Selecting the right gear ratio

[03COBRABOY]

wow..a real hot rod topic to discuss!! so how would u guys select the right gears for your car?

by engine rpm at the traps? what speed? what gear? tire size?

so far (for my car) this is what ive come up with....

4th gear is the 1:1 gear. with the stock 3.55's and 26" tires, 4th redlines @ 133....not a bad trap to shoot for!

same tires and 3.73's go to 125mph

same tires and 3.90's goes to 121mph (a more realistic goal for now)
and

4.10's brings it to 115mph which is too low.

im thinkin the 3.90's cuz after i get past 121mph trap i can go to a 28" slick which will bring it up to 131mph @ redline...comments please

[bottledbird68]

Yeah :thumbsup:

[bottledbird68]

Sorry, had to :D Just shoot for whatever gear will put you at the top of your useable rpm range in fourth gear as you cross the finish line and the rest will all fall into place :cool2:

[03COBRABOY]

well im thinkin ahead. cuz right now it would be 4.10's which is maxed out @ 115. i can hit 155 with 2 mods....then i need bigger slicks which would go to 125. im sure i can get to that. thats like a low 11. 3.90's will gove me another 6mph to work with on top of that sooo....i guess its 3.90s...

[bottledbird68]

Originally posted by Badass99RT
i can hit 155 with 2 mods.... Holy Fuck!!!!! I'm buying a new cobra. The hell with busting my ass on this old shit. Do those 2 mods void your warranty? :D :poke:

[03COBRABOY]

115 i meant.....hehehehe

[Jack ffr1846]

Good catch on the typo! I was thinking....hmm, the 2 mods must be a nitro burning dragster motor and a big crowbar to get it in.

[FATBLOCKMARO]

Originally posted by Jack ffr1846
Good catch on the typo! I was thinking....hmm, the 2 mods must be a nitro burning dragster motor and a big crowbar to get it in.


LOL .....OR A 350 SHOT OF JUICE AND A MOP.....:eh:

[SickboySS]

you have a stick, right? is it a close ratio or wide ratio? thats what really determines what gears you need

if you get 4.10's with a wide ratio tranny, then 1st gear is useless unless you're on the burnout pad

if you get sutin like a 2.73 or a 3.08 with a close ratio tranny, its gonna be a dog

3.42's are good all around gears, prob. the best for launching, street, and strip

[Feral]

Don't just calculate for Redline ... calculate for the end of the powerband ... at the HP peak (or within 500rpms of it). So unless redline is within 500 rpms of the HP peak you need to rethink your calculations and get some taller gears than you think.

The HP peak is where the torque curve begins to fall off faster than the RPMS go up ... which is not optimum.

I wish I could buy gears for my car ... I shift to 4th at 110 and at street boost I trap at 112-114. Fucking sucks ... just another 500rpms and I'd never have to leave 4th.

[540Malibu]

th eaton on your motor makes its power over a broad rpm range, so its pointless to drop to a low gear to just rev past the power. stick with 3.55's , it will be much easier on the tires when you leave the line and once you start messing with engine components it will be just right. i would only go to a 3.90 if you are going to run 28" tires all the time.

[H3llphyre]

Originally posted by Feral
I wish I could buy gears for my car ... I shift to 4th at 110 and at street boost I trap at 112-114. Fucking sucks ... just another 500rpms and I'd never have to leave 4th.

Why redefine your gears when you can redefine your rev limit? You know you can keep making power if you push it another 800rpms or so.

Either way, I agree with spenc. Leave the gears alone for now... Because, you will end up changing them once you start doing shit to the motor.

[03COBRABOY]

but see..once i get this axle..its gonna have 3.27's unless i get a BULLIT axle. so they have to be changed. if my goal is 125mph, dont i want my gear to run out right there?? if not with the 3.55's ill still have rpm left. from what i "thought" i knew and now what ur saying...im confused..

