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400 sbc to 6.2 diesel

77_Jimmy said:
Let's look at this differently. You have a empty engine bay , you wanna keep the price at 3k. Mpg take priority over performance. What engine?
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Starting from scratch? A 6.2 will fit that application. Starting with a 3000RPM cruising speed? That's a definite 'no.' Keep the 6.2 below 1800RPM at cruise if you're looking for mileage.

A 6.2 can be a very cheap and easy engine swap, especially if you find a $500 donor rig. But $500 5.3 rigs are out there, and you might find one of them is just as good a platform for your intended purpose. That engine would be much happier with your gearing.

But, most importantly, look into overdrive and/or axle gearing. None of the engines you mention will cruise efficiently at 3000RPM.
 
diesel4me said:
Fact is no square body will ever get much over 15-20 mpg regardless of what engine or fuel your using...
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You're correct that it's never going to have the efficiency of a Saturn, but I'll challenge your statement about 20MPG. I've had 3 squarebody rigs that beat 20MPG. It's possible, when the rig is built properly.

I'm not saying most folks want 3.08 gears with overdrive and small tires, but the combination did its job...
 
My dead stock 83 C1500, 6.2, 700R-4, 3.42's and 235/75 all seasons regularly returned 21-23 mpg with a high of over 25 a few times. That is not cruising at 75 mph though. Steady cruise at 65...

I've done the swap you are asking about, for the same reasons, with my 81 Jimmy. At the time I did it nobody had even heard of an LS swap though. I also did this swap when 6.2's and 6.2 parts were cheap and plentiful. As an example I got a rebuilt injection pump for under $300 at the time.

For the solution to the same problem today I would go 5.3/4L60/65/70E and never look back.
 
I have a 77 GMC Jimmy with 35s and 3.73 gears, TH350 and a fresh 400 (CA smog legal at that). Engine was rebuilt with everything for torque and an operating range below 3000 rpm. I don't check my mileage very often, last time I did I got 10.5 and I was fully loaded (7000lbs give or take) and was heading into the hills west of me and I was not easy on the throttle. Next time I will be more exact and use gps. I drive mine everyday just not very far.

7.5 mpg seems a bit low. I would look at engine rpm of both gas and diesel with your gearing and tires and see what you come up with. What's the max rpm of a 6.2? What I'm saying, is would you be able to go 75mph on the freeway with a diesel with those gears and transmission?

Joel
norcal
 
campfire said:
Governor starts kicking in at 3600RPM. Mine will reach 4000RPM (barely), but will not exceed that.

It's much happier below 2500RPM. 1600-1800RPM makes for good cruising.
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A big big plus in a 6.2 with a mechanical injection pump is you can run just about any kind of diesel/oil combination as long as its well filtered and water free. I had a Ford 7.3 that just loved transmission fluid mixed with whatever diesel I ran through it. Smoothed everything out, quieted the valve train down, more power...

Joel
norcal
 
And you can drive forever with no alternator - as long as you don't need headlights...
 
campfire said:
Governor starts kicking in at 3600RPM. Mine will reach 4000RPM (barely), but will not exceed that.

It's much happier below 2500RPM. 1600-1800RPM makes for good cruising.
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I agree with this. I think the best fuel economy is achieved when the cruising speed is 1600-1800.
 
Blue85 said:
And you can drive forever with no alternator - as long as you don't need headlights...
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Been there, done that. I wasn't the one driving, but we stopped after 200 miles and found the battery wasn't charged enough to crank the truck over. But it never missed a beat while running. Electricity is optional aside from the fuel shutoff solenoid.
 
I'd be unwilling to run anything but treated diesel fuel in my 6.2 in the winter....its hard enough to get started with that in it..
I added a quart of SAE 30 oil to the full fuel tank once about a year ago and the temps dipped below freezing,and it started hard,I was lucky not to kill the batteries trying to get it "lit"...

It will "usually" start down to about 20 degrees without being plugged in with only diesel ,but it doesn't like too..it requires two fully charged batteries (newer is better) and just the right combination of throttle and glow plug juggling to get it to go..

Had to plow my driveway the other day ,I waited till noon when it was supposed to be near 30 ,instead of 12 at 7 am...it did fire up ,reluctantly...as a side note,if your thermostat decides to stick or fail in the open position as I suspect mine has--I learned you'll get just about ZERO heat from the heater,the dash gauge wont even budge off 100 until I drove 5 miles with the plow on it,it finally hit about 130 degrees after that..sucks plowing with no defroster heat..
Diesels be cold blooded...:(
 
I have a 6.2 in front of a 700R4 and 4.10 gears with 35" tires.

