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03Panther
03Panther SuperDork
4/13/21 8:18 p.m.

I've never done a engine swap in anything except old carb'd stuff in the past. And back in those days, it was after more power, on the cheap... even if not always well thought out or successful.  I know LS is everyone's easy button of choice these days, but I don't have the access or contacts to do that (starting with zero parts) on a micro tight budget.

car is a large unibody , so not as versatile as a BOF, but large enough to not be a lightweight. Does have a more modern front suspension setup, but no mounts designed yet.(I do have a sawzall and a welder - scary as that is!)

Not worried about big power... just want good MPG to drive to work a few time a week.

SO.. wanting to know thoughts on 3 different engines/transmissions I already own, for the best MPG choice:

1)  Easiest to install and get running is a '78 305 2G (2 bbl carb) with a '92 700R4. I know this runs good - I put it in a 1 1/2 ton dually just to get he truck movable. Just no clue what the MPG potential would be in something normal sized. I would have to start from scratch for ac, though.

2) '99 Vortec 4.3 V6 / 4l60e from a Astro van. I have the running donor van, so would not be too hard to swap the entire harness and computers over, will all the AC parts Even have some mods to the trans and computer for beefing up the trans for towing. but all the post 92 vortec astros I've personally dealt with only got 17-19 MPG. Where the pre vortec 4.3's (86 to 92) got 20 -23. If I put that in I'd prolly either ugrade to a L98 350 one day in the future. Or a MT. Or both! MPG prolly be about the same, so might as have a better sounding toy, wit a bit more power when ya want it. But that upgrade might not ever get the budget approved

3) A '96 3800 Series II (Buick 231 90 deg V6)  / T5 from a F body. I have the engine, trans, and most of the wiring, and one of the computers from a different parts car. In a lighter / smaller car I know this would be the best MPG, and I feel they run better than the 4.3's. I doubt the target car weighs much more than the F-Body, but not as aerodynamic. I've gotten mid 30's from the series 2 engine in the FWD W-Body's in the past, but F-Body guys don't seem to be getting that, so I assume weight is a factor.

What are y'all's thoughts on one of these 3 engines? if its any other suggestion, you'll have to be willing to provide the engine, since these are the only three I have. I'll either us one of these three, or take the whole 9 yards down to the scrap yard, since none of it is anything special.

wvumtnbkr
wvumtnbkr PowerDork
4/13/21 8:22 p.m.

I'd bet the 3800 makes the most power and probably uses the least fuel.

 

That's my answer.   Also, supercharger for Shiggles if you change your mind!

03Panther
03Panther SuperDork
4/13/21 8:37 p.m.

In reply to wvumtnbkr :

I picked this one up, for that very reason! But the MPG reports from the F-Body guys are discouraging, The supercharger stuff will prolly remain out of reach, and I'm a bit lost in computer controls for that engine, without throwing money at it. Also, of the 3, its the only one I personally have ran. I was told it was driven onto the trailer, before they pulled it and scrapped the car; but not by folks I knew. They did at least carefully remove all the wiring - did not cut anything. put unpluged everything to remove it, and left the stuff they unplugged, with the car... including both computers.

Some of y'all modern car savvy guys could prolly whip something right up. I'm a bit intimidated!

It would be the coolest choice by far!

Javelin (Forum Supporter)
Javelin (Forum Supporter) GRM+ Memberand MegaDork
4/13/21 8:48 p.m.

The 3800 really does only get 17-19 mpg. It's a thirsty pig.

Honestly none of those are going to get decent mileage at all. What are you swapping into and why? What kind of budget is there?

03Panther
03Panther SuperDork
4/13/21 9:05 p.m.

In reply to Javelin (Forum Supporter) :

I figured I would have enough trouble keeping folks focused on only those three engine choices as it is with out including the car! I stuck with "not light".smiley Obviously a bit different depending on choice, but all except one of the three the same.

Honestly, just to do something different with stuff that I have laying around. Almost non existing budget... but my labor. I know even the cheapest one will nickle and dime me to death, but my wife knows I gotta spend a little on toys! Not looking for an econo-box kinda MPG, just wondering what would be the best, between the ones I already have.

Why would the 3800's in a F.Body be considered a thirsty pig? m\My friends LT1 Formula I had for a while did as good or better than 17-19. But I have heard that mentioned by F-Body guys... What was different from the FWD cars?

