I want to upgrade my rear end. Right now Ive got a 302 with a c4 tranny. The rear end ratio on my car is a 2.87:1. I am not sure whether or not to go with the 3.0:1 or the 3.25:1. The reason I have the question is the c4 obviously doesnt have a od and I dont want to screw up my gas mileage too much. The 2.87 gears are not good for ET times so what is your recomendations? Does spinning the engine slightly faster throw the freeway mileage to hell? I know that the city mileage shouldnt be effected to badly.
Gear Ratio Anytime you go to a deeper rear gear without od, it will increase the engine rpms and that will always use a little more fuel. As far as ET goes it should improve to a point, engine, cam, and carb size will come into play also. It is hard to have both mileage and performance, but it can be comprimised sometimes. My idea is to have a whole chunk set up for racing and swap it in the housing for the track and then go back to the higher ratio for everyday use. Is a bit of pain to chg. out but once you have it down can be done in less than 30 min. 3.25's will be a good choice for leaving in but don't expect to much increase in et times. The 302 with a decent cam and headers etc. will like the3.55's to 4.62's on the track only. The city driving should be worse on mileage because of the stopping and starting along with trans shifting up and down, on the highway at steady speed the rpms will be constant and should produce better mileage than in town. 60ft times is where most races are won or lost along with your reaction time, especially in bracket racing. There are million other factors to consider when choosing gears but maybe talking to other racers in your class you can get an idea what to run to be competitive. Good luck as always.
'What Old Guy said" about 60'. ___________________ Speaking of 60's Dave, Have you and your son had a chance to run this year yet? What were the 60's on both cars? Better? Worse? What changes to either the Fairmont or the Maverick did you guys make during the off season? Inquiring Mind, Rick
I ran a 4 speed (no OD) with 3.25 gears for a lot of years in my Mav. I thought they were a pretty good compromise. Reasonable highway rpm and mileage, yet good torque. In fact my city driving gas mileage increased slightly because I could keep the car in 4th gear for most of the time.
Rick Book Hey Rick, got to run a special on Jan 11, paid 2003.00 to win, of course I did not get any of it . During the break period in Nov. I decided to freshen up the engine and trans. Could have just as well left it alone, bearings etc. still good as new after many hard passes(Valvoline and Lucas are the greatest). Did not have the Maverick done yet and because of work schedules, I was at the track by myself. Temp was hovering at 35 and miserable. First pass was a wash, did not get temp up to 190 and the old girl coughed off the line. Second pass got her too hot and was pukeing coolant out of the overflow bottle, sent to the pits. Found out temp gauge not working. Next pass was a 9.20 at 115mph. This is good, wrong, bottom starter bolt fell out and let the mini starter disengage. Now at my age I don't relish getting under the beast in 35 degree weather but I did and replaced the bolt. Next run was 9.21, things are good again. Reaction times suck, 580's. First elimination was against a 72 Nova with a 11.50 dial, sat for almost two secs and stabbed it. No gauge and she was cold, burped and left late. I was toast, caught him at 1/8th mile but was not enough to run the number, he did! To cold, to tired and to mad. Put her on the trailer and headed to the house. Only thing I chgd. on this engine is getting rid of the heavy weight TRW 11.5 pistons. Went to SRP light weight 13.1 slugs. What a diff in throttle response, they weighed 6oz less per piston than the TRW's. First burnout with an 8000 chip in the box she jumped to 7200 immediately. Backed out of that quick, did set the shift lite from 6500 up to 6800, have not had a chance to run anymore(cold and rain for a month) so can't tune in what I need. I think when it's run more, 7000 shifts will work out to the good. The 60ft were 1.57 to 59 with a lot of tire spin on those 9in MT's. Need to back half it and get some big meats on the ground. The cam is a little small .544 lift roller but with the RPM heads it breathes just enough for that combo. All in all it's still a blast for me at 63yrs, win or lose(hate to lose as bad as anyone though). The Mav is back together with a 351 and Eagle rods this time, will let you know what it runs when we ever get a nice day again. Was running 1.47 60's and 8.70's @ 117 in the 1000ft with the 393 till mister connecting rod went for a ride inside the block and took everything with it to the scrap pile(stock rods you know). Forgot, I did go from the 8in to a 9 in the Fairmont with 4.86 gear, might try 56's???
You're certainly turning some high rpm's with that cam and heads! Jeez! My usable torque would peek out around 5900-6000 with my setup. I don't mind though - I stand less of a chance at breaking something with my small cam and AFR185's. I was doing 1.5X 60's with it (456 gears) last outing. Can't wait for the weather to start getting nicer. I'll be putting that engine and a C4 in the Maverick in 3-4 weeks. You mentioned being limited to the 9" tires - I was going to try different back space wheels, fender flare (Louisville Slugger method) to try to run 10's at least. My 9" rear isn't narrowed at all (that I can tell). If I do anything it'll be mini-tub it and go coil-overs (if I can get it to spin ) -it's not going to happen this season though. Good luck to both of you this year. Looking forward to hearing some good numbers from the Maverick too. Keep us posted on your progress and points standings, Rick
Keep in mind tire height has a lot to do with it as well. I have the 2.87 gears in mine, and after switching to much larger rear tires, I am now thinking on going to 3.25s.
