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This concerns a 460 efi Ford F350. 92 model. 5 spd trans.
So I have read dozens of pages of opinions about exhaust. Seems like people either choose the dual exhaust with 2.5 inch pipe through a pair of glass pack style mufflers or y pipe to 3" single pipe into one muffler.
My truck has no cat. Stock manifolds and stock H pipe. There is a Y pipe off of the H pipe where the cat used to be. It is 2.5 inch all the way to the inlet of the muffler which has a 3 inch inlet and 2 2 inch outlets. The muffler is a flowmaster copy. Not rusted out, looks pretty good.
It is LOUD. It has a terrible drone in the cab over 2000 rpm or so. I don't know for sure, but it seems like it doesn't flow as well as I would expect a 460 to flow.
Has anyone changed from a similar setup like mine to duals? Or is there something about my setup that could be changed to improve it?
The muffler is located under the bed and the 2 outlets turn down pretty close to the rear axle.
I am considering removing the Y Pipe and going to duals out of the H pipe to 2 walker 2.5 inch 33" long mufflers. Part no. 17893.
If the drone bothers you eliminate the turndowns and get the exit out from under the truck.
Out the back, out the side, doesn't matter as long as it is pointed away from the vehicle and ends where the truck ends.
I have a similar homebrewed system, a dual inlet single outlet school bus muffler from the Walker medium duty catalog connected to a 3" Magnaflow universal stainless tailpipe
If the drone bothers you eliminate the turndowns and get the exit out from under the truck.
Out the back, out the side, doesn't matter as long as it is pointed away from the vehicle and ends where the truck ends.
I have a similar homebrewed system, a dual inlet single outlet school bus muffler from the Walker medium duty catalog connected to a 3" Magnaflow universal stainless tailpipe
Agreed on the turn downs. All they do is MAKE DRONE.
I agree with ArdWrkn, get rid of the turndowns and run it all the way back. That should help.
As far as mufflers go, I might try a different one. I wonder which style Flowmaster copy you have. It could be one of the more aggressive mufflers.
Your true dual/H pipe/Walker muffler setup seems like it would get rid of that drone, especially if you took it all the way back behind the rear tires.
I looked closer and sure enough it is a flowmaster 50.
You can see the Y pipe that has been inserted in place of the Cat.
It would be easy enough to run the tail pipes out in front of the rear wheel. Does anyone think that would help? Or should I cut out the Y pipe and go to 2 mufflers.
It is just ridiculous how loud it is. I thought flowmasters would sound better than this. I am still surprised it isn't some generic muffler. This should be a 3 chamber design.
Could the pipe coming out of the Y be restricting it too much?
It definitely looks like you could make a much better setup as far as flow and sound goes. Flowmaster actually lists the 50 series as "minimal interior resonance".. but I'm thinking your drone is mostly coming from that turndown. I would run two pipes out of the H with 2 separate mufflers of your choice that are decently quiet, then all the way back behind the rear tires. It would be a little pricey, but definitely worth it to get rid of the drone. Not to mention it would flow a whole lot better. Also, like Brad stated, a single in single out muffler and single tailpipe would cut the cost and still be sufficient for flow. I also agree with running 3" for the 460.
I'd try to stay as far from the cab as possible if you're trying to eliminate the drone.
I think I am going to go the duals route. I don't see how it could be much worse. I really think the way they installed it is too restrictive.
I would have thought that if you would Y two 2.5" pipes together you would at least go 3". It is possible the single pipe leaving the Y creates too much back pressure.
A 2.5 inch pipe flows about 500 cfm. 2 of them is about 1000cfm. A 3" pipe flows about 750.
From what I can find the efi 460 can pull from 600-800 cfm. I don't know what if anything that the exhaust gas may add, but if you just go by how much air it pulls, it has to push at least the same.
If I take even 600 cfm and try to jam it into a pipe that can only push 500ish without bends or muffler restriction, it seems like too much back pressure.
I might be nuts, but I think part of the unfavorable sound is caused by this condition or at least adds to it.
I know this. We will know in about a week when my parts come in.
Imo duals are just twice as much hardware and twice as much to go wrong or rot.
3" is plenty for a street driven stock 460 engine.
More will just hurt scavenging.
A 2.5 inch pipe flows about 500 cfm. 2 of them is about 1000cfm. A 3" pipe flows about 750.
From what I can find the efi 460 can pull from 600-800 cfm. I don't know what if anything that the exhaust gas may add, but if you just go by how much air it pulls, it has to push at least the same.
If I take even 600 cfm and try to jam it into a pipe that can only push 500ish without bends or muffler restriction, it seems like too much back pressure.
....
Warning, boring fluid dynamics lesson ahead...
A 460 cubic inch engine pulls 230 cubic inches per revolution at wide open throttle if there is no restriction in the air flow (in or out). Doing the math, that's 600 cfm at 4500 rpm and 800 cfm at 6000 rpm. So actually pulling much over 600 cfm in a normally aspirated 460 isn't too likely.
But it does need to flow a lot more volume on the exhaust side than it does the intake. As air heats up it expands. Double the temp (on an absolute scale like the Kelvin scale) is double the volume (assuming constant pressure). I'm not sure what exhaust temps typically are, but assuming 400 deg F (= 204 deg C = 477 K) and 80 deg F intake (=27C = 300K), an engine needs to flow 60% more exhaust than intake (477 / 300 = 1.59).
So if my 400 F exhaust temp is close, 600 cfm intake would be about 950 cfm exhaust.
Imo duals are just twice as much hardware and twice as much to go wrong or rot.
3" is plenty for a street driven stock 460 engine.
More will just hurt scavenging.
A 460 cubic inch engine pulls 230 cubic inches per revolution at wide open throttle if there is no restriction in the air flow (in or out). Doing the math, that's 600 cfm at 4500 rpm and 800 cfm at 6000 rpm. So actually pulling much over 600 cfm in a normally aspirated 460 isn't too likely.
But it does need to flow a lot more volume on the exhaust side than it does the intake. As air heats up it expands. Double the temp (on an absolute scale like the Kelvin scale) is double the volume (assuming constant pressure). I'm not sure what exhaust temps typically are, but assuming 400 deg F (= 204 deg C = 477 K) and 80 deg F intake (=27C = 300K), an engine needs to flow 60% more exhaust than intake (477 / 300 = 1.59).
So if my 400 F exhaust temp is close, 600 cfm intake would be about 950 cfm exhaust.
I like it. This is probably why we see a lot of 2.5" duals and folks seem to be happy with it. I would say that 2.5 into 3 inch works out to be pretty close as well. Thanks for the science.
Hung the new mufflers tonight. Cut out the y pipe. Put in mufflers right after the stock h pipe. Runs very smooth, good acceleration and no drone. I brought the pipes out before the rear wheel.
Seems to run better. I can't believe how smooth.
The mufflers were $18ea from rockauto. Pipe was $30. Quiet truck. Priceless.
10-31-2015, 08:37 PM
