Speed in 3rd gear with 3.73s in automatic?

[95Batmobile]

Title says it all, want to know what speed I should hit at the top of 3rd gear with 3.73s compared to 3.42s
I know there is some formula that figures it out, I just don't know the formula.
Tires are 245/50/16 if that helps

[Devilboy28]

My car maxes out around 94mph with my 3.73s. I have no idea about 3rd gear though.

[HAZ-Matt]

<blockquote>quote:</font><hr>Originally posted by 95Batmobile:
Title says it all, want to know what speed I should hit at the top of 3rd gear with 3.73s compared to 3.42s
I know there is some formula that figures it out, I just don't know the formula.
Tires are 245/50/16 if that helps<hr></blockquote>

Ok...

With 3.42s the top speed is nearly 134mph in 3rd gear (assuming that you have a way to remove the speed limiter).

With 3.73s it is about 123mph.

[Bliggida]

Hey Bat, I did some calculation's for you. Your Overall Tire Diameter (OTD) was 27.57 inches. (for future reference)

I assumed that you were revving to 5,500 RPM so let me know if you are going more than that. But as I am seeing it it shows me...

3.42 = 127 MPH
3.73 = 116 MPH

I'm also assuming you have an automatic tranny with a 1:1 3rd gear. And not the 3rd gear of a manual T-5?

[95Batmobile]

Yeah it's an automatic with the stock 3.23s in it right now... I have no speed limiter(fastchip), I've had the speedometer burried past 115mph in 3rd gear, but it took so long to get there. I am thinking of 3.73s for the 1/4 mile cause I won't trap that high, so if my car maxes at 116mph thats fine [img]smile.gif[/img] I won't make it to that speed anyway so it won't matter. When I watch my RPMs while getting on it, it usually shifts like 5,200 or 5,300rpm out of first, maybe a little higher in 2nd. I never let it sit screaming in 3rd gear at 115mph tho, I let out a little bit and it shifts to 4th, but I maintain the same speed.

Anyway, thanks a lot Blig! Now I know I'll be fine in the 1/4 mile with the first 3 gears :D

[Harry94]

My speedo seems to be 10mph off with the 3.73 gears. I thought it would be a percentage off like everyone thought but it wasn't. So I would guess it would be 10mph less than what you are doing now. My car was checked with a radar gun and other cars with correct speedo readings at various speeds.

P.S. How is the fastchip reprogramming working? I have an extra ecm laying around I would like them to do.

[Bliggida]

3.73's will be great for the street.

But if you want drag action I'd reccommend 4.10's instead. You won't trap a MPH that will be faster than what 4.11 at 1:1 will pull. And the gain will be awe-inspiring.

at 5,500 RPM 4.10's will still net you 106 MPH in third gear. Top speed will be 150+ MPH in fourth and you'll cruise 70MPH at 2500 RPM.

What is your trap speed now out of curiosity? If you are online - AIM me.

[95Batmobile]

Harry94 - Fastchip is AMAZING. I love it more and more every day. The tranny shifts great and the power was a very noticeable increase. I ran into dyno problems, but hopefully this summer this shop will have their dyno installed so I can get some numbers for you guys.

Blig - Never taken my car to the track :( I want great street performance... I think 4.10s would be too much. I was initially thinking 3.42s, but I told my dad I wanted gears and he said to get 3.73s so I was just wondering what kind of mph I'd be able to pull in the 1/4 mile with those gears [img]smile.gif[/img] This August the CA guys are going to Bakersfield to race, so I will have some times then. Hopefully, by August, my car will be in condition to break the record for fastest N/A 3.4L... with an automatic too! :D

[Bliggida]

Yeah if you don't race all the time, but want a fast(er) [than normal] 3.4L I'd go with 3.73's. You'll see a gain with 3.42's but I think you will be much happier with the blend 3.73's give you. Your Dad is right on.

Its probably the best or most ideal street gear because it gives you the accerlation performance of drag gears and still allows you to cruise the highway withing pinging the motor with RPM.

[speedy-v6-camaro]

Why does my car seem to suck so bad. I have 3.08s and it shifts into 4th at 109mph. 70 is at about 2100 rpm. I bought it new so I know it didn't have gears swapped. Anyone have any clue?

[Bliggida]

Your converter may not be locking up?
3.08 with auto tranny are the worst power killing drivetrain combo though. Take that into account.
A gear change and a converter swap will probably be night and day difference for you.