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Thread: Rev range

  1. #16
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    I do not think that power would be climbing much at if at all over 6k, and certainly done by 6500 or before. It may have just been ready at that rpm to be nosing over..

  2. #17
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    yes, and the rods and pistons in the engine are more than needed for the combos rpm

  3. #18
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    Quote Originally Posted by BasicQ View Post
    A lot of options out there:

    Step up to a cdi box

    https://www.summitracing.com/parts/msd-5520

    Or a replacement module:

    https://www.summitracing.com/parts/msd-83647

    Or a stand alone rev limiter

    https://www.summitracing.com/parts/pnx-600

    I’ve used Summit as it’s pi55 easy to find parts. These or similar could be sourced locally but I always check with Summit for availability and price inc delivery as it is surprisingly sometimes cheaper.
    Great, i will have a look at these parts. Thanks


    Quote Originally Posted by GtoGeoff View Post
    In my opinion, the conrods become the limiting factor assuming that the combo can get into high rpms. Such as a rod exiting the block....
    So bolt quality & strength/material of rod are big factors.
    I agree, thats why i upgraded the rods



    Quote Originally Posted by desoto30 View Post
    yes, and the rods and pistons in the engine are more than needed for the combos rpm
    So basically the engine has power to 6000-6500rpm and the bottom end can handle more so i dont need to be too concerned if it revs bit past that i guess

  4. #19
    Senior Member JaseQ314's Avatar
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    Quote Originally Posted by 78HZSBC View Post
    So basically the engine has power to 6000-6500rpm and the bottom end can handle more so i dont need to be too concerned if it revs bit past that i guess
    Sorry mate, from your previous post to this one your concern clicked with me.

    Because it's so low geared the revs are climbing quicker than you expected so you're worried if they do before you catch up will the bottom end handle it. The answer would certainly be yes but valve float would be your next biggest concern from there. Obviously a rev limiter would help take care of that which you're already on to.

    Do you have an overdrive gearbox, otherwise it might be worth looking into some taller diff gears if you're keen. The engine should easily make enough low down torque to push a 3.5 gear, maybe even 3.25 assuming you only have a four speed with a 1-1 top gear. Good luck getting it run in and sorted.

    Jason.

  5. #20
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    hi
    265 50 15 646mm dia
    3.9 diff
    3200rpm at 100kph in top gear 1 to 1 no overdrive

    Trik HQ is running around 3300 rpm at 100kph for a 640 hp 400cuin

    Re geared to
    265 50 15
    3.5
    2870 rpm at 100kph

    Stock 195 75 14 648mm diam
    3.08
    2500rpm at 100kph

    A change of rear gear will help rpm control

  6. #21
    Senior Member BasicQ's Avatar
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    Being a manual I'd like the insurance of a rev limiter for that accidental missed gear doing a bit of spirited driving. Bottom end ok to withstand but valves kissing pistons wont.

  7. #22
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    Quote Originally Posted by JaseQ314 View Post
    Sorry mate, from your previous post to this one your concern clicked with me.

    Because it's so low geared the revs are climbing quicker than you expected so you're worried if they do before you catch up will the bottom end handle it. The answer would certainly be yes but valve float would be your next biggest concern from there. Obviously a rev limiter would help take care of that which you're already on to.

    Do you have an overdrive gearbox, otherwise it might be worth looking into some taller diff gears if you're keen. The engine should easily make enough low down torque to push a 3.5 gear, maybe even 3.25 assuming you only have a four speed with a 1-1 top gear. Good luck getting it run in and sorted.
    Jason.
    Exactly, with the gear ratio im at 6500 before you know it.
    And yes i have a VT V8 Getrag 290 5 speed so im happy with the gear ratios.



    Quote Originally Posted by swampy View Post
    hi
    265 50 15 646mm dia
    3.9 diff
    3200rpm at 100kph in top gear 1 to 1 no overdrive

    Trik HQ is running around 3300 rpm at 100kph for a 640 hp 400cuin

    Re geared to
    265 50 15
    3.5
    2870 rpm at 100kph

    Stock 195 75 14 648mm diam
    3.08
    2500rpm at 100kph

    A change of rear gear will help rpm control
    No i chose the diff ratio so will be keeping it, due to the 5 speed im around 1800rpm doing 80km and probably just over 2000 at 100kmph, the difference between 4th and 5th overdrive is huge... perfect.

    Quote Originally Posted by BasicQ View Post
    Being a manual I'd like the insurance of a rev limiter for that accidental missed gear doing a bit of spirited driving. Bottom end ok to withstand but valves kissing pistons wont.
    Yeah will look at getting one for sure

  8. #23
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    Yup, rev limiter essential if manual & a good idea if auto. Building a 455 Pontiac at the moment, owner on a budget, cannot afford better rods. Factory rods are 'cast' steel & are known to grenade around 5700 in a 455. So using the Summit HEI module in the HEI, has an adj built in rev limiter.

  9. #24
    Senior Member LXCHEV's Avatar
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    I like the idea of a rev-limiter too - even in an auto. I recall many years ago at Easternats, thrashing the Torana around the track. It's a 3 speed auto, but I accidently went 1st -> 2nd -> Top -> Top. The limiter got a good test that day.

  10. #25
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    hi
    2 stage soft limiter

  11. #26
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    https://www.summitracing.com/parts/msd-83647
    Ok looks like this one would be suitable for my set up but ive heard international shipping from the US has been suspended for the time being, guessing due to covid related postal issues. Anyone heard about that?

    Also Swampy, i googled 2 stage soft limiter and only found 2 stage limiters for racing, not much regarding soft limiter that i can see

  12. #27
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    hi
    Limiters can work way different one to another . Ideally a 2 stage unit that cuts 1 cylinder then 2 then 3 VS some that cut complete feed to engine then u get variations to them . Hard cutting of engine can cause damage if excessively used .

  13. #28
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    hi
    double post
    Last edited by swampy; 07-10-2021 at 09:43 AM.

  14. #29
    Not the Kingswood! hq308's Avatar
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    Quote Originally Posted by swampy View Post
    hi
    Limiters can work way different one to another . Ideally a 2 stage unit that cuts 1 cylinder then 2 then 3 VS some that cut complete feed to engine then u get variations to them . Hard cutting of engine can cause damage if excessively used .
    That sounds a bit like what MSD call "soft touch". It doesn't just cut all cylinders at once, it drops a couple at a time and brings them back while dropping different cylinders. At least that's the way I understand it, their description is a little vague "When the engine reaches your set rpm, the Soft Touch circuitry kicks in and drops the spark to certain cylinders. This limiter produces very accurate and smooth, backfire-free rev limits."

  15. #30
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    Quote Originally Posted by swampy View Post
    hi
    230/236 peaks about 5800--6000 for Hp influenced by carb ,Inlet manifold and headers
    A moderate set up D/plain 1 3/4 headers 750 carb modest heads on a 383 should go 6000 on a 400 cuin little less
    On a 395--400 s/plain , prefer 1 7/8 headers ,780+ carb, quality heads goes 6000rpm

    Then ... the cam duration and head port design become restrictive

    Valve springs and bottom end desiqn plus hyd roller lifter weight all reduce the limit .
    The limit for a std travel HR lifter 6000--6500 and thats using a better quality unit.
    ive used full travel hyd roller lifters to 7200 no probs at all, its all in the valve train weight and spring

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