3:91 vs 3:55 - Opinions please

[drewcrane]

"assuming the car even hooks up," thats just one of the many factors, im just using one your points to make another , gears , smears if it dont hook it dont go , just look at some of the tire sizes these guys run to get traction, and then if you get traction, you need to steer the car , shift, ect. consistantly too!

[sadil340]

I have 3.91s but have OD so run like 3.05. I cruise the highways a lot 50/50 driving for me, I'd give your engine a little less rotational strain and go for 3.55s. .55s will still offer a great launch. Hoe much highway driving DO you do?

I do a fair amount of highway driving since I like to get the oil good and warmed up every time I drive the car. But I hear from this thread that it's not too bad a trade off for the extra fun factor 

I think I'll take a cue from one of the posts and eventually get my 3:55 chunk rebuilt. I have a lift at home so swaps aren't a big problem and I'll have the best of both worlds.

As always, I can depend on interesting responses from this Board - thanks everyone, I really appreciate it!

[Moparal]

"assuming the car even hooks up," thats just one of the many factors, im just using one your points to make another , gears , smears if it dont hook it dont go , just look at some of the tire sizes these guys run to get traction, and then if you get traction, you need to steer the car , shift, ect. consistantly too!

Oh, contrare...  Street romping is different then drag racing in a lot of cases. Rolling along and someone gets up to your side...you are already hooked up so the spin is down, the tq and quick shifting with a bigger gear is going to put you ahead in the game.  You can never be the fastest, and if you are, it's short lived. Someone else will always have deeper pockets out there. For the most part, most hot rods have 350 to 500 hp to the ground.  So it is not super hard to get that power hooked to ashphalt with hot rod knowledge.  Where you loose the race is 355's keep pulling better on the top end then a 410. On the hwy, a 355 gear will take a 410 after 120 in most cases.

[sadil340]

Oh, contrare...  Street romping is different then drag racing in a lot of cases. Rolling along and someone gets up to your side...you are already hooked up so the spin is down, the tq and quick shifting with a bigger gear is going to put you ahead in the game.  You can never be the fastest, and if you are, it's short lived. Someone else will always have deeper pockets out there. For the most part, most hot rods have 350 to 500 hp to the ground.  So it is not super hard to get that power hooked to ashphalt with hot rod knowledge.  Where you loose the race is 355's keep pulling better on the top end then a 410. On the hwy, a 355 gear will take a 410 after 120 in most cases.

Excellent point

[moparniac]

Racing has always prdominately been light to light...... 3.91's 

[71chally416]

I remember the sick look on the face of a guy with a 396 Chevelle when we were racing side by side at 115mph and I shifted into 4th gear. That was in my first hotrod in HS. A 440 powered '65 Belvedere that I was in the process of removing parts from for my '67 GTX. I had put a 2.96(?) open rear in it so I could use the 4:10 posi pumpkin in the GTX. It also had these ridiculously tall McCreary cheater slicks. My boy looked sick and just let off when I shifted into high and waved goodbye  It was like a Nascar racer. 

[ntstlgl1970]

sadil340 - you never mentioned what size tire you have in the back, you can use this MPH/RPM correlation calculator to figure the RPM on the freeway.

http://www.bgsoflex.com/auto.html

[sadil340]

Pretty cool tool! I can use it to calculate my new speedometer gear too..

[torredcuda]

Input Parameters Are the Following:
Differential Gear = 3.55 to 1
Transmission Gear = 1.00 to 1
Tire Diameter (Inches) = 26.00
Vechicle MPH = 70
Computation Results:
Computed Engine RPM is 3213

Input Parameters Are the Following:
Differential Gear = 3.23 to 1
Transmission Gear = 1.00 to 1
Tire Diameter (Inches) = 26.00
Vechicle MPH = 70
Computation Results:
Computed Engine RPM is 2923


Input Parameters Are the Following:
Differential Gear = 3.91 to 1
Transmission Gear = 1.00 to 1
Tire Diameter (Inches) = 26.00
Vechicle MPH = 70
Computation Results:
Computed Engine RPM is 3538


Actual rpm will also depend on converter slippage if auto.There`s only a little over 300rpm difference so the 3.55`s won`t be that much better on the highway.I run 3.91`s but try not to cruise on the highway for more than 30-40 minutes or it gets annoying with thr revs and the loud exhaust.