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Old 01-09-2019, 02:57 PM   #11
voltdr
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Default Re: Super gas/comp/Street forums?

I wonder about this also. If we have a car that runs SG, 9.90 @ 160ish. If the stop stall is
4200 for 3.5 seconds. How fast is the car at 4200 for the 3.5 seconds? Lets just say it's
130 mph and then gets to 160 at the finish. If the same car is 4000 rpm for 2.5 seconds. Is that car now running 125 mph. Does it get to 165? The car is at a slower speed and has more time to accelerate, but can it over come the lower rpm while on the stop to run faster at the stripe? Or, is it better to be at a faster mph on the stop and not have as much mph to gain? I have heard many discussions about this but I'm still not sure which one is better?
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Old 01-09-2019, 04:31 PM   #12
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Default Re: Super gas/comp/Street forums?

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No, we go on cruise at the same time, just at a lower RPM. Because we run a lower RPM we don't have to be on the stop as long. Like anything else it depends on what the car likes. We've run it on 540 and 565 engines. I'm not sure it would work well on a small block.
If two identical cars have the same cruise RPM, the one that goes on the stop quicker should have more top end MPH.

If two identical cars go on the stop at the exact same time, the one with the lower cruise RPM should have more top end MPH.

My personal guidelines are:

1. The 'stop on' time should be just high enough for the car to cut a light.

2. The cruise RPM should be set so that the car can at least clear the 60' beam while on the stop every pass in any weather conditions.

There will be other things to consider in each case. Some cars may need to be WOT a little longer at the start to work the chassis properly. Some cars may come off the stop cleaner with a little higher 'stop on' RPM than absolutely necessary.

I run oddball combinations in both of my cars, so I can't always use these principles but I use one of them in each car.
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Old 01-09-2019, 04:34 PM   #13
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Default Re: Super gas/comp/Street forums?

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I wonder about this also. If we have a car that runs SG, 9.90 @ 160ish. If the stop stall is
4200 for 3.5 seconds. How fast is the car at 4200 for the 3.5 seconds? Lets just say it's
130 mph and then gets to 160 at the finish. If the same car is 4000 rpm for 2.5 seconds. Is that car now running 125 mph. Does it get to 165?
It doesn't really impact what you are trying to say, but those speeds on the stop seem really really crazy to me. 130 mph while coasting on the throttle stop? Not unless you turned the stop on at the 1/8 mile!
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Old 01-09-2019, 06:27 PM   #14
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Default Re: Super gas/comp/Street forums?

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Originally Posted by Lenny5160 View Post
It doesn't really impact what you are trying to say, but those speeds on the stop seem really really crazy to me. 130 mph while coasting on the throttle stop? Not unless you turned the stop on at the 1/8 mile!
That had me confused as well. I don't remember exactly, but I believe my datalogger showed MPH on the stop at just over 60mph. And my cruise RPM is on the high side.
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Old 01-10-2019, 07:28 AM   #15
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Default Re: Super gas/comp/Street forums?

my car with a 4.88 and 32 inch tire shows about82 mph at 4200. drop to a 4.30 would be about 93 doing the basic rpm tire diameter gear ratio calculations. ofcourse thats with no convertor slippage so its actually less
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Old 01-10-2019, 08:53 AM   #16
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Default Re: Super gas/comp/Street forums?

My completely uneducated guess would have been 40-60 mph for most cars.
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Old 01-10-2019, 10:20 AM   #17
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Default Re: Super gas/comp/Street forums?

Mine is probably slower than that since my cruise is 3,600 rpm's
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Old 01-10-2019, 11:49 AM   #18
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Default Re: Super gas/comp/Street forums?

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It doesn't really impact what you are trying to say, but those speeds on the stop seem really really crazy to me. 130 mph while coasting on the throttle stop? Not unless you turned the stop on at the 1/8 mile!
I just picked a mph for my discussion. I have no idea what the stop mph is. Those numbers are probably more indicative of the 1/8 mile mph. Just saying that if you start at a slower mph but have a longer time to get to the finish, versus a higher mph but shorter time to get to the finish... Will it change the finish mph much?
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Old 01-10-2019, 12:16 PM   #19
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Default Re: Super gas/comp/Street forums?

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I just picked a mph for my discussion. I have no idea what the stop mph is. Those numbers are probably more indicative of the 1/8 mile mph. Just saying that if you start at a slower mph but have a longer time to get to the finish, versus a higher mph but shorter time to get to the finish... Will it change the finish mph much?
Dan
Of course it will change it. More time WOT will produce more MPH unless your engine has its tongue hanging out by the finish line. The definition of "much" is up for debate. Will it be enough to change the appearance of the race for you and your opponent? Probably not unless your timer or cruise RPM change is dramatic.

My dragster is mechanically injected, so I go on the stop at 0.100 and shut it down to a dead idle. My cruising speed is almost a stop. I also come off the stop in Low gear. I've never run this combination wide open to the 1/4 but I only lose 2-3 MPH at the 1/8 mile when running 8.90 on the stop as compared to a wide open pass. 6.19 @ 145.86 compared to 4.69 @ 148.14.

I would hazard a guess that cars running a more traditional cruise RPM and coming off the stop in High gear are down 10+ MPH at the 1/8 compared to a WOT run.
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Old 01-12-2019, 09:56 PM   #20
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Default Re: Super gas/comp/Street forums?

I do know if you are low on power dropping that cruise rpm gets unpredictable. And if you make good power getting it too high puts too many numbers in the timer. It’s a test and tune fine tuning point til you find what works on your car. I’ve been on at .001 with a Maxspeed, on at .10 same carb...you just have to have enough power to do it that soon or it will know the breath out of it and you’ll get a dip. I had a big motor combo that liked .001 and shift at .020.at 4300 and it worked well. Tried it with a smaller motor and it was a no go
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