speedtigger

iTrader: (16)

I had chosen 3.90 gear for my 65 Lark to go along with the new TH200-r4 and LS motor. Then I find out that Motive gear is out of stock for 3.90s and won't have any for 6 weeks.

So, I am looking at the numbers on the 4.10s and the 3.73s and just cannot decide.

Most guys with Automatics say that the LS motors prefers a 3.73 with the 4l60e. However, the TH200-r4 has a 2.74 first gear as opposed to the 4l60e 3.06. The math says the with a 2.74 first gear, you need the 4.10 to give the same total ratio as the 3.06 first gear with 3.73s. Also the TH200-4R has a slightly better overdrive ratio of .67 as opposed to the 4l60e .70.

The 4.10s math comes out perfect for the quarter mile. The car is targeted to run about 110 MPH in the quarter the the 4.10s put me at about 5900 with 5% converter slip. The math also says i can go a little over 120 MPH in the quarter at 6500 RPM. So a nitrous shot would be covered. However a 75 MPH cruise RPM of nearly 2600 RPM and 80 MPH is over 2700 RPM.

The 3.73s put me at 5350 RPM in the traps. Not quite in the meat of the horsepower with the cam. But, the 75 MPH cruise speed is only just over 2300 RPM and 80 MPH is just under 2500.

The 4.10s have about 10% more rear wheel torque in 1st gear.

The car spends the majority of it's life in town and on rural streets and seldom cruises over 60 MPH. But, in order to get to the 1/4 mile race tracks, I have to drive an hour or two on the expressway at 75 MPH or so.

For me, the 3.90s were the perfect sacrifice between the two. Since I found out they were on back order, I have been about a wishy washy ****. I am knee deep in analysis paralysis. Set me straight here. Which way would you go?

gofastwclass

iTrader: (2)

For me the choice is simple, I drive highway too much for anything deeper than 3.73. At some point I want to do a Power Tour or similar antics since every car I own or have owned has been hundreds of miles from home on vacation with me at some point.

speedtigger

iTrader: (16)

Well, my indecision may be unnecessary. StreetSide Auto said they have the 3.90 gears in one of their warehouses. I say "may be" because I ordered these once already from a company on ebay called Gears Are Us only to have him call 2 days later and say they had an inventory error and actually did not have the gears. I am already pleased with StreetSide though because they were the only ones who had the 3" Dynomax Super Turbo mufflers that I wanted.

So, I am crossing my fingers that the gears show up.

gofastwclass

iTrader: (2)

Good luck. I hope the gears arrive on time and you're happy with your decision once they are installed.

speedtigger

iTrader: (16)

The gears arrived today. I have never received a package so beat to $%*t in my life! I don't know if they fell out of Fed Ex's jet at 30,000 feet or if StreetSide ran over them with the forklift at the warehouse. But, the Motive Gear packaging is well designed, there was not a scratch on the gears.

I will take them to the gear shop tomorrow and have my rear by the weekend.

gofastwclass

iTrader: (2)

Beat up packaging is scary.

Cool, good to hear!

Stu Cool

iTrader: (13)

Wow, when you said 65 Lark I thought you had a Studebaker! But the picture set me straight. Glad you got what you wanted, sometimes the wait is worth it.

Pat

gofastwclass

iTrader: (2)

Not everyone is cool enough to own a Gen III powered Studebaker like you Pat, the rest of us have to build "normal" cars. J/K