Need some advice please.
FTE Legend
Joined: Jun 2006
Posts: 31,930
Likes: 1,499
From: Ottawa, Ontario
I wouldn't worry too much about the transmission lasting, the AOD was never put behind a 351 either but mine lasted 10 years behind one and is still going. And with overdrive in the gearbox there is absolutely no reason to use anything less than 3.55 gears in the rear axle, if you went with a 289 or 302 that should be 4.10's. That means the motor would be turning a little more rpms at 75mph but that's what has to be done to get performance from a small motor in a heavy vehicle.
That depends, it's more than a simple bolt-in because the wiring harness is different and modification have to be made to it, but it is doable because several guys here have completed the task.
As for the motor itself a stock bottom end with GT40 heads, HO cam + 1.7 rockers, and a full exhaust will put out about 300HP and have you burning rubber every time you stomp on it from a dead stop.
As for the motor itself a stock bottom end with GT40 heads, HO cam + 1.7 rockers, and a full exhaust will put out about 300HP and have you burning rubber every time you stomp on it from a dead stop.
FTE Legend
Joined: Jun 2006
Posts: 31,930
Likes: 1,499
From: Ottawa, Ontario
Actually my 5.8 got a little over 17mpg cruising at 70mph on relatively flat highways.
Senior User
Joined: Apr 2010
Posts: 262
Likes: 0
The best mpg my 5.0 4x4 with 31's got was 17, mostly it would get 14 with an occasional 15 or 16. In the winter I would get a little worse like 13 from letting the truck warm up in the mornings. Thats with a auto and 3.55's.
With his truck being a little lighter and having smaller tires, I think getting over 15 is do-able.
With his truck being a little lighter and having smaller tires, I think getting over 15 is do-able.
Posting Guru
Joined: Jun 2003
Posts: 2,314
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From: southwest michigan
Do you attest that to anything in particular? I think my best mpg was maybe 13.5 highway and think 17 would be awesome.
Elder User
Joined: Nov 2006
Posts: 973
Likes: 2
From: Texas
17mpg was the highest i'v ever got with my 300. And that was when it was completely stock with the M5OD and 3.08 and i was driving 55-65 on only highways, day after day last summer.
I cant imagine 17mpg in a 351. But maybe if the conditions are right.
I cant imagine 17mpg in a 351. But maybe if the conditions are right.
Elder User
Joined: Nov 2006
Posts: 973
Likes: 2
From: Texas
I wouldn't worry too much about the transmission lasting, the AOD was never put behind a 351 either but mine lasted 10 years behind one and is still going. And with overdrive in the gearbox there is absolutely no reason to use anything less than 3.55 gears in the rear axle, if you went with a 289 or 302 that should be 4.10's. That means the motor would be turning a little more rpms at 75mph but that's what has to be done to get performance from a small motor in a heavy vehicle.
Thread Starter
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Freshman User
Joined: Apr 2010
Posts: 38
Likes: 0
what transmission should I try looking for? Is the T5 a good transmission for a truck? Also did for make or is there a way to change a motor to and overhead valve system? Also will increasing the stroke of a motor kill the gas milage?
Cargo Master
Joined: Mar 2010
Posts: 3,342
Likes: 294
From: Laramie, WY
351 Efficiency
I'm sure you'll all call bs, but I rarely get less than 17mpg (empty) highway with my 96' 351w 4x4 3.55 rear end at altitude. Manual lockouts, stock size tires (LT235/75/R15) and not going over about 68-70 mph do it every time. Oh no AIR pump either, and one hallowed cat, not sure if that makes a big difference. If I'm driving from CO to MN, I'll get 18 in NE if I don't stop for 300 or 400 miles. One winter, I drove 47mph (because of the icey roads) all the way across NE , went 300 miles on the rear tank- rediculous I know.
Whats odd is when in CO, I get 17mpg all the time, in MN 16mpg tops. I have a theory, the mass air sensor reads pressure, which is a whopping 19 inches of Hg at 7700 feet (I think 29.7 inches of mercury is at sea level?), so there is about 1/3 the O2 at this altitude. The computer recognizes this and leans it out to try to maintain the A/F ratio of (what is it, like 14.5:1?).
I used to think it was the non ethanol blended fuel we had in CO, but now we have E10, and I'm still getting the same mileage.
Whats odd is when in CO, I get 17mpg all the time, in MN 16mpg tops. I have a theory, the mass air sensor reads pressure, which is a whopping 19 inches of Hg at 7700 feet (I think 29.7 inches of mercury is at sea level?), so there is about 1/3 the O2 at this altitude. The computer recognizes this and leans it out to try to maintain the A/F ratio of (what is it, like 14.5:1?).
I used to think it was the non ethanol blended fuel we had in CO, but now we have E10, and I'm still getting the same mileage.
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Senior User
Joined: Mar 2010
Posts: 459
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From: Fayetteville, NC
recent trip to GA from NC, round trip mileage total 900......
bone stock 302, 308 rear end, e4od, '93 flareside, averaged 17 mpg, turning 2k at about 75 mph with 275/60/15 firestones.......
this is in a truck with the original 17 year old spark plug wires/cap/rotor....not sure about the plugs, it runs good so i havent looked at them....
with a proper tune up i see no reason i shouldnt get 18 or better......
this was about 90-95% open high way driving
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