383/6 speed mileage
Thread Starter
Racer
Joined: May 2007
Posts: 296
Likes: 4
From: London Ontario
383/6 speed mileage
I am considering putting a 383 in my car with about 400hp and I have a T56 which is already in my car. I have 3.55 gears right now and the trans has a .5 overdrive in 6th. I know a 383 is never going to get good gas mileage Im just wondering what I should expect. I also realize that 3.55 gears with a .5 overdrive is going to be pretty useless but I dont have the money for gears right now. Now that thats out of the way
Is there anyone who is running a similar setup. what kind of mileage are you getting? thanks in advance
Is there anyone who is running a similar setup. what kind of mileage are you getting? thanks in advance
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
From a low of maybe 5 (foot in it all the time) to a high of maybe 20+. A lot depends on the motor combo. If yo uhave a mild cam that makes good power in the 1500 rpm range it could provide good mileage. If your cam is big and does not make power until 2500 or above your mileage will be terrible. The motor will constantly be lugging around and will not be efficient. I run 3.70 gears with a .68 OD and it is terrible at anything below 50 mph. A modern FI motor can provide good economy at a low rpm with a mild cam. To many people build a high HP motor and want to run it at 1500 rpm and expect good mileage.
What is the motor combo.
Your mileage will differ due to driving habits.
What is the motor combo.
Your mileage will differ due to driving habits.
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
With that setup you have a 1.77 final drive ratio. At 1500 rpm you will be at about 67 mph give or take a few mph. You will not be in the cams range with this and it will lug at highway speeds. If you have it dynoed look at the torque curve then look at some of the LS motors torque curve. They make good torque from 1200 rpm on up. That is why they can cruise down the highway at 1200 rpm. I know mine won't cruise at 1200 rpm, it barely runs at 1000 rpm. Big cams and carbs are going to require some rpms to get it to run smoothly at highway speeds. 5th gear might be better but 6th is going to require 80+ mph to run good.
Racer
Joined: Mar 2004
Posts: 292
Likes: 2
From: Plumas Lake CA
I know it's not a Vette, but....
My 383/T56 equiped '94 Impala got almost 23 mpg from Vegas to Sacramento a couple of weeks ago, cruising around 80mph most of the way (about 2000rpm in 6th). It's got LT-4 heads/intake and a Comp 503 cam (224/230 duration), headers, 2.5in X pipe exhaust, 3.73's, and running a non-optimum tune. My car probably weighed over 4500lbs on the trip. I usually average about 20mpg driving to work and back. I'd think a Vette could do better.
There may be some truth to the "lugging" arguement. Maybe I'll try driving in 5th unless I'm doing 75mph and see if my mileage improves.
There may be some truth to the "lugging" arguement. Maybe I'll try driving in 5th unless I'm doing 75mph and see if my mileage improves.
Racer
Joined: Mar 2004
Posts: 292
Likes: 2
From: Plumas Lake CA
It's an LT1
Yep, it's based on a 95 Camaro LT1 block. Reverse cooling, optispark, etc..... It will smoke the tires through first, second, and most of third gear. It just rolled over 204,000 miles and I have no plans of ever getting rid of it.
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