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Old 09/07/08, 08:03 AM   #1
mountaincat68
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Most mpg's 302, 347, 351?

Hello all, I am in the planing/parts roundup phase for my 66 bronco and I am trying to decide which route to go with the engine. This bronco is going to be my daily driver so fuel mileage is a huge concern. It will have a 3.5 in lift with 33 10.50 s, a 4r70w tranny and a fuel injected engine, that much I have decided, I am just undecided on displacement. The bronco has no engine so I will be starting from scratch so my options are open.

Will the added torgue of the bigger displacements be better for fuel mileage when in overdrive? Will a 5.0 out of a mustang have enough bottem end to hold the eb in od? Which intakes for fuel mileage GT40, Edelbrock Performer?

Power is not a huge concern but if I can get more power with the same mileage I will do that.

Sorry for the lengthy post, any opinions will be greatly appreciated.

Thanks alot,
Jason
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Old 09/07/08, 08:48 AM   #2
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It takes torque to hold the overdrive. Your best Torque #'s should will be around 2k to 3k. better torque #'s come easier with bigger engines. So the 351 is the first choice. However the 302 based 347 due to its longer rod length will make good #'s too. With only having to turn the 33'' tires I would think the 347 would do better on gas than the 351. If you go up in tire size the 351 would be a better choice.

when I had my 400 / AOD combo together- the high torque #'s of the 400 would push the EB along in overdrive with no problems. You could go as fast as you dared, It also would hold the overdrive as slow as 30 mph. My point is good torque #'s is what you should be looking for.

1971 U15 Hunter 289/435/20/ 4,11. 1968 U15 - EFI 408C/C6/205/4.88/37's/hi9/ARB's/hydro-boost/full cage/4wdisk/PS/powerasswipe/bla-bla-bla!
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Old 09/07/08, 09:07 AM   #3
Socal Tom
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My 5.0 holds OD just fine, but I'm running 4.88s with 35s. It really depends on the gearing. The HO 5.0 likes to run at about 2K. If you are in hilly terrain, you may want to select gearing that will run a little higher rpm. At the end of the day, its not about the engine torque, its about the tranny. Holding OD on a big hill puts a lot of stress on that band, and if you set your computer to hold it will start to slip and eventually burn up the trans. With that in mind I would pick a 5.0HO and 4.11 to 4.30 gears with 33 inch tires for max economy.
Tom

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Old 09/07/08, 09:27 AM   #4
gpete
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egine

Quote:
Originally Posted by mountaincat68 View Post
Hello all, I am in the planing/parts roundup phase for my 66 bronco and I am trying to decide which route to go with the engine. This bronco is going to be my daily driver so fuel mileage is a huge concern. It will have a 3.5 in lift with 33 10.50 s, a 4r70w tranny and a fuel injected engine, that much I have decided, I am just undecided on displacement. The bronco has no engine so I will be starting from scratch so my options are open.

Will the added torgue of the bigger displacements be better for fuel mileage when in overdrive? Will a 5.0 out of a mustang have enough bottem end to hold the eb in od? Which intakes for fuel mileage GT40, Edelbrock Performer?

Power is not a huge concern but if I can get more power with the same mileage I will do that.

Sorry for the lengthy post, any opinions will be greatly appreciated.

Thanks alot,
Jason
Have you concidered a diesel?

Turbo D
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Old 09/07/08, 09:44 AM   #5
Broncobowsher
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Gearing and tire size will have an even bigger effect then engine size.

If you are staying with short tires, say 33" and under with minimal lift. A stock 5.0 will do fine. If you want it to breath a little better then swap in an Explorer intake. The Explorer/GT40/Cobra intakes have some of the best flow out there. Often so good that they are left off the magazine reviews as the aftermarket wants to sell product, and if the magazine articles say that a junkyard intake will work best for street applications, then the aftermarket will not advertise in the mags. Without advertising there is no income to the mags. So the mags are bias toward the advertisers (no real surprise).

