Deeper gears less effective ?

[273]

I've notice something with gearing it's hard to explain so I'll mainly show examples so say we have 28" tires auto with 2.45 1st gear.

So were gonna figure out what mph will 2.76, 3.91 and 5.13 will hit 3,000 rpm, 4,500 rpm and 6,000 rpm in 1st gear.

1st gear x 2.76 = 37 mph @ 3,000 rpm, 55.5 mph @ 4,500 rpm and 74 mph @ 6,000 rpm.
1st gear x 3.91 = 26 mph @ 3,000 rpm, 39 mph @ 4,500 rpm and 52 mph @ 6,000 rpm.
1st gear x 5.13 = 20 mph @ 3,000 rpm, 30 mph @ 4,500 rpm and 40 mph @ 6,000 rpm.

So what are we looking at here, in 1st gear it only takes 20 mph to get to 3,000 rpm with 5.13's and 37 mph with 2.76 so 3.91's are about half way choice between 2.76 vs 5.13 but given 65% of the results, it's only 6 mph from the 5.13's 20 mph vs 11 mph from the 2.76's 37 mph and does similar at 4,500 and 6,000 rpm and through out the other gears, now obviously you don't get the extra torque multiplication of 5.13 vs 3.91 but you do get a greater percentage of rpm per mph, which helps you get into your powerband easier.

So it seems you get some diminishing returns say after 3.91 gears, plus most don't need 5.13 anyways, going from 3.23 to 3.91 gonna be more effective than 3.91 to 4.56 to get your engine into it's powerband.

 

[gzig5]

Less effective at what? What is the goal in what application?
In racing, gears are selected to get the engine into the powerband and at some point, keep it there across the stripe to give the best ET/MPH. The trans type, gearing, and converter has an effect through that process, obviously.
On a street car, it's more about fuel efficiency, efficient torque range, and cruise rpm on the highway.

Cam duration is going to have a big effect on what gear works best for a combination. A 2.94 or 3.23 rear gear isn't going to make an engine happy that has a lot of duration (whatever "a lot" is).

I don't think you can apply simple math to the problem. There are too many variables.

 

[YY1]

OP is skipping from 2.76 to 3.91?

What about 3.23 and 3.55.....and 3.73?

 

[273]

OP is skipping from 2.76 to 3.91?

What about 3.23 and 3.55.....and 3.73?

It's the concept I was trying to get across, I used 2.76 vs 5.13 as two extremes and 3.91 are in the middle of those two but gets you 65% of the way there, 3.55 would get you 50% of the way there, 3.23 35% of the way there.

Point is the gains are a greater percentage for each step up in the higher gears and as you go deeper the gains get less and less. (mph for given rpm)

 

[273]

Less effective at what? What is the goal in what application?

To get you into the powerband, 2.76 gears took 37 mph in 1st to only get to 3,000 rpm (5.13 would be at 5,580 rpm @ 37 mph) That makes it hard to get into your engines powerband.

In racing, gears are selected to get the engine into the powerband and at some point, keep it there across the stripe to give the best ET/MPH. The trans type, gearing, and converter has an effect through that process, obviously.
On a street car, it's more about fuel efficiency, efficient torque range, and cruise rpm on the highway.

obviously where talking about getting into the powerband.

Cam duration is going to have a big effect on what gear works best for a combination. A 2.94 or 3.23 rear gear isn't going to make an engine happy that has a lot of duration (whatever "a lot" is).

Not talking about best gearing

I don't think you can apply simple math to the problem. There are too many variables.

My point was the gains in gearing isn't linear.

 

[318willrun]

I've notice something with gearing it's hard to explain so I'll mainly show examples so say we have 28" tires auto with 2.45 1st gear.

So were gonna figure out what mph will 2.76, 3.91 and 5.13 will hit 3,000 rpm, 4,500 rpm and 6,000 rpm in 1st gear.

1st gear x 2.76 = 37 mph @ 3,000 rpm, 55.5 mph @ 4,500 rpm and 74 mph @ 6,000 rpm.
1st gear x 3.91 = 26 mph @ 3,000 rpm, 39 mph @ 4,500 rpm and 52 mph @ 6,000 rpm.
1st gear x 5.13 = 20 mph @ 3,000 rpm, 30 mph @ 4,500 rpm and 40 mph @ 6,000 rpm.

