RPM - Gear ratios.

[G-man]

Hi

For argument sake Im going to simply use a 528ci hemi.

Lets say the engine makes 600hp and 650 torque.

If the peak power is closer to 0 RPM due to being built completely mild... does that mean 3:95 gears are pointless?

I think the taller gears (3:95,s 4:10s etc) allow the car to really rev high and rev high fast... if the engines built to have extremely fast 0-100 meters then the engines made to have peak power closer to 0... does that make the taller gears pointless and actually injure the desired application and therefor 3:23's would actually be better in the vehicle with power in the lower RPM ranges...

Or does the 4:10s just make it go through the power curve faster so even in this case they would be better.

[Ghoste]

In a sense, yes.  If you could make peak power and torque at idle then of course there would be no need to get to a higher rpm quickly.  That is why so many electric motors are direct drive.
Being said, think of the rearend as a lever and when you later the ratio you change the pivot point.  Now the question becomes do you want to move a load quickly or easily?  Somewhere there is a compromise.

[G-man]

well what would make that a 'faster' off the green light car? the 3:23s or 4:10s in that type of power curve... last I got was above 500 torque from 2200rpm-5900rpm or something rather. Basicaly it was completely mild camshaft that braught everything down to 1700-5900.

On a quarter mile definately the 5900rpm would injure the vehicle and someone with the same power at 7000rpm would be better off... but they would be 4000-7000rpm... in my case... from light to light street car... the 1700-5900 would be faster right?

So the right gears for that to be utilized best would be 3:23s (or less like 2:8 likevipers etc) or 3:95 4:10s etc...

I dont even know how to ask what im trying to ask on here argh

[firefighter3931]

Don't compare a 6spd Viper gearbox to a conventional ratio 833. First gear in a Viper box is much lower which accounts for the torque multiplication needed with the sub 3.0 axle ratio. You have to look at the total package....not just the axle ratio. 

Lots of factors come into play when selecting a rear gear ratio. The deeper the gear...the better the car will accelerate. It's basic physics. 


Ron

[Ghoste]

Right.  Planning for it to be all in at a low rpm isn't realistic because you aren't going to be at max torque at that off idle rpm.  A cam that makes power in your 1700-5900 range still has to be at that 5900 rpm acceleration trip.
You are talking about a car that is quick off the light and exactly as Ron said, the deeper gear is the better "lever" to do it.  The compromise that I spoke of earlier is to not have the lever pivot moved to the point where all of the owrk can't be completed.  In other words, to move your car to a certain speed as quickly as possible, you want a high numerical gear ratio but not so high that it runs out of breath before it even reaches that speed.
A good drag racing generalization is to have the steepest gear possible but have the car going through the finish lights at your shift point (approx.-some guys like a little more).  When accelerating quickly are you going to be shifting the car at 1700 or closer to the 5900 number?  Well then, you want a ratio that is going to get you to that shift point quickly.

[John_Kunkel]

Don't compare a 6spd Viper gearbox to a conventional ratio 833. First gear in a Viper box is much lower which accounts for the torque multiplication needed with the sub 3.0 axle ratio. You have to look at the total package....not just the axle ratio. 

Not actually, the 1st gear ratio in the Viper is 2.66 which is the same as the majority of pre-'71  833's.

[G-man]

The viper box is 2.66?

an A833 at 2.66 is the same thing for first 4 gears just not 5-6th to drop it further?

Or is an A833 say at 3.23 (1st gear)... vs a 6 speed (3.23 1st gear) different?

THis is the stuff that confuses the hell out of me.

[Ghoste]

I think you're confusing two separate things.  The rearend ratio is your final drive and it is a fixed ratio.  The gearbox ratios can be changed as you know.  What John is saying is that the Viper box and the 833 have the same first gear ratio.  This means that in 1st, two cars with those two different gearboxes and all else being the same will be turning the same engine rpm to travel the same speed.  In fourth they would also be the same as they are both 1 to 1 in that gear.  2nd and 3rd are different.  They are 1.91 and 1.39 in the 833 and 1.78 and 1.30 in the Viper.  And as you note, the 5th and 6th are overdrives in the Viper.

[0X01B8]

This doesn't answer your question but have a look:  http://vexer.com/68rt/speed.html

[G-man]

Thanks for link will have a look.

Ghoste... that tells me overall since 1st and 4th are the same the A833 with 2-3 slightly taller would make it a hair line faster (in theory ofcourse not talking about driver, road conditions etc that would pretty much make that difference not there)

What about the A833 OD boxes... ofcourse made stronger with 18 spline etc... would they hav the same ratio as the A833 1-3 only 4th would be lower being the OD gear?

