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Thread: Rev limit suggestion

  1. #1
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    Rev limit suggestion

    Hello all,
    I recently got a not yet installed pertronix igniter 3 module with a rev limiter to replace my igniter 2 which doesn’t have one. Looking for suggestions on what to set the limiter at. I’ve probably taken it to 6k but usually shift at max 5500 to 5800.
    Setup is an ‘88 5.0/302 short block with stock rotating assembly, stock cam, 100k miles approx. New GT40 Y303 heads, 1.72:1 roller rockers, performer RPM manifold and 650 DP.

    Thoughts and suggestions? I’m thinking 6200.

    Has anybody changed their distributor from an igniter 2 to 3? Pertronix tech guy on the phone says I have to change the magnet, which means taking the gear off. Pertronix instructions specifically say I don’t need to change it and their how to video also doesn’t show them changing it.

    Thanks as always

  2. #2

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    The primary limiting factor is your valve train. A hydraulic roller cam and associated parts are usually good for about 6,400 rpm's. Setting yours at 6,200 is about perfect.
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    Thanks Bob!

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    I am wondering whether when setting the rev limit , one would take into consideration the rpm at which max hp is delivered? I don't know whether there is a relationship between them but I don't believe your getting any additional pull past max hp. For example, if max hp is delivered at 5750, why not set the rev limit to 5800? Just asking.
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    Steve >> aka: GoDadGo
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    Like ThickCobra, I'd suggest setting the rev limiter about 100-200 RPM above the maximum operation range of your engine or your normal highest shift point.
    You'll save your engine and will quickly learn to adjust when to shift if you hear your motor popping when it is spinning up against the rev-limiter.
    As an example; right now I'm at 4,200 RPM because I'm still in break in mode but I will eventually go up to some place around 6,200-6,300.
    When tooling around I'll shift it at 4,000 RPM because I now know what it sounds like at that RPM so shifting by ear is a much easier task.
    Also, my rotating assembly is rated at 7,500 RPM so my intake and camshaft combination craps out below that number.
    Last edited by GoDadGo; 06-14-2019 at 08:05 AM.

  7. #6
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    I was thinking about that too. There is no reason to spin a stock block, stock cam, stock bottom end 80's 5.0 past about 4500 rpm. Max torque comes in about 32-3500, max hp somewhere around 40-4200. Ya got a good intake and heads, upped to 1.72's, lets it breathe a lot better, but its not moving the powerband much. I'd set it about 5000 and shift at 4-45.
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    Seasoned Citizen NAZ's Avatar
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    I've seen a variety of methodologies for establishing a high-end rev limit -- all had some justification for that limit. Setting it a couple hundred above your shift point is popular and makes sense if you don't see a need to turn the engine any higher such as a street driven car. But for a race car there may be times you turn higher RPMs -- like a long straight where you don't have another gear to grab, you may run several hundred RPM more than peak HP to keep building speed until the braking zone. In this case you may set the high-limit to the max limit of your valve train.

    Arbitrarily setting a couple hundred above the max HP RPM doesn't take into account that shift points will typically be several hundred higher than peak HP as you base shift point off the RPM drop into the next gear. And while the HP & torque start to fade past the peak there is still power being made far past the peak. The engine I'm building now peaks at 7000 RPM but drops less than 40HP at 8000 RPM. I won't be setting my high end rev limiter at 7000 as I will be going through the 1/4-mile lights at more than 7000 RPM and will be taking advantage of every fraction of HP I can.
    Last edited by NAZ; 06-14-2019 at 02:27 PM.
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    My cam spec sheet had information as to the max rpm it would sustain (6200-rpm.) I have a D.U.I. ignition system with their rev limiter and put the 6000-rpm chip in it.

    Ray
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  10. #9
    Senior Member SSNK4US's Avatar
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    About 5 rpm below valve float....
    Hope that helps LOL! (joking)

    Agreeing with NAZ.... nothing worse than hitting a rev limiter if the motor can take more.... less HP is better than no HP.

    Kurt
    Last edited by SSNK4US; 06-14-2019 at 04:46 PM.
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  11. #10

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    Quote Originally Posted by ThickCobra View Post
    I am wondering whether when setting the rev limit , one would take into consideration the rpm at which max hp is delivered? I don't know whether there is a relationship between them but I don't believe your getting any additional pull past max hp. For example, if max hp is delivered at 5750, why not set the rev limit to 5800? Just asking.
    Quote Originally Posted by Boydster View Post
    I was thinking about that too. There is no reason to spin a stock block, stock cam, stock bottom end 80's 5.0 past about 4500 rpm. Max torque comes in about 32-3500, max hp somewhere around 40-4200. Ya got a good intake and heads, upped to 1.72's, lets it breathe a lot better, but its not moving the powerband much. I'd set it about 5000 and shift at 4-45.
    Your shift point and your redline are two different things. Redline is the maximum safe limit before the valves begin to float or the rod caps let go - whichever comes first.

    Remember that overdrive gears divide torque, and underdrive gears multiply torque. When you upshift into a higher gear (lower numerically) you multiply your torque less than in a lower gear. Holding that lower gear a little longer increases your delta-V, even if your torque peak is, say, 4,500 rpm's. If you're racing, this can shave seconds off your lap time.
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  13. #11
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    I swapped from an igniter 2 to igniter 3 module. I remember having to take the gear off to swap the module. Don't remember having to swap the magnet. Pretty easy.

  14. #12
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    Thanks for the replies all.
    The reason I want the rev limiter is I’d like to try some autocross and be able to hold 2nd without risking reving it too far. Rev limiter seems highly recommended for autocross. Also to potentially save the motor if something breaks. Last summer I blew 3rd in my transmission at full throttle and the tach instantly went very high! If I break something else in the drivetrain hopefully I won’t blow engine too.

    I don’t have a problem shifting it on the street without over reving. It still pulls hard in the 5-6000 range, I wouldn’t want to give that up.

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