Since it doesn't look like I'll ever get a gasoline sponsorship and would like to drive my Jimmy more thinking of putting in a 6.2. When I had a m1008 it would always get around 15 mpg. My Jimmy is at 7.5 no matter what. Jimmy is a 77 , could get a 6.2 to work?
CK5
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400 sbc to 6.2 diesel
- Thread starter 77_Jimmy
- Start date
I'd say you could move to more modern running gear and have similar fuel economy to a 6.2 diesel.
I ran a 5.3/700r4 combo in my '91 for 5 years, the first two years I didn't have the camper, the last three I did. For comparison purposes, I'll give you the details prior to tossing the camper on the back of the Blazer. I'm running 4.10 gears and tires that are just under 35" tall. With that combo, the mileage average was in the high twelves to low thirteens. I had tanks that were higher and some lower. Could the average get bumped higher? Sure, less tire and or less gear would help.
Just about anything you do is going to get better fuel economy than a carb'd 400 small block and direct drive transmission. How much you want to gain is going to be up to how much you want to spend. Dumping the direct drive trans for an OD unit is going to net you a good chunk of mileage when combined with a reasonable tire and gear ratio. Tossing the carb for an aftermarket fuel injection system will add more. But you are going to not be measuring double-digit gains. You still are driving the aerodynamic equal to a barn door. It's only going to be so good.
I have tracked every tank of fuel in mine. I'm nuts this way. But even with the modern fuel injection over the 5 years without the camper and with it I've seen as low as 6 mpg and as high as 20 mpg. Highway, semi-DD duty, off-road, flat ground, and mountains. My point is you have to be realistic on the idea of getting significantly better fuel economy in a 5000+ pound brick-shaped solid-axle 4wd truck. Major changes to LS power or 6.2 diesel is going to require refitting the entire fuel system at great cost. That cost would take years of driving to recoup.
I ran a 5.3/700r4 combo in my '91 for 5 years, the first two years I didn't have the camper, the last three I did. For comparison purposes, I'll give you the details prior to tossing the camper on the back of the Blazer. I'm running 4.10 gears and tires that are just under 35" tall. With that combo, the mileage average was in the high twelves to low thirteens. I had tanks that were higher and some lower. Could the average get bumped higher? Sure, less tire and or less gear would help.
Just about anything you do is going to get better fuel economy than a carb'd 400 small block and direct drive transmission. How much you want to gain is going to be up to how much you want to spend. Dumping the direct drive trans for an OD unit is going to net you a good chunk of mileage when combined with a reasonable tire and gear ratio. Tossing the carb for an aftermarket fuel injection system will add more. But you are going to not be measuring double-digit gains. You still are driving the aerodynamic equal to a barn door. It's only going to be so good.
I have tracked every tank of fuel in mine. I'm nuts this way. But even with the modern fuel injection over the 5 years without the camper and with it I've seen as low as 6 mpg and as high as 20 mpg. Highway, semi-DD duty, off-road, flat ground, and mountains. My point is you have to be realistic on the idea of getting significantly better fuel economy in a 5000+ pound brick-shaped solid-axle 4wd truck. Major changes to LS power or 6.2 diesel is going to require refitting the entire fuel system at great cost. That cost would take years of driving to recoup.
For the OP.
Not to be a dick, but I think square body trucks/blazers are for fun and not great for daily’s or long trips.
Just my opinion.
Not to be a dick, but I think square body trucks/blazers are for fun and not great for daily’s or long trips.
Just my opinion.
beags86
Eastbound and Down
Do we care what your opinion is dean?! Lol jk!
To the original poster. A couple quick thoughts.
A 6.2 is a slug of an engine. If your looking for a fuel mileage look for at the 2.8 crate engine Cummins.
Second thought.....
The cost of swapping. Wheather it's a stock 6.2 or a 8000 dollar crate engine. Plus the fact that diesel is typically a few cents more at the pump. How much do you drive it to pay for that return?