[540Malibu]

Originally posted by Badass99RT
but see..once i get this axle..its gonna have 3.27's unless i get a BULLIT axle. so they have to be changed. if my goal is 125mph, dont i want my gear to run out right there?? if not with the 3.55's ill still have rpm left. from what i "thought" i knew and now what ur saying...im confused..

in that case, i'd go 3.90 and run a 28" tire on the street as well and start out with a 28"slick and work up to a 29.5"

[03COBRABOY]

?? if i go with 3.90s and 28" tires then im just running 3.73s basically. plus now that i think of it......will a 28" tire even fit??? :lol: the best thing is to run 4th to redline through the traps right? stock itll run 110mph. (if i can drive it) itll prolly run a bit faster the first time for me with the axle, weight out ect...

on 26" tires (street and slick)
3.55s, redline in 4th is 132mph
3.73s, redline in 4th is 126mph
3.90s, redline in 4th is 120mph

itll take me a while to get 120mph traps but this is what gets me the better gearing right? once i hit 120 and want more...a 28" slick will get me to 130mph. thats a better explaination i think.

[bottledbird68]

Like was said earlier, set the gearing up so that you are at the end of your powerband in 4th gear as you go through the traps. I know you're changing stuff later so either compromise now or change gears when you change the powerband. Ahh, the joys of modifying a car. The money just never stops leaving your wallet..... :D

[Feral]

Originally posted by Badass99RT
?? if i go with 3.90s and 28" tires then im just running 3.73s basically. plus now that i think of it......will a 28" tire even fit??? :lol: the best thing is to run 4th to redline through the traps right? stock itll run 110mph. (if i can drive it) itll prolly run a bit faster the first time for me with the axle, weight out ect...

on 26" tires (street and slick)
3.55s, redline in 4th is 132mph
3.73s, redline in 4th is 126mph
3.90s, redline in 4th is 120mph

itll take me a while to get 120mph traps but this is what gets me the better gearing right? once i hit 120 and want more...a 28" slick will get me to 130mph. thats a better explaination i think.

You do NOT want to end the 1/4 at redline in a car with a roots style blower ... as Spencer said the car is much more efficient in the lower end of the RPMs. Make it so you hit the traps at your HP peak (which is what ... 5700rpms??) or within 500rpms of that. There's more power (hence more acceleration) between the torque peak and the HP peak than anywhere else in the engine ... hence this is why they call this the "powerband". Mine is from 4000-6500 rpms ... yours is probably from 2500-5700 ... or something like that. You want to keep the car in there as much as possible ... not just bounce off redline all the time and overheat your S/C

[igotasweetride]

Originally posted by Feral
You do NOT want to end the 1/4 at redline in a car with a roots style blower ... as Spencer said the car is much more efficient in the lower end of the RPMs. Make it so you hit the traps at your HP peak (which is what ... 5700rpms??) or within 500rpms of that. There's more power (hence more acceleration) between the torque peak and the HP peak than anywhere else in the engine ... hence this is why they call this the "powerband". Mine is from 4000-6500 rpms ... yours is probably from 2500-5700 ... or something like that. You want to keep the car in there as much as possible ... not just bounce off redline all the time and overheat your S/C

his power band doesnt drop off, it goes right till redline

http://members.aol.com/bnasplt/images/comparison1.gif

blue is the stock dyno, so he wants to hit redline right before the traps, if anything he'd want it at like 6300-6400 because it gets bouncy after that

[Feral]

Originally posted by igotasweetride
his power band doesnt drop off, it goes right till redline

http://members.aol.com/bnasplt/images/comparison1.gif

blue is the stock dyno, so he wants to hit redline right before the traps, if anything he'd want it at like 6300-6400 because it gets bouncy after that

wow ... ok your right ... go for redline.

I'd be curious what the powerband on the 500RWHP mustangs like brad who are running the stock blower at like 16psi looks like ... because at that point I imagine the top end starts to drop off ... but stock looks like the '03's could use more RPMS ...

Oh I get it ... its DOHC ... forgot that I was assuming pushrod since it was domestic ... nevermind

[540Malibu]

Originally posted by igotasweetride
his power band doesnt drop off, it goes right till redline

http://members.aol.com/bnasplt/images/comparison1.gif

blue is the stock dyno, so he wants to hit redline right before the traps, if anything he'd want it at like 6300-6400 because it gets bouncy after that

power band on that motor is 4300-6k

going past that is a waste of rpm

[igotasweetride]

Originally posted by 540Malibu
power band on that motor is 4300-6k

going past that is a waste of rpm

my god spence, this is 3 posts in a row you've commented on and are wrong, stay away from EFI, carbs are a lot easier for you youngsters.

it still gained 10-15hp from 6000-6400. therfore its still making more power and worth staying in rather then gearing for it now and when he mods it losing out on that much more top end.

