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| djxib | Calculating the optimum gear ratio for my car | ||
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Senior Guru
 
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(1992 C4)
Assuming that all goes well with my new motor, it should be good for about 7000 RPM. It is a forged 383 and I will be upgrading the supercharger from an old S trim to a newer T (or later) model running about 14 pounds of boost. Target HP around 650. The car has stock gears (it is an MN6). My last time out to the strip I saw 12.3 at 117 with a 2.3 60'. The tach was showing around 5700 RPM across the line in 4th gear. I definitely want to see low 11's, and I'm thinking that with the new motor, a better launch, and decent tune, I should see 11.2 at 120 or better. So.. given that the motor 'could' go to 7000RPM (although I'd probably stay less than that), I'm thinking that I could also go with a lower gear ratio. I see a lot of guys run 4.10 gears but I cant find a calculator that would definitely tell me what RPM that would be at 120 MPH. Does anyone here have a calculator or real experience of 4.10 gears at the track with a MN6? Cheers! |
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Posted on: 2011/4/20 21:43
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Andy 1996 Greenwood Collectors Edition LT4 Previously 1992 Convertible Polo Green. 383 LT1/LT4 forged/balanced. V7-YSi, Alky. 608RWHP... Now sitting at a dismantler with a salvage title. Still runs... |
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| SpectatorRacing | Re: Calculating the optimum gear ratio for my car | ||
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Elite Guru
 
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Here ya go!
http://www.f-body.org/gears/ Hmmm. Don't see the MN6 as an option in the transmission list though. Are the gears close in ratio to another one, like the M6? |
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Posted on: 2011/4/20 22:19
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aka Scaryfast |
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| djxib | Re: Calculating the optimum gear ratio for my car | ||
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Senior Guru
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Awesome - thanks! MN6 is the same as M6, it's a stock ZF6 black tag 'box.
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Posted on: 2011/4/20 23:02
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Andy 1996 Greenwood Collectors Edition LT4 Previously 1992 Convertible Polo Green. 383 LT1/LT4 forged/balanced. V7-YSi, Alky. 608RWHP... Now sitting at a dismantler with a salvage title. Still runs... |
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| tjpreul | Re: Calculating the optimum gear ratio for my car | ||
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Elite Guru
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What compression ratio are you aiming for in the new motor? This is more of a curious question, not gear related.
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Posted on: 2011/4/21 2:48
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Vegas wasn't built on winners. '92 auto, MSD, Banski, Taylor wires, SS lines, C5 rims, 3.07 gears, white gauges, seats from a '96. Motor: Forged rotating assy, Probe pistons, CC valvetrain, AFR heads, Procharger P1SC |
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| djxib | Re: Calculating the optimum gear ratio for my car | ||
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Senior Guru
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Quote:
According to the builder, 9:1. |
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Posted on: 2011/4/21 12:26
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Andy 1996 Greenwood Collectors Edition LT4 Previously 1992 Convertible Polo Green. 383 LT1/LT4 forged/balanced. V7-YSi, Alky. 608RWHP... Now sitting at a dismantler with a salvage title. Still runs... |
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| rklessdriver | Re: Calculating the optimum gear ratio for my car | ||
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Senior Guru
 
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with a 4.11 and a 315/35R17 rear tire (25.6") your good to 130ish MPH in 4th gear at 7000RPM.
I personally think a 4.11 would be too much gear for a supercharged 383 with a 6spd. My 92's 383 is normally aspriated and the car is hard to hook up on anything but a VERY well prepped track. Just from 3 weeks ago (perfect track) to this week (no track prep) my 60fts went from 1.77 to 2.04 using the same tires, tire pressure ect... the car lost over 4 tenths ET but ran the same mph so it wasn't a hp difference because of the warmer weather. With all the TQ that blower is going to make, I'd think just to get traction you'd need to have a 3.54 or maybe 3.91. I had a 3.91 gear in my 92 last season and I had to leave way harder to get the car to launch. Will |
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Posted on: 2011/4/21 14:57
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1984 Corvette. 434 SBC with a Powerglide. Best pass - 8.48@160MPH 1.23 60ft on MT 275/60R15 Radials. 1972 Corvette. LS5 454 BBC with M20 4 speed. Best Pass - Doing good to just pass a gas station. |
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| CentralCoaster | Re: Calculating the optimum gear ratio for my car | ||
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Senior Guru
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Just because you motor can do 7000rpm, doesn't mean you're making any power there.
You really need the dyno curve to determine the optimum gear ratio.. whenever you rev high enough to make less hp in that gear than your average power through the run, is where you want to cross the finish line. Should be close to the rpm you shift it. |
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Posted on: 2011/4/21 16:18
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1985 Z51, ZF6 |
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| corvettelou | Re: Calculating the optimum gear ratio for my car | ||
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Guru Newb
 
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MPH x rear gear ratio x trans ratio ( ussually 1 depending on what gear you intend to be in though traps) x 336 divided by tire diameter. Example; 120 mph x 4.10 = 492 x 1= 492 x 336 = 165312 divided by 26 = 6,358 (rpm). hope this helps.
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Posted on: 2011/8/20 18:13
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| BeachBum | Re: Calculating the optimum gear ratio for my car | ||
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Master Guru
 
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Quote:
Just as a note, you probably want to run your present gear and see how much power you have and what you actually trap and then make the decision on gear. If you actually hit your target HP of 650 HP.... your trap speed won't be 120 mph (Which is achievable with right around 475 HP).... you'll be up around 130 minimum and probably in the 135 mph area. If you gear for 120 mph.... you'll be way off. In addition, you'll have a better idea of where your HP peak and shift point are. Just food for thought. |
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Posted on: 2011/8/21 4:34
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| pur28 | Re: Calculating the optimum gear ratio for my car | ||
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Guru Newb
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Hi, I found this Size calculator which was quite informative for me:Tyre Calculator
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Posted on: 2012/6/18 17:34
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