That puts me right in the sweet spot for highway cruising: 1800RPM at 65MPH, 2000RPM at 75MPH.

Works great, mileage is about 17 on the highway (truck has a 4" lift). Oh, it does have a turbo which helps a lot.
 
diesel4me said:
I'd be unwilling to run anything but treated diesel fuel in my 6.2 in the winter....its hard enough to get started with that in it..
I added a quart of SAE 30 oil to the full fuel tank once about a year ago and the temps dipped below freezing,and it started hard,I was lucky not to kill the batteries trying to get it "lit"...

It will "usually" start down to about 20 degrees without being plugged in with only diesel ,but it doesn't like too..it requires two fully charged batteries (newer is better) and just the right combination of throttle and glow plug juggling to get it to go..

Had to plow my driveway the other day ,I waited till noon when it was supposed to be near 30 ,instead of 12 at 7 am...it did fire up ,reluctantly...as a side note,if your thermostat decides to stick or fail in the open position as I suspect mine has--I learned you'll get just about ZERO heat from the heater,the dash gauge wont even budge off 100 until I drove 5 miles with the plow on it,it finally hit about 130 degrees after that..sucks plowing with no defroster heat..
Diesels be cold blooded...:(
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It doesn't get quite that cold here in Norcal, at least in the valley. That 7.3 I had was a cranky bastard and me it never quite jived. I had a choice, to either fix it, or fix the Jimmy. GM wins again...

Joel
norcal
 
I live in Indiana, not unusual for it to get to 0F in Jan/Feb and I don't have any issues starting my 6.2 or the wife's 6.5 Burb. It takes everything being in good shape, strong batts, all 8 glow plugs good, winter fuel, both have extended glow plug mods and I usually have 5w-40 oil in both.

The wife's Burb starting at 0F would frighten your average none car guy, sounds like somebody dumping a 5-gal bucket of ball bearings down the intake, I love it.

I've have GM diesels for two decades and with a slight learning curve they are good reliable half decent engines that can deliver good fuel economy if your not in a huge hurry.
 
I just pray I'm never in a situation where I need to move the truck "immediately" or go somewhere right away,outrun a threatening person,etc,because your chances of getting my 6.2 started even with everything in as good a condition as it'll ever get is still "iffy" and any diesel requires at least a minute or more of "warm up" before you put a load on it..

A gas engine can usually be fired up and driven away almost instantly ,though its not very good for it...as long as the choke works right (or better yet you have a manual choke)..

Many fire trucks and ambulances usually dont accumulate a lot of miles,but all those stone cold starts to wide open take offs in a matter of 20 seconds does accelerate engine wear dramatically..

Sometimes they get started and left idling for hours a day to avoid dead cold starts and the increased potential of a no start condition..
Idling does engines no justice either,especially diesels..
 
I've owned a '90 K5 with a 6.2/700r4/3.73 gears/32" tire combo since 1994 when it had 49,000 miles on the clicker. Always thought it was a decent daily driver and consistently got mid to high teens MPG even running it hard all the time. Granted I live in the midwest with no moutain passes and lower elevation but it never had any issues on the freeway running 70+mph. If I was in the mountains and dealt with higher elevations I would probabably feel different. The 6.2 is very simple and you should be able to find one pretty cheap. I think a 700r4 trans is almost mandatory for this engine for both the lower first gear and overdrive.

In my opinion a lot of the bad rep comes from people not understanding diesels at the time when they came out, and many of the early trucks had stupid high axle gears. Anybody remember driving a mid-80's K10 with a 305 and 2.73 gears when they were new! I remember back in the 90's I did a decent amount of trouble-shooting for other people on the 6.2's and most of the time it was just very simple maintenance, or lack of maintenance, that was going on. Low on power.....when was the last time you changed the fuel and air filter? Mine was very finicky about both, and diesel fuel for passenger vehicles wasn't nearly as common so it sat in tanks for a long time. Always carried a spare fuel filter with me because several times I got fuel while out of town at a small place and it started running like crap shortly after. Then it was the starting issues......when was the last time you replaced the glow plugs and made sure they worked? They are also picky about having good batteries.
 
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