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question about gearing + tire size + overdrive

 
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Nate81camaro
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Joined: 18 Jul 2006
Posts: 36
Location: closer than you think
1482.38 points


1981 Chevrolet Camaro

PostPosted: Sun Feb 18, 2007 12:04 am    Post subject: question about gearing + tire size + overdrive Reply with quote

I have an 81 camaro, with the mods in my signature. It weighs roughly 3750 with me in it. I really don't know what I'm running (1/4-wise), so I think this would be hard to answer, but you guys really know your stuff so here goes:

If I had a 200-4R, a 28" tall tire, and some 4.10's, what would I be crossing the 1/4 at and in which gear??? My cam runs out of breath at 5200. Intake is good until 5500, and I have 1.94/1.50 heads.

I'm debating on wether I'd get 4.10's or 3.73's IF I got a 200-4R.
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SMOKEmUP
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65149.84 points


1979 Chevrolet Camaro

PostPosted: Sun Feb 18, 2007 12:52 am    Post subject: Reply with quote

If you're looking for quarter mile then go with the 4.11's.

Transmission Ratios:
1st: 2.74 2nd: 1.57 3rd: 1 4th: 0.67

Tire Diameter 1: 28 inches
Rear Gear Ratio 1: 3.73:1
MPH
RPM---- 1st---- 2nd---- 3rd---- 4th
1000----8----14 ----21 ----32
1500----12----20----32 ----48
2000----16----27----43 ----64
2500----20----34----54 ----80
3000----23----41----64 ----96
3500----27----48----75 ----112
4000----31----55----86 ----128
4500----35----61----96 ----144
5000----39----68----107 ----160
5500----43----75----118 ----176
6000----47----82----129 ----192
6500----51----89----139 ----208
7000----55----96----150 ----224
7500----59----102----161----240
8000----63----109----172----256


Tire Diameter 2: 28 inches
Rear Gear Ratio 2: 4.11:1
MPH
RPM---- 1st---- 2nd---- 3rd---- 4th
1000 ----7 --------12----19 ----29
1500 ----11----19----29 ----44
2000 ----14----25----39 ----58
2500 ----18----31----49 ----73
3000 ----21----37----58 ----87
3500 ----25----43----68 ----102
4000 ----28----50----78 ----116
4500 ----32----56----88 ----131
5000 ----36----62----97 ----145
5500 ----39----68----107----160
6000 ----43----74----117----174
6500 ----46----81----126----189
7000 ----50----87----136----203
7500 ----53----93----146----218
8000 ----57----99----156----232

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Nate81camaro
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Joined: 18 Jul 2006
Posts: 36
Location: closer than you think
1482.38 points


1981 Chevrolet Camaro

PostPosted: Sun Feb 18, 2007 3:31 am    Post subject: Reply with quote

Cool. So with my setup, I shouldn't have to shift into 4th even with 4.11's?

I should have good driveability too, even with our normal posted speed limit of 65, with 75 being the highway posted speed.
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SMOKEmUP
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1979 Chevrolet Camaro

PostPosted: Mon Feb 19, 2007 11:28 am    Post subject: Reply with quote

I'd take the car to the track and see what it runs now with the gears and tire size you have. That way you'll get an idea of the mph and can select the gears accordingly.

Another thing you can change is tire size. For example 3.73 with a 26" tire is about the same as a 28" tire with 4.11's. If you think the 4.11 will be too much you can go with the 3.73's using a 28" tire for the street. When at the track you can run 26" slicks to give you a bit more gear. Just something to think about.

Transmission Ratios:
1st: 2.74 2nd: 1.57 3rd: 1 4th: 0.67

Tire Diameter 1: 26 inches
Rear Gear Ratio 1: 3.73:1
MPH
RPM----1st----2nd----3rd----4th
1000----7----13----20----30
1500----11----19----30----45
2000----15----25----40----59
2500----18----32----50----74
3000----22----38----60----89
3500----25----44----70----104
4000----29----51----80----119
4500----33----57----90----134
5000----36----63----100----149
5500----40----70----109----163
6000----44----76----119----178
6500----47----82----129----193
7000----51----89----139----208
7500----54----95----149----223
8000----58----101----159----238


Tire Diameter 2: 28 inches
Rear Gear Ratio 2: 4.11:1
MPH
RPM----1st----2nd----3rd----4th
1000----7----12----19----29
1500----11----19----29----44
2000----14----25----39----58
2500----18----31----49----73
3000----21----37----58----87
3500----25----43----68----102
4000----28----50----78----116
4500----32----56----88----131
5000----36----62----97----145
5500----39----68----107----160
6000----43----74----117----174
6500----46----81----126----189
7000----50----87----136----203
7500----53----93----146----218
8000----57----99----156----232

_________________
Stop running from your pain and embrace your pain. Your pain is going to be a part of your prize.

I challenge you to push yourself.
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Nate81camaro
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Joined: 18 Jul 2006
Posts: 36
Location: closer than you think
1482.38 points


1981 Chevrolet Camaro

PostPosted: Mon Feb 19, 2007 10:50 pm    Post subject: Reply with quote

^^. Huh. Didn't know that. That's really not a bad idea. If I had a 200-4R with a 28" tall tire and 3.73's, I'd turn about 2300rpm's at 75mph, vs 28" tire with 4.11's turning about 26-2700.
Thanks for that chart, helped alot!
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Nate81camaro
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Joined: 18 Jul 2006
Posts: 36
Location: closer than you think
1482.38 points


1981 Chevrolet Camaro

PostPosted: Mon Apr 16, 2007 4:48 pm    Post subject: Reply with quote

Hey smoke, I have another question for ya. I'm going to be keeping my 350 tranny (since it works and everything). I do want to get gears, but I'm debating on either 3.73's, or 3.42's. The local speed limit out here is 75, so I'd like to drive at least 70mph comfortably.
If I run 3.42's with a 26" tall tire, would it be nearly the same as 3.73's using a 28" tall tire? If it is, I'll run the 3.42's with a 28" tall tire on the street, and when I go to the strip I'll put 26" tall drag radials on it.
I plan on getting an Eaton posi (thats what the guys at Nastyz28.com are recommending), as I'll need a new carrier anyways (I have the carrier for 2.56 gears, and it's open Embarassed )
Thanks in advance!!! Very Happy
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Nate81camaro
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Joined: 18 Jul 2006
Posts: 36
Location: closer than you think
1482.38 points


1981 Chevrolet Camaro

PostPosted: Tue Apr 17, 2007 11:22 am    Post subject: Reply with quote

Never mind, I found a chart very similar to what you posted at f-body.com
Looks like if I run a 26" tall tire with 3.42's, it'll be within 1 mph of running a 28" tall tire with 3.73's.

I'm still debating on it, because if I ran 3.73's with a 28" tall tire on the street, I could switch to a 26" tall tire for the strip.

What do you guys think?
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cutlass389
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Posts: 268
Location: NC
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1978 Oldsmobile Cutlass

PostPosted: Wed Apr 18, 2007 8:29 am    Post subject: size matters Reply with quote

First off, why use drag radials if switching at the track? Secondly, the tire sizing works exactly as Smoke said. I run 24.5" slicks to make 3.73's act like 4.00's.
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