Cruising at 80mph with turbo 400

[Smoothk9]

Go with the 4L80. The 454s are torquey, but still a dog. I had an 88 with a 454/TH400, had 3.42s and 35s, it would light the tires up around a corner, but was a dog on the highway at 70s. It would do it, but foot was always mashed, so defeating any better gas mileage. Have to realize these trucks have the aerodynamics of a small barn, are heavy, and will never get good mileage with a 454.

Thanks for the advice yeah I’ll finish the top end kit and cooling system upgrades then I’ll go switch trans

 

[Aeroscream]

Gear Vendors in El Cajon, CA sell units that handle crazy stupid HP and Torque.
A bit pricy though. plenty of their units are out there, and a quality product.
Simpler than the 4L80E conversion IMO.

Unless Smoothk9 is trying to straighten all the twisty's on the Oatman Hwy (Cool Springs to Oatman Rt66) between his house and mine in Fort Mohave, there are a lots of hwys around where the speed limit is 70-75mph. The main hazzard is wild burros whose eyes don't reflect when headlights shine on them at night.

My rule of thumb is staying 2800 rpm or lower in the final drive gear. Plenty of apps out there to calculate that once one decides tire height etc., as we all know.

Keep researching. Lots of good choices and advice out there.

 

[L31MaxExpress]

Where roads are good, I routinely cruise 85-90 and get decent mileage in my brick of a van with the 383. Most of our roads have a 75 mph speed limit and if you are not rolling 90 you will flat get run over. Then again I have 5.13s with 32.5" tall tires now and cruise a little slower if I want good MPG. 80 mph keeps me down around 3,000 rpm. 4L80E and 5.13s is about like having a TH400 with 3.73s.

With the Tahoe and its 8.1/4L80E and 3.42s rolling on 32" tall P305/50R20s I have seen 18 mpg at 75 mph. 8.1 is turning about 1,900 rpm at that speed.