you know what is annoying? when you assume you have the 2.73 rear end that came in the car, so you figure you can upgrade to a 3.23 or 3.42 and make it alot quicker, come to realize that someone changed something or got some option and you already ahve 3.23's. thisis after you ahve already set up to buy a parts car for a 3.23 posi rear. at least it would have posi i guess, i have open now, and im SURE of that. im guessing that i have 3.23 becuase i dropped it in 1st and went to 3k rpm and i was going 23 or so. then i went second to 3k and was going about 45 then third 75. so i went into the tech equations and checked each and the answers come out right around 3.23. just a little bit lower.

when i opened my rear-end and changed fluid a month or two ago. i saw thta it definitly is an open carrier and i tried to count the teeth and came up a little off 2.73 so i assumed i miscounted by one tooth added that to my calculation and it came out around 2.73 maybei was off in the other direction....

i mean i guess im glad that i have the 3.23 and i can get over 25 mpg on it with my 305 tbi, but i was really looking forward to the performance/quickness boost and puttinghtat posi to use. as it is right now i can only spin my tires from a dead stand if i have 1/2 tank of gas or less. maybe a little more than that.

am i calculating this wrong? i really don't want to crack the diff cover again after i just puta new gasket and oil in it.....

also what shoudl be the rear out of my donor? its a87 iroc with origionally a 305 tbi im fairly certain.. i know for sure that it has a posi... could it be lower than 3.23????? please??? lol... of course i don't think i wna tto go to much lower and loose on gas...


i can't figure out why i can't spin the tires so more with the 3.23 that i have with an OPEN carrier. i figured if i had the 2.73, then if i jumped to the 3.23 i woud get more spin, but that the posi would minimise that problem..... but if i alredy have 3.23's

can you guys let me know what could be going on?
mycar is a 90 rs camaro with a 305 tbi a k&n drop in, a little mod to let more air to the filter, and a 3" American Thunder cat-back...

where should i go next for mods to make it quicker? especially if i can't get anythig from teh rear-end like i was so looking forward to...

thanks guys,
tj

 

well, what kind of tranny is it? on a TBI car, with an auto i would say you probably DO have 2.73's. dont' trust your factory tach for calculating htat, my factory tach is so far off, the calculator told me i have 4.56's . go with what you count, i would put the rear end in the air, spin the driveshaft 1 revolution, if you wheels turn less that 3 times, you have 2.73's.

if you have 2.73's upgrade it to a posi and steeper gears, personaly with the TBI i like 3.42's and i run them, and no loss in MPG after the swap , i still get 30mpg + on the freeway.

 

This post is the "poster child" for taking off the cover and looking, instead of believing the "codes" or whatever else.

Pull off the cover and look. It's the only way to know for sure. All this other foolishness is the road to extra work and spending. The tach that comes in these cars is notoriously inaccurate; don't believe it.

How many times did you use words like "guess" and "figure" and "maybe" and such? That's what's wrong with all this turns-counting and tach calculation and all that, not to mention the "codes".... it is all unreliable.

The ratio is stamped on the edge of the ring gear. 2.73 = 15 and 41. The tooth count does not lie, ever; but it's even easier than that. Just read it off the gear.

Take off the cover and look. Wipe it off first so you don't get dirt in the fluid, re-use it, and use the tubular style of gasket.

 

right before i read those responces, i said hell with it and lifted one wheel i spun the wheel one time, and what do you know? the driveshaft turned just under 2.75 times. i was about to get on here and say, why the heck is my engine running so fast, but if the tach is know for being way off that could explain it, but wow, thats way off... i was thinking i would go with 3.23 or 3.42 and couldn't make up my mind, but this parts car just fell in my lap. and im pretty sure it has a 3.23. i know its posi.. we'll find out the ratio soon though when i open it up and check it out and replace oil, it looked like it was leaking to me... didn't feel any clunkin or grindin though when i drove it... hey, if it eats itself, i still have my origional one untouched and i didn't even have to touch gear set-up to do any of what i wanted. i figure if i ahve 2.73 now.. and i change to 3.23, it will be a good jump and with the posi, i can really come off the line... now i want to do headers.. lol

i origionally got a zexel torsen take off cause i figured if i needed it i would have it on hand and not have to wait, and you can't beat the $100 price. i figure if i do this i will probably auction it...

how can i read my true rpms then?

also I DON"T UNDERSTAND. how is it possible that a car's mpg can not change with such a change in gearing? i mean before you are running 2k at 75, now its closer too 3k and your mileage is the same??? i don't get it... i understand that engines can have asweet spot, but 3k?? can anyone explain???

 

also, i ahve never herd of the tubular style gasket.. ? different style taht gts a better seal?
tj

 

"Tubular gaskets" are the kind that come in a tube. A.k.a. RTV silicone gasket maker.