So when somebody says 3:95 gears... thats talking about the differential?

Which equates to gears being what 1-4 or 1-6?

And then you can change the gears in gearbox (still maintain the 3:95s) yet will act like 4:10's cause of the different ratios set up to be all tall?

[Ghoste]

The 833 overdrive has a 3.09 1st, a 1.67 2nd and 1 to 1 3rd with a .73 od.  I don't know if the Passon od has a different ratio set or not.  Yes, when someone says "X" gears, they are talking about the differential ratio.
Yes, if you can alter the ratios inside the gearbox it can have the same effect as changing the final drive ratio.  By that I am talking about acceleration characteristics and once you hit direct drive or overdrive, that effect will be negated.
As for your other question, I'm not sure what you mean.

[G-man]

for argument sake (dont think it is, but if it is possible) lets say

3:91 gears (differential) A833 custom ratios to act like 4:10

4:10 gears (differential) A833 stock ratios.

Would both work identical...

Having different gears vs different final drive ratio to work out the same (so 3:91s working like 4:10s cause of gear ratios just final drive is 3:91) would both ways accelerate etc the same or having the gears different vs drive ratio does effect the car differently meaing 3:91s will not work like 4:10s exactly even if the gers are made for it to work like 4:10 cause its the gears not the differential.

[Ghoste]

Not exactly, remember that for maximum acceleration part of the reason for the spacing between gears being what it is is to have rpm drop remain in the proper part of the power curve.  There may be a way to do it but I'm no engineer so I can't even begin to do the math.
That's probably why it's so much easier to have a couple of differently spaced gearbox choices but ultimately base your requirements through the final drive.

[G-man]

I c.

Well the conclusion I gather (correct me if im wrong) is this.

A: Stick to the general 3.91, 3.55, 3.23, 4.10 etc rear end...

B: Pick whatever gearbox I like (4 speed- 6 speed doesnt matter)

C: 4.10s even in a low power band application still makes car faster than lower gears cause even then I would shift at 5900 for maximum power and 4.10s would get u through the power band quicker than 3.23s hence being faster...

D: C means also that 1st gear will not be as high speed as 1st gear in a 3.23 application but it will accelerate faster (if you can shift propperly overall is quicker)

E: being a 6 speed gearbox there will still be plenty of top end speed even with 4.10s

F: being a 6 speed box you can actually get the benefit of taller gears (4.10s or higher) while still maintaining cruising RPMs because you have 2 extra gears to play with... this way 1st 4 gears can be used for drag while last 2 for cruise... where as in a 4 speed application, all 4 = drag (if its 4.10 etc) and no good for cruise which means less gears = lower ratio needed to have cruising potential while more gears allows u to go higher in the ratio while still maintaining the cruiseability due to the extra 2 gears

G: once Ive picked the gearbox (6-speed) and rear end (4.10) then its a matter of matching that 6 speed gearbox ratios (tweak them to get the best for desired application) within the '4.10' final drive ratio.

Have i got everything right?

[Ghoste]

I think so. 

[G-man]

Ok thanks!

So basically wanting a car that goes hard and yet can cruise all day... I need more gears hence 6 speed for what I would like.

Heres a quickie  then.... the viper runs a 2.66 gear... it goes hard when you nail it, and I mean it is a very quick accelerating car 0-60mph, and isnt bad on the quarter either.

If we then just stuck a 3.91 in the rear, would it stick you in the seat even more and really tare 0-60mph and 1/4 significantly more than with a 2.66  (just top end speed would suffer... but nobody can drive 200mph on the street anyway so whocares).?

If not why?

[flyinlow]

Can't resist this.  Anyone trying to hook 500 +HP to the ground with a manual Transmission has the wisdom of Obama.

Slushboxes rule!

There, I said it.  


A modern automatic like the Kiesler kit (4l60 chevy)  has a 3.06 first gear and a .65 OD. The torque converter can multiply the engines torque by 2 at the initial stall. No clutch can do that. The converter can lock up at cruise, to reduce rpms and help gas milage. At the dragstrip an automatic car is accellerating all the way down the track. Manual cars acceleration pauses durring the shifts.

[G-man]

Can't resist this.  Anyone trying to hook 500 +HP to the ground with a manual Transmission has the wisdom of Obama.

Slushboxes rule!

There, I said it.  


A modern automatic like the Kiesler kit (4l60 chevy)  has a 3.06 first gear and a .65 OD. The torque converter can multiply the engines torque by 2 at the initial stall. No clutch can do that. The converter can lock up at cruise, to reduce rpms and help gas milage. At the dragstrip an automatic car is accellerating all the way down the track. Manual cars acceleration pauses durring the shifts.

