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#21
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Quote:
as for the OD on these cars, wasnt that before OD was around or used on a wider scale? OD didnt come around until the early to mid 80's for GM with the 700 & 200 trans. |
#22
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I never checked the mpg on my '75. I'm guessing its around 14-15mpg. the car has been de-smogged and has true dual exhaust. My '73 averages 13-14. my old '70 RAIII 4 speed got 13 on the highway.
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Current Pontiacs - 1973 Formula SD455 - #'s auto orig paint 1972 Trans Am - 4 speed orig paint 1974 Formula 400 - Ram Air automatic 1966 2+2 convertible - 421 4bbl automatic 1967 Grand Prix - 4 speed orig paint 1967 GTO - 4 speed orig paint 35k orig miles Last edited by 71GP76TA; 10-31-2021 at 01:12 PM. |
#23
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That's terrible mileage for a 400!
Even before installing a Tremec TKO 600 5 speed, i was averaging 20 mpg in my '70 Formula 400 RA III with a 4 speed and 3.73 rear end at 60 mph. With the Tremec, the car averages 25 mpg at 75 mph. While better fuel economy is certainly a plus, the real benefit to me was dropping the RPM at highway speeds by a third and gaining a steeper first gear (the car came with an M21). As I've said in previous posts, that's the best money I've spent on the car (and I've spent lots!)... |
#24
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I have bypassed the vacuum solenoid but have not had a chance to drive the car and test it yet. I will report after I drive it.
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1970 Trans Am 1971 Trans Am 1974 Trans Am 1978 Y88 Trans Am W72/auto 1979 10th Anniversary Trans Am 1984 Trans Am 1993 Trans Am 1999 30th Anniversary Trans Am 2001 10th anniversary Firehawk #104 2006 GTO |
#25
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WoW, I need a couple of you guys to tune up my car. I have a 77 with a 400. Slightly warmed over but nothing crazy. I figure about average 12 mpg. I remember when these cars were new they didnt get much better than that. Heck, my wifes new mustang with a v6 barely hits 24 mpg!
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#26
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My '77 consistently hits 17MPG on longer trips. The long block is totally stock. Recurved HEI, rejetted Q-Jet, headers, PYPES tranverse exhaust, 3.23 gears.
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1976 LeMans B09 Freeway Enforcer, 455/M40 Smokey 1977 Trans Am, 400/M21 Black/Gold Bandit. 44K actual miles 2017 Sierra SLT 1500 Z71 4X4 2019 Canyon SLT Crew 4X4 |
#27
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I have driven the car now with functioning vacuum advance. The fuel mileage is better, but I have not given it much of a test yet. I can say that it is not running quite right yet, I will do some more trouble shooting.
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1970 Trans Am 1971 Trans Am 1974 Trans Am 1978 Y88 Trans Am W72/auto 1979 10th Anniversary Trans Am 1984 Trans Am 1993 Trans Am 1999 30th Anniversary Trans Am 2001 10th anniversary Firehawk #104 2006 GTO |
#28
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Couple points.
1. My Buddy has basically same car, but a Formula factory 3.42 posi, Muncie, late April build. Has emissions unhooked, so no EGR Or vacuum modification. He runs 235 60's which are 26" tall tires. He is going 3k at 70 easily. Fuel economy is around 12 with varied town, highway driving. 74 was last year of factory Duals and a 3.42 gear in second gen ( for the most part) . 2. Your 455 is working less than the 400 as it has more torque down low. 3. All cars today on alcohol fuel get WORSE fuel economy than when new. Look at a window sticker on any new 1/2 ton truck. Cruising range is cut by 40% compared to "real" gas. 4. Even 2.46 rear wouldn't help as much as a .68 overdrive . Silversport has a bolt in 5 speed, No mods needed.
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"The Future Belongs to those who are STILL Willing to get their Hands Dirty" .. my Grandfather |
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