V8 conversion exhaust question, over or under? Options

[ringerdc]

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

[matthepcat]

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.

[mgp4591]

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. (IMG:style_emoticons/default/shades.gif)

[shoguneagle]

Very simple - clearance and half-shaft maintenance along with all the reasoning mentioned in the foregoing comments.

[chads74]

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.

[sb914]

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.

[Bruce Hinds]

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.

[Andyrew]

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.

[mgp4591]

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.

[Mike Bellis]

Here is my old setup. Over the axle.

[computers4kids]

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.
(IMG:http://www.914world.com/bbs2/uploads/post-4253-1233890821.jpg)

[messix]

good reasonable 2-1 merge collector http://www.jegs.com/i/Magnaflow/642/10778/10002/-1

[mgp4591]

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.

[matthepcat]

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.

[bobo914]

"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.

[Mueller]

"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!
(IMG:style_emoticons/default/smile.gif)

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?

[messix]

"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.

[bobo914]

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.

[messix]

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.

[bobo914]

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.