So what are we looking at here, in 1st gear it only takes 20 mph to get to 3,000 rpm with 5.13's and 37 mph with 2.76 so 3.91's are about half way choice between 2.76 vs 5.13 but given 65% of the results, it's only 6 mph from the 5.13's 20 mph vs 11 mph from the 2.76's 37 mph and does similar at 4,500 and 6,000 rpm and through out the other gears, now obviously you don't get the extra torque multiplication of 5.13 vs 3.91 but you do get a greater percentage of rpm per mph, which helps you get into your powerband easier.

So it seems you get some diminishing returns say after 3.91 gears, plus most don't need 5.13 anyways, going from 3.23 to 3.91 gonna be more effective than 3.91 to 4.56 to get your engine into it's powerband.

I think you'd have to know the engines needs before the determination of it's % of effective results would be in gear ratios.

 

[273]

I think you'd have to know the engines needs before the determination of it's % of effective results would be.

Sure but that's not the point I'm making, Say 4.10 are gonna work best for your combo but you got 2.76 but really don't want 4.10 but want to make the most out of your combo, 28" tires 2.45 1st gear, mph at 3,000 rpm (start of powerband) 2.76 = 37 mph, 2.94 = 34.5 mph, 3.23 = 31.5 mph, 3.55 = 28.5 mph, 3.73 = 27.5 mph, 3.91 = 26 mph, 4.10 = 25 mph.

If look at the difference between 2.76 & 2.94 vs 3.91 & 4.10 both are about 0.20 increase in gearing but the 2.76/2.94 is a 2.5 mph decrease and 3.91/4.10 is a 1 mph. Going from 3.91 to 4.10 doesn't really help as much.

Going from 2.76 to 3.23 a 0.47 gain, decreases mph by 5.5 mph where as 3.55 to 4.10 a 0.55 increase only decreases mph by 3.5 mph.

And side note 5.13 a 1.03 increase (4.10) only decreases mph by 5 mph making it 20 mph @ 3,000 rpm, the 2.76 to 3.23 a 0.47 change made a larger 5.5 mph change.

Not saying there's not other factors or benefits, but just showing it's not linear and do with that info as you will.

 

[318willrun]

Sure but that's not the point I'm making, Say 4.10 are gonna work best for your combo but you got 2.76 but really don't want 4.10 but want to make the most out of your combo, 28" tires 2.45 1st gear, mph at 3,000 rpm (start of powerband) 2.76 = 37 mph, 2.94 = 34.5 mph, 3.23 = 31.5 mph, 3.55 = 28.5 mph, 3.73 = 27.5 mph, 3.91 = 26 mph, 4.10 = 25 mph.

If look at the difference between 2.76 & 2.94 vs 3.91 & 4.10 both are about 0.20 increase in gearing but the 2.76/2.94 is a 2.5 mph decrease and 3.91/4.10 is a 1 mph. Going from 3.91 to 4.10 doesn't really help all that much.

Going from 2.76 to 3.23 a 0.47 gain, decreases mph by 5.5 mph where as 3.55 to 4.10 a 0.55 increase only decreases mph by 3.5 mph.

And side note 5.13 a 1.03 increase (4.10) only decreases mph by 5 mph making it 20 mph @ 3,000 rpm, the 2.76 to 3.23 a 0.47 change made a larger 5.5 mph change.

Not saying there's not other factors or benefits, but just showing it's not linear and do with that info as you will.

too much math hath made you mad.... lol
i don't see why anyone would care what the mph is at 3k rpm's if they have a engine that shifts at 7500 rpms and has a 5500 rpm stahl

 

[toolmanmike]

I've notice something with gearing it's hard to explain so I'll mainly show examples so say we have 28" tires auto with 2.45 1st gear.

So were gonna figure out what mph will 2.76, 3.91 and 5.13 will hit 3,000 rpm, 4,500 rpm and 6,000 rpm in 1st gear.

1st gear x 2.76 = 37 mph @ 3,000 rpm, 55.5 mph @ 4,500 rpm and 74 mph @ 6,000 rpm.
1st gear x 3.91 = 26 mph @ 3,000 rpm, 39 mph @ 4,500 rpm and 52 mph @ 6,000 rpm.
1st gear x 5.13 = 20 mph @ 3,000 rpm, 30 mph @ 4,500 rpm and 40 mph @ 6,000 rpm.

