Does an increase in airflow (intake or exhaust runner) move peak torque up or down the RPM band?

Small Block Mopar Engine

  1. Oldiron440

    Oldiron440 Well-Known Member

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    And always will be.
     
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    • famous bob

      famous bob mopar misfit FABO Gold Member

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      I have posted this before; I built a pretty hot 406 sbc, ended up with it in a 92 gmc shortbed. I built the 3" exh. system to dump in front of the axle, it did have a fuel cell, so real headers. I got the bright idea of having tail Pipes bent to go ever the axle and dump behind the rear tires , camaro like, FULL 3" . I COULD NOTICE A DIFF IMEDIATELY WHEN I STARTED IT TO BACK THE TRUCK OUT OF THE MUFFLER SHOP , I DROVE HOME "ABOUT 6 MILES" , AND PULLED THE TAILPIPES OFF, .
      I still have them in the shed if anyone wants them , they are just barely starting to get rust spots on them . I paid the guy $100 to bend them up.
      Free to a good home ,just pay the shipping.
      Will fit any chevy/gmc with headers . shipping from 74021 ---------bob
       
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      • rumblefish360

        rumblefish360 So close, yet so far away

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        Ahhhhh, Bob, ummmm, this is a MoPar board, you know that right......
        :lol:
         
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        • Garrett Ellison

          Garrett Ellison Amateur driver on public roadway, do not imitate.. FABO Gold Member

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          Like I said, full exhaust system, as in exiting the rear of the car. Also agreed that most header collectors are tuned to the short side. The way to tune extensions is to put a stripe of marker paint on them and trim them off where the paint stops burning off after making a pass. The point where the heat drops drastically in an exhaust system is were extra tubing starts fouling out the scavenging.
           
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          • Wyrmrider

            Wyrmrider Well-Known Member

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            many headers and especially collectors are too large and too short
            start with PIPEMAX to check
             
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            • Oldiron440

              Oldiron440 Well-Known Member

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              You can manipulate torque and power curves with intake manifolds even to the point of covering up head runner size, just look at the LX runner size and tell me that's perfect for stop and go traffic in your halfton pickup.
              It's sure good for making 500 hp na with a carb and cam.
               
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              • greymouser7

                greymouser7 Vagrant Vagabond “Veni Vidi Vici” FABO Gold Member

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                That sounds good Bob!!
                 
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                • Mattax

                  Mattax Just the facts, ma'am FABO Gold Member

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                  Best to keep the collector diameter to the H (about 20 inches after the individual tubes end) or mufflers.
                  Power levels your discussing, a muffler with 2.5 inch in/out willgenerally flow with noticibly less restriction at the high rpms than a 2.25.
                  And muffler is the biggest restriction in the system.
                  If you want to join into single exhaust, Calvin Elston has done that....
                  He's been pretty generous in sharing his experiences. Here's one about merging to a single tailpipe.
                  Flowmaster Outlaw muffler - anti-reversion? - Page 3 - Don Terrill’s Speed-Talk

                  He has blog, but most of his discussions are on speed-talk, and some on YB.
                  Exhausting 101

                  Also, results from open headers vs 2 into 1 near the bottom of this page.
                  2017: Revisiting 4:2:1 vs 4:1 headers w merge collectors in the modern era - Page 4 - Don Terrill’s Speed-Talk
                   
                  Last edited: Oct 14, 2019
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                  • famous bob

                    famous bob mopar misfit FABO Gold Member

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                    You want them ?
                     
                  • famous bob

                    famous bob mopar misfit FABO Gold Member

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                    I did that 50 plus yrs ago on my hemi car, didn't help at all , my problem was always hooking it up on my budget ---14 and 16" slicks/s.s springs on a piss poor track.
                     