Now if you start pushing larger tires 33" and up, then start looking at bigger engines. People love the 347, but remember that most every 347 is a built engine with aftermarket heads and good heads and lots of cubes make for a powerful engine. A 347 actually has a horrible rod ratio, the rod is angled sharply into the cylinder wall at mid-stroke. The ring package is in the wrist pin. Excessive oil consumption at 30,000 miles is common. There is a fix, a shorter rod with even worse angles to it.

351 is a much better big cube engine. It was designed to handle the larger cubic inches. It will cost less then a 347 as well and can be stroked even larger. Rod ratio is much better as the deck is taller and will fit a longer rod. Head and main bearing bolt size is larger as well. main bearings are larger. Overall it was designed to be that size. Trouble is intakes are a little harder to find. Best find is a Lightening intake.

There are other factors as well, how much hill do you deal with? If you drive on flat ground, less gear is needed. But if you must climb hills, more gear.
How fast do you want to go? Aerodynamics hit the Bronco hard. My 351/4R70W/4.88/33" combo is actually overgeared most of the time. If I only had a 5.0 HO <or> only had 4.56 <or> went to 35" tire it would be a better package overall. But the current package actually starts working good when I get to about 80MPH. I am pushing so much wind that the tire/gear/engine combo work happy (although sucking gas at alarming rates while doing so).

My current combo is also very happy if I keep it at 45 MPH, which is a good speed back when I lived in KC and drove around surface streets. Out here in the wild west, 55MPH through residentail neighborhoods is a common cruising speed with traffic.

So the answer comes down to...
Who knows. We don't have enough info. Even if we had it all there are still many opinions on what is actually right and wrong. Often 2 different things will both work with little difference.

Keep in mind that too little gear and lugging the engine will make for poor performance and poor mileage.

"She's built like a steakhouse but she handles like a bistro"-Zapp Brannigan
“How hard can it be?”-Clarksonius 4th century BC.
Full throttle, it either solves the problem or ends the suspense.
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Old 09/07/08, 09:58 AM   #6
mountaincat68
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Thanks for the reply guys

I have thought about the 4bt (I am kind of a diesel fan) but initial costs and I am stuck on an auto tranny have swayed me away from that.

My gearing will be set up to spin the engine (whichever one I choose) with 33's and the .67 overdrive at that particular engines acceptable rpms (wherever it makes acceptable torgue) to push the bronco at about 65 mph.

I guess the root question is which setup will get better mileage, a 5.0 spining a little higher at 65mph or a 347/351 spining a little lower at 65mph?

Any dyno sheets of a 5.0 and a injected 5.8 with torgue numbers and fuel lbs/hr? That way one could see the different rpms that the engines make the same torgue and how much fuel they are both consumeing.

I am way over analyzing this, I know.
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Old 09/07/08, 09:59 AM   #7
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pheww!!!! who wants a stinky azz diesel??

Go with a 351w cheapest Ford power build going with the extra stroke will help with tire and od Issues

Last edited by Bronk; 09/07/08 at 10:57 AM..

If it has tires or tit's you'll probably have problems with it.
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Old 09/07/08, 10:47 AM   #8
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Quote:
Originally Posted by Broncobowsher View Post
If you want it to breath a little better then swap in an Explorer intake. The Explorer/GT40/Cobra intakes have some of the best flow out there.
What year/vehicles do we look for to find one?
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Old 09/07/08, 10:53 AM   #9
Broncobowsher
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Quote:
Originally Posted by pmctighe View Post
What year/vehicles do we look for to find one?
'96 to '01 Explorer 5.0 are the most common to find. Of those there are 2 versions. '96 and some '97 have internal EGR and most '97 through the end of '01 have external EGR.

5.0 cobra started in '93, intake changed with the new body style in '94 and ended in '95.

