Inline 6 Fuel Mileage

[BigRed76]

I am just curious as to how the inline 6's do with fuel mileage. Assuming one is in good running order and properly tuned, in a 4wd with a 700R4 what could I expect for mpg's? Theoretically I would think they would be better than a v8 but I dont know anybody that still has one so thats why I'm asking for input from the board. Thanks in advance for your 2 cents

[bubba327]

Mine gets around 15mpg, 230 inline 6 with mild cam, head slightly shaved, HEI, Offenhauser intake with 350 cfm Holley 2 barrel ,TH350 trans , 3.08 gears 235/60/15 tires,

[1LowToy]

Do you have a 700 R4 with a six? If so I'd sure like a pics of the throttle pressure cable mountings (at the cable mount and the carb). I have an 80 model with a six and wanting to go with a 700R4. Mileage is unknown right at the moment other than 2 or 3 gallons has lasted for months just going up an down the driveway

[BigRed76]

I don't have that setup currently. Mine currently has a SM465 and I'm wanting to convert to a 700R4, and I'm considering putting in a 230 or 250 if the fuel economy is worth it compared to a 350.

[bubba327]

Now beware, it it not all about mileage, do not forget the horsepower issue, with a 700R4 you may not have the acceleration or passing power you need.
Sixes have lots of torque and low end, but it ain't no rocketship.
Most of the reason I have left the six installed, is just the coolness factor, but I will replace it in a heartbeat with a smallblock if it ever gives me any trouble.

[1LowToy]

The 700R4 has a lower ratio 1&2 gears than the th350. I have 342s now could go to 308s (would = 700r4 overdrive ratio) but I'd loose power and living in the mountains I need all I can get out of the six. Going the 700r4 with 342s would get me both worlds. I don't think that can be beat

[BigRed76]

Yeah i understand the power difference. The 350 i have now has decent horsepower and torque, but the acceleration is limited by how fast I can shift my dump truck trani If I think I can get considerably better fuel mileage out of an inline six than I'd be willing to take the power loss because my truck isnt a hot rod anyways.

[geezer#99]

1LowToy. Here's a pic for you of a 250 six banger with 700 r4 tv cable set up. Just an idea for you. Can be done. Bellcrank used for hook up.

[1LowToy]

Very nice. Only thing is I have to stay stock with the engine set-up here in California. We have smog thugs that will give me a complete very short sentence for the smog report. NO!

[geezer#99]

It was just a pic to show you how to hook up the cable. Could be done on a stock set up too!

[lilpoindexter]

I think a 4wd, big tire truck with a 250 would suck. Keep the 350, get a beater if the mpg is killing you for a daily driver. I have the og carbed 250 in my short step '78. I got 12mpg in mixed driving with the crappy OG 3 spd...after my T5 swap, I'm getting 17mpg in mixed driving. I have 3.73's in the back.

Ok...16.7...but that's close enough.

I got the straight 6 because I like odd-ball combinations that not everyone has, but frankly, a 350 is just a better engine for these trucks.

[BigRed76]

Originally Posted by lilpoindexter

I think a 4wd, big tire truck with a 250 would suck. Keep the 350, get a beater if the mpg is killing you for a daily driver. I have the og carbed 250 in my short step '78. I got 12mpg in mixed driving with the crappy OG 3 spd...after my T5 swap, I'm getting 17mpg in mixed driving. I have 3.73's in the back.

Ok...16.7...but that's close enough.

I got the straight 6 because I like odd-ball combinations that not everyone has, but frankly, a 350 is just a better engine for these trucks.

Well I've got a 93 grand am for a DD right now but I really miss driving my truck everyday. That is what brought up the idea of a smaller engine than a 350. But it appears that the I6's arent as fuel efficient as I had imagined

I do enjoy the great mpg's im getting in the grand am, but nothing can replace the feeling of driving one of these trucks.

[tucsonjwt]

Even a fuel efficient brand new truck won't get much better gas mileage, be it a V6 or V8 or I5 or I6. The best I ever got on a new truck was 19/23 in a 2000 Silverado work truck V6 driven very carefully, and you really could not haul or tow with that truck like most people would expect to do with a big truck. My last new truck was a 2010 4.8 Ext Cab Sierra with a 3.23 axle and 5 speed auto - that got 15.5 city and 18.5 highway, driven carefully with no load in the box. The new Ford V6 pickups are getting better gas mileage with more horsepower (16/23 and 302 hp 3.7L V6), so maybe GM will get the message and match or beat the Ford performance when they do the next GMT redesign. Unless you drive a lot, a few mpg improvement won't offset the cost of any engine/trans/axle swaps. Of course, if you have a 1/2 short bed, with F/I 4.3L V6 with 2.XX axle ratio you will get 20 mpg city, but you likely won't like the lack of acceleration either city or highway. I think this explains why most GM pickups are 350 fuel injected 1/2 tons.

