Best Shift Points For 2v

Discussion in 'The Garage' started by KillNThrill24, Jun 8, 2014.

  1. KillNThrill24

    KillNThrill24 Legend

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    I've been out and about this year and having some runs and just having fun. I've noticed a lot of people online saying shifting at or near redline is a waste because the power is gone.... I have to say I swear it feels like my car pulls hard and steady up to the 6, maybe 6100 point. All that's done to it is a bullitt swap and MSD's (I know not much of an upgrade, if at all, but it's what I could afford.) Everything else, engine wise, is stock. Just curious to see what other gt/bullitt owners think about the matter. Hell even 4v/pushrod guys feel free to chime in if you've owned a 2v
     
  2. MadStang

    MadStang Well-Known Member

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    if you swapped to the bullitt intake you've shifted your rpm band slightly higher. still though, the only true way to gauge where exactly you should be shifting is with a dyno sheet. it'll tell you exactly where you need to shift.
     
  3. RichV

    RichV Well-Known Member

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    Yep, dyno.
     
  4. Wichers123

    Wichers123 Well-Known Member

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    When I had svo I would run all the way to 6500 to keep myself in the power band now with stock npi mani I only run to 6000.
     
  5. g36 monkey

    g36 monkey Moderator Staff SN95 Supporter

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    Like Brett and Rich said, the only true way to know is the dyno. The basics:

    You figure out how much your RPMS drop between shifts. So, say you're pretty good, and only lose 500 RPM between each shift (this takes a while to dial in, and most people lose a different amount for each gear, so pay attention to that and adjust accordingly, the 500 is for the sake of easy math)

    Once you get the car dyno'd (most shops charge $80 for 3 pulls and a print out, but sometimes you can go on a special dyno day and get the same treatment for $30 or so) and get your print out, pay attention to peak torque.

    Say you hit peak torque at 5,000 RPM. So, you want to shift in every gear at the RPM that drops you back down to peak torque to pull you through the power. So, in this particular argument, you would shift at 5500, anything past that is pretty much a waste of time.

    So, if you wanna spend a few nickels to really dial this in, you can definitely increase speed that way.
     
  6. Goldmember

    Goldmember Well-Known Member

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    My method isn't scientific whatsoever; I just hang it out until it feels like it's not really pulling.

    First I'll run to 5800 (I don't go past redline); Second the same; Third about 5500 RPM. Past that... I've never been past that, Third will get you past 90 on 3.27's.
     
  7. MadStang

    MadStang Well-Known Member

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    I posted this tech article awhile back on another site. Should give you some insight on how to figure out where to shift.

    When Should I shift? This seems like a simple question but there really is a lot more behind it then just shifting at redline. Having a better shift point does not make you "make more horsepower" all it does is increase the effectiveness of your rpm band as well as maintain a steady increase of momentum in a foward motion. Realistically, to get an accurate reading for when you should shift you need the following:


    Dyno Graph showing the Horsepower and Torque Curve
    The RPM drop between a shift from 1-2, 2-3, 3-4, 4-5, or 5-6 if you have a 6th gear.


    There's a reason for me listing all of the different gear selections. This is because not all transmission gears nor drivers are created equal, meaning that not each gear is evenly spaced out in a transmission nor does every driver shift the same so RPM drop can very from car to car or driver to driver. Now that we've got this covered, let's dissect a Dyno Graph.


    [​IMG]


    Here's the basic layout of what a dyno graph will look like. Horsepower and Torque on the Y-Axis and RPM on the X-Axis. Let's use this graph as an example.


