302 mpg problems
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302 mpg problems
I know that this is beat to hell on all sites but I need to improve my mpg on my truck.I have a '77 f100 with a 302 and a c-4 trans. Motor is stock besides a weiand stealth intake and a Holley 600 4 barrel. I have long tube headers going to true duals. Rear gearing is 2.73. It is timed correctly, carb is well tuned and starts, runs and drives fine, but I still get within 9-12 mpg. It doesnt burn very much oil, and I drive it easy. My other '77 I had before this one had a 351m and it got 15+. Not tryin to shoot for the moon, but just to make it drivable and any input would be helpful.Thanks
Posting Guru
Joined: Jul 2013
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From: Oregon
What truck configuration? Long bed short bed, 2wd 4wd? Is your transmission in good shape? In the engine section there is a member Conaski IIRC (sp) he could probably recommend a cam that would be better for mpg and daily drivability. Just some questions and suggestions. Good luck.
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What truck configuration? Long bed short bed, 2wd 4wd? Is your transmission in good shape? In the engine section there is a member Conaski IIRC (sp) he could probably recommend a cam that would be better for mpg and daily drivability. Just some questions and suggestions. Good luck.
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Joined: Feb 2013
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From: South Louisiana
I'd ditch that intake and carb, get a performer and a small 390-450 cfm carb, check your compression numbers on all 8 cyl's and just see where things are with the motor. my 82 f150 with a 302 2bbl,c6 and 2.75 geared 9" rear got 18-20 mpg. your truck should get close to that. whats your usual cruise mph on the hwy?
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I'd ditch that intake and carb, get a performer and a small 390-450 cfm carb, check your compression numbers on all 8 cyl's and just see where things are with the motor. my 82 f150 with a 302 2bbl,c6 and 2.75 reared 9" rear got 18-20 mpg. your truck should get close to that. whats your usual cruise mph on the hwy?
Cargo Master
Joined: Apr 2009
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From: South west Idaho
I think the rear gears are okay , i had the same 2:75 gears in a 79 short box , 302 , stock exhaust c/4 and got about 16 to 18mpg. It had a 2bl carb. I took the same engine out and put it in my 73 , short box , c/4 with 3:25 rear gears . Topped it of with a Edlebrock 600 on an early 80s era aluminum intake, small passages, and got 12 to 13 mpg. Just pulled that off and went back to the 2bl. I think your problem with the stock engine is the carb setup.
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Cargo Master
Joined: Apr 2009
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From: South west Idaho
If you have a good running engine then i would leave it as is and think about an AOD transmission. You might want to change the rear gearing then with the AOD. I'm going to try the AOD in mine when i get the money to rebuild one i have. I will try it with the 3:25 gears and maybe go to 3:50s since i have an extra rear as a spare for it.
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Senior User
Joined: Feb 2013
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From: South Louisiana
yea I agree wit hJim, your rear gears are plenty high enough. I know that stealth isn't any sort of super high rise single plane Intake but that 302 is probably out of steam around 4000 rpm. I'd swap a stock intake and 2bbl carb on it or find a performer or similar low rise/dual plane intake with a small 390 cfm carb. No reason your truck shouldn't get close to 17+ mpg IMO.
Posting Guru
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From: Sedro-Woolley, WA
Gotta agree that the tranny/rearend is all good, keep the headers and get the Performer cam/intake/carb recommended for the motor. The cam has three settings(at least mine does) for performance, stock and ecomony, your choice.
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From: South Louisiana
exactly, thats pretty much what I was gettin at with the hwy speed, 55-60 is about tops for speed and good fuel economy for most trucks, faster then that and you start to use more fuel at a higher percentage to speed. I do honestly think there is a good 5 mpg left to tweak out of this rig for sure.
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yea I agree wit hJim, your rear gears are plenty high enough. I know that stealth isn't any sort of super high rise single plane Intake but that 302 is probably out of steam around 4000 rpm. I'd swap a stock intakes and 2bbl carb on it or find a performer or similar low rise/dual plane intake with a small 390 cfm carb. No reason your truck shouldn't get close to 17+ mpg IMO.
When I got the truck, mpg was same as now but no power when i need it. Im building a flatbed to put on it which should take off a couple hundred pounds. Its a love hate thing to drive it but there has to be some way to squeeze a few more mpg.
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I disagree with the smaller carb suggestion. Car Craft did a tech answer and in theory a larger carb (within reason) will get better mileage than the smaller carb on the same engine. With the larger carb you are opening the throttle less at a given engine speed and using less fuel to maintain it.
I think it's all going to come down to carb tuning and your ignition timing.
I think it's all going to come down to carb tuning and your ignition timing.
Postmaster
Joined: Nov 2011
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Holley's are often shipped with "safe" (rich) jetting. I'll guess its richer than it needs to be and is hurting mileage. How do the plugs look? Is there a dyno tune shop near you? A few hours on the dyno with jet changes and maybe timing adjustment may help a lot. Another approach is to fit a wideband AF meter. Tune slightly lean (14.7 or a bit higher) on light cruise and about 12.5:1 under heavy load. The other approach is to step down the primary jets and watch the plugs.