So what are we looking at here, in 1st gear it only takes 20 mph to get to 3,000 rpm with 5.13's and 37 mph with 2.76 so 3.91's are about half way choice between 2.76 vs 5.13 but given 65% of the results, it's only 6 mph from the 5.13's 20 mph vs 11 mph from the 2.76's 37 mph and does similar at 4,500 and 6,000 rpm and through out the other gears, now obviously you don't get the extra torque multiplication of 5.13 vs 3.91 but you do get a greater percentage of rpm per mph, which helps you get into your powerband easier.

So it seems you get some diminishing returns say after 3.91 gears, plus most don't need 5.13 anyways, going from 3.23 to 3.91 gonna be more effective than 3.91 to 4.56 to get your engine into it's powerband.

So if you have a 5.13 in your race car you would have to spin her to 12,000 rpm to hit 80 mph? I think you had better go back and recheck your math.

 

[318willrun]

So if you have a 5.13 in your race car you would have to spin her to 12,000 rpm to hit 80 mph? I think you had better go back and recheck your math.

AJ needs to get in here and take 273 back to class..... lol

 

[273]

too much math hath made you mad.... lol
i don't see why anyone would care what the mph is at 3k rpm's if they have a engine that shifts at 8500 rpms and has a 6000 rpm stahl

It's not about 3,000 rpm, it's about being in your powerband at average road speeds, if it takes your car 37 mph to just reach 3,000 rpm then 6,000 rpm is gonna be twice the mph (74 mph). If your powerband is 3,000-6,000 rpm you got to be going 37-74 mph in 1st, 2nd is gonna be a bunch of more mph, where as 5.13 (not saying to run them just an eg.) only needs 20-40 mph to cover 3,000-6,000 rpm powerband. But like I'm pointing out 3.91's is about 50% of the gear ratio different but lowers the needed mph by about 65% 26-52 mph for 3,000-6,000 rpm, 3.55 = 28.5-57 mph which is about half way 2.76 = 37-74 mph vs 5.13 = 20-40 mph.

Point is 3.55 get you about 50% the way, (2.76 vs 5.13) 3.91 65%, 4.30 75% but the main point is deeper you go the less the gains.

 

[33IMP]

Im not sure I understand the point, but I know this:
The last two gear changes I made on two different cars (from 4.56 to 3.91, bbm, and from 5.14 to 4.57, n/a small block) the cars ran virtually the same et and mph.
Both cars had plenty of stall speed, that might have been a mitigating factor.
But I'm still changing my current car from 3.50 to 4.10.

 

[273]

So if you have a 5.13 in your race car you would have to spin her to 12,000 rpm to hit 80 mph? I think you had better go back and recheck your math.

I'm not talking about the race track per se.

Say we got a 360 and it's powerband stall to shift points is 3,000 to 6,000 rpm and it's a street car never gonna see over 100 mph.

We want to gear it so it's real easy to get into the powerband especially 1st gear.

Well the deepest is obviously gonna do it the easiest, 5.13 = 20-40 mph = 3,000 - 6,000 rpm and the highest gonna be hardest 2.76 = 37-74 mph = 3,000 - 6,000 rpm.

Now most aren't gonna want to run 5.13 even thought it's gonna be the easiest so say we figure half way 28.5-57mph is a good compromise so is the answer 3.91 gear since they sit halfway between 2.76-5.13 turns out no it's even better cause the results aren't linear you only need 3.55 to get your powerband in the 28.5-57 mph, 3.91 will actually get you 65% of the way there 26-52 mph if you choose them.

 

[273]

Im not sure I understand the point, but I know this:
The last two gear changes I made on two different cars (from 4.56 to 3.91, bbm, and from 5.14 to 4.57, n/a small block) the cars ran virtually the same et and mph.
Both cars had plenty of stall speed, that might have been a mitigating factor.
But I'm still changing my current car from 3.50 to 4.10.

I'm just trying to show this one aspect of gear ratio ain't linear if we use 2.76 and 5.13 as book ends going from 2.76 to 3.55 (0.79:1 gain) gets you 50% there mph per rpms, and going to 5.13 from 3.55 (1.58:1 gain) only gives you the other 50%.

I think post #13 I explained it best.