I had a 96 FWD Series II that got 34-36 0n the hwy and 29-31 around town. And a 92 3800 (later called the Series 1) FWD that got 29 on the hwy, and I got 19 with it pulling a 3500 lb trailer through N AL/TN mountains (OK, foothills to the western guys!) I knew the heavy Park Ave's weren't far off that either? Did GM "neuter" them for the F-Body crowd for some reason?

QuasiMofo (John Brown)
QuasiMofo (John Brown) GRM+ Memberand MegaDork
4/13/21 9:09 p.m.

What kind of car?

The 4.3/3.8 options are relatively reliable but I can't imagine if a 305 fits why not locate a wrecked or rotting 5.7L Vortec or TBI engine from a later GMT400 wouldn't make more sense. Twice the power and better fuel economy from the get go. Also quite easy to swap.

wvumtnbkr
wvumtnbkr PowerDork
4/13/21 9:09 p.m.

Not sure.  The t5 trans behind them had a .72 or .74 5th gear ratio which is WAY the he'll up there, so you would think it would do okay...

03Panther
03Panther SuperDork
4/13/21 9:22 p.m.
QuasiMofo (John Brown) said:

What kind of car?

The 4.3/3.8 options are relatively reliable but I can't imagine if a 305 fits why not locate a wrecked or rotting 5.7L Vortec or TBI engine from a later GMT400 wouldn't make more sense. Twice the power and better fuel economy from the get go. Also quite easy to swap.

The 4.3 is free, and I have no access to inexpensive engines around here, sadly. Stupid money are the only options at the junk yards around. They all go straight to scrap, or have gold plaited cylinders, I guess. surprise That's why I mentioned any other options would have to provide me the engine! smiley

From the factory, the 305's or 350's don't seem to do better than the 4.3; just not really any worse. But there are lots of things to do to a SBC for dirt cheap - the 4.3, not so much. But these are the only three I have.

I never have figured out why the early astro vans got better MPG than the later... The vortec 4.3's are a bit smother with he ballance shafts, and have more power on paper, but the butt dyno can not tell the difference.

Car is absolutely nothing special. Just something "different" to put around with. And now one would ever car what engine was in it. I'm just being odd, and working with what I already own!

03Panther
03Panther SuperDork
4/13/21 9:26 p.m.

I do actually have a 4th option... but the 67 390 GT FE / C6 would def. not get the MPG. 'Course might not be much worse than the carb'd 305 as is! and that would be getting into a tighter squeeze! cheeky

QuasiMofo (John Brown)
QuasiMofo (John Brown) GRM+ Memberand MegaDork
4/13/21 9:26 p.m.

If you have a 4.3 and transmission it will make nearly the same power with slightly better consumption as a carbed 305. I've had all three. The 3.8 if it's an F-Body setup is slightly more likely to have issues in my experience. The 4.3 would be my choice given those options only.

 

03Panther
03Panther SuperDork
4/13/21 9:38 p.m.

If I had a 302 (5.0 for the metric guys) w/ MT, that would be my first choice, but alas, I don't know of one cheap enough. The 3800 supercharged would be my second, but again, I doubt I'll ever be able to devote the budget.

Just these few answers in this short discussion, has reminded me to save the 3800 I have for a smaller project one day!

 

03Panther
03Panther SuperDork
4/13/21 9:41 p.m.
QuasiMofo (John Brown) said:

If you have a 4.3 and transmission it will make nearly the same power with slightly better consumption as a carbed 305. I've had all three. The 3.8 if it's an F-Body setup is slightly more likely to have issues in my experience. The 4.3 would be my choice given those options only.

I believe you may have summed it up quite nicely!

Just for my curiosity, why od you think  the F-Body is more issue prone / worse mpg than the fwd in that engine? I've heard both f these before, but havent got my head wrapped around why.

dclafleur
dclafleur Reader
4/13/21 9:56 p.m.

The 4.3 in the astro vans got a bunch of different MPG because those vans came with half a dozen different axle ratios. Could be all your later ones had different gearing. As for the F-body getting worse MPG with the 3800 it's because it is a heavier car than a lot of the FWD cars with the same engine.

Curtis73 (Forum Supporter)
Curtis73 (Forum Supporter) GRM+ Memberand MegaDork
4/13/21 10:01 p.m.

Of those three, my choice hands down is the 4.3L.  Nothing wrong with the 3.8L, just that it has a displacement deficiency.  The 4.3L is a 350 with two cylinders missing.  It is bulletproof, parts are dirt cheap, and you can't walk down a sidewalk without tripping over parts for it.

