Nope, meant 3.73. Of course, that's dependent on what differential you have. In this case I was thinking 8.8". 3.73 is a common between 3.50 and 4.00 for the Ford 8.8 which I have in my Mustang with overdrive. I have a 3.89 in my 9", but you can also get 3.70 and 4.11 on either side of that. That's in my Maverick drag car. If you have the 8" then .380 is a good tweener for that. Again, for cars with overdrive or big tires. In any case, as another poster so clearly said, tire size is important. I made the assumption that most folks would be running something like a 26-28" tire size. For the 26-28" tire size, and without overdrive, I'm much happier with the 3.25 in a street car (8" differential). Now, all this is for street cars. For a pure drag car, match the ratio and tire size to go through the traps right on redline.
I just put a 3:55 in my car a few weeks ago. The car runs a lot better, but at a cost. I have a Holley 600 with vacuum secondaries. At 65mph, I run about 3200rpm. Unfortunately, the stock spring in the secondaries opens the secondaries at about 2800rpm. Uses gas like crazy. I put the black spring in, and keep it under 3300rpm, and it is reasonable. Be carefull if you have a Holley with vacuum secondaries. Gas it expensive!!!!!!!
remember the higher you go on gears the more gas it will drink (unless you have o.d ) this weekend part-time and i went for a 6 hour tour to jacksonville and back. he used a little over 2 tanks of fuel and i used a little over 1 tank. he has 3:55posi with c/4 and i still have the factory 2:79 with c/4. very similar engine mods. just be prepared as gas keeps going up. the 3:55's are great for takeoff but you should keep highway to a minimum ( or stay at the speed limit) what fun is that?
3.73s are not made for the 8-inch (or the 9-inch). You can get 3.70 and 3.80 for the 8-inch, which is close enough...
You didn't have the stock spring in that Holley, but you do now. Every 600 I've had, was equipped by Holley with the black spring. I have a purple spring in the 750 on the 5.0 in my Ranger now and did also with the 600 it had before and it didn't open the secondaries at cruise on the highway with 3.73's and 28" tires (2687 rpms @ 60)
The Holley was new when bought, and had a plain or unpainted spring in the vacuum unit. I changed the black spring in. The spring kit sheet says the plain spring is stock in the unit.
The black spring is the slowest-opening and it never opens the secondaries all the way. Get rid of it if you have one in your carb...
