Just about ready to have this thing put together. It's not a Chevelle but seems like this forum is where people with big power motors are.

It's a 1975 vette with a EFI 540 BBC w/AFR 315heads, converting to solid rear axle and should be between 700-750 hp with a 4L80E and Nitto drag radials.

I want to cruise at low rpm on the freeway so I've been thinking about using 2.94 gears. I'm only driving on the street and figure it should have plenty of power to pull at low speed.

Anyone with lots of power running freeway flyer gears that's got any advice for me.

what's the O.D. ratio of the tranny?

I'm using 3.73 behind a 200-4R, about 1800 at 70 on the fwy.

The overdrive in a 4L80E is 0.75

what's the O.D. ratio of the tranny?

I'm using 3.73 behind a 200-4R, about 1800 at 70 on the fwy. Hi Tom, a 4l80 has a .75 O.D. ratio. I wonder if it also has a lockup converter? It's going to make a ton of heat if it doesn't. Needs a real good trany cooler for sure. Talk to Hutch on SilverBullet.com website.

It's going to have a lock-up converter and a bigtime tranny cooler. Tranny will be heavily built to take the power. It'g going to be built by "The Toy Shop" in Pomona, CA.

that would give overall 2.205:1. You live near Bonneville? at anything resembling a normal fwy speed it's going to drive your rpm down closer to 1000 than 2000. A little stiff, a lot stiff, especially if the converter is locked. high-perf engines never like to be lugged.

think about a 3.36 or 3.42 or something along that line.

3.36 x .75 = 2.52

3.42 x .75 = 2.56

3.55 x .75 = 2.66

3.73 x .75 = 2.79

My motor's EFI so it should run clean at low rpm. New Z06's do it. Should be around 1,800--1,900 rpm's at 70 mph.

Anyone around here with over 500 hp running high speed gears?

a 540 with 315 heads does not resemble a Z06 in any way. Are you kidding? What cam do you have in that 540?

a 540 with 315 heads does not resemble a Z06 in any way. Are you kidding? What cam do you have in that 540?
Not so different. Both are high performance pushrod motors with EFI. Mine may be putting out slightly higher hp per cubic inch but not too much more. My 540 has a mild hydrolic roller. Don't know specs off the top of my head.

What about something like a 3.25 rear gear.....should be about perfect.

Not so different. Both are high performance pushrod motors with EFI. Mine may be putting out slightly higher hp per cubic inch but not too much more. My 540 has a mild hydrolic roller. Don't know specs off the top of my head. A motor will get it's best mileage at or near peak torque. A rat motor that will be comfortable at under 2000 rpm isn't going to make anywhere near 750 H.P. and conversely, one that will make 750 H.P. will likely not start pulling until it hits 3500 rpm. The 3.42-3.55 gear set with the .75 overdrive will run way better and get better mileage than a higher gear unless you plan on cruising it at 90-100 MPH. Find the torque peak for your motor's cam and gear accordingly. I had a '72 Buick, Stage 1 G.S., that got way better mileage at 70 MPH (14.2 mpg) than it did at 55 MPH (12.5 mpg) with 3.42 gears and no overdrive.

I've run 2.29 gears (with a TH350) behind a 400 Pontiac before and I believe that it would have gotten better mileage with a bit lower gears.

Since you're going EFI you should watch your pulsewidth vs rpm's while you cruise on the freeway. on the same stretch of road try it in 3rd gear (1:1) and in 4th (.75). also take note what the map is with and without the OD (all of this at the same speed of course). this will be a more definitive answer as to what is the best freeway gear for you.

3.31's will create a 2.48 final drive ratio w/ the .75 OD.

And should be about perfect for the rest of the tranny gears too, imho.

pdq67

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Anyone with lots of power running freeway flyer gears that's got any advice for me.

"freeway flyer gears" .............Is a phrase commonly used by the VW crowd.........referring to the 3.88 gear sets that relace the 4.12 common to those trans-axles........funny to hear you use it here........