RPM range, so I wouldn't categorize that as "drone city." I can easily drive around it. Any pieced together exhaust has the likelihood for droning, but it can be cancelled out. Production car systems are engineered and developed and tested to avoid/cancel drone. Much of the time, they can design chambers within the muffler that can cancel the drone of a specific engine configuration; one size does not fit all! In my case, knowing the RPM range of the drone, I can now configure a 1/4 wave drone cancelling chamber. To help soften the exhaust note, I can also cut the exhaust tips at an angle, but I don't think I'd like the look in my particular case.
Andys
Had them on a pickup. It was unbearable.
Posted by: andys Jan 18 2015, 11:42 AM
[quote name='mgp4591' date='Jan 17 2015, 08:53 PM' post='2135435']
Andys
[/quote]
I really like this setup- compact and well done. Do you have any sideshots of this or is it in a link for your build?
[/quote]
Here's a link to my retrospective build thread. If you don't see what you're looking for, let me know.
http://www.914world.com/bbs2/index.php?showtopic=204625&hl=ls1 retrospective
Andys
Posted by: BIGKAT_83 Jan 18 2015, 12:01 PM
I'm running Magnaflow glasspacks under the axle and have no problem with drone. These are great mufflers I had them on a new mustang and when I sold the car I replaced them with the stock mufflers. I think the stock ones were louder
I tried some Flowmasters 40's Used them for less than 1 mile. Way to loud.
Bob
Posted by: speed metal army Jan 18 2015, 01:09 PM
I'm running Magnaflow glasspacks under the axle and have no problem with drone. These are great mufflers I had them on a new mustang and when I sold the car I replaced them with the stock mufflers. I think the stock ones were louder
I tried some Flowmasters 40's Used them for less than 1 mile. Way to loud.
Bob
+1 on Magnaflow. Best sounding, least drone.
Posted by: andys Jan 18 2015, 01:13 PM
I'm running Magnaflow glasspacks under the axle and have no problem with drone. These are great mufflers I had them on a new mustang and when I sold the car I replaced them with the stock mufflers. I think the stock ones were louder
I tried some Flowmasters 40's Used them for less than 1 mile. Way to loud.
Bob
Bob,
Mine are Flowmaster 50's. According to their literature (interior/exterior db charts), they're a lot quieter than the 40's. Just FYI.
Andys
Posted by: BIGKAT_83 Jan 18 2015, 01:19 PM
I kinda figured yours were 50's they look a little longer.
Bob
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