Exhaust opinion

Mopar Exhaust Systems

  1. 496 polara

    496 polara moparts id gch

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    Need to get out of my head and bounce it off of other people.My 360 currently has long tube headers,2.5 pipe to a flowmaster merged Y pipe Flowmaster Scavenger Series Y Collectors Y250300 to a full 3" single exhaust (tailpipe is late model F 150 take off and mandrel bent).
    Engine is 8.75-1
    Lunati hyd cam 220 @ .050
    308 heads with 2.02/1.60 valves and bowl work
    Port matched edelbrock performer intake
    Proform 650 dp

    904 tf with 2500 stall
    8.25 with 3.90 limited slip

    Sounds real fun till I tell you it is in my 87 Dodge D150 2wd.

    Is my 3" single exhaust costing me much hp?
     
  2. doug 371

    doug 371 Well-Known Member

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    no
     
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    • George Jets

      George Jets 1967 Dart 2 Door FABO Gold Member

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      I can understand why you went out the back with the 3" tail pipe. Dodge pickups have the plastic gas tank running down the driver's side so the exhaust all gets run down the passenger side.

      Lot of fun stacking 2 Dual mufflers in there and then a maze of dual pipes snaking up over the rear end and exiting as Duals under the rear bumper.

      Think you are alright with the 3" tail pipe to handle the volume after the 2.5" coming off the headers. Exhaust is coming out in pulses as each cylinder fires alternating the pulses into your 3" tailpipe, allowing the hot gases exiting area to expand into and exit out the back.

      As long as you are able to expand the hot gasses out to the back you are good.

      76 D100 with a 360 here, 2" duals with H-Pipe in front of mufflers.

      20200625_073837.jpg
       
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      • burdar

        burdar Owen's Dad

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        Walker makes a single inlet dual outlet muffler. They were used on F150s from the 80s. When I used to work at an exhaust shop we replaced a lot of them. On the Fords, the dual tailpipes ran out the same side but you could run the tailpipes out both sides pretty easily. That would be much easier then mounting dual mufflers on one side. Walker probably also makes a dual inlet dual outlet muffer.

        If all of your pipes are mandrel bent, I don't think you are leaving much on the table. It just depends on if you like the look of one tailpipe or if you want 2. I always heard that a 2" mandrel bend pipe flows the same as a 3" pipe that was bent on a traditional bender.(crimped bends)
         
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        • AJ/FormS

          AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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          that cam powerpeaks up near 5000rpm, but peak efficiency will be near 3500rpm. With 28" tires that will be ~28 mph with tires blazing. So you can't measure performance in first gear .
          3500 in second will be ~47mph.
          So what you can do is time your progress from 42 to 52 mph,in second gear, with a stopwatch.
          Then repeat with open headers. You may have to rejet the carb.
          Then decide if the improvement is worth the cost.
          If yur still spinning at 47 mph, you don't need more power....
           
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          • 496 polara

            496 polara moparts id gch

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            Thanks for the opinions.Easy for me to give someone else advice and also easy for me to overthink my stuff.Now to get rid of the straight through muffler that is waaaaay too loud.I am getting old and like it quiet.

            Truck has 30" tall tires at the moment but thinking on stepping down a size and moving the gears back to 3.55 for drive ability sake.
             
            Last edited: Jun 25, 2020
          • AJ/FormS

            AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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            FWI;
            3.91s and 30s is the same as 3.55s and 27.25s
            With the former; 65=2848@zeroslip
            With the latter 65=2846@ zeroslip

            My 223* cam pulled double overdrive where 65=1588rpm (clutch-car) no problem. That would be the equivalent of a final-drive ratio of 1.97 (3.55x.71x.78) and 27" tires.
            I did this with an A833od box plus a GVod behind it. Low gear was 3.09x3.55=10.97 about the same as the standard A833 where 2.66x4.10s (=10.91)