    For this exercise assume a 7500rpm redline (off the chart) and a 2000 RPM drop between gears. If I were to shift at 7500RPM would I be taking advantage of every bit of power available to me? The Short answer is no. See Graph 1 Below:


    Graph 1
    [​IMG]


    First off, I apologize for 7500 rpm being off the graph, just assume it goes all the way up to 7500 before shifting. If we have a 2000 rpm drop from say, 1st to 2nd gear, that would put us at 5500rpm in second. Why is this shifting habit not optimal? For one, you're going way out of the RPM range of the car, it doesn't have enough air to be able to go that high so you'd be losing a lot of forward momentum. And secondly, you're completely avoiding the most important part of the car's power. It's Peak Torque. As they say, "horsepower sells cars, torque wins races." Torque is what makes the car accelerate horsepower just maintains that acceleration. Now if you were to shift at 6000rpm, that would have you shifting right where you want it, right? Max horsepower then putting you in the grunt of the Torque curve. Actually no, this is not what you want.... See Graph 2 Below:


    [​IMG]


    Shifting at this RPM, sure you're shifting right before your Horsepower drops off, but by doing so in a 1-2 gear shift, you will experience what is known as bog, which will absolutely kill any forward momentum you may have. I said it once and I'll say it again, Torque is what will accelerate you, horsepower is just there to maintain that acceleration. By shifting at 6000RPM's you are shifting much too early and putting yourself before the full rise of the torque curve.


    Now, if you were to shift at 6800rpm's with a 2000 RPM drop, that is your winning ticket of a shift. Are you going past your peak horsepower? Sure, and it may kill some momentum, but of all 3 options you have, this will keep the most momentum going forward and you will see either faster ET's or if you road race, quicker lap times. See Graph 3 Below:


    [​IMG]


    By shifting at 6800RPM's, you are putting yourself right where the peak torque band is at 4800 RPM's. In fact, an engine will operate most effectively, resulting in maximum acceleration, when the rpm is maintained at the torque peak all the way up to the next gear shift that puts the rpm right back at peak torque. In a perfect world, you would have Peak torque and Peak Horsepower perfectly spaced so that as soon as you hit peak horsepower, you would shift and have it put you right back at peak torque. Unfortunately this is often not the case with street cars and oem transmissions built for Miles per gallon versus smiles per gallon. But always keep in mind the following:


    An engine will operate most effectively, resulting in maximum acceleration, when the rpm is maintained between the torque peak and horsepower peak
     
  8. g36 monkey

    g36 monkey Moderator Staff SN95 Supporter

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    If you don't wanna throw it on the dyno, that's pretty much how you have to do it
     
  9. KillNThrill24

    KillNThrill24 Legend

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    Awesome write up there Brett that actually really puts it into a perspective that I never really took the time to think about. And thanks all for the advice there. I see that the dyno is really the only true way of measuring the perfect point to drop me back into the peak tq/hp range that Brett was talking about.

    As for actually putting it on the dyno, I was hoping to wait until I got my build finished to do it. But I suppose in the name of racecar maybe I can. Tho I'm pretty good friends with the local tuners, they'll just tell me "don't waste your money on your stock 2v Karate Kid" Haha. At any rate if I don't want to spend the money on it.. I definitely have thought about pulling my 6250 or 6300 limiter off and running it out to 6500 and see where it starts dropping. I've hit rev limiter a few times and it felt like it pulled up to it but it's really hard to judge that when it bounces off rev limiter. The only 2v dyno sheet that I've seen offhand that I remember the stats on is my buddy's 01 with a P1. His rev limiter was set at 6300 (because he scurrrred to blow it up) by the tuner, but his car peaks out right around there. Tho, again, every car is different and with a blower on that obviously would change things around a little.

    Thanks for the advice guys I'll definitely take into consideration maybe tossing it on the dyno and seeing what it puts out as far as a curve
     
  10. Wichers123

    Wichers123 Well-Known Member

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    Don't be scared I bounce off 6500 like its nothing.
     
  11. MadStang

    MadStang Well-Known Member

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    and I bet your valve springs, oil pump, timing chains, guides, and tensioner are all screaming help me. Never a good idea to bounce off the rev limiter especially on a stock block mod motor.
     
  12. Wichers123

    Wichers123 Well-Known Member

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    It's does just fine. My motor have 4 broken pistons and I still run it full boost and all, it takes it and smiles :)
     
  13. justinschmidt1

    justinschmidt1 Legend

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    I like this guy.

    As far as shift points go, id just test different shift points out...if you put the car on the dyno you can do the math and figure out exactly where to shift to get the highest avg hp/tq using your gearing and hp/tq by RPM.

    Mod motors are pretty rev happy....wouldnt suprise me if your best shift points were north of 6k.