Theoretical gear question (lets get some real tech in here)

[Grn92LX]

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.

 

[Blackened302]

you're a lucky man not having to be conerned with highway gas mileage--i wish i were that free, heh.

i think it's really intimidating that an ls1 can manage strong pulls at around 60+. i'd love to see a mustang do the same.

subscribing.

 

[18mustangs]

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.

I hear that the steeper the gear the lower the top speed. I'm not sure how that affects pulling on a bowtie or pontiac at 60+.

 

[bimmertech]

not having enough gear doesn't really play a role when roll racing as you can always downshift again.

i have 3.73's and from a 70 ish roll down shift to 3rd. if you had 4.30's you could not go to 3rd as you would be at too high an rpm already.

hope this makes sense, cuz frankly i don't really understand what you are tryin to ask.

 

[Blackened302]

not having enough gear doesn't really play a role when roll racing as you can always downshift again.

i have 3.73's and from a 70 ish roll down shift to 3rd. if you had 4.30's you could not go to 3rd as you would be at too high an rpm already.

hope this makes sense, cuz frankly i don't really understand what you are tryin to ask.

dropping to 3rd @ 70 mph = teh awesomeness

 

[Guero]

dropping to 3rd @ 70 mph = teh awesomeness

why is that?
i beleive i can go all the way to 90+ in 3rd. i dont have to shift into 4th at the track.

 

[stprorolla49]

I hear that the steeper the gear the lower the top speed. I'm not sure how that affects pulling on a bowtie or pontiac at 60+.

yea it lowers the top speed, but 60' times significantly decrease because of the gear ratio....

 

[GTS347]

If you have a five speed in your car I'd stay away from anything numerically higher than 4.10's. 3.73's are good for street performance. I prefer 3.90's (motive gear) for street/strip. If you've a race only car 4.30's are the best bet.

 

[DFG 5OH]

with steeper gears you wouldn't have to downshift as far, and the rpms would climp faster...so i think they would help somewhat.

 

[Black95GTS]

To actually give a response to your question:

I would think for a from-a-roll highway application, with your powerband, the 4.30s would be better then the 3.73s. Well I guess you'd have to figure out how fast you want to end up going on the highway. If you're trapping 115 in the quarter around 5700, then if you were theoretically going much higher then 125ish then a move to a "steeper" ratio could force you to shift into 5th.

The steeper gear ratio will keep you higher up in the RPMs whether you're in the 1320 or on the highway. Which is where your motor likes to be. (Very cool by the way!) But like I said before, if getting up to a 125+ speed on the highway is important, then maybe a 4.10 compromise. I personally give the thumbs down to going that fast on the highway.

Adam

 

[nmcgrawj]

I think that you kinda answered the question...atleast of what i can tell is the question. Just like at the track, the right gear ratio gets you into your power band faster and lets you accelerate faster through it.

So on the highway, when you down shift to 3rd, shift to 4th and get ready to let off, you arent where you want to be in your power band...so just like on the track when u cross the traps, on the highway you could be farther ahead of your opponent, a 4.30 gear will let you get higher in that power band, allowing your car to take advantage of all the power, letting you accelerate faster.


In your combo, when racing a 4.30 is more efficient compared to a 3.73. Maybe you should clarify what the question is....

 

[Grn92LX]

Its tough to explain through a keyboard what i'm asking. Basically what I am wondering is, is the same gear thats ideal for the track, the same gear thats ideal for running from a rolling start on the highway?

Another way to look at it is, lets say I start from a 2nd gear roll, when I shut it down in 4th I still have a ton more rpm to go so i'm only using my full powerband twice (in 2nd and 3rd). With the 4.30's i'd be using my powerband 3 times probably.

Adam, when I play around on the street with friends cars, we do it on roads that are empty at night. Tracks are closed for winter and I do not have a local track here anymore. No where else to speed in my street car but on the street

 

[bimmertech]

Its tough to explain through a keyboard what i'm asking. Basically what I am wondering is, is the same gear thats ideal for the track, the same gear thats ideal for running from a rolling start on the highway?

Another way to look at it is, lets say I start from a 2nd gear roll, when I shut it down in 4th I still have a ton more rpm to go so i'm only using my full powerband twice (in 2nd and 3rd). With the 4.30's i'd be using my powerband 3 times probably.

Adam, when I play around on the street with friends cars, we do it on roads that are empty at night. Tracks are closed for winter and I do not have a local track here anymore. No where else to speed in my street car but on the street

depends on how fast you want to race to. if you guys let off at 125 then go with the 4.30's, but if you go faster with 4.30's then you will have to shift into 5th--we all know what happens then.

i say put some 4.30's and a T56. more shifting required, but you can use 5th gear to race and not just to cruise. you could also get a road race tko, but then cruising will be murder on the MPG.

 

[final5-0]

OK Mike

Here is how I look at answering your Question.

First thing is you will not be at as much of a disadvantage with the chevy considering you match his cubic inch size.

Now for the gear ratio part of this deal.

As long as you don't punch it from a mph that is too high

or

say no higher that mid rpm's in 3rd

You have the top end of 3rd and all of 4th to show him your tail lights.

Seems to me if you could do the above one time with 410's and another with 430's

The 430's would allow a quicker rate of acceleration and you would distance him quicker.

Grady

 

[Zero Signal]

You really can't answer that question without at least a dyno sheet and tranny ratios to go from.

The difference between 3.73's and 4.30 at that speed could be huge. You don't really know until you simulate it on paper. It's pointless to sit here and say I think this will happen or that will happen becuase these questions tend to have counter-intuitive answers. But with a dyno sheet, you can figure it out.

 

[OrangeMustangGt]

IN MY OPINION, thowing gas miledge to the wind, the higher gear #, the better acceleration......Because no matter if your on the track or the street, it makes it easier for the engine to accelerate the car. So, If your in a race on the highway, i would think that the easier your engine can accelerate your car the better.

 

[Zero Signal]

Problem is that it can mean the difference between being in 3rd and 4th gear which will change matters. Then you hit 5th and it's over for you.

 

[Blackened302]

Then you hit 5th and it's over for you.

no where to go after 5th

 

[ninjacoupe]

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.

 

[mo_dingo]

Going from 3.73's to 4.30's will multiply your RWTQ output by looking at this equation. Lets say you put out 500 FWTQ at 6000 RPM's, for instance. Then you multiply that by your trans ratio and then again by your gear ratio and then again by .85 to approximate driveline drag (15% in this case).

So that's 500*1*3.73 *.85 = 1585rwtq.

Now using 4.30's, you get = 1827rwtq.

So you are losing that much torque output across your entire powerband. Somewhere around 30% across the board.

But for a highway race, you don't necessarily stop at the speed you hit in the quarter mile. So you will run out of gear faster w/ the 4.30's and might "lose" or have to use 5th.

So that's my synopsis. I can't translate that into a number that we can relate to. Too tired and sick to think about it further.
Scott