My absolute last choice is the 305.  It is by far the heaviest, has the smallest bores, and probably makes less power than the 4.3L.  The 305 is best used as a bare block to make a coffee table.

None of them will get great MPG.  Size rarely makes a huge difference, especially when you're looking at very similar HP numbers.  It takes X amount of hp and tq to move the car in the way you want to move it.  Since there aren't any major engineering wonders inside any of those three, you can expect pretty similar numbers.

Please (for the love of all that is holy) do not try to spend money making a 305 perform better.  The old saying of "it's what I have" does not in any way apply to the 305.  As soon as you spend $250 on an intake that nets you 10 hp, you're better off spending $250 on a running 350 which gets you way more than 10 hp and more tq at a lower RPM, plus you have a viable engine for mods later.  I know you mentioned not having access to other engines, I'm just saying, spending more than 45 cents on a 305 is a losing battle.  I honestly spent a weekend swapping a 350 into a K20 instead of spending $12 on valve cover gaskets for the 305 that was in it.  I refused to spend money on it when I had a perfectly good 350 sitting on a tire.

The 99 4.3L gets you 190hp which is way more than the 305 makes, it's lighter, its mostly a bolt-in where any SBC was before, and the aftermarket is plentiful if you ever decide to spend money on it.

03Panther
03Panther SuperDork
4/13/21 11:04 p.m.
Curtis73 (Forum Supporter) said:

Please (for the love of all that is holy) do not try to spend money making a 305 perform better.  The old saying of "it's what I have" does not in any way apply to the 305.  As soon as you spend $250 on an intake that nets you 10 hp, you're better off spending $250 on a running 350 which gets you way more than 10 hp and more tq at a lower RPM, plus you have a viable engine for mods later.  I know you mentioned not having access to other engines, I'm just saying, spending more than 45 cents on a 305 is a losing battle.  I honestly spent a weekend swapping a 350 into a K20 instead of spending $12 on valve cover gaskets for the 305 that was in it.  I refused to spend money on it when I had a perfectly good 350 sitting on a tire.

The $0.45, or even the $12.00 is stretching things a lot, but you diminishing returns points are entirely valid! Even when you sort out all the ridiculous comments made by the "i gotta hab a chebby" crowd, the engineering does support the small bore vs SBC head design problem!

The 305 I have would benefit from a well tuned q-jet and manifold, and headers, but would still be a dog next the a 350 with the same stuff, and prolly not as good a mileage, and I def. ain't gonna spend any money on it. And its my last choice as well.

I did once have a 267 - even worse - with those minor mod's done on the cheap, and was adequately pleased with it. Better mpg than similar 305's, and nice and crisp power (what little there was!) Again, I agree, and would never spend money on either!

 

03Panther
03Panther SuperDork
4/13/21 11:12 p.m.

In reply to dclafleur :

There has to be more to it than that for either one.

I've been around a lot of early Astros and talked to lots of folks with vortec 4.3's. except for specific conditions the axle ratios dont seem to affect overall long term mpg a lot. Before I bought my '99 I assumed driving style might be partially responsible. But nope, only 17 to 19, (had a 3.42 gear, and I switched to 3.73 with no difference) and I had several different ratios in eariler ones.

On the FWD/RWD 3800's, can't just be the weight. I've never looked it up, but I cant beleive a park ave weighs less than a F-Body. Something else has to be causing the dramatic difference. There has to have been someone with a F-body that drove it like a little old lady, as well (OK, not many!)

03Panther
03Panther SuperDork
4/13/21 11:15 p.m.
dclafleur said:

The 4.3 in the astro vans got a bunch of different MPG because those vans came with half a dozen different axle ratios.

3.23, 3.42, or 3.73 in 95 % of them. I've seen 4.11 on an rpo code, but I've never seen one in the wild smiley

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
4/14/21 11:40 a.m.

I'm partial to the 3800, they can get stellar economy.  In a front driver.

they probably get awful economy in the F-body because hypoid gears suck efficiency.  GM and Ford now specify synthetic oil, about a half quart "low" from the fill plug.

 

Engine swaps for economy never make financial sense, unless you are doing an engine/drivetrain replacement anyway.  It's better to focus on things like low rolling resistance tires, making sure the wheel bearings are properly adjusted, brakes aren't dragging, alignment is perfect, and so on.  A thousand little things.  But if you need to re-engine it anyway... "Smaller" is not always as better as "higher compression" and "better combustion chamber shapes".

