It takes the SAME amount of horsepower to push you down the road... regardless of whether it comes from a V6 or V8. The efficiency of the engine at that given horsepower should determine your fuel mileage... assuming correct fuel/air mixture.

Smaller engines have to work much harder to push larger vehicles. When properly tuned and geared, the 4.3 is an excellent match to the stock Astro. My last 2000 Astro cargo got 17mpg towing a motorcycle... and others will probably boast even better figures. But modify or load down the vehicle, and those numbers seem to start suffering quickly. My current 2000 AWD gets about 12mpg avg with larger tires and mismatched stock gear.

A V8 properly equipped with mild cam, intake, and headers can get quite good fuel mileage... and may actually excel over a smaller engine when pushing or pulling an extra load.

I have a V8-350 that has gotten as much as 18mpg, with carburetor. Fuel injection will likely improve those numbers.

There are a lot of smaller V8's, with intention of obtaining better efficiency. The 350 is probably the best all around candidate for an upgrade... as well as being the most common and most popular. If your going to upgrade, make it worth the trouble!

If your purpose of switching from a V6 to V8 is for better economy, then you probably won't achieve much. But if your V6 is struggling, then a V8 will be a great solution!

My 92's stock 4.3 went 282,000 amazing miles! It developed a knock and is now being replaced with a high-performance 350. The V6 coming out was worn, and getting about 10-12mpg.

I'm certain the V8 will be an improvement all the way around!

 

I'm getting 16.5mpg at best out of my 5.7 vortec, but I've heard that the 5.3 can get some decent mileage. My Mother in Law had a silverado single cab 2wd with the 5.3 and would get slightly above 20mpg with it. It's a matter of what fits and can be serviced without having to take the doghouse off every time you want to check the oil.

 

While not as easy to retrofit and not as cheap to purchase, an engine with variable displacement(active fuel management) would be your best bet for improved MPG as they can shut down some cylinders as they are not needed.

 

I get 19-20 mpg with my 99 aluminum blocked 5.7/350 V8 wit an overdrive tranny in my 98 Astro. roughly 350 hp and turning 33x22 rear tires with ease

 

WOW, was that hard to put in ?

 

No, guy who did it, "said piece of cake & planned on doing it 20 more times. Thank you again Stan for doing the work of installing the motor & tranny, selling it to me so I could finishing building the masterpiece that it is now.

 

I'm going to be in the extreme minority, but I could understand a 305 being installed. I know its a ton of work for minimal gain on size. But the sound of a v8 with excellent mpg could be possible. My reason for stating this is my 86 Chevy caprice had a 305 w an automatic and 3.08 gears in the rear. That car got around 25-27 on the highway and no mufflers. It sounded great. I pulled a 17 ft fiberglass boat regually w it. All that being said, its a lot of work for a 305. Just a thought that I've pondered in my brain. (I know the caprice is a big car, but I'm not sure how the weight compares to an astro).

 

It bears mentioning that what you do to the rest of the van will have a significant impact on fuel economy - more than engine size alone will.... Lowering it will help, lifting it will hurt, electric cooling fans help, large rooftop racks hurt, etc.... How much each thing matters depends on your exact situation....

Oh, and don't forget driving style....

 

It bears mentioning that what you do to the rest of the van will have a significant impact on fuel economy - more than engine size alone will.... Lowering it will help, lifting it will hurt, electric cooling fans help, large rooftop racks hurt, etc.... How much each thing matters depends on your exact situation....

Oh, and don't forget driving style....

Well driving style isn't a problem, I cruise control 99% of the time since my Astro sees a lot of highway. I cruise her never abuse her.

Cooling fans definitely do help and I'll be looking into "used set" for my 4.3L and I'll get a brand new set the day I plan my V8 swap.

I removed the rear back bench simply because I don't use it. I left the middle bench. Damn those benches were a lot heavier than they look.

I have the stock factory roof rack. You can see in my pictures. Nothing additional will happen there.

I do plan on lowering her just looking for the right lowering kit. I'm looking for a max of 2.5 inch drop and a minimum of 1.5 inch drop along with sway bars and wheel spacers. Also looking for light weight aluminum rims 15-17 no bigger.

 

Ok, what exactly are you planning on doing with your Astro? That is the real question. If you're just looking to cruise with it, not pull or carry anything, and you just had a "new" 4.3L put in, I say stick with the V-6. Any cash outlay on a V-8 to get "better" mpgs is a waste of time & money. You'll have to drive a lot to make up any gains moneywise on "better" mpg to equal the cash outlay of the swap, and it sounds like you'd have a shop do it so even more $$$$$$.

Now if you're doing it just to have a V-8, I say GO FOR IT! A V-8, properly installed and tuned, will probably match the V-6 in mpg, just don't expect astounding numbers.

My reason for a V-8 swap is I wanted the torque from a V-8 for pulling a travel trailer, and I did the 5-speed for an attempt for some fuel savings. My van gets about 6k miles a year, mainly winter and inclement weather use. I balance the van's poor mpgs with a motorcycle 6-9 months of the year (good weather). So for me, while I don't want dismal mpgs, I knew that a V-8 wasn't going to be better than the V-6, except for heavy loads.

-Andrew

p.s. For my next swap, I'm looking into a 5.3L, think that would improve both mpg & power...

 

ya I'm not looking to race my Astro in any form. This is simply to get more or less the same mpgs that I'm getting now but with just a little bit more power for when it's needed. A nice exhaust note doesn't hurt the ears either. So I'm learning that the 305V8 seems to be the best choice for this exact purpose. Great stuff.