[Feral]

Originally posted by igotasweetride
my god spence, this is 3 posts in a row you've commented on and are wrong, stay away from EFI, carbs are a lot easier for you youngsters.

it still gained 10-15hp from 6000-6400. therfore its still making more power and worth staying in rather then gearing for it now and when he mods it losing out on that much more top end.

Nope ... wrong. Spencer knows everything ever ... don't forget it. :no:

[03COBRABOY]

ok..well im glad thats settled. im gonna do the 3.90s. if it gets bad..owell. they change stang gears for $150 so its all good. thanks for the opinions guys..

[540Malibu]

Originally posted by igotasweetride
my god spence, this is 3 posts in a row you've commented on and are wrong, stay away from EFI, carbs are a lot easier for you youngsters.

it still gained 10-15hp from 6000-6400. therfore its still making more power and worth staying in rather then gearing for it now and when he mods it losing out on that much more top end.

how many motors have you built? ok shut the fuck up, how many professional classes have you raced in? again shut the fuck up. Just because your gaining power doesnt mean your using it and unitl you can understand that simple fact maybe you should just stay away from cars, he'res 2 things dyno's don't measure, useable power, and rpm port velecity change between shifts, go back to watching fast and furious and playing need for speed, when you get a fucking clue you can comment.

[igotasweetride]

Originally posted by 540Malibu
how many motors have you built? ok shut the fuck up, how many professional classes have you raced in? again shut the fuck up. Just because your gaining power doesnt mean your using it and unitl you can understand that simple fact maybe you should just stay away from cars, he'res 2 things dyno's don't measure, useable power, and rpm port velecity change between shifts, go back to watching fast and furious and playing need for speed, when you get a fucking clue you can comment.

:lol: you're retarded spence. 1. building engines doesnt mean shit when it comes to selecting gears and calculating usable power. 2. racing doesnt mean shit when you race, it just means you can drive 3. try getting straight As in 2 years of physics courses that were based on mechanical engineering. i never said it was the BEST power increase, but its still making power and its better to stay at the higher RPM at the top end then to be in the lower end with less power at the beginning of the gears. and dont give me this port velocity shit because it doesnt mean shit when you're NOT SHIFTING, we're talking about the end of a gear, thats it, not shifting. and FYI, i dont have the new need for speed yet, go tune a carb :lol: :headbang1 :thumbsup:

[540Malibu]

Originally posted by igotasweetride
:lol: you're retarded spence. 1. building engines doesnt mean shit when it comes to selecting gears and calculating usable power. 2. racing doesnt mean shit when you race, it just means you can drive 3. try getting straight As in 2 years of physics courses that were based on mechanical engineering. i never said it was the BEST power increase, but its still making power and its better to stay at the higher RPM at the top end then to be in the lower end with less power at the beginning of the gears. and dont give me this port velocity shit because it doesnt mean shit when you're NOT SHIFTING, we're talking about the end of a gear, thats it, not shifting. and FYI, i dont have the new need for speed yet, go tune a carb :lol: :headbang1 :thumbsup:

so i guess jake is going to go down the track and launch ONLY in 4th gear, port velocity is 99% of the time highest at peak VE and peak torque IS the hgihest VE point. obviously you don't know shit about how a motor runs. because if you did you'd notice that port recovery times caused by over-rev-ing a motor and loosing velocity can account for between 1 and 2 tenths in 1/4 mile et

the object is to get the most USEABLE power from each gear and this requires EVRYTHING to be considered, not jsut where peak power is.

[igotasweetride]

Originally posted by 540Malibu
so i guess jake is going to go down the track and launch ONLY in 4th gear, port velocity is 99% of the time highest at peak VE and peak torque IS the hgihest VE point. obviously you don't know shit about how a motor runs. because if you did you'd notice that port recovery times caused by over-rev-ing a motor and loosing velocity can account for between 1 and 2 tenths in 1/4 mile et

the object is to get the most USEABLE power from each gear and this requires EVRYTHING to be considered, not jsut where peak power is.

we're not discussing each gear right now, we're talking about 4th and only 4th, so shifting doesnt mean shit and VE means something, but what he will lose on the top end has to be compared to what he would lose on the bottom end.

