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brainstorming: What is the optimum runner length?

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  • Engine: brainstorming: What is the optimum runner length?


    This post is a little different. I apologize if this is not the right place to brain race ideas, I just don't know where the best place would be for answers. Also my mind moves a lot faster than my projects do. So here i sit with my '60 champ on blocks with its axle quirks and in search of an aerostar front end. With the front end swap the motor is going to have to be put back in its correct place (couple inches up and forward).

    So since things need to move anyway, I was wondering if I was to attempt to build a tunnel ram intake manifold for a 289ci studebaker engine w/R2 grind cam, what would be the optimum runner length? For a street engine. I remember seeing Ted Harbit's Chicken hawk in a really great article in Hot Rod magazine (must have been 3 or 4 pages) I think in August '06 there was a picture of his homemade intake manifold. It looked like it had short runners like maybe anywhere from 4 to 6 inches. I understand that this particular example was force fed (twin turbos) and it was a drag car, not a street driver.

    I also remember those wild mopar intake manifolds of the early '60's (crossram?) had runners that were like 30 inches long.I hear that those engines ran out of air at 4500 RPMs. The Edelbrock catalog gives measurements on their tunnel rams. I think those measured around 9 inches. Not very scientific but I ran a steel tape on a Studebaker manifold that I had lying around and its front runners measured around 9 inches.

    I have thought about doing a "ramchargers" thing (making my own with runners made out of hard rubber so i can try different lengths) like that '49 plymouth high and mighty. However I am worried about the carburetor being forever cold since it will be so far away from the heat of the engine. My original plan was to make it out of steel and maybe start at 12 or 14 inch runners. All I am looking for is to make the most power out of what I have. I am not trying to go racing, but I also want to be getting all the power I can out of the fuel I am burning. Also don't know if it would be better to build the top of the plenum for a single 4 barrel or dual 2 barrels for fuel distribution

    I would love to hear thoughts, thanks in advance

  • #2
    Especially without forced induction, supercharger or turbocharger, you will experience a lag between carb/carb's and cylinder action when you go to too long of a runner.
    Do you have a reason for these other than appearance?
    Gary L.
    Wappinger, NY

    SDC member since 1968
    Studebaker enthusiast much longer


    • #3
      Ram effect depends upon many factors. Temperature, size of the port, size of the valve, cam timing all affect pulse strength and timing. Optimum ram effect is when the reflected wave hits the back of the intake valve at the same time as it opens in effect having a positive pressure wave there at the same time. In reality, this only happens over a narrow RPM and isn't effective in a varied RPM street driven engine in traffic.
      Bez Auto Alchemy

      "Don't believe every internet quote" Abe Lincoln


      • #4
        thehot -

        There is NO optimum for all circumstances...

        Well, with modern equipment, "lag" is pretty much a thing of the past..!
        Especially with belt driven blowers. That's never been much of a problem. And with todays turbochargers, the "lag" is VERY minimal. I've seen cars with the turbo's sitting on the rocker covers, I've seen turbo's over by the front tires. BOTH combinations can produce very similar 60ft. times..!

        As for naturally aspirated, as bezs says, it depends on a lot of things. Plus the fact, that a given engine combination...can be "tuned" with the use of shorter or longer runners, depending on the track surface..!

        Longer runners = lower rpm power.
        Shorter runners = higher rpm power.

        One thing you ALSO...need to ask, is the plenum volume..! This will also make a BIG difference on the way the engine makes power.

        A couple of us have expensive/very accurate computer engine modeling programs.
        Post ALL...of the engine specifications, along with ALL of the car specifications.

        Details matter..!


        P.s. - I'm currently working on a cross ram manifold for my 299 Stude engine. Keeping it all under the hood you know..!


        • #5
          Interesting Studegary, I never thought about a lag. hmm. I think it would look cool, but I am also interested in performance gains as well. I liked the idea of a larger plenum and longer runners. I thought I could have my torque and horsepower too. I have thought about those EVANS manifolds but I worry I would be throwing away torque down low. A tunnel ram seems like the perfect answer.

          Bezhawk: I have thought about that ram effect. And I was hoping to take advantage of that. seems like from everything I've seen the longer ones runners are the more torque one will have. . . to a point. Also the longer the runner the lower you move peak engine power in the RPMs. I often think back to G.M.'s"tuned port" engines with how at the time they made good power and just about the only negative thing I read is about how those specific motors "ran out of power "north of 5,000 RPMs and I think. . . When on the street do you ever go over 5,000?

          I am also looking forward to the cooler more dense air the engine will get once its pulling air not found under the hood


          • #6
            Mr Mike Van Veghten: You forum people are so resourceful and helpful. I am rather spec-less I'm afraid. I can say this though. I just rebuilt the engine last winter so some stuff is still fresh in my mind.

            R2 cam. Full flow block bored .030 over(292 or 294ci?), 289 crank turned .010 under. 15557570 heads w/thin head gaskets w/ dished 289 pistons, valves are stock. I estimate static compression to be 8.5 to 1. It did have a bigger carter A.F.B on it like 625cfm? but nothing now. I don't have any specifics on the distributor but I can tell you its the one without the window, still run points. I think at idle and for my elevation I am around 12 degrees BTDC and when hooked to ported vac it was if I remember like 48? total. Way too much. it would make the motor shut off until RPMs came back down, now plugged into reg vac I think total is around 36-ish. No heat riser, and exhaust is duals, starts off as 2" then steps to 2-1/4 then steps to 2-1/2. Transmission is 3speed w/electric O/D converted to floor shift. I think its the T-85 (its the one with the cover/lid on the same side as the shift forks). And rear end is a twin traction w/4.09 gears. in a shout stepside '60 champ door tag says 5E6-112 as model. I think it weighs 4800 lbs.