How much do you drive your truck?
3rd thought, if your only getting 7.5 something is probably wrong. Your tune up isn't right. Or possibly your engine isn't even healthy. Have you checked the compression on that thing?
Never checked compression. I do plugs etc once a year. It runs fine. I put about 10k miles a year on it. Its probably ready for a new engine. Not looking to change the transmission , phoenix transmission built me a th 350 a few years ago , works great. I can get a 6.2 from Boyce equipment for 2200 bucks. I had a m1008 with 6 inches of lift and 37's and it got 15 mpg all day long. The m1008 felt same as for as performance goes.
What gears do you have? What size tires? Either of these engines will need OD or slug gears to get good MPG. If you could actually get 15MPG with a 6.2, at 10k miles a year = $1k savings, or 3+ years to break even.
However, a 6.2 swap isn't a magic transport to the world of high MPG. Basically it gives up to 50% better than your SBC. Since just an engine swap will leave the rest of the setup in place, don't hope for more than 11MPG from a setup currently giving 7.5 (and now it takes 10 years to break even on fuel cost). Might be better to start with a trans swap and engine tuning.
However, a 6.2 swap isn't a magic transport to the world of high MPG. Basically it gives up to 50% better than your SBC. Since just an engine swap will leave the rest of the setup in place, don't hope for more than 11MPG from a setup currently giving 7.5 (and now it takes 10 years to break even on fuel cost). Might be better to start with a trans swap and engine tuning.
My 6.2 on my M1008 with 37's SUCKS on power going up the passes. But I'm also 6000' in elevation. Honestly I'd rather have a SBC or LS. A turbo would greatly help though. It would be easy to convert it. You must have no emissions where you live. Here in Denver that would be a nope. Something else to consider if you were to ever sell it, it would be harder to sell with a 6.2.
I own two 6.2's and say stick with gasoline!..
Neither of my trucks,a '82 K2500 and an '85 K10 burb,never got more than 16 mpg in any type of driving--doesn't seem to matter if your going 65 mph on a highway or putting around town at 30-45 mph,it stays the same..
Those who claim higher mpg figures are either lying,lucky,or driving a light 2wd 1/2 ton very gently ...
Since the 6.2's are known hard starters in the cold unless you have brand new batteries,glow plugs and a "perfect" fuel system,and diesel costs 50 cents a gallon more here than gas,I'd pass on ever owning another one..
Many parts are getting scarce,are "one of a kind" and not available new any more,and the fact their crankshafts have a nasty habit of fracturing with little or no warning,I'd much prefer a good old school 350,which I've owned many of,got up to15 mpg with,and didn't need to waste money on new starters,glow plugs (that often wont come out easily,if at all),and having to "plug it in" in the cold weather..they always started up..
I'm not a complete diesel hater,but I'd spend money on some other diesel over a 6.2...they just weren't that great..
I know a guy with a pickup like mine,that swapped a 7.3 Ford/IHC diesel and automatic into it and he loves it..but it cost him more to do the swap than buying a Ford with one would have..their are many "better" choices of diesels if you must have one..
The only reason 6.2's stuck around this long is the military used them and still have some variants of them ..otherwise they are an obsolete platform IMO..that and the fact they have no computer control,on the fuel injection,its all mechanical,and they bolt in where any gas V8 would fit ..
In the long run buying twice as much gas to run the 400 SB would likely cost less than swapping a 6.2 in the truck ..diesel fuel went up 50 cents here in the past month and gas is still $2.29 a gallon..
Neither of my trucks,a '82 K2500 and an '85 K10 burb,never got more than 16 mpg in any type of driving--doesn't seem to matter if your going 65 mph on a highway or putting around town at 30-45 mph,it stays the same..
Those who claim higher mpg figures are either lying,lucky,or driving a light 2wd 1/2 ton very gently ...