[bubba327]

Originally Posted by lilpoindexter

I think a 4wd, big tire truck with a 250 would suck. Keep the 350, get a beater if the mpg is killing you for a daily driver. I have the og carbed 250 in my short step '78. I got 12mpg in mixed driving with the crappy OG 3 spd...after my T5 swap, I'm getting 17mpg in mixed driving. I have 3.73's in the back.

Ok...16.7...but that's close enough.

I got the straight 6 because I like odd-ball combinations that not everyone has, but frankly, a 350 is just a better engine for these trucks.

I agree
I like the Six for the oddball coolness factor but she is definitely not any tire smoking powerhouse. I had hoped for better mileage also

[BigRed76]

Originally Posted by lilpoindexter

I think a 4wd, big tire truck with a 250 would suck. Keep the 350, get a beater if the mpg is killing you for a daily driver. I have the og carbed 250 in my short step '78. I got 12mpg in mixed driving with the crappy OG 3 spd...after my T5 swap, I'm getting 17mpg in mixed driving. I have 3.73's in the back.

Ok...16.7...but that's close enough.

I got the straight 6 because I like odd-ball combinations that not everyone has, but frankly, a 350 is just a better engine for these trucks.

If i could have that setup I'd do it, but mines a fleetside, so more weight from the bed. Its also a 4wd, so more weight from the front differential and transfer case. And it also has 33" tires, so more rolling resistance. I've also got 3.73's, but with the 33's its almost like stock gearing with stock tires.

Currently with the 350 and SM465 I get 11 mpg's, so with an I6 & overdrive I'd be looking at 13 or 14 mpg's...maybe, from what you guys have told me.

But as mentioned earlier, the cost to swap the engine and transmission to that setup would much outweigh the money I'd save in mpg's. So it all appears to be wishful thinking

[txinliner]

Originally Posted by bubba327

Mine gets around 15mpg, 230 inline 6 with mild cam, head slightly shaved, HEI, Offenhauser intake with 350 cfm Holley 2 barrel ,TH350 trans , 3.08 gears 235/60/15 tires,

ive got a 230 il6 in my 65 and im keeping it just want to know how you like the 350 2bl ive thought about a 390 4 bl but thought that might be a little much on a stock cruiser

[ChevDog1]

My 2wd 1980 has the original 250, with a TH 400 and (I think) 3.42 gears. It has been getting about 17mpg on my commute so far. Commute is mostly highway, with a traffic jam mixed in both morning and evening. The engine is running a large rochester 2GV carb and true dual exhaust from the manifold back. It would sure be more pleasant to drive with either a T5 or 700R4.

[bubba327]

Originally Posted by txinliner

ive got a 230 il6 in my 65 and im keeping it just want to know how you like the 350 2bl ive thought about a 390 4 bl but thought that might be a little much on a stock cruiser

Reviving an old thread here are we??.
I liked the Holley 350 Cfm two barrel on the Inline six I think it was model 7448, the smaller version of the 4412.
Since 2011 I have replaced the inline six with a 283 V-8 with a 390cfm 4160 Holley.
It now has a whole lot more go, and getting 18 MPG. Wahoo!!
The inline six went into a 71 Toyota landcruiser

[Oregoon]

First and foremost: Screw a V8! Gear-whine is music, and low-end torque is why a truck is fun to drive! (No offense V8 fans!)

I daily-drive my '74 LWB. It's got a desmogged 250 with an HEI, a 3OTT and 3.73 rear end gears. 2WD, and stock-sized tires.

I get 15 in and around Portland, 17 average, and I've made as good as 20 mpg, though that was 100 miles of level backroads taken at a leisurely 40-50 mph.

I've owned six-bangers of almost all descriptions: Ford 240 and 300 (Carb and FI), Jeep 258, Chevy 250 and 292, Toyota 2F and 3FE, Mercedes, and I've worked on just about all of it--everything from Jimmy 302 to Waukesha 817, Chrysler-Crown Marine, Cornbinder, Volvo, and some really freaking odd industrial stuff from Continental.

