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Building for MPG?

Crankme69

Crankme69

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With today's fuel prices what would be the most economical engine to consider in my 1500?

Not looking for something that can not pull a dick out of a lard pale but something that you could hook up to the car hauler (BE PATIENT when pulling it maybe 6K #'s) and still be able to pull down 20+mpg with when unloaded.

My old NA 7.3 had hiway gearing, at 65mph it would run a tad over 1600rpms. It had decent power (not a power house by any stretch of the imagination) but it got the job done. Maybe this is the solution, big cubes with no turbo?

So is no turbo the answer or turbo with low to no boost unless loaded more logical & flexible?

My neighbor has ole 91 6.2 & I have drove it, man is that thing SLOooooow. He does get very good milage, maybe that is the answer? We have towed 6K pounds with it, albeit you can not be in any hurry & also not for any extended distance but it will do it for a short run...

Just throwing ideas around & hoping for some of your thoughts & feedback.

I have no horse in the race & am not set on doing anything here at present, at least not until the time comes for my 217K mile motor to need replacing. Hoping that won't be for another 217K but who knows...:???:
 
It's really a matter of gearing, fueling and displacement.

Taller gears + "leaner" fueling + smaller displacement = better MPG (driving style is really the biggest factor though).

Of course, too much to the extremes and you end up with a real "dog".

As a rough guess I'd say something that drives decent, pulls a decent load and gets 20 mpg ish is doing pretty good. My 98 is 2/3 the way there......:grumble:

4BT engines are reported to get somewhere around 32-ish mpg when in a reg cab shortbox 2wd. A couple 'burban guys claim the same from a 4bt.

There's a couple vids on youtube about 4bt GMT400 combos.

The 4BT is not what you would call "smooth" or "quiet". They can post some pretty good HP number for a 4 cyl diesel, although MPG will start to drop off again.

I don't care what they have written on the sign out front, there is no free lunch....:(
 
i always wonder what a built 6.5 running like 24:1 comp ratio with 6 psi of boost would do mpg wise. i bet it would be pretty dam good
 
I had a 91 k2500ld 6.2 N/A regular cab 3.70 gears and 700r4 tranny. It could knock down as good as 28mpg on a interstate run. It had a banks exhaust system,new injectors and ip turned up 1/4 turn. It struggled pulling 9000. I can't seem to break 20mpg with a 6.5.
Injectors for a 6.2 and small prechambers may increase mpg.
 
I've heard those Toyota diesels in the land cruisers are prettty awesome. Especially that 4cyl that was in the older wagons(30+mpg). I was looking at those HDJ-81 imports from Japan that came with the straight 6 diesel before getting my truck. I believe they were pulling 25-30mpg from them, and that's with a turbo and full time 4x4. That straight 6 would be pretty sweet in our trucks I'd think.
 
Where is the cash benefit for the increased MPG's: Towing or unloaded?

Now how many miles are you going to travel in a year or 30 days?
Figure current MPG then refigure MPG improved by 1 MPG. Use $3.00 a gal for diesel or current price - your choice.
Then you can see when the MPG improvement will pay you back.
FWIW 1 MPG when you are getting 20 MPG is "So what?" 5%. However 1 MPG when you are getting 7.5 MPG (over 10% improvement) towing is the difference between making money or not.

I figured one point in 2009: at 9MPG and 550 miles a day a 1MPG improvement would pay $500.00 in 45 calender days working 5 days a week.

The cash outlay to improve MPG may not make sense depending on the number of miles you are going to travel esp. if this is personal use. For profit - still how many miles? For the above 550 miles a day it would make a lot of sense.

Towing MPG is by getting the restrictive turbo out of the way. Assuming exhaust and intake have been improved as well. The more these engines are loaded the worse their economy gets. I feel the turbo causes this at anything over ~2200 RPM. My DB2 reaching it's fuel limit may also cause this feel.

Unloaded you will want smaller precups, higher compression, better breathing. The 6.2 engines make their economy by high compression and small precup openings. Then they added a turbo and doubled the HP. The exhaust valve was also made smaller over the 6.2 heads.

Yes the 6.2 could hardly get out of it's own way on a hill smoking like a freight train desperate for more air via a turbo. Adding a trailer to the 6.5 turbo is still a orange triangle event for some hills.
 
I would like to see what the engine and transmission out of my International would do.

I would think with that 6 speed and the proper rear end you could arrive at a very satisfying power/economy solution
 
I would think the scenario the OP decribed would be an ideal canidate for the vacuum controlled wastegate (with the right program) low to no boost for no load running around. And then more boost for occasional loads. That coupled with the small precups should help
 
A-Team maybe? Sounds like SOME people see increases in mpg unloaded but I would think loaded might be where the mileage could be increased.

Vacuum controled tunes seem good to me so far. I have had my 6 stage in for abit over a week but havent had a chance to check mileage as I have hardly left the pasture and when I do I hit racing tune taking off :cool: . I dont have a boost guage and my lap top hasn't been working too well so I havent been able to check the boost at cruising speed. Dont worry I wont be running too hard until I can get guages. It generally will stay in one of my econ settings.
 
