got a new gear 3.15 was 3.73 - manual transmission needs it

[twistedneck]

just got a 3.15 gear put in, results are the following.

1. no gear whine - had tons with the 3.73's (both of them).
2. less head snapping torque now i have to actually hit the power band (3500+) before the tires go into orbit.
3. longer gear pulls, 1st to 52mph @ 7000 rpm, 2nd to 72 mph, etc.. and thats with a mt82 and 26" tall tires.
4. less gear changes
5. 4th gear up to 132mph is incredible.
6. 5th gear is 172mph @ 7000 rpm.

LOng story short, if you have an mt82 and unlock your rev limiter i guess a 3.73 works - but if you have even the slightest of mods its too much. automatic is the opposite.

anyone else make the change to a taller gear?

 

[slow306stang]

I run a 3.25 ring and pinion with a 28" tire. The car is probably making in the 675-700whp range right now and I should be able to finish the 1/4 strong in 4th gear.

 

[pufferfish]

I went from 3.73 to 3.55 when I changed from the 27" tall 19" wheels to 26" tall 18" wheels. It was an RPM neutral transaction.

With the gt intake, I run out of my powerband to complete the 1/4 in 4th... Running through the traps at 7200. Aside from that, it's been a great all around gear for street, strip and track.

 

[twistedneck]

I went from 3.73 to 3.55 when I changed from the 27" tall 19" wheels to 26" tall 18" wheels. It was an RPM neutral transaction.

With the gt intake, I run out of my powerband to complete the 1/4 in 4th... Running through the traps at 7200. Aside from that, it's been a great all around gear for street, strip and track.

have you considered 28" drag radials? that should get you through the 1/4 mile in 4th depending on your hp.

 

[pufferfish]

I'm a "run what ya brung" guy. No DR's or slicks in my future.

 

[Quesplosive]

Im about to make the switch to a 3.27 gear. Was thinking about the 3.15s but I think that's a lil too low.

 

[11Sec_Lx]

I had 3.73's swapped in last year. They whine more than I would like. I am seriously considering going back to my stock, 3.15's just to remove the noise. I might wait until I get a GT500 axle back on first, just to see if the added noise masks it enough.

 

[dirtyd88]

Friend of mine recently installed 3.15s on his M6 car with a KB setup. Car is setup for 1/4 racing, so with his power level and rear tires, he wanted to cross the traps at as close to top of 4th as he could.

 

[sambandit]

I took the 3.73 out and went with 3.31. One of the best mods I've done!

 

[Rdrcr]

just got a 3.15 gear put in, results are the following.

1. no gear whine - had tons with the 3.73's (both of them).
2. less head snapping torque now i have to actually hit the power band (3500+) before the tires go into orbit.
3. longer gear pulls, 1st to 52mph @ 7000 rpm, 2nd to 72 mph, etc.. and thats with a mt82 and 26" tall tires.
4. less gear changes
5. 4th gear up to 132mph is incredible.
6. 5th gear is 172mph @ 7000 rpm.

LOng story short, if you have an mt82 and unlock your rev limiter i guess a 3.73 works - but if you have even the slightest of mods its too much. automatic is the opposite.

anyone else make the change to a taller gear?

Nice. I've been thinking about it...

What mods do you have?

Mike

 

[dead man walkin]

Instead of swapping to a granny gear you should have got tires and learned to launch. . Only reason to change from a 3.73 to a slower gear is if you are FI, but hey to each their own, some people like the neck snapping torque associated with launching hard.

 

[twistedneck]

Instead of swapping to a granny gear you should have got tires and learned to launch. . Only reason to change from a 3.73 to a slower gear is if you are FI, but hey to each their own, some people like the neck snapping torque associated with launching hard.

Granny gear is the 3.73... Its for stump pulling or hill climbing if you have a manual car w mt82.

The swap was never about gaining launch grip, that wont matter much w the 3.6 first gear in the mt82. And now I can do standing. Mile events and not top out at 156mph.

 

[pufferfish]

i assume you have tested this standing mile theory of getting past 156mph with your new gear choice? i ask because the math says you will be worse off. you need to get up to as fast a speed as possible in 1 mile, right? i show a reduction in aprox. 600lbs of wheel torque going from 3.73 to 3.15. sure, thats great for reducing wheel spin in first, but thats not what the standing mile is about. you need to push this brick through a wall of air and you need as much wheel torque as you can to get it done in a short enough distance. your max potential mph in a gear is nothing if you don't have the power to do it in the distance alotted.

