Starting Line Ratio .... Help

[grego37]

68 mustang
408 stroker Windsor
500hp , 500tq
25.7 rear tire
Mostly used for street , weekend car, may see drag strip once a year

Trying to work out Tranny and rear gear options,

For my application and use:
what would be a perfect SLR?
what would be too much SLR?

For my certain assortment of parts , my 2 choices are 9.94 and 10.66

I dont want to go so much where 1st gear is unusable like a dump truck granny gear

 

[68RCodeConv]

It all boils down to whether you have an OD tranny or not.

In my 67 GT350 I have a 347 with a T5. 3.89 rear gears with a 2.95 first gear = 11.48. People will tell you that is WAY too much effective first gear but for urban driving (Houston) it is great. The .62 5th gear offsets the 3.89 rear.

Since you obviously have more torque than that let's talk about my 68 vert. 462 cubic inch FE motor with a mild cam (I don't care for lumpy idles). 480 hp at 5200, 580 ft/lbs of torque at 3900. C6 with a 10% low gear kit and a 3.25 rear end giving me 8.80 for first gear. It hooks up really well even with lousy little BFG T/As on it BUT (and this is a big but) I have Calvert racing mono leaf springs with Caltracs and a Detroit Locker. This is pretty much the ultimate traction setup for a leaf spring car.

At the end of the day it depends on how radical a cam do you have? Does it pull below 2000 rpm at all? What kind of driving are you doing? For me it is stoplights every half mile with 40 mph speed limits so I need enough gear to get the car rolling without having to rev the crap out of it.

If you have a cam that makes power from 3500 - 7000 then go with the bigger number. If you have something with decent low end then the small number should be OK.

 

[grego37]

first off, thanks for your reply. Thats what im looking for, real feedback with your S.L.R. (or launch ratio) and if you think its too much or not enough.


I am running a 5 speed trans with a .77 overdrive , and with my 25.7 tire @ 70mph on the freeway, i'll be at 2260rpm.

My cam is a Crower 15359
Flat Tappet
Duration: 282/288
Lift: 538/555
Duration at 50 : 242/250
Lobe Seperation : 112
the cams powerband is 2500-6500 i believe.

I did talk to Crower and asked them if my 70mph speed @2260 was a problem with this cam, and they said shouldnt be a problem

Now back to the SLR, you said you had 11.48 ? , that seems quite high for a street car, how tall is your rear tire? It doesnt have the Dump truck granny gear effect (almost useless 1 st gear?)
thanks

 

[65coupe408w]

Hi,

I have a similar setup to you. 408w with T5 26.5in tall tires. I used to run a 3.80 rear gear and just switched down to a 3.70

If you are going to stay naturally aspirated then I would suggest the 3.80 this is just from my personal experience, I have a .58 OD (GForce T5). I also have a 2.95 first gear. This ratio is still perfectly streetable.

I only geared mine down to 3.70 becuase I plan on adding a supercharger in the next year and need less gear to trap faster.