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Intake manifold test

Discussion in 'Modified Alpine' started by Bill Blue, Nov 9, 2019.

  1. Bill Blue

    Bill Blue Diamond Level Sponsor

    I decided to see how evenly my intake manifold flows. The short answer is "like crap". First question:
    Are the readings a valid indicator of what the cylinders see at wide open throttle?

    My test rig is a leaf blower "hard plumbed" (no air escape) to the intake. Throttle was removed. All cylinder ports open. Readings are deflections (in degrees) of a cardboard flap. Results.

    Port #1 25 degrees
    Port #2 50 degrees
    Port #3 80 degrees
    Port #4 20 degrees

  2. puff4

    puff4 Gold Level Sponsor

    Interesting test rig! What manifold is this, Bill?
  3. Bill Blue

    Bill Blue Diamond Level Sponsor

    This is a manifold that I fabricated for use on the Duratec I4. Made up of exhaust pipe shapes, an "over the top" design with long (16"), skinny (1.54") dia runners. This is the third one that I have made for the D'tec and worst performer. Trying to figure out why. According to the math, it should be the best. I want to validate the test before going any deeper.
  4. 260Alpine

    260Alpine Silver Level Sponsor

    Trumpets.jpg Sheet metal.jpg Bill, What length are stock and are they equal length or uneven length. I can do simulations on my Desktop Dyno to compare how different lengths move the TQ and HP curves. Rover V8 uses different length trumpets to tune their fuel injection for equal length to each valve. Sheet metal intakes for race cars use V tubes for equal length from ram log.
  5. Barry

    Barry Platinum Level Sponsor


    Manifold or port flow for normally aspirated engines is normally measured with a vacuum applied to the downstream end rather than applying pressure to the upstream end. Your throttle body is pretty well lined up with the middle two runners, but not with the outside (#'s 1 & 4) runners which may help to explain your results (higher "flap deflection" in the middle than on the ends).

    Can you post pictures of the three manifolds?
  6. husky drvr

    husky drvr Gold Level Sponsor


    Since you are trying to measure flow that involves just one runner at a time, you may want to test with only one runner open at a time for more comparable results. Your leaf blower might be a bit much at a single port test level. Maybe you could hook the port outlet to LB intake and test at throttle body mount?

    Just a couple of thoughts.

    Have fun,
  7. Bill Blue

    Bill Blue Diamond Level Sponsor

    Stock for this engine is about 13", equal length. Valve ports add another 4". What is a V tube?

    I've decided that blowing air through the manifold is not a valid approach. I'm going to try to use the leaf blower as a vacuum source and simualtaneously suck air through all the ports. That would be a fairly close approximation of the conditions created in a running engine. Measuring is where things get sticky. Could I get meaningful data using a Pitot tube at each port?

  8. husky drvr

    husky drvr Gold Level Sponsor


    Trying to test all ports at the same time is unrealistic. The flow will find the path of least resistance. You've already found that for continuous flow in all runners. The throttle body port is the restriction that will not allow enough air to flow to fill all ports at your test airflow level. Your test is only showing how much air you can push or pull through the TB. Which is less than the combined flow of the four runners.

    OTOH, if you want to use a Pitot to test and do each port individually, you can construct a way to measure at the TB port while using a shop vac to pull air through the manifold. Ideally you might want to have a plenum between the Intake Port and vac to reduce the possibility of a vortex extending from the hose into the runner.

    I suspect when all is said and done, you will find that you will only have a small difference as measured by inches of water.

    Last edited: Nov 9, 2019
  9. Bill Blue

    Bill Blue Diamond Level Sponsor

    Trying to test all ports at the same time is unrealistic. The flow will find the path of least resistance.

    We might have a problem with language and the phrase "test all ports at the same time". My goal is to take individual port readings while pulling air through all ports, as I feel it is important to know the plenum is doing a good job of providing air equally to all runners. Testing while flowing air only through the port being tested would be a test of the runners, not the entire intake manifold.

    I agree totally about the need for a second plenum.

    I hope you are correct about suspected conclusion. I'm really not in the mood to build another manifold, that's why I'm testing this one.

    Someone asked about pictures. I'm out of the picture taking business. The entire picture downloading/uploading process befuddles me as there are no screen prompts. My last two requests for computer help were met with silence, I ask for help only when the damn thing quits working.

  10. husky drvr

    husky drvr Gold Level Sponsor

  11. Bill Blue

    Bill Blue Diamond Level Sponsor

    They briefly discuss the importance of equal flow manifolding. They are using TBI injection, which should deliver the same air/fuel ratio to each cylinder regardless of volume. Compare that to Port Injection, where fuel delivery is independent of air flow. If each cylinder receives a different volume of air, each cylinder will be operating at a different air/fuel ratio. Tune that.

  12. Bill Blue

    Bill Blue Diamond Level Sponsor

    Jim, rereading your post, I've decided V tubes are velocity stacks and are used to compensate for uneven runner length.

    I would be interested in seeing printouts on the impact of runner length. I made this manifold so I can "trombone" the runners without a whole lot of trouble. I can vary the runner length from about 12" to 17".

  13. 260Alpine

    260Alpine Silver Level Sponsor

    Bill, I'll look at the Duratec specs and vary the runner length and see how the HP and TQ changes. Is yours the 2.3 or 2.5?
  14. husky drvr

    husky drvr Gold Level Sponsor

    Actually, I thought you would find this statement most interesting:

    The manifold should flow about 20% to 30% more than the heads or else they will cause a restriction to the flow potential of the system. Most of the manifolds we tested did not equal, let alone exceed, most well-ported iron heads, to say nothing of the Edelbrock, Indy or other aftermarket aluminum heads.

    So what have you found to be the flow potential of your heads? It's not just a theoretical number from a formula.
  15. 260Alpine

    260Alpine Silver Level Sponsor

    Bill, My Performance Trends simulator only had specs for the 2.5 Duratec. HP stayed within 1000RPM. 5500-6500RPM. TQ varied quite a bit from 12" runner length for higher RPM peak to 17" for lower RPM TQ peak.

    12" 5700-6400RPM depending on cams, mild to HP
    13" 5300-5900
    14" 4900-5500
    15" 4500- 5100
    16" 4300-4800
    17" 4000-4500
  16. Bill Blue

    Bill Blue Diamond Level Sponsor

    husky drvr, I'm not sure that I am interested in the flow potential of the head. The redline for the 2.5 is 6500, which is also the rpm for max stock hp (170). I feel I would be a lucky SOB if I could find 170 hp with homemade manifolding and tuning. The previous intake, with short fat runners, had more hp at 5500 plus than this one, so I know there is more top end potential than I'm using. That does not bother me, I made this intake looking for more low end grunt. I am somewhat disappointed in that I seem to have picked more in the midrange than low end. I was hoping for the opposite. Right now, the engine really comes on at about 3200. That is not bad, the engine tachs 3,000 @70 in 5th.

    Jim, my engine is the 2.5. Do the lengths include include port length?

  17. 260Alpine

    260Alpine Silver Level Sponsor

    Bill, Total length to the valve.
  18. Bill Blue

    Bill Blue Diamond Level Sponsor

    Uh, maybe we need to extend the scale to 21".

  19. 260Alpine

    260Alpine Silver Level Sponsor

    I can do that Bill.
  20. 260Alpine

    260Alpine Silver Level Sponsor

    Bill, Here you go. Remember this is only a simulation, but it does show a trend.

    18" 3800-4300RPM
    19" 3600-4100
    20" 3500-3900
    21" 3300-3700

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