[540Malibu]

Originally posted by Badass99RT
wow..a real hot rod topic to discuss!! so how would u guys select the right gears for your car?




this is what we are discussing, the right gears for the car, not what gears get you to peak hp in 4th.

[igotasweetride]

Originally posted by 540Malibu
this is what we are discussing, the right gears for the car, not what gears get you to peak hp in 4th.

ok, so please tell me what relevance 1st, 2nd and 3rd have to do with this conversation? besides the obvious. right now, it really doesnt mean shit to me, because all he needs to know for now is what gear gets him in the optimum rpm in 4th, thats it. 1, 2 and 3 can be gone over later with a discussion on shift rpms. next time you qoute someone, dont take it out of context.

[540Malibu]

Originally posted by igotasweetride
ok, so please tell me what relevance 1st, 2nd and 3rd have to do with this conversation? besides the obvious. right now, it really doesnt mean shit to me, because all he needs to know for now is what gear gets him in the optimum rpm in 4th, thats it. 1, 2 and 3 can be gone over later with a discussion on shift rpms. next time you qoute someone, dont take it out of context.

i dont give a shit what it means to you, he asked the right gears for THE CAR no the right gears for 4th gear, we have already stated that you should not gear for trap speed.

1-2-3-4 and what ever other gear he uses relies on the most efficient time spent in the power band.

if the motor revs say 2000rpm/sec and he swithec to 4.10's which in theory will let the motor rev 3000rpm/sec , but the motor can physicaly only rev 2000rpm sec than the other 1000rpm/sec potential is wasted and the car is not accelerating as fast. its like having a a lever with a pivot point 6" down from the top of the handle, and hving the actuator 1" down from the pivot point, sure you have an easier pull. but if you can physicaly only pull it at 6mph, and you can also pull a lever with a 2" handle above the pivot with 5" below at 6mph, the action will be MUCH faster with the same amount of effort without being "too easy"

[03COBRABOY]

so why would i want to shift at a LOWER RPM which in tunr will take me into LESS POWER in the next gear? if im still making power why not go to the peak, then when i hit the next gear i am that much higher up in the powerband???????

[540Malibu]

Originally posted by Badass99RT
so why would i want to shift at a LOWER RPM which in tunr will take me into LESS POWER in the next gear? if im still making power why not go to the peak, then when i hit the next gear i am that much higher up in the powerband???????

because every gear in your car does not have the same percentage rpm drop between shifts.

[03COBRABOY]

i think ur thinkin TOO deep into theis spence. i know how technical u are n shit, and i DO know what ur saying about the rpm drop.

[540Malibu]

you can never get too technical, you don't win races by sticking to basics.

[03COBRABOY]

so with all ur tech stuff, your saying stay with the 3.55s? just dont seem good to me cuz ill have gear left in 4th all the time. everyone i know ups gears a bit and always gains..i dunno..

[540Malibu]

Originally posted by Badass99RT
so with all ur tech stuff, your saying stay with the 3.55s? just dont seem good to me cuz ill have gear left in 4th all the time. everyone i know ups gears a bit and always gains..i dunno..

once you get into the motor you're just going to have to change back, if your running a 26" tire stay with 3.55's if a 28, up to 3.90

[H3llphyre]

Originally posted by 540Malibu
once you get into the motor you're just going to have to change back, if your running a 26" tire stay with 3.55's if a 28, up to 3.90
I agree.

[bottledbird68]

Originally posted by 540Malibu
if the motor revs say 2000rpm/sec and he swithec to 4.10's which in theory will let the motor rev 3000rpm/sec , but the motor can physicaly only rev 2000rpm sec than the other 1000rpm/sec potential is wasted and the car is not accelerating as fast. I understand what you are saying from an efficiency standpoint but math equations don't move a car down the track. I understand your point about revving too quickly but the car will still physically cover more ground faster with a deeper gear. Granted you may be forcefully revving it but it will still go faster regardless, just not as efficiently. Say you have an 85 delta 88 with 2.73's and a stone stock 307. I think we'd all agree it won't rev all that fast correct? But, sucky motor regardless, if you put 4.10's in it it's going to go faster. More mechanical advantage = more acceleration. Maybe not "efficient" acceleration, but acceleration nonetheless. I'd love for you to explain to me how 4.10 would make a car accelerate slower than 2.73's? I know you're talking finesse, but, there's something to be said for brute force. Not flaming, just looking for a nice tech discussion, if I am wrong enlighten me :cool2:

[03COBRABOY]

thanks for the insight chicken....figured this would be a good discussion!

like i said before going form 3.92s in the r/t to 4.56's gave me .2 in the 1/4 with no other mods. mainly gained it all in the 1/8 mile. quicker reaction, 60's and way faster acceleration.

im trying to plan ahead...which is HARD in the drag world i know!