            I hope this helps

            And I would love to hear/see more about your motor too
            Last edited by thehotrodder; 03-15-2020, 08:57 PM.


            • #7
              Interesting subject. About like selecting beer.
              Tunnel rams are a naturally aspirated high RPM specific item.
              Meaning, the work best at wide open throttle at extremely high rpm.
              So, to cut to the chase. Are you drag racing? Or do you want 'the look'?
              As to your runner length question. (Naturally aspirated carburetor answer).
              Runner length (optimal runner length) is a function of the combined intake port size/length in the head matched to the intake runner size/length of the intake manifold taking into account the plenum volume...all in the desire to have the reversion pulse (caused by the intake valve closing) run all the way up to the throttle blade bottom and have that pulse actually help move the intake flow into the cylinder. A longer port runner length is not necessarily nirvana to your engine operation. And everything affects this size/length. Cam, valve size, carb size, rpm, temperature, air density, piston speed, 401K, yada yada yada.
              Does your head hurt yet?
              So, unless you have all this mapped out to your specific combination, you will end up chasing your tail.
              Sure, hard core racers have figured it out...Mostly by trial and error, and years of experimenting.
              Studebaker types think they have it figured out....Mostly by being stubborn <g>..
              Good conversation, though... Thanks for bringing it up on the forum.

              PS: There will be a tech seminar at the upcoming SDC Int'l meet in Chattanooga on intake manifolds and cylinder heads.

              HTIH (Hope The Info Helps)


              Get your facts first, and then you can distort them as much as you please. Mark Twain

              Note: SDC# 070190 (and earlier...)


              • #8
                I apologize if this is not the right place to brain race ideas, I just don't know where the best place would be for answers. Also my mind moves a lot faster than my projects do. . . . I have thought about doing a "ramchargers" thing (making my own with runners made out of hard rubber so i can try different lengths) like that '49 plymouth high and mighty.
                Here in the frozen northwest, the bench-racing season is drawing to a close, but with a low of fifteen degrees and snow this weekend, we're still thinking rather than doing.

                As already suggested, define your wants, goals and budget:

                1. Most important, does it have to fit under the stock hood? If yes, fuggediboudit. If no, then an original Ramchargers ugly-on-a-stick intake is a possibility.

                2. Do you have the budget to spend $2000 on professional head porting, $1500 on a custom intake and $2500 on a custom roller cam? If yes, then a tuned port ram intake can be designed and built to make power at a specific RPM range. If no, fuggediboudit.

                3. Will the car be street driven? In cooler weather? Always with premium fuel?

                4. Do you have the tuning skills or the budget to put it on a chassis dyno?

                5. Have you checked your state motor vehicle code for obstructed vision? Some tunnel rams and/or GMC superchargers are prohibited in some states. They block the drivers's vision to the right front.

                These are just the first few questions to be answered.

                jack vines


                • #9
                  Mr jack vines: it’s great to hear from you. This project doesn’t have to fit under the hood or even need a hood. I haven’t thought about obstruction laws, I will have to look into that. I don’t really have any plans to use large amounts of money on this project. I would like to get my heads ported at some point but right now that will have to wait. I was thinking I would build my own. I get the impression that Studebaker thought that about 9” of runner was good enough for their engines not knowing what plans future owners would have. I guess I’ll start with that. Who knows, this whole thing might be headed for the scrap bin but only time will tell. I’m willing to try ugly on a stick.
                  Last edited by thehotrodder; 03-17-2020, 08:50 PM.


                  • #10
                    I am a CASO, i would use 2 cheap turbo's with waste gates. they are usually set at 7 to 10 lbs boost. flip your exhaust manifolds over. add 2 studs and 2 new drilled and tapped holes for mounting. build an adapter from exhaust manifold flange to turbin inlet (Hot Side). oil from turbo's must return to oil pan ABOVE oil level. use an R2 carb bonnet and seal a carb of your choice. above about 7 psi boost an intercooler is highly recommended! water injection is an option. i have run 18 lbs boost through a warmed over 289 with nothing but the loss of 2 head was a very eye opening experience! i run a 3in pipe from the turbo to a 3in muffler then split to 2, 2 1/2 tail pipes. this is with a single turbo. the twin turbo set up feeds a 224 with lite flywheel, all i could find at the time. feeding 3 in side pipes for a different look/ sound. you can "Size" your turbo's for boost right off idle or they can "Come In" farther up the RPM scale. new turbo's can be had for $100 bucks on up. or go scrounging in the junk yards. just use something near to the same CID as you are working with ,IE 2 thunderbird turbo coupe units on a 289. i have a pair of mitsubishi twin turbo's for the 224. the wastegate can be cheated for more boost simple, straight forward,fun and cheap! Luck Doofus


                    • #11
                      By the late, great, usually technically pretty solid Roger Huntington -
                      Inertia // or // resonant ram effects.
                      A simplified runner length equation, and a graph for those in a hurry or a nice cross check for those going the mathematical route.


                      1950s - 1960s tech. 10% more torque at 2800 rpm.
                      Poifect for Studebakers, or most any street car.

                      The Mopar superstocks and maybe letter cars had the shared inner wall cast several inches shorter to create the "short ram version" to work better at high rpm..


                      • #12
                        Keep in mind that one of the design constraints of those MOPARS, with things like cross rams, was to get everything to fit under the existing hood (where there wasn't much spare room).
                        Gary L.
                        Wappinger, NY

                        SDC member since 1968
                        Studebaker enthusiast much longer


                        • #13
                          Looks like you would have iceing problems in cool damp weather. Old VW long tube intakes had exhaust heated intakes. When the heat was plugged frost developed on runners. Something to do with refridgeration.