 

[twistedneck]

i assume you have tested this standing mile theory of getting past 156mph with your new gear choice? i ask because the math says you will be worse off. you need to get up to as fast a speed as possible in 1 mile, right? i show a reduction in aprox. 600lbs of wheel torque going from 3.73 to 3.15. sure, thats great for reducing wheel spin in first, but thats not what the standing mile is about. you need to push this brick through a wall of air and you need as much wheel torque as you can to get it done in a short enough distance. your max potential mph in a gear is nothing if you don't have the power to do it in the distance alotted.

I gained another 40 lb-ft of torque over the winter - still NA, so I went with the 3.15. with the 3.73 last year I could bounce off 7000 easily in 5th.. way too easy.. it got there in a hurry. there have been a couple Boss cars with similar power levels as me hit 180+ in the mile - so the air wall didn't stop it. this car still melts the tires off in 2nd and 3rd finally hooks now its actually usable.

I use short 26" tires on 18x10, and its cheap to get take off slicks from Rehagen etc. that are 275/35/18 equivalent size, so the gear gets even shorter - I run 275/40/18's on the street. guys who run 20's do not want a 3.15 if you are NA - I agree.. 3.55 or 3.31 better for those people.

 

[pufferfish]

what's your torque number now? i notice when i swap from my gt intake (413rwtq) to the boss (388rwtq) i want my 3.73's back and the shift calculator verifies this. i can essentially gain back every ounce of wheel torque i lost and with the extra 1000rpm, i can still end up with more mph at the top of each gear.

using my calcuator, i input your 3.15 for the gt's powerband and 3.55 for the boss' powerband, i get the same top speed in all gears and get 6% more wheel torque everywhere. just food for thought if you happen to be using the gt intake.

 

[twistedneck]

what's your torque number now? i notice when i swap from my gt intake (413rwtq) to the boss (388rwtq) i want my 3.73's back and the shift calculator verifies this. i can essentially gain back every ounce of wheel torque i lost and with the extra 1000rpm, i can still end up with more mph at the top of each gear.

using my calcuator, i input your 3.15 for the gt's powerband and 3.55 for the boss' powerband, i get the same top speed in all gears and get 6% more wheel torque everywhere. just food for thought if you happen to be using the gt intake.

My torque last year was 372, this year its 413 - actual gain was 41 ft-lbs.. I wish I could use 7500+ but I have stock GT rods that wont handle it, especially on top speed runs with long times near redline. I've heard that's when oil pump gears fail, so I got those covered with some mmr's.. but I also heard the rods stretch and that would not be good.

 

[pufferfish]

Funny you've got the same torque! Yeah, the lower rpm does help keep the motor together. Can't fault ya for that!

I went with a complete boss long block and mmr oil pump gears, so I am clear for all the rpm's the boss or CJ manifolds can use.

 

[dead man walkin]

So you gained 41 torque. .. I assumed this car was NA, since mods were not posted, if the car is FI I agree swapping to a 3.55 is recommended 3.15... not south of 600 hp.. I just don't see it . Sure tiny 18's will help that a bit.. I don't know if your entire plan is for the mile run and you geared it just for that and trailer it from event to event. . Ok .. but if you have to drive it every day that 3.15 flywheel, would suck the fun out of taking off from a light every day.

 

[pufferfish]

gotta re-read that, dead. he gained from bone stock to a tune and whatnot.

 

[twistedneck]

So you gained 41 torque. .. I assumed this car was NA, since mods were not posted, if the car is FI I agree swapping to a 3.55 is recommended 3.15... not south of 600 hp.. I just don't see it . Sure tiny 18's will help that a bit.. I don't know if your entire plan is for the mile run and you geared it just for that and trailer it from event to event. . Ok .. but if you have to drive it every day that 3.15 flywheel, would suck the fun out of taking off from a light every day.

The car was useless in first before.. even with DR's.. 7600 rpm is like 42mph with my tires and the 3.73 and the crazy mt82 first gear. now, when i come off the light i can actually use first - sure if i try to launch hard it still melts down the tires but at least i have a first gear now. second is the same way, under 3500 its usable, over 3500 its simply not and you need 3rd to put down power.

mods are simple.

cj cams, boss heads, cj intake and tb. stock GT short block with mmr gears. makes 489hp 413 tq on a mustang dyno. i gained 41tq from the boss mani setup, combined with a retune of my cams by Shaun. i shut it down at 7400 on the dyno to save it. there is no peak in the curve, its still gaining HP at 7400.