Ralph LoGrasso

09-22-2004, 08:55 PM

Matt and I need your help to settle a slight disagreement.

Here's the deal. Matt and I are trying to select the best rear gear for Fantom, in order to meet the project goals.

Project Fantom should make 600rwhp(Blown LS1 @ 12psi), hopefully more.

The goals for the car are as follows:

Mid-High 10 second 1/4 on either slicks or ET Streets.

185mph top speed

Here's the data

Power: 600rwhp

Max RPM: 6600 (est.)

Tire diameter for 1/4 duty: 28"

Street tires (top speed): 26.1"

Here is the gear ratios for the T56. I think these are the correct ratios for the LS1 T56.

1st: 2.98

2nd:1.99

3rd: 1.35

4th: 1.00

5th: .79

6th: .62

Basically what we need here is the lowest gear possible that will net the 185mph top speed.

You may find this link helpful: http://www.csgnetwork.com/rearendgearcalc.html

I, personally want to run a 3.55 or 3.73 gear. Matt recommends 4.33.

From a pure math perspective using that calculator, 6500rpms, 3.73s, .62 final gear ratio, and 26" tire equals a possible top speed of 217mph.

4.33s = 187mph.

My arguement is that, the Coefficient of drag is going to drastically reduce the possible top speed. I personally don't see the car running 185 with anything in excess of a 3.55 or 3.73, Matt obviously sees it differently. Matt knows much more than I do, so I am probably wrong, but we'd both like a second opinion..

Any opinions on what ratio to run /comments/expertise is welcome.

I asked Tony (nineball) his thoughts, and his recommendation was for a 4.10 gear for a 10 second car, with the T56.

Here's the deal. Matt and I are trying to select the best rear gear for Fantom, in order to meet the project goals.

Project Fantom should make 600rwhp(Blown LS1 @ 12psi), hopefully more.

The goals for the car are as follows:

Mid-High 10 second 1/4 on either slicks or ET Streets.

185mph top speed

Here's the data

Power: 600rwhp

Max RPM: 6600 (est.)

Tire diameter for 1/4 duty: 28"

Street tires (top speed): 26.1"

Here is the gear ratios for the T56. I think these are the correct ratios for the LS1 T56.

1st: 2.98

2nd:1.99

3rd: 1.35

4th: 1.00

5th: .79

6th: .62

Basically what we need here is the lowest gear possible that will net the 185mph top speed.

You may find this link helpful: http://www.csgnetwork.com/rearendgearcalc.html

I, personally want to run a 3.55 or 3.73 gear. Matt recommends 4.33.

From a pure math perspective using that calculator, 6500rpms, 3.73s, .62 final gear ratio, and 26" tire equals a possible top speed of 217mph.

4.33s = 187mph.

My arguement is that, the Coefficient of drag is going to drastically reduce the possible top speed. I personally don't see the car running 185 with anything in excess of a 3.55 or 3.73, Matt obviously sees it differently. Matt knows much more than I do, so I am probably wrong, but we'd both like a second opinion..

Any opinions on what ratio to run /comments/expertise is welcome.

I asked Tony (nineball) his thoughts, and his recommendation was for a 4.10 gear for a 10 second car, with the T56.