 

My 91 Safari with a LT1/4L60E out of a 1994 Z28 with LT4 cam and heads runs about 14mpg in the city and around 20 on the highway with 3.73 gears. That is with me being a little heavy on the go pedal because it sounds so good it's practically irresistible

It would be better if I had room to actually get cold air into the intake and get the IAT readings lower. Right now it's showing 130+ degrees when ambient temps are in the 80s. Due to lack of space the cone filter is currently right behind the radiator.

 

With my 6.0 I'm getting around 23 to 26mpg on the interstate @ 65mph

 

OK so my opinion : If your gonna do a V8 then go with a newer engine if your garage guys can do it. Like a LS series 5.3 or bigger the LS series get better mileage and they last indefinitely if you do your regular maintenance. A 305 is fine but its now old school and quickly becoming obsolete. The 350 can still be bought new from GM but is no longer being built in new cars. If your van is AWD then your choices are simple 4.3/305/or 350 since I have yet to see a LS put in a AWD van. If you choose to go with an LS series engine then talk to DRZ he has done this swap. Mark

 

LS2 Done right here

http://www.astrosafari.com/viewtopic.php?f=42&t=23553

OK so my opinion : If your gonna do a V8 then go with a newer engine if your garage guys can do it. Like a LS series 5.3 or bigger the LS series get better mileage and they last indefinitely if you do your regular maintenance. A 305 is fine but its now old school and quickly becoming obsolete. The 350 can still be bought new from GM but is no longer being built in new cars. If your van is AWD then your choices are simple 4.3/305/or 350 since I have yet to see a LS put in a AWD van. If you choose to go with an LS series engine then talk to DRZ he has done this swap. Mark

 

Mic (V8AstroCaptain) said he was getting 23 on the highway with his 305 TBI engine running a mild cam (something like a 204/214) lightly ported heads and a lightly ported TPI intake along with 3.73 gears. The person he sold it to backed up that figure as well. If I were going to do a mpg V8 this would be very, very close to the engine I'd build. Give it long tube headers, a good collector setup, free flowing exhaust, run a wide band (at least to tune initially, preferably in closed loop) and tune the chip. Cheap to build, and would probably be ~100hp over a 4.3L and still get virtually identical mpg if you kept your foot out of the happy pedal all the time. Matched gears and you may do even better tbh.

Best I ever got out of my 89 with the 4.3L was about 25mpg drafting a semi at 55, and 22 was typical. Funnily it didn't matter if I had 3.0s or 3.42s for the highway rating, and I probably lost a mpg or two when going to 3.0s.

 

This is all great stuff guys thank you. My purpose for this is so that my Astro has the power available for when I need it. Let it be simply to pass some asshole on the higher or to pull my bay boat. Nothing crazy otherwise, that's it. I doubt that I will consider anything larger than a 6.0. Either way I'm leaning towards an aluminum V8 for weight savings off the front end. If I can incorporate an active fuel management/variable valve timing then even better for mpgs.

I'm not completely hopeless when it comes to cars or engines. There's simply a lot that I don't know and I'm not gonna act like I do. Luckily I've become great friends with the guys at the shop that I take my previous vehicles to. I told them I would even have a sticker made up with their company logo on it and place it somewhere nice on my Astro. Free advertisement, and when the owner found that out he dug deep into his heart for me and said he would help me as much as possible.

If you're ever in South Florida, specifically the Homestead area, I highly recommend Carl Pelt's Goodyear on Krome Ave. Just google it and mention David from Vega Properties.

Guys thanks a lot I really appreciate all of this information.

 

you need to do what I did, bought a totaled 2500 hd and swapped everything.

 

you need to do what I did, bought a totaled 2500 hd and swapped everything.

please tell me more.

 

you need to do what I did, bought a totaled 2500 hd and swapped everything.

What year do you think is best? I'm only going to do it if I can get an all aluminum engine. Weight savings equal gas savings.

 

My goal is obviously power and efficiency. I want the power to pass someone without losing a quarter of a tank and to pull my bay boat. Plus if it can get me close to the gas savings the V6 offers then I'll be happy. I see that a few guys here are getting in the mid 20's on the hwy. That's perfect for me. I plan on going with a really nice cooling system, ignition, and free flowing exhaust

I'm planning on

3 row radiator with upgraded hoses
oil cooler
trans cooler
8.5-9mm spark plug wires
upgraded spark plugs
equal length shorty headers (longtubes if possible)
larger y pipe with 3inch out (found on on CAR-ID dot com)
high flow cat/resonator
no big muffler

I want to install performance gauges so keep an eye on everything

A/F ratio
Tachometer
Econometer (works on 2004 and up models. If I buy a wreck and swap everything and the years are 2004 and up I can't see why I can't use this with the new computer)
Vacuum gauge (If I can't use the econometer)
fuel pressure
oil pressure
water temp or anything else miscellaneous that I might be forgetting.

 

I have also thought about going with a manual transmission conversion. I always felt like I got better gas mileage from a vehicle with manual than automatic. Plus they're much cheaper, easier to repair, and weigh less than a typical automatic.

 

viewtopic.php?f=42&t=23553

 

okay, don't hate me, but I used to read your screen name in my head as "grandma lee", I just realized my mistake...lol

 

okay, don't hate me, but I used to read your screen name in my head as "grandma lee", I just realized my mistake...lol

That's actually my nick name on here. Started along time ago. I think it might of been you that started it...lol