do you guys think i should put in 3.23's or 3.42's, i havea 90 305 tbi RS with 700R4 / 2.73's now.. i need to be able to get good gas milageoo, unless its just a few mpg, i think i will go with 3.23's and i hope to pne day put in a 6 speed, in which case i would still feel a nice jump if i went to 3.73's how much gas mileage difference between 3.42's and 3.23's?
right now, i can jsut spin the tires, well one... after i willg et traction from both so i figure if i go to 3.23's then will it be th esame situation? will teh additional torque froma LSD make it so thta i can just spin them like now? will 3.42s get alot of wheelspin? i wodl rather be hooking up more and not burning my tires, as long as i don't break my tranny mount....
tj

 

what else do you have in this 305? is it bone stock?

 

bone stock with a drop in K & N and a 3" Flowmaster catback...

oh and a little mod i did to get some more air to the filter, jsut gutted a tpi intake and ran it into the front of teh air cleaner...

previous owner was guessing it was between 200-210 max hp

tj

 

ahhhh umm... you have a RS 305 TBI but yet some how have a plenum? TPI or TBI DAM IT!! hehehe well, im gunna go on the assumtion that you have TPI and say that 3.73's are deadly for stock or near stock tpi. 3.42's tops.

 

i don't follow as to how you got that i ahve tpi, but im guessingit is how i explained that little mod....

i do have TBI

what i did was takea tpi air duct part of the intake, and gutted it and fit it where it belongs right in the front center near the hatch release and ran the tube strait back as if it was going into the plenum, (i think i ahve my terminology correct) but since i ahve TBI i have a round metal aircleaner... so i got the spout off of another car (a cougar cause i found that it is rivited on and was practically the same diameter aircleaner pan) and cutted a hole/rivited it on to the front of mine as we as leaving the stock tube that runs to teh side and up next to the headlight on...

so i do have TBI

why are 3.73's so deadly for 305 TPI? in what way? gas mileage? how does the fact that i ahve TBI change that?

tj

 

Do the math. Find out what you want to spin the motor to (rpms)
Then the circumfrance of you tire.
There are calculators out there that will help. In a TPI/TBI car that's stock, I doubt you'll make enough power in the upper RMPs to use 3.73's.

In other words (manual terms) you would have to shift into an OD gear to keep in your power band.

 

gottcha.... i think im gonna go with 3.23's and if i get a t-56 consider lower.....
tj

 

4.10's or 4.56 , when you get a t56 you should get 4.56 , that new zl1 camaro has 4.56s. My gas mileage sucks with 4.10s but they are great for stop light racing. I ve been getting 7 with my 305 tpi.City driving and flooring it too much . Are you going to get a different rear end that can handle more power?That will affect gears choices .

 

3.73 up is useless. u cant compare a new ZL1 to a TBI injected RS. what kinda reasoning is that? go with the 3.42s thats ur best bet. and 3.73s will kill ur gas mileage and acceleration basically u dont have a use for em.

 

I'll try to actually help here. What plans do you have with the car in the future? What trap speeds do you think you will have?

 

3.73's range for power does not go to well with the TPI's short power band. Unless it was modded for better breathing, i wouldnt touch more the 3.42 or 3.45. Even still in your car, since you dont have a heck of a lot of power(that 200hp is a little over the top if you ask me) I say go with maybe a little more to make up for less power. 3.73's would be good, but will eat up the gas a tad more. With teh 6spd, that 3.73 will be reduced to so low it wont matter. With teh 6spd, you could probably get away with 4.10's actualy.

 

im thinking i will jsut get a pair of 3.23's that someone swapped out of a fourth gen.... and put them in myself... i have another rearend at home in worst case, and it woud be a good experience.... this way (3.23) i will feel a good change, def still be in my "powerband" and still have a nice jump possible in the future, and also not kill my mileage.....

thanks,
tj

also, how difficult is it to swap the gears with the rear in the car???

tj

 

yea, the previous owner was claiming it should have around 220 lol.... for some reason i thgouth base was 180 so 200 cold be, but idk withthe base being 170, myself i woudl think 190 sounded reasonable... wish i had a dyno in my garage....
tj

 

i went from 3.08s to 3.27 and i felt a big difference just from that small of a swap. the 3.27s are decent but my car needs 3.45s.

 

my plans are a very spirited daily driver, maybe occasional track trip, stoplight fun.... AND i woudl really love to keep up with my friends 85 vette.... (he is all stock with K&N drop ins) and i am all stock other than 3" flowmaster cat back and drop in K &N and the little mod i explained above...

i wan tit so i can spin the tires when i want, but tht its not hard to keep tracktion and really launch/feel the car throw you back and accelerate well,

but the car willl be used for some significant highway milage, i really wod lliek to stay above the 25 mpg like im getting now..... i codl stand a few loss thgouh....
thanks,
tj

 

no lower than 3.55's i had upgraded from a 3.08 peg leg to a 3.27 9 bolt posi and i felt a nice difference. I wouldn't even bother doing gears. i would just go get a used rear (i prefer 9 bolts) with a posi and whatever lower gears you can find (3.27 or 3.42's) they usually cost around 2-300 bucks and you wont need any special tools. Besides if you get a 9 bolt its a significant upgrade in strength too

 

3.73's would be your best bet. 4.10's would propbably be even better. Considering you have a redline of 5,000 rpm and might even benefit from shifting even higher than that. And anyone who says that the tbi is worthless after 4500 rpm or whatever has no idea what they are talking about. At the track I dropped .5 seconds off of my et by manually shifting at 5,000 rather than letting the car shift itself at 4400 rpm. You most likely wont be trapping more than 85 mph in a stock tbi which would put you right at around 4500 rpm crossing the traps which leave you plenty of room for upgrades. 3.42 would be the least gearing I would put in the car. 3.23 is a worthless upgrade and you wont be getting anywhere near your max performance. With the .7 overdrive gas mileage won't suffer too much. GO WITH ATLEAST 3.73's!

 

3.73s, look at sig and times with stock heads, cam, intake, and tbi, all on a 160K miles engine and tranny. And i still get about 22-25 miles to the gallon on the freeway driving 250 miles from home to college, but mod ive ever done.

 

I'm going with 3.42's. You can find em in almost any of the v6 cars from 82-90. WIth the 700r4, it'll be a nice noticible jump, and shouldn't kill mileage too much.