Having a problem with my gear ratio i think

[SUX2BU99]

Breaking tire belts from hard shifts? Wow, never heard of that before. It must give you a real kick in the seat. My truck has ran a best of 14.88 @ 93 but that was with the 3.40 ratio and a non-working posi. I was hoping to see some improvements with the new 3.73 setup but I keep wiping out ring and pinions before I get a chance to hit the track!  There might be enough spring wrap happening to affect how your pinion to driveshaft angle is changing under load, but I'm no expert.

[rick_c]

Breaking tire belts from hard shifts? Wow, never heard of that before. It must give you a real kick in the seat. My truck has ran a best of 14.88 @ 93 but that was with the 3.40 ratio and a non-working posi. I was hoping to see some improvements with the new 3.73 setup but I keep wiping out ring and pinions before I get a chance to hit the track!  There might be enough spring wrap happening to affect how your pinion to driveshaft angle is changing under load, but I'm no expert.

That has crossed my mind..the spring wrap thing, don't know how to get the spring rate checked. Gonna call a suspension shop I know of and see what they say.
Thats not too bad on your time I guess, I'm hoping for 13's but based on that number I don't think I'll be there.

[malibu795]

Hello again, been gone for a while...

Have an 82 swb, just built a 350 9.7:1 flats .030 over 4 bolt main 010 block.
A lunati 489/504 lift voodoo cam 268/276 duration, 1.5 roller rockers, untouched 76cc heads with 1.94/1.50 valves with 550 max lift springs, edel rpm intake a 1406 carb. Built a TH350 with a tci pump red eagle clutches koleen steels and a b&m stage 2 kit. Also a jegs 2200-2400 stall (that doesnt stall right). Oh and a melling high vol. pump (big mistake)...don't ever use one of those...I run 80psi at 1000 rpm! all my seals are starting to leak.

just so everyone knows where I'm at.

Ok so the problem I'm having is figuring out what gears I need to run.
I've always thought this truck had a 3.08 geared 10bolt.
i serviced the diff today and counted the teeth.
Apparently it is a 2.73? which I didn't even know existed.

With what I'm running, the truck runs okayish on the street, I can pretty much take anything in my neck of the woods except a couple of sleepers( a stroked 05 GTO, and a wrx with a huge turbo).
I can smoke the tire(no posi) on a 20 roll manually shifting it at about 6000rpm.(very fun!)
I can make the dotted lines blurry in 2nd gear going into third running about 6300rpm. Don't know how fast that is because the speedo stops at 85.

My question is, what gear would yall recommend to keep my highway running conditions but be able to tear up the street on take off?
Right now if I stomp on it from a stop it will spin the tire but it lags real bad.
I'm thinking a 3.90ish gear...if thats even possible with the low numbered carrier.
I hear the old heavy halfs had a factory 12 bolt 4.10 posi...

All advise is appreciated...Thanks

here is what i see...
your cam is toobig for your heads killing power
the torque conveter is little on the tight side ESPECIALLY wiht a 2.73 gears.
melling HV op .. they are in every motor i have all 3 sbc and both BBC i have.. never had a problem of draining a 5qt pan either..  at 7000rpm.. granted i make sure my drain holes are clean and free of obstruction...  and my cleanace are mid-upper .020" on bearings.   but thats me..
3.42 or 3.75 will be a good choice of gear.. with a 28" tire.

275/60/15 =28" tire
~70mph cruising wiht 28" tires and 3.73 is 3100rpm
~70mph cruising with 28" tires and 3.42 is 2900rpm
my 75 is runing  with  32" tires and 4.10 is 3000rpm at the same speed.
2.73s are very much highway gearing.. not stop light racing...

and for the record i dont agree with racign on the street.
~6000rpm shift points with 2.73 and 28" tires and a th350 1st gear is 2.52:1 2nd is 1.52:1.. are as follows
1-2 is 73mph
2-3 is 120mph

[rick_c]

Wow thats the info i've been looking for...whats the formula to figure all that out, so if I decide to change gears and tire size, i'll know what I'm looking at...

[Irish_Alley]

this ones is kind of a plug and play but it will tell you what you need to know
http://www.idavette.net/tech/ratioc.htm
this one is more of a chart tires vs rpms
http://www.4lo.com/calc/geartable.htm

[malibu795]

this ones is kind of a plug and play but it will tell you what you need to know
http://www.idavette.net/tech/ratioc.htm
this one is more of a chart tires vs rpms
http://www.4lo.com/calc/geartable.htm

heres then formula that i use

gear ratio * tranny gear * 336 / tire diameter * mph= engine rpm

[Irish_Alley]

lol the formula use is
rpms x tire size / 336 / mph = ratio
http://forum.73-87chevytrucks.com/smforum/index.php?topic=10879.0

[malibu795]

lol the formula use is
rpms x tire size / 336 / mph = ratio
http://forum.73-87chevytrucks.com/smforum/index.php?topic=10879.0

nice how you and re-argane a math problem right?

[Irish_Alley]

what

[malibu795]

its algebra
a+b=c
c-b=a
c-a=b

[Irish_Alley]

i don't have anyproblem with algebra just grammer and English 
but just look at that link i posted be low my formula it explains it all, it's  dated February 08, 2009, 02:19:40

[choptop]

Here's some more if you ever need them.
http://conversiontrucks.net/Forum/index.php?topic=55.msg175#new

[oldredtruck]

I aint too sure about all these equations...something is missing...DOLLARS...
it's all basically a function of dollars!
works EVERYTIME!

[malibu795]

I aint too sure about all these equations...something is missing...DOLLARS...
it's all basically a function of dollars!
works EVERYTIME!

everything is possibly with then "cubic" dallor   

[rick_c]

lol the formula use is
rpms x tire size / 336 / mph = ratio
http://forum.73-87chevytrucks.com/smforum/index.php?topic=10879.0

Based on that at 55mph I have a 3.13 gear...doesnt sound good to me.
Thinking a 3.55 will wake it up some if I can get that gear in my carrier.