GT40 is a Motorsports aftermarket intake. Mandrel bent aluminium tubes instead of cast. The upper was factory on gen 1 Lightenings

"She's built like a steakhouse but she handles like a bistro"-Zapp Brannigan
“How hard can it be?”-Clarksonius 4th century BC.
Full throttle, it either solves the problem or ends the suspense.
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Old 09/07/08, 10:58 AM   #10
Viperwolf1
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Quote:
Originally Posted by pmctighe View Post
What year/vehicles do we look for to find one?
Cheapest is probably the explorer from a wrecking yard. 96-01 is the year range. Any explorer with a 5.0 should have it but there are some differences in EGR. Some were internal and some were external. You need upper and lower to match.

74 Sport U151, 5.0 must-plorer EFI, C4, PS, front discs, twin sticks, 3.5" susp/1" body, 33's, 4.11's, ARBs, Hickey Sidewinder, cobra hydroboost
http://www.coloradoclassicbroncos.com
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Old 09/07/08, 12:18 PM   #11
Madgyver
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Welcome to the site.....
I'd say 351W all the way...
Gas cost, it's a sacrifice we take with V8s..
You could drive a Honda but what fun is that?

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your so full of shit your eyes are brown.
Haha.
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Old 09/07/08, 01:09 PM   #12
greasypigeon
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Be like me and stroke it!

77 Sport, 500hp 347 stroker, nv3550. d44 w/ disk brakes w/ power lock up front. BB 9in with detroit locker in the rear. 5.5 wh coils up front and custom 3 link w/ 70 f150 coils.
Stuff for trade for soft top. Trade for soft top
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Old 09/07/08, 04:13 PM   #13
bmc69
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Quote:
Originally Posted by mountaincat68 View Post
Thanks for the reply guys

I have thought about the 4bt (I am kind of a diesel fan) but initial costs and I am stuck on an auto tranny have swayed me away from that.

My gearing will be set up to spin the engine (whichever one I choose) with 33's and the .67 overdrive at that particular engines acceptable rpms (wherever it makes acceptable torgue) to push the bronco at about 65 mph.

I guess the root question is which setup will get better mileage, a 5.0 spining a little higher at 65mph or a 347/351 spining a little lower at 65mph?

Any dyno sheets of a 5.0 and a injected 5.8 with torgue numbers and fuel lbs/hr? That way one could see the different rpms that the engines make the same torgue and how much fuel they are both consumeing.

I am way over analyzing this, I know.
no yr not. You are illustrating a basic fundamental..it takes x HP to go y MPH and it matters not one wit whether yr running 6 Briggs an Strattons or a 514 stroked 460. What matters is one thing only..how well you matched up whatever you are running with its highest SFC operating point and the speed yr wanting to travel.

'69 w/ Oz-408, T-18/NP-205, D44/ARB, D60 Detroit
39.5 IROK Radials/Champion Beadlocks
Hydroboost- F-250 dual-piston frt disk/ F-250 drum
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Old 09/07/08, 04:18 PM   #14
bax
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Quote:
Originally Posted by bmc69 View Post
no yr not. You are illustrating a basic fundamental..it takes x HP to go y MPH and it matters not one wit whether yr running 6 Briggs an Strattons or a 514 stroked 460. What matters is one thing only..how well you matched up whatever you are running with its highest SFC operating point and the speed yr wanting to travel.
Yeah,that is what I said too

1971 U15 Hunter 289/435/20/ 4,11. 1968 U15 - EFI 408C/C6/205/4.88/37's/hi9/ARB's/hydro-boost/full cage/4wdisk/PS/powerasswipe/bla-bla-bla!
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Old 09/07/08, 06:32 PM   #15
green77bronco
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Uh, what he said

77 Bronco,5.0 EFI,C-4,dana 20, 3 1/2 suspention, 2in body. dana44 4.88 gears, Aussie, yukon axles, super joints. 9in, 31sp Yukon, Detriot, 35in X-terrin
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