Factory Five Racing Forum banner
1 - 7 of 7 Posts

·
Premium Member
Joined
·
61 Posts
Discussion Starter · #1 ·
I have a 3.55 IRS and am trying to decide on the standard .82 overdrive 5th gear on a TKO 600 or the .64 5th. I have tried to model the RPM and MPH on one of the Inernet gear calculators but just haven't had the experience of driving one of these cars at cruising speeds of 65 to 80mph to know which is best. The .64 looks like it may cruise well but it must feel like stepping into a hole coming out of 4th.
 

·
FFCobra Craftsman
Joined
·
2,238 Posts
.64 is a bit steep, but at that speed you can sit back and ejoy the ride ... I run 3.55's w/ 275's & a .82 --- use 5th on track a bit so I went w/ the .82, but cruzing at 65 - 70 I am spinning 2700 +/- ... requires ear plugs and is just a real pain, so unless you plan to race it I would go w/ the .64 ... just my 0.02 !!!
 

·
Junior Charter Member
Joined
·
1,066 Posts
It really depends on your engine. If it is happy at 1800 - 2200 RPM then the .64 will be fine. I went with .80 because my power band starts at 2200 and 5th was useless between 55 and 70 where I do 80% of my driving.
 

·
Premium Member
Joined
·
3,110 Posts
Exactly right. It's quite a drop.

The .64 is for cruising and mileage. If you want to be able to continue to rapidly accelerate in 5th, as in road racing or extrememly high speed driving, you would probably want the .82 5th.

For example, I have heard the road course guys say that shifting into 5th at 130, there is almost no more acceleration to be had. This is because of aerodynamic drag and the fact that overdrive is the opposite of torque multiplication. Not enough horsepower/torque with such a high overdrive. (Of course, they are running 2.73 rear gears)

I think .64 is OK for the street, especially with 3.55s.

I'm sure some experts will add their opinions.

Steve
 

·
just another builder
Joined
·
8,238 Posts
Originally posted by Gear Head:
It really depends on your engine. If it is happy at 1800 - 2200 RPM then the .64 will be fine. I went with .80 because my power band starts at 2200 and 5th was useless between 55 and 70 where I do 80% of my driving.
same here but with 3:55's
 

·
Premium Member
Joined
·
12,393 Posts
I have 3.55's and the TKO2 with .82 OD. I had a roadster with 3.73's and the .63 OD and I didn't like 5th because the RPMs were way too low to get anything besides noise when the pedal was pushed. After I looked at all the possibilities, I settled on .82 for the coupe, which isn't running yet.

PS, also look at your tire size. A big tire (like 27"OD in back) will take a little of the curse off the .82 OD.
 

·
Premium Member
Joined
·
861 Posts
I have run both these 5th gears via a 327 rear gear and 225/50/15 tires on another car (works out almost exactly to 355 rear gear and 295/50/15 tires) and believe the advice already given by McMahon is spot on -- if you are REALLY serious about track events then go with the short 5th -- you will need it to pull the car on the straights -- though keep in mind you are talking about pulling from 115/120 MPH or so depending on your shift point.......how important is that to you?

However if you just have fun on the track on a weekend here and there and spend most of your time on public roads, then get the tall 5th (.64) -- your ears, your passenger, your gas card, even your body will thank you for the lower revs.....having to drop it down a gear to get some zoom is a very minor price to pay for all the benefits of a cruising gear on the road........

Bill
 
1 - 7 of 7 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top