Any one know what I should be running for RPMs with my C4. I have 73 4 dr that had a 250. I replaced it with a 302. From the Spec on door, I should have 2.79 gears. I thought I should run about 2150 RPMs at 65 MPH. I am running closer to 2600 RPMs. Is this right? I am currently getting about 15 MPG. Other than it being a late model 302 reman, Edlebrock intake with 600 CFM eldlebrock carb, and dynomax headers the rest is off the 250. I am at about 2000 RPMs at 40 mpg as well. I am shifting at about 1800-2500 RPMs. What should I be expecting in terms of MPG and RPMs? I have about 400 miles on the new motor. Thanks Tom
a 302 wont get the gas mileage that the 250 would.. i had a 170 in my car and got 34mpg in it.. and now that i have the 302 in mine. i get 14 i think.. but i am also running my car with 4.11 gears.. and thats a story in itself when i had the 2.79 in mine.. i would run right about 2500 at 65mph.. but it also depends on the size of tires you have on the back.. taller tires= less rpms at freeway speed, smaller tires=more rpms you just need to get out on the freeway, have someone in a new car get next to you and have them set the cruise control at 55 60 65 70 75 and you look at your tach and speedo and see what your car does, as all cars are different, you can also tune your engine and new plugs, wires, tune the carb, all plays a factor on mpg.. but like i said.. its a 302... not designed for great gas mileage good luck
To figure rpms at any speed : take the tire diameter, multiply times Pi (3.1416) this gives you the circumference of the tire (distance around the thread in inches) Divide that into 63,360 (inches in one mile) this gives you how many times the tire rotated in one mile. Take that and multiply times the rear gear ratio to get rpms at 60 mph. This will not be completely accurate though with a C-4 (or any other auto trans without a lockup converter) but it will be close. To figure other rpms @ speeds, divide or multiply the speed into 60 and multiply or divide the rpms @ 60 to figure. 90mph in a car that turns 2500 @60 would be 2500 X 1.5 . rpms at 30 mph, divide 2500 by 1/2.
With a stock 302 you should be able to get 20 mpg or close to it. I have two Mavericks with 302's and C4's and they both get 20 mpg. The one variable that affects gas milage more than anything else is the driver. If you accellerate hard and find yourself working the brakes and throttle a lot then your gas milage is going to suck. If you rarely have to touch the brake and you accelerate smoothly then you will get better milage. You can tune your car for better milage without hurting performance by adjusting the timing for the most advance that your engine can take without preignition occurring. Make sure your vacuum advance is working properly because that will give you a big boost in milage. Keeping the engine temperature down to 180F will help - hot engines cause more friction. Using the proper oil viscosity will improve your milage - too low and you get added friction and if you use too heavy an oil it will cause drag because the pump has to work harder to get it through the engine. Tires and their air pressure can make a big difference. You want to run near the maximum tire pressure so smaller tires give better milage - if you need to run fat tires then keep the pressure as high as you can and still get even wear on them.
MPG also depends on the terain. If you have straight level roads it will be much better than if you live in the mountains. I know I live in the east tn. mountains.
You must drive wide open on the downhils then. Every time I go in the mountains (real ones, not those foot hills in the east) My mileage either doesn't change or it gets better. The down hills cancel out the uphills.:Handshake
I guess we really dont" have mountains here. Because we do go down them fast. I drive 126 miles to work and back every day and 25 of those are in " our foot hills " . I can tell you that it takes nearly as much gas to drive those as it does to go the other 101. May be something is wrong with my truck.
Maybe it's just carbed vehicles. Been a long time since I drove one with a carb in the mountains. With my 89 Ranger, 95 E150 van, and now the 06 Stang, all get as good if not better mileage running mountain roads out west as they do or did here in Louisiana. Ditto for the trucks I've driven out there.