I do not understand why someone would want lower boost for economy purposes... a diesel does not need to add fuel to boost. If you are at X fuel rate, the more air you pump in the cylinder the more efficient that fuel is going to combust.
 
turbo is a restriction in the exhaust
Click to expand...

That is why ATT[being a non-wastegated turbo] gives a little boost in economy, pun intenged. I also saw two to three mpg. better when I bought my truck and it wasn't boosting properly, due to bad vac lines. After putting a TM on I went from 21/22 to 18/19 mpg. But I also lost the black smoke and got some power back.

In theory then, twin turbos properly sized should give you both more power, less back pressure, and even better fuel economy?

If I could get 25/28 mpg. with a twin turbo setup under regular driving, and 20/21 under moderate/heavy towing, I would be willing to build it and share the build on the board if there was some way to prove that this is feasible.

I know T/T are not new, just that all the feedback has been about how much power they make, and not one mention of fuel economy that I can find.

I'm no engineering grad. and don't know how to put this theory on paper to see if it is possible, heck if I searched the net long enough I might even find the data to point me in the right direction.

I would love to build it as I plan on keeping my burb forever, and get a bigger camper down the road someday.

Sorry for the rant , I was dreaming out loud.
 
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Your apology is accepted but certainly not required here on this post. ;)

Thoughts dreams & experiences along with theories is exactly what this post was intended for...everything started out as a dream that someday become reality…right?
 
I do have one thought on lowering back pressure that I'm going to experiment with on my current setup. I will be putting a D/E exh. on next month, and closing the waste gate on the gm8 that I'm currently running, and installing an electronic header dump in the cross over pipe and plumbing it into the exhaust/bypassing the turbo to reduce exhaust back pressure yet maintain boost at 2500 rpm and above.

Leave it closed at low load/rpm and open it at high load/rpm and if it works I could tie it in to a controller to do this at preset boost or IAT levels.

It has a potentiameter switch that allows you to open it as little or as much as desired.

Kinda like a poor mans ATT. I want to see if I can maintain the high boost levels with one bank taken out of the equation, and still have fast spool up/and boost up at lower rpms, and keep the high boost and lower the backpressue/IATS at higher loads/rpms.

Let me know if you think I'm crazy or if that sounds plausible. Doing this with WMI will help with my towing this summer I hope.

Once again thinking out loud, would like to hear other voices besides the ones in my head.
 
robzombie4551 said:
I do have one thought on lowering back pressure that I'm going to experiment with on my current setup. I will be putting a D/E exh. on next month, and closing the waste gate on the gm8 that I'm currently running, and installing an electronic header dump in the cross over pipe and plumbing it into the exhaust/bypassing the turbo to reduce exhaust back pressure yet maintain boost at 2500 rpm and above.

Leave it closed at low load/rpm and open it at high load/rpm and if it works I could tie it in to a controller to do this at preset boost or IAT levels.

It has a potentiameter switch that allows you to open it as little or as much as desired.

Kinda like a poor mans ATT. I want to see if I can maintain the high boost levels with one bank taken out of the equation, and still have fast spool up/and boost up at lower rpms, and keep the high boost and lower the backpressue/IATS at higher loads/rpms.

Let me know if you think I'm crazy or if that sounds plausible. Doing this with WMI will help with my towing this summer I hope.

Once again thinking out loud, would like to hear other voices besides the ones in my head.
Click to expand...

Unequal backpressure sounds like the perfect reciepe for a 2 piece crankshaft to me.
A supercharger with a electric clutch and bypass valve sounds like a better idea.
 
How is that unequal backpressure. Just less as far as I can tell. EDUMACATE PLEASE.

I think I understand now. More stress on pass. side as it is bolted directly to the turbo.

But if the restriction is reduced by redirecting some exh. pressure from driver side, wouldn't that also lessen the pressure on the pass. side, by having the pass. side do all or most of the work. I assume there would be a flow difference, but enough to break a crank?
 
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2100-2200 RPM is the sweet spot on these engines that I have seen, DB2's. This may be the peak torque. I found this by the small hills here with a trailer being as fast as she would go before loosing some power. Shifting to 3rd with the TCC locked would not generate any more speed with the higher RPM's. Turbo exhaust choke or whatever.

Point is with 4.10's this is about 62 MPH. This body style and newer ones tend to use fuel at a faster rate over 65 MPH. So limiting your speed unloaded to the slow lane in a 75 MPH zone may be the best MPG improvement. Time is money and CDL logs/daily hour limits may not give you this option to go slow and run yourself out of hours. Trailer tires are rated for 65 MPH max anyway.

If you have the power, lower gears can be ok. Otherwise if you are in 3rd all the time you need to move the engine's peak torque to the lower RPM or gear the engine to rev higher to it's peak torque with 4.10's. You could up the engine's power (TQ and HP) to maintain speed with the higher gears.

Upping the boost and fuel over factory settings got me the same loaded MPG but better top speed. Just turning the fuel up alone got smoke and less MPG. Others have noticed a MPG penalty for higher boost when they are unloaded. This is why the GMx is seen as so limited.
 
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