In reply to STM317 :
Although I agree with your advice, and all 4 items in my post will prolly go to the scrap yard, for pennies (not really much liquid at all at current prices) like most (except Curtis
) you might be misunderstanding my “goals. “ not expecting great mileage. I know the limitations of that. Just wondering what one of the 3 choices, will get better mpg in a say, 3800 lb car, (just a guesss) than the other two. Doesn’t matter if it’s single digits, or mid 20’s, for the sake of this theoretical think tank!
l’ve offered most of it for around scrap price, with no interest, so if I don’t make one drivable from parts on hand, scrap it will be.
In reply to 03Panther :
What's the weight difference between the Astro & the vehicle you're swapping into? Also, what will be the final drive ratio? That should at least give you an idea if the MPGs will go up or down relative to the Astro.
On page 2 and OP still doesn't want to share what the swapped power train is going into?
Do whatever you want I suppose
Pete Gossett (Forum Supporter) said:
In reply to 03Panther :
What's the weight difference between the Astro & the vehicle you're swapping into? Also, what will be the final drive ratio? That should at least give you an idea if the MPGs will go up or down relative to the Astro.
As noted, from personal experiences with a lot of Astro/Safari vans, the weight (within reason) and the gear (within reason) doesn't seem to make a huge impact on them. 17-19 on the "newer vortec's, +/- 1000 lbs. And 20-23 with the older. Driving style was the most effect on the earlier vans; not as much on the one later I owned.
But, yea, I would expect the same 19 mpg ball park out of my theoretical swap if I use the 4.3. And that would prolly be the best choice, out of the limited options, given the reliability and other factors.
For around town, no towing, I've always thought the 3800 would actually do better than the 4.3 in a astro van. I think one could nurse mid / high 20's from one. Not enough savings to be worth a swap, but would be cool!
And thanks to all for y'alls patience in dealing with my oddball thoughts!
In reply to seadoorider :
Thread was started for a question of 3 specific engine possibilities. Car is irrelevant (other than describing the weight) Yes I would be curious as well! 
But I didn't want to influence any sidetracks other than the theoretical discussion of a swap the may not ever even happen, and as has been pointed out, probably shouldn't!
In reply to 03Panther :
Ok fine but I'd have to disagree that the car is irrelevant. This forum has subject matter experts on virtually every chassis imaginable and might be able to help you decide what would be easiest to do with regard to motor mounts, accessories. Wiring and so on. All are not created equal and there's a lot of difference between the 3800/t5 swap ability and the v6/305 auto setups.
also at a bit of a loss as to what RWD unibody yet fairly heavy Gm car you're working with (assuming it's a GM otherwise things could get more complicated for the swap) - third gen F body comes to mind. Am I close?
Javelin (Forum Supporter) said:
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?
A thirsty pig?
I've never heard it described that way. In fact, the opposite would be true:
https://www.roadandtrack.com/car-culture/a9382/buying-mileage/
seadoorider said:
In reply to 03Panther :
Ok fine but I'd have to disagree that the car is irrelevant. This forum has subject matter experts on virtually every chassis imaginable and might be able to help you decide what would be easiest to do with regard to motor mounts, accessories. Wiring and so on. All are not created equal and there's a lot of difference between the 3800/t5 swap ability and the v6/305 auto setups.
also at a bit of a loss as to what RWD unibody yet fairly heavy Gm car you're working with (assuming it's a GM otherwise things could get more complicated for the swap) - third gen F body comes to mind. Am I close?
I understand, completely. But I did not start the thread for advice on any of those things. In effect, you have just described why I did not include what car it might be. Amount of work, or how to mount will not affect the question on mpg between 3 specific engines in a car none of them came in.
Those questions could become relevant in a different thread, but not the reason I started this one.
A 401 CJ said:
Javelin (Forum Supporter) said:
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?
A thirsty pig?
I've never heard it described that way. In fact, the opposite would be true:
https://www.roadandtrack.com/car-culture/a9382/buying-mileage/
I always liked Mr Egan, although I've read more of his motorcycle stuff.
