92blue

iTrader: (1)

I still had up until not too long ago the original 2.73s. When I installed the T56, I was able to use a radar gun to adjust my speedo exactly. I don't have access to it anymore, so even though I tried adjusting it with another car, I know my speedo is a little off. Can anyone with the same tranny/gear/tire combo tell me what they have their SGI-5 box set to? I have the 97 version (wanted to clear that up, cause the 93 has different gearing), 3.73s, and 16 inch wheels with a tire profile of 45.

Thanks

Kingtal0n

hey just tell me your exact tire size, and what gear of the T-56 you want me to calculate Ill use thirdgen.org's calculator to figure what RPM @ what MPH that should help you....

92blue

iTrader: (1)

Thanks man, thats how I adjusted it the first time, and it was a little off. I wanted to have it as close as I could to the real speed, so I wanted to see if anyone had calibrated it with a radar gun. i think the equation in this website doesn't take into account air resistance, rolling friction, and things like that.

Kingtal0n

<b>i think the equation in this website doesn't take into account air resistance, rolling friction, and things like that.
</b>

things like that shouldnt affect RPM vs Speed. thats always the same, providing theres no clutch slippage. no matter what.

however fast your engines moving (rpm into tranny) multiplied by the gearing (tranny X rear) gives you how many RPMS your tires are spinning. By knowing exactly how tall the tires are, we can tell exactly how many revolutions you will need to go 1 mile. thats gives up MPH. very very simple. wind resistance and friction dont add into the equation at all. Thats how i know my 1st gear @ 6000 RPMS ends at 65 MPH, minus converter slippage. but you have no converter, its always 1:1 when engaged, making it really easy to tell actuall road speed.

demonchild

speaking of calibrating the speedometer, does anyone know how to do it if i was going put the 145 mph overlays in my car? right nowi have and automatic 86 trans am with the 85 mph speedometer. thanks.

Will's Fiero

Time yourself between mileposts on the interstate. They're not all exact, but if your average several, you'll be fine.

graebz28

iTrader: (5)

Now that you got those 3.73's in there, would you rather have went with 4.10's. I was debating 4.56's or 4.10's and decided on 4.10's after looking at a table I made in excel for gear and rpm computing speed.

92blue

iTrader: (1)

Since I don't like to shift much past about 2200 rpms when I'm driving around, I'm constantly shifting. If you don't want to be shifting constantly, I guess 3.42 would be a better choice for the street. Now, if all that shifting doesn't bother you, 3.73s are a rather conservative gear with a T56. At 60 mph, I'm well under 2000 rpms in sixth gear. I get more mph in relation to rpm now in 6th than I did with 2.73s and a 700r4. With that said, 4.10s are not too short for the street. Actually, most LS1 guys with 6 speeds end up with 4.10s for the street.

KingTal0n, what you said makes sense to me, but I did try to adjust my speedo twice with the equation, and both times I was off. The first time was when I put the tranny in and I had 2.73s, the second was now that I got a gear change. Thats why I want to calibrate it with a radar gun, I can't mess up like that.

BOTTLEDZ28

iTrader: (9)

How about the simpliest way yet. Drive on the side of a buddy and see whathes running. Then if your off just refer to the directions and figure out the equation to move the switches as noted.

graebz28, 4.46's???? are you nuts. I have a t56 with 3.73's and I hat them. I wish i kept my 3.42's in. Im always shifting. the engine doesnt get a chance to stay in its RPM range.


also,92blue, how the hell are you under 2000RPM's in 6th gear. My car is lot higher then that. I am running a 275/40/17 tire but the height of it is the same as a 245/50/16.
did you ever figure out why your speedo was acting up while stopped? Mine is still doing the same thing. It reads 80MPH when I come to a stop.

graebz28

iTrader: (5)

Bottled Z,

I guess it depends on what you are gearing the car for. Right now I pulling into the traps at the instant I could shift into 4th or stay in 3rd. For 1/4 mile, I want to be at the end of forth when I'm pulling into the traps.

A 3.42 / T-56 set up hits 5000/5500 at 107/117mph. To hit this you would have to have about 320 hp at the crank in a 3500 lb car. That I do not have, yet.

I think a 3.42 and a 700R4 is a good combo. It produces a final drive ratio of 10.47:1 for 1st gear. To achive the same w/ T56, you need a 4.10 that gives a 10.91:1 ratio. I'm sure I can get my car to hook with that cause I had the 700R4 in prior to the T56.

I don't want something like a 4.10 in a 700R4, 12.55:1 ratio. A friend of mine had that and 1st gear lasted about 2 seconds before it would shift into second. To get that crazy with a t56 would need greater than a 4.56, that is at 12.13:1.

These calculations are with a 94-97 t56. The 93's have a steeper 1st gear and the aftermarkets have their own ratio's. If you find yourself shifting too much, the start skip shifting. I do a lot of 1-3 or 2-4-6 shifts when I'm just crusing. If you have 3.73's then you should be able to pull the car off the line in second gear.

xxwarrior36xx

Hey go to www.smokemup.com
It will give you the rpm and mph for severla different rear end configurations, with your tires. It is an excellent easy to use website
Happy Hunting

graebz28

iTrader: (5)

Yeah, I found tha site when I was building an excel spreedsheet to do the same thing basically. It's got a lot of cool equations.

XX, what is your first gear ratio on your trans. Do you spin fast out of 1st. How well do you hook.

Check out the t-5 for mustangs. No wonder why they are so much faster than the auto's. Unless the site is incorrect, it has first gear at 3.97. That's almost a whole number up from the 700R4.