[TunedPort 335]

Well here's some food for thought. On TPI cars like mine (run out of steam at around 4500-4800rpm), going to 3.73 or higher gears actually hurts your quarter mile times. With steep gears like that, it rips through the low and midrange too quickly (a part where TPI shines) and gets itself caught in upper RPM's really fast. You also pass through the traps at around 5500+rpms, making no power (depends on how fast your car is, and what your traps speeds are though).

I personally know of someone with a TPI 350 Camaro that had 2.77's and ran consistent 13.7's and 13.8's... then he swapped 3.73's and ran consistent 13.9's and 14.0's. It's all about powerband and where you want to match everything up, so to make a long story short... I kinda agree with Spence.

[540Malibu]

Originally posted by bottledbird68
I understand what you are saying from an efficiency standpoint but math equations don't move a car down the track. I understand your point about revving too quickly but the car will still physically cover more ground faster with a deeper gear. Granted you may be forcefully revving it but it will still go faster regardless, just not as efficiently. Say you have an 85 delta 88 with 2.73's and a stone stock 307. I think we'd all agree it won't rev all that fast correct? But, sucky motor regardless, if you put 4.10's in it it's going to go faster. More mechanical advantage = more acceleration. Maybe not "efficient" acceleration, but acceleration nonetheless. I'd love for you to explain to me how 4.10 would make a car accelerate slower than 2.73's? I know you're talking finesse, but, there's something to be said for brute force. Not flaming, just looking for a nice tech discussion, if I am wrong enlighten me :cool2:

simple, look at the timeslips from my small block in the malibu, it ran 2 tenths faster short shifting it and making the motor work harder, where as ikm sure you know it "should" have been a top end high revving motor.

you can't "force" a motor to rev faster than at idle unless there is a HUGE force pushing it. in terms of ET you will get a better ET if you do less shifting in the 1st 8th mile because that is more time spent accelerating.

also, most of the high torque guys running low et's are using power glides, if having a shorter gear is all that moreimportant to acceleration why don't they all run 3 speeds if an auto takes no time to shift and the 3 speeds are jsut as strong and weigh about the same?

[bottledbird68]

Originally posted by 540Malibu
also, most of the high torque guys running low et's are using power glides, if having a shorter gear is all that moreimportant to acceleration why don't they all run 3 speeds if an auto takes no time to shift and the 3 speeds are jsut as strong and weigh about the same? As far as I understood the main reason for switching to a glide in a high torque low weight application was because the lower first gear of a 3 speed would just blow the tires off at the line.
And Chris, I know what you are saying about revving past the useable powerband, but, in Jake's case he has dyno sheets of engines exactly like his so he can see where to be geared for.

Spence, I understand what you are saying and agree with you to a certain point. But, if what you are saying is a be all end all then why doesn't everybody run 2.73's at the drags? More mechanical advantage = more acceleration in MOST instances, assuming of course the engine is equipped to make good use of it. Granted I understand there is a fine balance between perfect and too much, but, you at least have to agree that both sides are correct depending on the application :thumbsup:





(Oh and um, just felt the need for a debate cause the initial explanation came across as odd to me. I fully understand too much gearing, I'm dropping the bird from 4.10's to 3.73's or 3.90's next time around so I do get it.:D I just think Jake would probably benefit the most from stepping it up a little right now while he has it apart :cool2: )

[540Malibu]

Originally posted by bottledbird68
As far as I understood the main reason for switching to a glide in a high torque low weight application was because the lower first gear of a 3 speed would just blow the tires off at the line.


which is another reason not to got too much if he goes to a 4.10 or 3.90 with 26" tires traction will be much more difficult t achieve (especially in a mustang) than with a taller gear or tire. combined with the t56's low 1st gear he would most likely be shifting before the 60 foot and not launching worth a damn. Alot of LS1's lose ET with a rear gear change, and not necesarily due to tire-spin.