            Your A904 and 2500stall is a nice combo. The TC acts like a super-low gear at zero mph, and automatically " upshifts" as rpm and roadspeed increase. And even at it's minimum ratio it is still close to our less than one gear size higher than the rear end would seem to indicate. That makes your 3-speed automatic act like at least a 4-speed and more like a five speed.
            How is that possible you might ask?
            Well the way the TC is built, it has an internal fluid multiplication feature that is approximately equivalent to 1.8 at zero mph. This turns your 3.91s to 7.04.
            As the car begins to move out, this 1.8 ratio slips less and less, automatically, and eventually might couple to 1.1 or a little less .... and dare I repeat,it does this automatically.
            So what does this mean to you?
            At zero mph then your starter gear could be 1.8x2.45x3.91=17.24. And whatever torque your engine makes at stall,2500 in this case, is gonna get multiplied by that amount. Say your engine made 290 ftlbs at 2500, then to the rear axles, this would be 17.24x290=5000 ftlbs.
            Then as your vehicle accelerates, this 1.8 ratio begins to drop lower, while simultaneously your engine torque output is rising. So soon, say 3200rpm, your engine may be be peaking at 300 ftlbs, and the ratio may still be the same, so now you are at 4023 ftlbs. Go up another 1000 rpm and the torque may have fallen to 280, and the ratio to 1.5, so to the axles is now 4023.
            Go up to 5200 now, and torque may be 240 and the ratio 1.4, so 3219 to the axles.

            Now comes the shift into second (1.45 ratio) and the Rs fall to .59x5200=3070. Here your engine may be making 295 ftlbs, and the Tc ratio maybe 1.3, so to the axles is now 2174. Notice that is quite a hit from 3219. So now from this point on the TC ratio is gonna change only a little, and by 5200, again the torque might be 240 as before but the ratio may be down to 1.2, so to the axles is 1633.

            Now into third/direct the Rs fall to .69x5200=3590rpm. Torque may be 290 and the ratio may be 1.1, and so to the axles might be 1247; another hard hit. But it's ok , 3590rpm with 30" tires is 75mph, and if you are a streeter, that is speeding in most places,lol.
            If you had a manual trans, you would lose that Torque Multiplication feature, which is serious business. At zero mph, this is equivalent to one lower gear in the box or 80% more rear gear. By 75 mph, if the TC has dropped to 1.1, it is still equivalent to 4.30s.
            So lets line up the overall ratios
            17.24 at zero mph, diminishing to
            13.41 at the top of first. Since this is a difference of .778,lets count this as 2 gears. then
            7.37 at the bottom of second going to
            6.80 at the top of 2nd and since this is only 7% difference,lets count this as one gear. then
            4.30 at the 2-3 shift,one gear, and then
            3.91 to cruise with,the last gear
            That's 5 gears by my reckoning.

            Lets compare that to an A833 also running 3.91s. the box ratios are 2.66-1.92-1.40-1.00 so the rear axle ratios are
            10.40
            7.51
            5.47
            3.91
            No matter how you slice it, the auto has at least one more gear.
            Lets line them up to see how they compare;
            17.24-13.41-7.09*-4.30-3.91 (* is averaged)
            .......... 10.40-7.51-5.47-3.91

            How nice is that

            So whats the point?
            Well, 5000rpm in second gear at 20% slip with 30s and 3.91s comes to about 65mph; that is a fairly nice place to be with that cam.
            and 3.55s with 28s will be about 67mph, not much difference.
            But
            5000rpm in second gear, with 28s will be ~61mph with the 3.91s, or just about perfect. and
            30s with 3.91s cruses 65=2850 at zero-slip, and up to 3130 as you roll into the throttle,at 10% slip. So what you really need, IMO, is a loc-up ...... depending on just how much hiway traveling you do.
             
            Last edited: Jun 25, 2020
          • AJ/FormS

            AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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            I forgot to mention;
            you can do a pressure test just ahead of the muffler. You are looking for a maximum of 4psi at WOT, as the engine moves thru it's peak efficiency rpm somewhere between 3000 and 4000 rpm in your case; Less is better. Do not buy into the myth that an engine needs some backpressure. What an engine really needs, is a hi-powered vacuum cleaner on the end of the pipes!
             
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