Two step rev limiter with blown engine

Discussion in 'PSI Superchargers Tech Questions' started by Bob sherry, May 5, 2021.

  1. Bob sherry

    Bob sherry Member

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    I am curious about holding a blown motor on the start line with a two step rev limiter. It’s just a 469 cui big block chev with a 15 percent over 871 with a bug catcher and hat nozzles only. It goes very competitively leaving off idle. I would like to set the launch RPM at 2500 on the two step rev limiter as a first try and work my way up untill it starts blowing the tyres off, do you think I would hurt the motor with the throttle wide open against a rev limiter at 2500? On methanol with the square barrel valve, thanks .
     
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  2. aj481x

    aj481x Member

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    Some people use setups that bleed off fuel, but in your case I would just chip it and go. Full tree racing, most will put the throttle down when first bulb lights.
     
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  3. Bob sherry

    Bob sherry Member

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    Sounds good thanks
     
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  4. Bob sherry

    Bob sherry Member

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    Has anyone else had experience with this deal?
     
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  5. dcovey

    dcovey Member

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    500 CI Mopar wedge with an 871, bracket dragster. I run a Grid. I chip the Burn out to 5200 and launch to 3200-3400 depending on conditions. I have never had an issue, bearings always look good enough to reuse if i wanted to. I also use a pro stage, which holds stage RPM to 1900 rpm, I suppose if I wanted I could use the pro stage for launch RPM if I didn't want to chip it but what I am doing works so I seen no reason to change.

    Dave
     
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  6. Bob sherry

    Bob sherry Member

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    Thanks for your info, do you hold the throttle flat out at your launch RPM? I don’t know what a pro stage is I presume it is some sort of air operated throttle stop.
     
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  7. Bob sherry

    Bob sherry Member

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    Well I ran the car on the weekend and it was a great success, I set the limiter to 2500 and floored the throttle at the release of the button and all is good, 5.20 at 136 mph in the 1/8 th with an .020 light . Very consistent so I can now run in a couple full tree delay box classes. The delay box setting is so short that you can hardly hear it banging on the limiter on the start line, but testing it out in the pits sounds a lot worse. Thanks again.
     
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  8. td3829mk

    td3829mk Member

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    Normal. 4k+ on the step. Just keep an eye on your thrust bearing, it’s a little hard on them. We do use 2step leanouts in outlaw trim, but not needed when you aren’t trying to rotate the earth.

    You’ll do more damage doing a burnout on the chip. If you need to rely on a rev limiter instead of your right foot to do a burnout correctly you have no business driving these cars.
     
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  9. Bob sherry

    Bob sherry Member

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    Thanks, all worked good as from my last post and no I don’t need a limiter in the burn out.
     
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  10. greg e

    greg e New Member

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    On our 532 we use a air cly on the throttle and when the transbrake button is pushed. my driver pushes the pedal to the floor and it opens the hat just enough to launch at 3800 and can be adjusted to more or less rpm’s and pulls the throttle wide open when he lets the transbrake button go.he cuts .004 to .008 lights on the pro tree all day long. Works perfect and not bouncing the belt off the rev limiter or loading the motor up with fuel.
     
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  11. Bob sherry

    Bob sherry Member

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    Yes I’m familiar with that system over here in Australia but I didn’t want to outlay the dollars for it , but now we are in the off season it might we worth considering, it certainly sounds like a better idea .
     
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  12. greg e

    greg e New Member

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    Bob I have less than a hundred dollars in this set up. 1 Bosch realy and a 2 way solenoid and a 2 way air cly and a used co2 tank and regulator and used my lathe to make the adjusting nut to hook the cable to the air cly.
     
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  13. Bob sherry

    Bob sherry Member

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    Have seen them on the top door slammers over here they look expensive, is there anyway you could send me photos so I can duplicate what you have? I’m a good machinist so it shouldn’t be a problem.
     
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  14. Graham Brown

    Graham Brown New Member

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    Hi Bob
    I made my launch control ~20 years ago by mounting a Bimba air cylinder to the hat with an adjustable stop. The barrel linkage would push against it at just above idle when the brake was engaged. Pedal up against it until it's released and then mash it.
    Would probably do it differently now like what "greg e" described.
    Yeah you'll also need an air/CO2 supply, 12V solenoid valve etc.
    Below is the Bimba air cylinder PDF.
    https://pneumatics.com.au/wp-content/uploads/BIMBA-Original-Line.pdf
     
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  15. greg e

    greg e New Member

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    Hope these pics work
     

    Attached Files:

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  16. Graham Brown

    Graham Brown New Member

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    Thanks Greg.
     
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  17. Bob sherry

    Bob sherry Member

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    Thanks for the info your input helps me immensely, you give me some great ideas to work on.
     
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  18. Bob sherry

    Bob sherry Member

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    Thanks Greg I’ll try and round up those parts over here in Australia, you have been a big help.
     
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  19. greg e

    greg e New Member

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    Bob when you get it all together let me know. I can walk you thru setting it up. Glad I could help
     
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  20. Graham Brown

    Graham Brown New Member

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    Bob,
    Try to mount the solenoid valve as close as practicable to the cylinder. Gases are compressive so you need to reduce the volume in the lines. This will minimise the cylinder movement response times whether you energise or de-energise it on the launch.
     
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