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Drag Racers: Optimum gearing suggestion

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Old 02-19-2012, 10:14 PM   #1
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Default Drag Racers: Optimum gearing suggestion

To get the best et, is it best to cross the traps at the rpm where the engine makes its peak power? For example, peak hp @6700 rpm--cross traps@7100 rpm? Any suggestions is greatly appreciated, thank you.
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Old 02-20-2012, 12:10 AM   #2
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Your ET is most affected in the first 60ft.

Figure out what MPH and RPM you want to be at... and gear the car accordingly.

If my motor lays over at 7500RPM... I'll want to cross the finish line at 7499.

Tire diameter, RPM (assuming 1:1 trans gear) and MPH will dictate what rear gears to use. It's just Math.

Here's a cool calculator I like to use...
http://www.race-cars.net/calculators...alculator.html
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Old 02-20-2012, 12:28 AM   #3
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What he said! Don't get hung up with the peak number as much as when the car starts to lay over. I'm not really a MPH guy but most people watch it closely.
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Old 02-20-2012, 10:45 AM   #4
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It depends how quick power falls off.
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Old 02-20-2012, 11:41 AM   #5
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So if peak hp is @6700 and stays flat and keep pulling to 7200 rpm before it starts to lay down, that would be the optimum rpm to be at the traps? Also, would 400rpm above peak hp considered optimum shift points as well? I apologize with all the questions.
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Old 02-20-2012, 12:00 PM   #6
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With a 28" tire and a 4.30 gear should cross the traps at around 6700 rpm at 124 mph. And thats at around peak hp as well. Am I in the right direction here?
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Old 02-20-2012, 01:10 PM   #7
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The question proposed here is not specific. "Gearing" requirements are completely subjective to the confines of what the combination of the set up. There is only optimum to the given car setup.
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Old 02-20-2012, 04:13 PM   #8
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If it stays flat untill 7200 and the motor can take the rpm shift it there. If I had to guess there might be 1 more mph going from 6700 to 7200 on a flat graph.
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Old 02-20-2012, 09:50 PM   #9
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Butch, your in the same boat I'm in.4.30 seems to be about right. I go threw the traps at about 6,000 now with my 4.10's and will be close to 6,400 with the 4.30
remember though stepping up the gear will essentially tighten up your converter. something to think about.
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Old 02-21-2012, 12:51 AM   #10
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Butch, your in the same boat I'm in.4.30 seems to be about right. I go threw the traps at about 6,000 now with my 4.10's and will be close to 6,400 with the 4.30
remember though stepping up the gear will essentially tighten up your converter. something to think about.
Jeff, according to my calculations with the times on your sig, you should have been crossing the line @6289 rpm. With 4.30 gearing, you will be at about 6600 rpm at the traps. Have you done any weight reduction on the car? It's very impressive for a full weight car running those times.
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Old 02-21-2012, 01:10 AM   #11
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Man it seems like there has been a ton of gearing threads lately. I can tell you its way easier if you've got a Lenco. We had a motor that made peak at like 6200 but it would fall off if you shifted it lower than 8K. Everybody's stuff is different. You look like you're hauling *** where ever your shifting now. Fast car man!
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Old 02-21-2012, 06:25 PM   #12
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Quote:
Originally Posted by BOLO View Post
Jeff, according to my calculations with the times on your sig, you should have been crossing the line @6289 rpm. With 4.30 gearing, you will be at about 6600 rpm at the traps. Have you done any weight reduction on the car? It's very impressive for a full weight car running those times.
Butch, I use the wallace racing caculator and it's dead on for my car except the sixty foot. I haven't done any real weight reduction but I'm starting to now as we speak.

Power to Weight Ratio: 6.70
60 Foot E.T. : 1.53
1/8 Mile E.T. : 6.93
1/8 Mile Trap Speed : 98.11
1/4 Mile E.T. : 10.98
1/4 Mile Trap Speed : 122
1/4 Mile Trap RPM : 6,009
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Old 02-21-2012, 07:18 PM   #13
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Quote:
Originally Posted by BADHAWK51 View Post
Butch, I use the wallace racing caculator and it's dead on for my car except the sixty foot. I haven't done any real weight reduction but I'm starting to now as we speak.

Power to Weight Ratio: 6.70
60 Foot E.T. : 1.53
1/8 Mile E.T. : 6.93
1/8 Mile Trap Speed : 98.11
1/4 Mile E.T. : 10.98
1/4 Mile Trap Speed : 122
1/4 Mile Trap RPM : 6,009
I didn't think you were crossing the traps at only 6000. I know your stroker is gotta be making its maximum peak power at 65-6700 rpm, maybe a little higher. So you do have to gear it accordingly and be at your maximum power at top end of the track. Jeff, with more weight out, I think you still have plenty on the table. 10.4's, 10.5's easily.
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Old 02-21-2012, 07:30 PM   #14
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Quote:
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I didn't think you were crossing the traps at only 6000. I know your stroker is gotta be making its maximum peak power at 65-6700 rpm, maybe a little higher. So you do have to gear it accordingly and be at your maximum power at top end of the track. Jeff, with more weight out, I think you still have plenty on the table. 10.4's, 10.5's easily.

Butch, I don't know about 10.40's but I think once I get it down to 3,300 and put the spool and 4.30's in it will go 10.60's pretty sure.
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Old 02-21-2012, 08:48 PM   #15
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Jeff, you changing your class this year at the Shootout? Mod n/a? You'll be competitive for sure.
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Old 02-21-2012, 09:35 PM   #16
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I'm going to run Extreme street again this year so I can only lose 150lbs to get down to min weight. Then next year lose another 100lbs and go to aftermarket ecu, singleplane and a solid roller then run Mod.

Funds permitting of course.
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Old 02-22-2012, 10:12 AM   #17
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since im running 3.73s, I wonder if I switch to 4.10s if Ill still have enough gear for nitrous passes.

Jeff if your running a lose 4500 converter and going through the gates at 6000, I would THINK id have room to push to 6800 with 4.10s but I dont know what MPH that would put me at. Is there any good way to calculate for this?
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Old 02-22-2012, 07:20 PM   #18
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since im running 3.73s, I wonder if I switch to 4.10s if Ill still have enough gear for nitrous passes.

Jeff if your running a lose 4500 converter and going through the gates at 6000, I would THINK id have room to push to 6800 with 4.10s but I dont know what MPH that would put me at. Is there any good way to calculate for this?
You'll have more than enough gear for the spray. I have sprayed mine running 4.10 gear/28" tire and 4000 stall, going thru the lights at about 6500-6600 rpm
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Old 02-22-2012, 08:14 PM   #19
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Quote:
Originally Posted by 355z28 View Post
since im running 3.73s, I wonder if I switch to 4.10s if Ill still have enough gear for nitrous passes.

Jeff if your running a lose 4500 converter and going through the gates at 6000, I would THINK id have room to push to 6800 with 4.10s but I dont know what MPH that would put me at. Is there any good way to calculate for this?


Like Butch said, if I hit my car with a 150 shot it would cross between 6500 6600 at somewhere around 133mph.


http://www.wallaceracing.com/accel-calc.php
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Old 02-22-2012, 10:20 PM   #20
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That calculator says I should be running 11.90s lol It doesnt like the 388hp and 3700lb weight. Ill take your guys word for it. I might give the 4.10s a shot.
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