 

Not knowing the vehicle but with an idea given your options, I'd seriously look into how cheap one of the new direct injected 4.3s could be had.

obsolete
obsolete Reader
4/14/21 12:14 p.m.
Pete. (l33t FS) said:

Not knowing the vehicle but with an idea given your options, I'd seriously look into how cheap one of the new direct injected 4.3s could be had.

I've been intrigued by the LV3s too, but they're still going for $2-3k at the junkyards around here.

Curtis73 (Forum Supporter)
Curtis73 (Forum Supporter) GRM+ Memberand MegaDork
4/14/21 1:16 p.m.
Pete. (l33t FS) said:

Engine swaps for economy never make financial sense, unless you are doing an engine/drivetrain replacement anyway.  It's better to focus on things like low rolling resistance tires, making sure the wheel bearings are properly adjusted, brakes aren't dragging, alignment is perfect, and so on.  A thousand little things.  But if you need to re-engine it anyway... "Smaller" is not always as better as "higher compression" and "better combustion chamber shapes".

 

Not knowing the vehicle but with an idea given your options, I'd seriously look into how cheap one of the new direct injected 4.3s could be had.

I agree, but I get the impression his goals are more like "I have a shell and these three motors - which one will work and not suck too much fuel?"  It doesn't sound like he's swapping to increase MPG, more like getting something to move under its own power with parts he has.  I'm trying to stay within his parameters of "no access to other engines."  No one lives in a vaccum, but sometimes it's easier to say "no other engines" than to go into the deep end of "I can't drive to the junkyard right now for [insert] reasons," or "I just really wanna do it my way."

I, too, am curious about the vehicle.  On the one hand, if he tells us the vehicle we can provide more precise recommendations.  On the other hand, if he tells us the vehicle we helpful GRMers will likely spin off into 6 pages of the history of said vehicle, how an LS swap would be easier, and generally offer him advice he didn't ask for laugh   (I say that knowing that I would be one of those "helpful" GRMers)

03Panther
03Panther SuperDork
4/14/21 3:15 p.m.

In reply to Curtis73 (Forum Supporter) :

Curtis, you just became my favorite person ever!

100% accurate description. I’d be the last guy with the right to complain about someone taking a thread down a different rabbit hole... I’ve been rather guilty of that myself! Just tryin’ to forestall it here!

Inexpensive used automobile parts are essentials in a vacuum in my area. Craig’s ads have stuff like “ chebby 350 motor. Runs great. Except for the whole in the block. $600, firm. I know what’s I got.”

The mom and pop yards are not close, with no competition, and they are high. Nearest pic a part type was an hour and a half away, and they have since closed.  If I was traveling still, I’d drive out to stampie’s and follow him around his favorite spots!

Stampie
Stampie GRM+ Memberand MegaDork
4/14/21 5:54 p.m.

In reply to 03Panther :

I can get anything from a 2.3 four banger to a 6.0LS for $150.  Just have to come out and sweat in the yard with me.  I think I have $40 in my T5?

03Panther
03Panther SuperDork
4/14/21 11:19 p.m.

In reply to Stampie :

My wife, the financial manager, is really really glad I don't live anywhere you. She really likes a clean yard. Cotton is her new BFF... he took some stuff out of her yard.

My question will prolly never amount to me doing this project, or maybe by the time I do I'll have a different engine option - she really wants the empty shell and the parts  vehicles 2 of the engines are in gone!

03Panther
03Panther SuperDork
4/14/21 11:29 p.m.
Pete. (l33t FS) said:

1) they probably get awful economy in the F-body because hypoid gears suck efficiency.  GM and Ford now specify synthetic oil, about a half quart "low" from the fill plug.

2)  I'd seriously look into how cheap one of the new direct injected 4.3s could be had.

1) That's the best thought I've heard so far on the difference in mpg! Combing that with the difference in typical owner driving style and we may have it figured out.

2) Between the cost of an engine that new, and complexities of wiring that in, I'd be way over my comfort level. Unfortunately, I now, with changes in life and the economy, have less money coming in than the guy that had no job, and got kicked out of his dads house. I can't really afford to even be asking this question, I just can't help myself!

STM317
STM317 UberDork
4/15/21 7:08 a.m.

Sorry to be Buzz Killington here but if things are tight, there's no budget for this project and you've got 3 parts vehicles and an empty shell sitting in the yard, (no combination of which will make a particularly good finished product for your goals) then I agree with your wife. It's time to sell them for whatever you can and have fewer projects hanging over your head and more liquid funds available.

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