 

[fishmens67]

I can guarantee one thing, an engine that requires a 5.13 gear is going to take a long time to reach 6000 rpm with a 2.76 gear. BTDT

 

[273]

I can guarantee one thing, an engine that requires a 5.13 gear is going to take a long time to reach 6000 rpm with a 2.76 gear. BTDT

What I'm trying show is the gain ain't linear in this one aspect, kind of like cr going from 7:1 to 8:1 gives a higher hp % increase than 15:1 to 16:1.

 

[318willrun]

What I'm trying show is the gain ain't linear in this one aspect, kind of like cr going from 7:1 to 8:1 gives a higher hp % increase than 15:1 to 16:1.

What your saying is.....
kind of like putting a intake and carb from a 318 2bbl on a 450 HP 408. You'll gain more switching from the 2bbl to a 600 holley than you will taking the next step and going from a 600 to a 750.

 

[273]

What your saying is.....
kind of like putting a intake and carb from a 318 2bbl on a 450 HP 408. You'll gain more switching from the 2bbl to a 600 holley than you will taking the next step and going from a 600 to a 750.

I say that's a good way to look at it

 

[318willrun]

I say that's a good way to look at it

that's a lot of math to say something pretty simple... lol. I've not heard anyone ever say that the gain remains equal throughout every change.
Did you know on a 440, that the gain from going from a 3 hp lawn mower air filter to a 14x2" air filter is greater than going from a 14x2" to a 14x3" air filter? Once you go from the lawn mower air filter to the 14", the gains will not be the same even if you stack three 14" air filters on top each other. The % of change dwindles.

Gotta tease ya...

 

[273]

that's a lot of math to say something pretty simple... lol.

I notice it when I was figuring something else out, thought might be of help/interest for some, Yes in the end of the day it didn't add anything much new, basically confirms that 3.55-3.91 give the most bang for the buck, It might give some explanation why though.

I've not heard anyone ever say that the gain remains equal throughout every change.

Some do some don't, now I know at least this one aspect of gears don't.

Did you know on a 440, that the gain from going from a 3 hp lawn mower air filter to a 14x2" air filter is greater than going from a 14x2" to a 14x3" air filter? Once you go from the lawn mower air filter to the 14", the gains will not be the same even if you stack three 14" air filters on top each other. The % of change dwindles.

Gotta tease ya...

lol


Another thing I noticed 5.13 only has a 20 mph gap between 3,000-6,000 rpm (20-40mph) and 2.76 has an almost 40 mph gap (37-74mph) so not only do you have to get up to 37 mph with 2.76 to get into the powerband but almost have to accelerate 2 mph for every one mph (twice the rate) 5.13 would have to, luckily 3.55-3.91+ will also get you to 50-65%+ of that too.

 

[66 Sat]

So if you have a 5.13 in your race car you would have to spin her to 12,000 rpm to hit 80 mph? I think you had better go back and recheck your math.

His calcs are in 1st gear so his maths are probably correct.

To the OP - I actually do understand what you are saying and it is interesting.

 

[92b]

What I'm trying show is the gain ain't linear in this one aspect, kind of like cr going from 7:1 to 8:1 gives a higher hp % increase than 15:1 to 16:1.

7:1 to 8:1 is a 12.5% increase in compression vs 6.25% increase from 15:1 to 16:1 you would have to go from 15:1 to a little over 17:1 for the same 12.5% increase. I think. lol

 

[Oldiron440]

If you were to use the Moroso hp/speed calculator you can figure out what gears you need to run your car in its power band in the quarter mile.
Sometimes when you’re looking at cams they will give a recommendation on converter and gears.
You pretty much need to build the engine/converter/drive gear's as one combination and it doesn’t matter if it’s for cruising street/strip or a full on drag car. If you compromise on the engine you need to make a change in the converter and possibly the axle gears, they all work together.

 

[cookietruck]

So if you have a 5.13 in your race car you would have to spin her to 12,000 rpm to hit 80 mph? I think you had better go back and recheck your math.

In first gear in the trans..

 

[273]

In first gear in the trans..

It still holds in 3rd gear but the speeds to do 6,000 rpms are crazy high except 5.13,

5.13 = 98 mph, 3.91 = 127 mph and 2.76 = 181 mph but 3.55 are still about half way at 141 mph,

In 2nd 6,000 rpms is at 2.76 = 125 mph, 3.91 = 88 mph, 5.13 = 67 mph and again 3.55 are about halfway at 97 mph.

So 3.55 being halfway still holds in 2nd and 3rd.