Theoretical gear question

Grn92LX

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#1

• Dec 4, 2005

• #1

Ok, this isn't gonna be the typical "which gear should I buy" question. I'm hoping for some experienced people to chime in. Here goes..

We've all been on the highway cruising and had that trans am or corvette or whatever pull up to us and we downshift and run from a roll. My question is, how do steeper gears play a role in this. Basically for a car like mine that is undergeared for the combo (have 3.73, NEED 4.30) how does not having enough gear play a role when we downshift from a punch on the highway and take off? My car doesn't use the stock 6250 limiter, I spin it a little high as thats where I make power so "running out of gear" isn't happening so. I should have useable power to 6,800.

I'm thinking the 3.73's will hurt me as when I shift into 4th gear and the "run" is almost done, i'll be too low of an rpm like I am at the track (crossing the traps 1000 rpm too low)

Ed Curtis told me in an Email that a 4.30 gear swap is a good move since the quicker I get into high gear, the better. That was for the track though, how do the gears plan when having fun on the highway or open road from a punch?

Hope this makes sense.

 

T

TheUser

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#2

• Dec 4, 2005

• #2

ok, well looking at an excel spreadsheet that figures RPM's given the rear end gear, lets say you're cruising at 70mph @2300rpm in 5th gear w/ 3.73's. You downshift to 4th going 70mph, you hit 3500rpm. If you went to 3rd gear, you'd hit 4500rpm. So basically, if that's where your power is at, I guess theoretically, that's where you'd want to shift, but that's gotta be hell on a clutch going from 2500 rpm to 4500rpm lol. 3rd at 6800rpm is 107mph, hit 4th and ride it the rest of the way out (139mph @ 6800).

w/ 4.30's going 70mph in 5th at 2700rpm, if you hit 4th gear, you'd be at 4000rpm, if you hit 3rd, you'd be at 5100rpm. If you ride out 4th to 6800rpm, that's 120mph w/ 4.30's - lets hope the race ends around that point.

Is this what you're asking? I mean, if you had the 3.73's and topped out at 107 & 6800, and hit 4th, you'd basically go down to roughly 5300rpm's or so (that's around 107mph).

 

5spd GT

"the 5.0 owns all"

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#3

• Dec 4, 2005

• #3

Yep, the 4:30's are going to be quicker up to the point of 120mph or so. The same principle applies to why a 4:30 gear can help you accelerate quicker in all gears. Pretty easy figuring...

 

cleanLX

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#4

• Dec 4, 2005

• #4

what you want to avoid is needing to shift into 5th racing.
4th to 5th is a major bog as I'm sure you know.
Figure out what speed you want to end the race at, and gear 4th accordingly.
Looks like 4.30's or 4.56's would be the ticket.

 

N

NC85

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#5

• Dec 4, 2005

• #5

With the 4.30s you'll just end 4th gear faster and be back in 5th before you know it.

My car is driven 90% highway 10% city.

4.30s-306-60mile commute

 

bluevenom867

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#6

• Dec 4, 2005

• #6

The 4.30's are what you'll want for the track (unless you plan on runing some spray soon),get out of the hole qwik and pull hard.Only thing is,you better be good at shifting,cause if not,you'll kill your e.t. because you now have to shift faster.

The 3.73's you got now will be better for the street simply because you got more usuable gears,like TheUser said,you would just drop down into 3rd instead of 4th.

btw,what kinda trans do you have?

 

ninjacoupe

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#7

• Dec 4, 2005

• #7

The 4.30 will multiply your torque more than the 3.73 in the same tranny gear. Meaning your car will be faster in 4th gear with the 4.30's as opposed to the 3.73's. This follows in every gear.

Now if the speed you are starting from would allow you to downshift into 3rd with the 3.73's You would gain the advantage here. As your transmission is multiplying your 3.73 by ~1.34 giving your tires a percieved 4.99 gear ratio.

So 4th gear roll goes to 4.30's

IF you could grab 3rd with 3.73's you have the advantage over the 4.30's in fourth but your gonna have an added shift as well probably negating the very short lived advantage.

Gear the car for your powerband. It will be quicker in every gear 1-4 everytime. The jist of it is your gonna drop down to whatever tranny gear best puts you into your powerband. At this point your car will accellerate the best when it is properly geared.

 

Grn92LX

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#8

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Thanks Sam. I PM'd you again

Bluevenom, I have a tremec tko trans.

 

N8Miller

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#9

• Dec 4, 2005

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Mike,
being that the 4.30 gears are more optimal for your setup according to ED, whould it be better for you? I know that you live in a highly congested car area and i am not sure that your gonna wanna shift every 2 seconds due to the gearing. I do think that the 4.30 swap is a good thing though.

 

bluevenom867

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#10

• Dec 4, 2005

• #10

Grn92LX said:

Thanks Sam. I PM'd you again

Bluevenom, I have a tremec tko trans.

Click to expand...

Oh,ok.

I just was wondering if you still had like a worked T5,but a TKO wont break.

What ever gear you decied then....it will launch hard at 6000rpms

 

Rick 91GT

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#11

• Dec 5, 2005

• #11

26" or 28" tire at the track and on the street?

 

Grn92LX

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#12

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Rick, eventually once my nitto's get worn down I plan to switch to a 26" Mickey Tompson drag radial for my pony wheels.

Nate, I won't have to shift as much with the 4.30's, i'll go from first to fourth like the skip shift in a 6spd LS1/LT1

 

M

Mark89coupe

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#13

• Dec 5, 2005

• #13

With 4.30's quarter mile MPH should drop and ET get lower. Correct?

 

Grn92LX

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#14

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Mark89coupe said:

With 4.30's quarter mile MPH should drop and ET get lower. Correct?

Click to expand...

If I hook, ET should drop like a bad habbit. MPH should jump up nicely too since i'll be crossing the traps at the right rpm. These 3.73's have me crossing way too low. I am more concerned with mph.

 

S

stang2841

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#15

• Dec 5, 2005

• #15

why a 70 roll your no supra

WAY differnet cars and power levels but same principle..


real life experience..


running a 20 roll with 3.08s compared to 3.73's in my bolt on car with explorer intake and 1.7's improved drastically with the gear swap.. and I really didnt think it would..

I'm sure it will help.. hell it did in my T/A until I hit 5th gear..


I went from 3.42's to a 4.10 and I pulled harder on a roll..

I really dont know the scientifics/mathematics of it .. but I got experience with it and it did help me.

I do majority of racing on the street and I really wouldnt do a gearswap if it slowed me down from a roll