Engine swap/what mileage do you get??

Hey guys, I am contemplating an engine swap. It wasn't planned but the situation has arose to where I may.
First off, I would REALLY like to know what kind of mileage you get with what set up.
I put a fresh built 292, 700r4 and it had a 4.11 rear, in my '64.
My mileage might be around 12. Sucks and that is why I don't drive it as much as I want.
Now the swap idea.
I have a low mileage VW TDI engine available to me. A buddy did a TDI swap in a full size '70 Ford truck. Loves it. He says it's a great driver with plenty of power. He claims 34 mpg. I'd be tickled with 20+. I understand it is kind of a common swap for different cars.
I believe a '70 ford truck would weigh more than my van but our vans are like pushing a barn door down the highway.
So, what kinda mileage do you get with what combination and what do you think about the swap?

It's the rear gears that are hindering the mileage...... 336 or 323 is what you should be using with a 292/700r4.......Many of the 91 whale wagons had a 323 posi that is perfect width for these vans.....
Not a chance I will ever be installing ANY four cylinder in mine, but certainly not something from an import.....

I think the 700r4 helps offset the rear gear a bit but, I am interested in what you mean by '91 whale wagon? Station wagon? 1991? Do you know of other rears that work?
I would definitely be interested in a rear swap as mine is also whining.
I am not happy about a smaller engine let alone foreign but my ultimate distaste in all this is diesel. I am no fan of diesels but, a van like ours, which I would prefer to be my daily driver, getting at least high 20's fuel mileage would make the "sting" a little easier to bear. Hell, I would actually plan vacations around the van but, I would need something close to 20+ to do that with a gas engine.
Thanks!!!

91-96 GM wagons are know by their tribe as Whale wagons because of their profile.....
Chevy, Buick and Olds wagons all had a 305/700r4 combination in 91 and most of those had a 323 posi.......For 92 & 93 a 350 was optional and likely had different gearing.....
The RPO/SPID sticker is in the tailgate jamb on the right side in these wagons and you'd be looking for GU5 and G80 for a 323 posi

Awesome!!!!!!!!!!!!!!!!!!! thanks!!

I used a 91 wagon posi in mine and there are a couple of other things I should share.....
The wagons are triangulated four link on coils, so you'll be removing unwanted bracketry and welding on some leaf pads and lower shock mounts..... The wagons also have much bigger brakes (wasn't an issue) and they are 5on5 lug pattern....
And a different e-brake setup...

Dang, I was already looking for one on car-parts.com after your last post but, the 5 on 5 shoots it down for me. I have my wheels and do not want to change. Bummer.
All the other stuff was no big deal. (I have a fab shop.) I might have even looked at making the 4 link work.
Well, I guess I will have to try to find a different rear. Since this one whines, maybe I'll just change gears when I have it worked on. (???)
Thanks a BUNCH dude!!!! I totally appreciate ALL the help!!! Now, I have to get back to the body work......

A friend of mine used a wheel spacer as a drilling jig to re-drill his lug pattern on his vehicle.....There are lug pattern re-drill jig kits that work essentially the same way, but have a drill bit guide tube to hold the bit straight....
I did mine before I'd learned of this method, so I had the lug nut holes in my wheels slotted by a machine shop and had hub-centric spacers made for my wheels, but would do the re-drill of the axles and drums If I could do it over....

just read the 1st or 1st 2 posts...
no, its more than rear gear.
It’s tire sz, (transfer if 4 WD), tranmis. This = “final drive' ratio.
Here you have more to ‘play with’ to get your results. As can B seen this
allows less expensive ways (Less labor)to get what U seek. But even better
than putting out the labor or money to experiment U can use one of the on-line
‘gear caculators’ or look up final drive and do it asa caculation. Good luck.
( Seperate note: I’d never do an ‘off model’ engine swap. Transmis? x-fer? yes x2 )

More power? ford’s other i6s from the Thriftpower line 250/4.1 is plenty. They hada 240
and 300/4.9 that are "the gasser that’s a diesel” very durable/long lasting (known thru out the automotive industry) in this gen. MPGs? good luck there too, U gota 4850 pounder there. 12v? allison? aahahaha

My answer to the thread question is ..... Less.

I went from a 360 to a 408 in my A100.....gas mileage is worse, but it's more fun at the same time.

I bought mine already converted to a 360, so it wasn't my fault....lol

Mileage should be the least of your worries.. LS swap is no joke, as I have learned but well worth it. Don't cut any corners. Good luck!

the 250 (or close) i6 was plenty for me to live in/gain a nice income
in my 108. I hada bed I pulled out the back doors when time to really
load or other reason. Mostly moving projects. Longest distance (5, 6 hrs,
300 mi) Marthas Vinyard to Burlington VT ( a couple & their lill dog,
ina blinding sno storm, w/bald summer tires). This one went well, like all
others. Boxes stacked in back like brick wall against brick wall, the
‘wife’ sitting on the engine cover, the weight holding us on the rd better
than manya driver we passed (still pretty slippery!) Ahhh, the things a
young man ‘ill do~