Thanks for the input but a torque/stall converter doesnt make the car very good for low cruising (eg 20-30mph - traffic driving)

A manual vs auto (no stall) manual is better for both drag and street.

An auto with a propper stall, yes, drag better than manual but crap on street.

So conclusion to me is manuals best for street for performance/streetability.

A stall converter tries to act like a clutch and has no shifting time wasted hence slightly better but an auto with no stall will not be like a manual. Also If i was building 800+ hp then yeah I would see the sense in an auto... but when the power I want to make is limited by the MPG im trying to get... 550-600hp is maximum. Stick a stall converter and auto in and I lose 60 HP vs the manual and definately will NOT achieve the MPG desired for a 'street cruiser'... sure no shift time wasted but a person that can shift gears well, the front nose will not drop down during shifts anyway, thus the manual again is quicker.

Im also considering a sequential 6 speed box that reduces the shift time by more than 50% as its either up click or down click to go through the gears, not your generic H pattern... it also loses less power than even your manual H pattern...

So a 600hp car with an auto and stall would work out below 540hp. A Sequential manual setup will be close to the 600 and next to nothing loss in shifting gears thus at that power level the car should and will be fastest set up with a manual AND retain propper street driving as thats its main purpose 'street driving with occasional nailing the gas at a green light'

So thats what im working with and trying ot get the best possible speed out of that 550-600hp by setting the car up perfectly to suit that.

G-

[FLG]

Can't resist this.  Anyone trying to hook 500 +HP to the ground with a manual Transmission has the wisdom of Obama.

Slushboxes rule!

There, I said it.  


A modern automatic like the Kiesler kit (4l60 chevy)  has a 3.06 first gear and a .65 OD. The torque converter can multiply the engines torque by 2 at the initial stall. No clutch can do that. The converter can lock up at cruise, to reduce rpms and help gas milage. At the dragstrip an automatic car is accellerating all the way down the track. Manual cars acceleration pauses durring the shifts.

Thanks for the input but a torque/stall converter doesnt make the car very good for low cruising (eg 20-30mph - traffic driving)

A manual vs auto (no stall) manual is better for both drag and street.

An auto with a propper stall, yes, drag better than manual but crap on street.

So conclusion to me is manuals best for street for performance/streetability.

A stall converter tries to act like a clutch and has no shifting time wasted hence slightly better but an auto with no stall will not be like a manual. Also If i was building 800+ hp then yeah I would see the sense in an auto... but when the power I want to make is limited by the MPG im trying to get... 550-600hp is maximum. Stick a stall converter and auto in and I lose 60 HP vs the manual... sure no shift time wasted but a person that can shift gears will, the front nose will not drop down during shifts anyway, thus the manual again is quicker.

Im also considering a sequential 6 speed box that reduces the shift time by more than 50% as its either up click or down click to go through the gears, not your generic H pattern... it also loses less power than even your manual H pattern...

So a 600hp car with an auto and stall would work out below 540hp. A Sequential manual setup will be close to the 600 and next to nothing loss in shifting gears thus at that power level the car should and will be fastest set up with a manual AND retain propper street driving as thats its main purpose 'street driving with occasional nailing the gas at a green light'

So thats what im working with and trying ot get the best possible speed out of that 550-600hp by setting the car up perfectly to suit that.

G-

The only way i see a manual as being better in terms of performance is not in the street, but on the road courses. Id rather be stuck in traffic going between the brake and gas then constantly getting a workout with the clutch. Also on the track an automatic will stress the driveline alot less then a manual car will.

[flyinlow]

G Man ,  Just stirring the pot a little ...   Interesting tread.  I have 5 and 6 speed manual gear boxes on my Honda and Suzuki ( 2 wheeled type) and enjoy them.

I run a 518 trans in my 440 Charger.  2.45  first gear  and a .69 overdrive with a lock up  converter. Works well with  3.55 gears  .  Sometimes wonder about a 6 speed manual with a .50 overdrive and 4.10 or 4.56 gears.

Craig

[G-man]

Flyin, which point were you trying to bring across with that or was it just information... *scratches head*

6 speed with 4:10 is what I was thinking for the 550-600hp bench mark.

That way going to be good MPG (good considering whats being driven) due to 5-6 gears and still fun for nailing it (1st 4 to race through and then smoothing off to economy with 5-6)

If i stick with the 4 and mak them 4:10 itl be good for race but suck for street (driving distance)... so I knew with my goals id have to add more gears wanting to be able to do both not just one.