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Diesel Vs Gas

pma4x4

pma4x4

AKA Yankeeroad
Joined
Sep 10, 2012
Posts
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Location
Apache Junction, Arizona
So which do you think would be a better option

5.7 Tuned Port injection with vortec heads and a very mild roller cam

or a 6BT 12V cummins

current is a 5.7 TBI in a 91 burb
 
For me I plan on someday doing a 12 valve swap more for the simplicity, there's nothing to a mechanical Cummins. Being in CA I lean towards the Cummins mainly for smog, once it's BAR'd as a diesel smog isn't an issue anymore. There is more "fab" involved in a Cummins swap but there are companies that sell everything you need to do the swap and what's not to like about all the power you'll ever need and 20 mpg.

I've also considered a 6.0 LQ9 swap but from what I've heard the mpg is not that impressive.

Hopefully Larry chimes in on the Vortec swap
 
The most logical swap would be the 5.7L.


My vote is for the 5.7
 
here is what i see

5.7 project
get a hold of a donor 350 and rebuilt it
install vortec heads
TPI
wire harness
injectors maybe
Cam
roller lifters
may go roller rockers

Cummins project
find complete donor truck running
motor mounts
flywheel
Bellhousing adapter
re do the front end for the cooler.
intake
different tranny (currently a 700r4)


The cummins will definitely cost more but will net better MPG and more power

the TPI project is easy and all bolt on/in and will cost less then the cummins swap. wont net as big of MPG but if I can gain power while keeping my 15mpg i would be happy.
 
The TPI swap is easy, but it will need to be tuned, and done right (particularly if MAF) it's not necessarily easy. EGR? EVAP? AIR? Then you get into parts, 8 injectors are not necessarily cheap. What about the ~$400 Vortec TPI base?

I vote for the diesel. If economy is significantly better, then you spend less time fueling, and more time wheeling. Even Vortec/TPI off-road economy is still only going to be 10-13MPG (and thats in my rig, which is probably lighter than yours), which is a fair bit of fueling, even with the 31 gallon tank.
 
3 -4 mpg gain isnt worth the time n effort for the cummins:dunno: specialy when diesel is higher than gas at the pump. for the same amount of money I'd go 5.3. same or close mpg gains, more than enough power and still on gas. diesel is my fav dont get me wrong, but I dont think its worth it here
 
Dyeager I am getting 11-15 right now. I want to keep this or better and gain power.

I know the TPI brings more torque in the bottom end so that would help, plus the flow of the vortecs.
 
It helps, that is true. Just adds a bunch of expense and complexity.

I wasn't aware the 6BT got such horrid economy. I was expecting 6.2L numbers. 25MPG freeway is signifcantly higher than you'll get with any gas engine in one of these trucks.

Then again, 3-4MPG on 31 gallons is pretty significant when talking range.
 
dyeager535 said:
It helps, that is true. Just adds a bunch of expense and complexity.

I wasn't aware the 6BT got such horrid economy. I was expecting 6.2L numbers. 25MPG freeway is signifcantly higher than you'll get with any gas engine in one of these trucks.

Then again, 3-4MPG on 31 gallons is pretty significant when talking range.
Click to expand...


No, my 5.7 TBI is getting 11-15. a 6BT is in the 20MPG range.
 
pma4x4 said:
Dyeager I am getting 11-15 right now. I want to keep this or better and gain power.

I know the TPI brings more torque in the bottom end so that would help, plus the flow of the vortecs.
Click to expand...

I get 20 mpg exactly in my '84 K30 with a 1st gen 12 valve at 70 mph on the highway, it would be a bit better at slower speeds.

The swap is fairly involved, having a donor truck is definitely the way to go as clutch/trans linkage, transmission and t-cases all get really expensive behind that engine if you don't get them with a complete truck. And you have details like the intercooler, exhaust, intake plumbing, etc. that add up.

On top of that, your axles are geared too deep for the ideal RPM for mileage. Mine is 4.10's with 37's and it's great for towing, 3.73's would be better for unloaded mileage.
 
From mosesburb's epic thread...click


Quote:
Originally Posted by y5mgisi
So i gotta ask, are you just poking fun at the other burb for needing so much gas or was yours so much more efficient that it was actually annoying to stop for gas that much?

Yes, I am just poking fun at him and yes, we did stop for gas quite often. Being stock, it has the original 20gal tank in it. He gets about 10mpg. That equates to a 200mi MAXIMUM range, wheras I have a 31gal tank and get about 20mpg. That is about a, say, 500mi PRACTICAL range. He would stop for gas and say aren't you going ot top off?? Then I would laugh and say my needle has not come off of full yet. That would usually net me a dirty look or some non-repeatable comment. I topped off when we got back on pavement just for grins, and he filled up for the third or fourth time. I razz him about it now because I still can. We recently put a 41gal tank in his truck so the next run I won't have the ability anymore. I will still have more range, but he will have more gas.
 
Well I've already got the front geared at 4.56 and the original plan was with the 5.7 was with 4.56s and 35s with the 700r4 at lockup comes out to be almost exact rpms as stock maybe a 100 or 2 higher which is fine.

Yeah I kind of forgot about not needing that deep of gears if I go cummins.

Maybe with the gears i got, the ease of swapalogy, known parts and better pricing. Maybe I go TPI Vortec.
 
supersize75k5 said:
For remote driving and exploring..I say tbi, simple, plentiful and cheap.
Click to expand...
thats what i was thinking. do a vortec roller cam engine, with the tbi. you already upgraded and renewed the tbi setup, why not use it on the new vortec setup. wham bam, easy peasy.
 
I say gas motor this time.

If your not going to use it for towing and such then you don't "need" the diesel.

The diesel will get better mileage have more power but the overall cost is way more than the gas motor stuff.

I doubt I would swap a cummins in just about anything I didn't plan on doing a lot of towing with.
 
one thing i noticed when i wheeled my cummins, when its at low rpm peak torque situations when you get the 20-22mpg.
when your in 4x4 using the grunt and spinning up over 2ks, your mileage doesnt really stay that good. where gas will go 15 highway, and 10 wheeling, my diesel would go 20-22 highway, 7-8 wheeling.
ymmv.
for the record that was in a 6 speed truck doing mostly sand on 35s.
 
Hey thanks guys, this was a really quick thread that helped me make my decision. I will be staying gas and going to vortec.

I am actually already waiting for a response back on a possible trade. a guy has a full TPI setup with ECM and vortec heads.
 
How much expo stuff are you planning on doing? Ever going to leave the country? If so, I'd lean toward diesel for the availability (thought gas may be plentiful south of the border, too, I don't know). And the extra mpg would extend your range a bit, which may or may not be important depending on where exactly you want to go.
 
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