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                    • 273

                      273 Well-Known Member

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                      The big three are probably head flow, cam and displacement. Take 67 273 and 318 there both identical to each other besides bore size (displacement). Cam and head flow is the same. Both engines will flow the same amount of air over time. The 273 is 86% the size of the 318 but the 318 would need about 86% of the rpm to displace the same amount of air through the engine (cfm). Now if you put more cam in the 318 so both would have similar air flow over time per cid ratio the both should have similar powerband. But also if the 318 had the same head flow to cid ratio as the 273 but same cam than both should have the similar powerband. Obviously there other factors but I think there the main 3.
                       
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                      • 273

                        273 Well-Known Member

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                        Another way to look at it. Take the somewhat useless formula that people use for carbs.
                        CID x RPM/ 3456 = CFM

                        Take A 273 @ 6500 rpm or 318 @ 5580 rpm both would move a theoretical 514 cfm. To fed those engines at those rpm your gonna need enough air flow to support them. Though a combination of mainly cam and heads. There’s many ways to get there less head more cam or more cam and less head or in between. No matter which way you go should have a similar powerband but more head and less cam should be the most streetable.

                        P.S. that’s why the formula doesn’t work for picking a carb because even though we know we need 514 cfm it doesn’t help with which head we need even though we know the head cfm.
                         
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                        • greymouser7

                          greymouser7 Vagrant Vagabond “Veni Vidi Vici” FABO Gold Member

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                          yes sir, thank you
                           
                        • moper

                          moper FABO Gold Member FABO Gold Member

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                          X2
                           
                        • RustyRatRod

                          RustyRatRod 30 Degrees Outta Whack FABO Gold Member

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                          They have to have some kind of mod on the intake side to be used on the Cleveland blocks if they are true BOSS 302 heads. Although they are almost identical to the Cleveland 4V heads, there is a difference. I have a complete 1970 M code Cleveland. 4V closed chamber heads and all. They are pretty formidable engines when built right. I agree about your 400 statement. I've always said the 4V heads would have been just right on the 400. Those intake ports are just too huge for the 351......but they can be made to work if you're careful.
                           
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                          • RustyRatRod

                            RustyRatRod 30 Degrees Outta Whack FABO Gold Member

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                            That'll just be your little secret.
                             
                          • Oldiron440

                            Oldiron440 Well-Known Member

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                            :rofl:
                             
                          • RustyRatRod

                            RustyRatRod 30 Degrees Outta Whack FABO Gold Member

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                            He would have to think the Cleveland is junk too. They are all the 335 (Cleveland) family engines. The only difference is the deck height. The 400s got an especially bad rap for two reasons. 1) They were never offered with a four barrel carburetor from the factory. 2) Although Ford did all they could do, the 400 was prone to detonation. The piston was too far in the hole at TDC to take advantage of any quench, but Ford kept going the opposite direction. They kept increasing the piston dish which made the problem worse. All they had to do was put a closed chamber, two barrel head on it and bring the piston up to close to zero deck, and given it some quench. Problem solved, but they never did it.

                            The 351M never had that problem, because of the shorter stroke. To say that those engines were junk is a stretch at best, especially considering Ford put them in everything from the 400's introduction in 1971, until its demise in 1982. That's a lot of models and a long run for "junk". Although the 400 did have its problems, it is a fine foundation for an HP build. As long as you give it some quench and or use a camshaft with a later IVC event, you got it licked. They can be stump pullers. I have a 351M in my 75 F250 and it's hardly junk. I have a hot 400 under the work bench I plan to swap in it that's also not junk. I remember a time when people said the Chrysler 360 was a boat anchor truck motor. They were wrong, too.
                             
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                            • famous bob

                              famous bob mopar misfit FABO Gold Member

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                              YOU missed the point !

                              I have a guy wanting those tailpipes already too .
                               
                            • justinp61

                              justinp61 Well-Known Member

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                              Actually, I like the Cleveland. I have never seen a Ford "M" engine run hard at the drag strip. My brother and I had several of them over the years in 4X4 trucks both stock and well built. While they may be fine for a daily driver if you could afford the gas they are junk for a base for a hot rod. There are better starting points.
                               
                              Last edited: Oct 15, 2019
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