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2-Step Rev Limiters |
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Rebel Machine
AMC Addicted Joined: Jul/03/2007 Location: Western Il Status: Offline Points: 5121 |
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Posted: Mar/27/2021 at 11:14am |
I asked my engine builder about
2-steps as my Super Sniper EFI has one built in. I'd read some people
prefer to just hit the limiter with the throttle, others say put the
pedal to the rug. Some 2-steps limit RPM by either retarding timing and
others by not firing cylinders at the set RPM so I was concerned about
possible engine damage from using one. He said it's hard on the timing
set and he's seen timing chains broken as a result of using a 2-step. Anyone have experience with these things? I don't have a transbrake so I'd run it off the brake light switch if I were to use it. -Steve- |
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Ken_Parkman
AMC Addicted Joined: Jun/04/2009 Location: Ontario Status: Offline Points: 1814 |
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I ran a 2 step for years no issue. Once both cars were staged I would pin it, so a couple seconds on the 2 step. MSD 6AL
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Rebel Machine
AMC Addicted Joined: Jul/03/2007 Location: Western Il Status: Offline Points: 5121 |
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From what I've read in the manual the Holley Hyperspark retards timing for the lower RPM limiter. It also has a launch control which probably also retards timing versus time or RPM. This is just a pump gas street car. I typically stall at 1800 then launch full throttle at the green light. Maybe I'll give it a go and see what transpires. -Steve-
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matty 401
AMC Addicted Joined: Jul/06/2007 Location: Iowa Status: Offline Points: 1727 |
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have a msd set up not in use yet that has different chips and rev limiters
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72 matador 401 the beast
79 concord 2 door 72 matador 304 grasshopper 68 Rogue 406 93 Cherokee 4.0 5 speed |
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WesternRed
AMC Addicted Joined: Aug/03/2010 Location: Australia Status: Offline Points: 5808 |
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I'd like to jump on this 2 step bandwagon and I'm wondering the best way to wire it up.
Foot braking as above, so it seems logical to have it linked to the brake light so that it is activated when you have your foot on the brake at the start line. Now I also have a line lock that is on the rear bake lines to disable them during the burnout so I would have my foot on the brake during the burnout and obviously want the lower rev limit there. Should I set it up so that the 2 step is always active when on the brake but disabled when the line lock is on, that way it would be ready all of the time and I wouldn't have to think about it. Or is it better to just have a switch to enable it at the start line only. |
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I've finally given up drinking for good...........now I only drink for evil.
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Steve Obertanec
AMC Apprentice Joined: Nov/26/2012 Location: Lodi Ohio Status: Offline Points: 246 |
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In HNRA Stock Eliminator 2 steps are allowed but not trans brakes or a 4 wheel line lock. Most of them just footbrake with the 2 step on a micro switch on the brake pedal. Others use a brake pressure switch to activate the 2 step. To stop it from coming on when on the brakes at the big end they put a micro switch on the shifter so it is deactivated when not in 1st gear.
If you are allowed to leave off a button, a 4 wheel line lock is how we used to do it back in the day. I still have it hooked up on my car in case something happens to the brake. Hope this helps.
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Steve Obertanec
www.stevandracing.com |
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WesternRed
AMC Addicted Joined: Aug/03/2010 Location: Australia Status: Offline Points: 5808 |
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Cool, I did think of the shifter option, just a little more work. Would it be an issue if the limiter kicked in at the end of the track while on the brakes, that was my concern with the way I was thinking of setting it up?
I can see it would be an advantage to have a consistent launch RPM and would also help prevent it pushing across the line if you get too happy on the throttle while stalling it up, which I have been known to do in the past. As far as I know we are allowed to run a two step in our Super Street class as well as transbrakes and pretty much everything other than traction control systems (traction control is allowed on modern cars where it is factory fitted) . It's dial your own handicap racing, so consistency is the key.
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I've finally given up drinking for good...........now I only drink for evil.
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Steve Obertanec
AMC Apprentice Joined: Nov/26/2012 Location: Lodi Ohio Status: Offline Points: 246 |
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I cant see it being good on the motor hitting the limiter at the big end but then again people hit the top end rev limiter all the time. I'd say avoid it if possible.
A trans brake & 2 step are the most consistent way to launch, 4 wheel line lock is 2nd & footbraking on a 2 step would be 3rd. A powerglide with a brake is definitely the ultimate in consistancy but maybe not for the fastest ET. It's kinda like leaving in 2nd gear (Leaving in 2nd with a 727 & a 4 wheel line lock was always a lot of fun & consistent. Lost a bunch of ET but no mph.)
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Steve Obertanec
www.stevandracing.com |
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WesternRed
AMC Addicted Joined: Aug/03/2010 Location: Australia Status: Offline Points: 5808 |
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I've actually had the 2 step setup with my Sniper system for a little while, but haven't got a lot of runs on it yet.
I'm interested to know what others do in regards to using it and how you tune the system with EFI. I'm running it with the foot brake activation and seems like it takes a little while for the engine to recover after I release the brake. I feel using the 2 step is hurting 60' times a little bit. I have been pressing the throttle until the 2 step starts to kick in and then going WOT when I launch it, haven't tried going WOT on the 2 step yet, maybe that will give better results. Also wondering how to tune it as the AFR goes a little bit crazy while the car is misfiring on the 2 step, the system should be in open loop mode at this time, so not sure how to set this up. Data log below for posterity, notice there is a little bit of a delay between hitting the throttle and the revs starting to pick up, this is almost instantaneous without the 2 step. |
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I've finally given up drinking for good...........now I only drink for evil.
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Gench
AMC Apprentice Joined: Oct/09/2021 Location: Boulder CO ish Status: Offline Points: 182 |
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Steve - I have the super sniper as well and plan to use it with a line lock… PLAN being a key word, I’ve yet to implement. Wiring to your brake should work, not sure about latency in brake light system vs line lock switch? Harshness on engine, depends on how it’s setup, it should be soft on the engine but any accel/decel will hit the timing chain. Foot to the floor during two step seems proper.
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