Since the 6.2's are known hard starters in the cold unless you have brand new batteries,glow plugs and a "perfect" fuel system,and diesel costs 50 cents a gallon more here than gas,I'd pass on ever owning another one..
Many parts are getting scarce,are "one of a kind" and not available new any more,and the fact their crankshafts have a nasty habit of fracturing with little or no warning,I'd much prefer a good old school 350,which I've owned many of,got up to15 mpg with,and didn't need to waste money on new starters,glow plugs (that often wont come out easily,if at all),and having to "plug it in" in the cold weather..they always started up..
I'm not a complete diesel hater,but I'd spend money on some other diesel over a 6.2...they just weren't that great..
I know a guy with a pickup like mine,that swapped a 7.3 Ford/IHC diesel and automatic into it and he loves it..but it cost him more to do the swap than buying a Ford with one would have..their are many "better" choices of diesels if you must have one..
The only reason 6.2's stuck around this long is the military used them and still have some variants of them ..otherwise they are an obsolete platform IMO..that and the fact they have no computer control,on the fuel injection,its all mechanical,and they bolt in where any gas V8 would fit ..
In the long run buying twice as much gas to run the 400 SB would likely cost less than swapping a 6.2 in the truck ..diesel fuel went up 50 cents here in the past month and gas is still $2.29 a gallon..
How will we recognize you on CK5 after you change your username?
You have TH-350? Did you correct the speedometer? MPG calculations could be off. Somebody should definitely tune the carb and curve the distributor, but overdrive is probably the biggest single thing you could do. I'm not encouraging you to do the diesel swap, but it wouldn't be happy cruising at 70MPH @ 3000RPM.
Is this a Quadrajet? How fast do you usually drive and what else are you doing with the truck?
Yeah th350. Correct on quadrajet. Fastest speed for any length of time such as interstate driving, 75 mph. I've had it for 12 years stock with full-time 203 and lifted with a 205. Has a 31 gallon tank. Always have to start looking for a gas stion around 200 mile mark. I go off of gps not the speedo.
Maybe I'll just switch it to "No More Diesel4Me"...
Fact is no square body will ever get much over 15-20 mpg regardless of what engine or fuel your using...they are heavy trucks,3 tons usually,and physics cant be changed--the high wind resistance,rolling resistance with tall wide tires,all adds up to "poor" mileage..
I've had trucks that came with 36" or taller tires and was lucky to get 10 mpg..
After I put stock rims and tires back on them,I gained nearly 5 mpg..and the engine wasn't lugging all the time ..3:08 gears and big tires suck down fuel and fry transmissions..
I've had a few 454's in square body trucks,one in a '74 C-10 with a 450 cfm Holley economaster carb often got about 15 mpg in mixed driving..
The 350's I had were a bit worse,but they had Q-jets or Carter AFB carbs and were working harder to propel the trucks,and I "booted" in the secondaries too often...often a bigger engine combined with highway gearing and normal sized tires will get better mpg loafing along near idle,than a smaller engine straining to tug it around..
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At 75 mph the engine is spinning almost 3000 rpms with your specs. A 700r4 would drop that 1000 rpms at the same speed.
If you don't change anything else, that's where the biggest change in fuel economy is going to come. Next is the state of tune to the engine/carb. Getting the engine to spin less at the same speed is going to keep the secondaries from getting pulled into play just to maintain speed. It's going to require some adjustments but the q-jet is probably the most fuel efficient carb you can have on it.
I would first use that money to buy a 700R4, you will get more bang for your buck with an overdrive instead of swapping engines. secondly look into adding fuel injection to your 400, its a lot cheaper than all the nickel and dime stuff needed for an engine swap.
2x on the overdrive trans. Either engine. And the diesel will want low rpms.
400sb/700r4/4:88/38s with FAST efi got me 11.5mpg with the one long drive I had it on. GPS and math
400sb/700r4/4:88/38s with FAST efi got me 11.5mpg with the one long drive I had it on. GPS and math