A six is a joy to work on. Utterly rugged and simplistic. And they can be utterly frustrating, since they're so simple: Sometimes, you have to wonder whay they aren't working right, given that they're not much more than overgrown lawn-mower engines...

My advice is to definitely keep the six, and find an overdrive. They work well with OD auto-trannies, but the slush-box makes them suffer in town. It's really a question of how you drive, where you drive, and which six you have. They are best with an educated foot on the pedal and an educated ear on the engine. In other words, they thrive with a manual-tranny.

And while OD is largely essential, it totally depends on the motor. My '81 Bronco got 22 mpg with 33" tires. It also had a 2BBL, no smog controls and a header. No overdrive, but with gears around 3.50, it did pretty well. Torque is what really saved it.

My 250 isn't anywhere near as torquey as a 300 Ford, though the more conservative my driving, the happier it is... It delivers some useful low-end grunt when needed, though it's not an economical situation.

In the same vein, my old 292 Chevy could've pulled a barn down, but the head flowed poorly and the stock carb really sucked. With some mods (lump-ports, small 4bbl) and a better intake/exhaust, that 292 would've performed way better and probably delivered economy as good as my 300 Ford. With an OD, it might've really shined. There's a reason UPS used both motors for 30 years.

Conversely, my 2FE Toyota had more vaccum lines than you've ever seen, and it got 11 mpg, regardless of where and how you drove it. My buddy had an identical 1984 FJ-60 (he was out of the smog-control boundary) and with a Weber and a desmog, his economy approached 19 mpg.

Food for thought. You can build a six as hot as you want, or you can tune it for economy and enjoy the old-school simplicity. Your call... And regardless of manufacturer, they are inherently balanced by design, with 120-degree firing which results in smooth balance and longer-life. They are absurdly long-lasting.

Eithr way: KEEP THE SIX!!!

[greg64]

Great post, Oregoon. I've been running chevy sixes for the last 20 years. Both 250 and 292. The 250 got better mileage (shorter stroke), but the 292 has more low speed torque. I'd agree that the manual tranny is a better option. I'm using an SM465, and although I'd love to have an overdrive, I don't do much highway driving these days.

It's too bad the stock head is pretty lousy. There's a million aftermarket aluminum heads for the SBC, but not one for our sixes (well, Brazil has a couple). I'd love to see an LS style cross flow head for the six. Maybe one day.

[walkerb]

I get 15-17 in my 74 all stock 250 Saginaw 3 with the stock 373- short stepper. Non-ethanol fuel

[Oregoon]

Originally Posted by greg64

Great post, Oregoon. I've been running chevy sixes for the last 20 years. Both 250 and 292. The 250 got better mileage (shorter stroke), but the 292 has more low speed torque. I'd agree that the manual tranny is a better option. I'm using an SM465, and although I'd love to have an overdrive, I don't do much highway driving these days.

It's too bad the stock head is pretty lousy. There's a million aftermarket aluminum heads for the SBC, but not one for our sixes (well, Brazil has a couple). I'd love to see an LS style cross flow head for the six. Maybe one day.

I know it, cross-flow would really wake one up. I saw an Arias head on a 302 once... Way out of my pay-grade, but man, talk about a gorgeous 6!

Lump-ports are supposed to be a big help for our 250/292 head. I just came across a copy of Leo Santucci's Chevy-Six Power Manual. Fascinating read, for sure!

[greg64]

I've got both the first and second editions of Leo's book. . Some nice looking engines in there. I like the idea of the hybrid head, but it's just too much work (for me).

[Russ_the_truck79]

I have 2wd and I'm unsure of my gear ratio but truck gets around 17 to 20 mpg with 3 on the tree. I would bet that it'd be more efficient (and way cooler)than a v8 but you'd be sacrificing power. speaking from experience my truck has some trouble passing other cars.

[Bigstevex4]

Got an 83 250 sm465 and realy tall gears and slightly taller stock tires.
Got speedo fixed checked it an 50 mi trip to rapid city last week 20.8 down hill tail wind
15.6 up hill head wind. Got rid of var jet and put an old Mono jet on no smog stuff .
Went over to Hullet wyoming sunday strong head wind on I90 maintaining 65 was a chore
Comming back with tail wind could cruze at 85 no proplem.