Oh, and the rears are a complete and easy bolt-in swap, as I even am using the 78 drum rear on my 79 rear disc car. My future plans call for the 3:73s to go back in, but with the addition of an overdrive transmission, so I can enjoy the performance AND still get decent mpgs with it. The 3:73s always kept the revs up there, as to make the header collecters heat up the floor so bad, I used to get the hot foot driving the darn thing.but it sure did have a great pull to it up to 5000 rpm!! The MPGs are now up to 20 mpg on the highway, and the car is an overall more comfortable car to drive. I'm now using a rear out of a 78 T/A (Pontiac 400/ auto, A/C car) that is 2:56. If I remember correctly, I was turning 3-3300 rpms at 60 with a 26" rear tire, and that equated to about 9 MPGs. I ran 3:73 for a few years back in the '80s, but I found them far to much for highway use. Some automatics may have came through with 3:08 or 3:23, but were most likely A/C delete cars. If we are talking factory 77-79 automatic Trans Ams, the gear ratios were most likely in the 2:41-2:73 range. In fact I just returned from taking it on the Hot Rod Power Tour this year.( over 3000 miles in 1 week) Only problem I had was an alternator issue, otherwise the car ran great. The way it is setup now I can cruise all day long with no worries. I obviously don't know enough about how to get horse power from an engine. The next time I do an engine I will either buy a crate engine or have a performance shop do it for me. At least the dyno results say it's only mild ( 245 rwhp) I tried to build up this engine myself years ago, but was never successfull it getting it to the 300 rwhp I was looking for, so now I just drive it and enjoy it for what it is. ![]() My 1978 T\A has 400 Poncho that is a 1976 bored 30 over with 10.75:1 pistons, Ram Air III heads ( #12 ) Performer intake, fairly agressive cam ( forget the specs- would have to look it up ) 750 holley, headers, MSD distributor and a 6AL box, roller rockers, etc.so I would consider it a mild build up. the rev's were way too high for my comfort level. don't know for sure, but that is why I changed gears. The only way I would go 3:23 factory ratio is if you are into top end highway performance and willing to sacrifice some of the off the line advantage the other gears would give you for 1/4 times, but 3:23 are still a decent setup just the same for a daily driver/performance car where gas mileage is a concern aswell.Ĭlick to expand.Maybe. Either a 3:42 factory ratio or 3:73 set-up. I had three of your body style through the years (77,78,79) and if I was you being an automatic there would only be two potenial ratios I would run for maximum utility. Unless the cars were the next step up and were Pro-Street because those cars were either trailer queens or just never saw the highway. When I was growing up and hanging with the racing scene most automatics that were street and strip saw 3:55 (Ford) and 3:73's (GM), while the manual cars were usually 3:90(Ford/GM 12 bolt), 4:10 (Ford/Mopar), and 4:11's (GM). There is a reason for this and you will find that a manual can utilize gears better. ![]() Where a Manual usually was always had a lower gear ratio (higher numerically). ie: an automatic Trans Am usually had a 3:08 gear ratio or a 3:23 gear ratio commonly unless special ordered or modified. No all will bolt together but a manual car usually carries heavier gears with a Trans Am and will handle them better.
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