But Mr Javelin as calling the 3800 in a rwd a thirsty pig. I still never heard it put that way before, but I have head quoted numbers in red being WAY less than my experiences in fwd ones.
So far the only explanation for this has been the parasitic losses of the rwd components. And I suggested typical driving style differences.
I still find it hard to believe a 40% difference, though.
Are you trying to get the most economical daily driver out of this? If this is for fun, I think I'd rather get the motor I want for the shell I want and make that the project. And just keep something cheap to run for day to day driving.
The problem I have, from personal experience with a FWD 3800, is how the accountants took away a lot of that legendary reliability with crappy top end gaskets, the plastic intake that liked to burn around the EGR passage, and other related issues. They also sound like garbage. But if you want to turn wrenches, I assume (key word) there's enough aftermarket and junkyard cross-polination available to make them decent if you get one of the wrong years.
I'd rather build a 305 with select components though; 5.7 Vortec heads, aftermarket spreadbore intake (I believe one or two were sold), Quadrajet, good condition OEM HEI ignition setup, etc. Or just go with Stampie and find a 4.8 and plan a swap around that. I assume he runs a summer camp for wayward GRM forum members.
In reply to pres589 (djronnebaum) :
Hey, thanks! When you want to drop those parts off? Instead of trying to put good parts on the 78 305 I have sitting around, if you want to buy me a ls, a t56 and a stand alone wiring harness with all the computers, that would be my preference. Very generous of ya.
From personal experience with many fwd 3800, and a ton of reading about them, and talking to others that own them, I have forms them to be one of the most dependable engines made. I know one member has a multi page complaint because he can't get one to run right, but I don't recall the name. But the responses seem to indicate that he feels points and carbs. are more dependable than fi and that newfangled electronic ignition stuff
I've had to do gaskets on the 60 deg 3.1, but not in a 90 deg. 3800/3.8/231.
Unfortunately, I current don't have a fwd. 3800 setting around. Although a cheap fwd 3800 can still be bought, that is not one of the three engines in the discussion at hand.
You came to GRM and you want only your narrow selection of frankly uninspiring engine options to be considered, for a swap into a car that you've yet to name, and you're going to get a 'tude when I make a selection that is partially based on one of the options given? I wish you the best of luck with this "tell me what GM turd motor to swap into my unnamed car project because I want a daily but I need it to be more complicated than usual" thread.
In reply to pres589 (djronnebaum) :
Not sure what attitude you are referring to. I am simply sticking to the parameters listed in the original post I started.
if you want to cop a 'tude (you words) simply start your own post. No reason to bring a bunch of keyboard komando stuff to mine. Have a nice day.
My money goes on that the car is some sort of Jaguar
I would choose 4.3 V6.
Ok fine. All you care about is which powertrain uses the least fuel. Well the answer is the 3800/T5. Now I'm not saying that's the best plan...wouldn't know. But since you couldn't figure out that he smallest displacement engine and manual transmission would likely use the lest amount of fuel, well now you know.
good luck on your "mystery" project.
In reply to Rocambolesque :
It would be even more controversial than that! But looking at it from the outside, and hoping not to encourage guessing, that is an awesome guess!
I think you won the internet tonight. Does perfectly explain why I don't want to distract folks into suggestions that I'm not asking about.
The question of the best option of the three pitiful engine choices I am stuck with, has been covered as the 4.3. Still don't know why the 3800 has such a bad rep for mpg, in rwd, when they are one of the best fwd engines gm made, but we did get some good thoughts in that direction.
I'll have to decide here in the next few weeks of the whole 9 yards is headed to the scrap man, or if I want to be silly, and waste some of my time and energy! I'm thick skinned enough to take the abuse after I finish it... Just not sure I want to start.
seadoorider said:
But since you couldn't figure out that he smallest displacement engine and manual transmission would likely use the lest amount of fuel, well now you know.
I've seen many cases where that is not correct. Expecially in the case of the rwd 3800. Since, if the f-body fan boi sites are correct, the factory V8's get as good or better. Personally, I don't believe that, but I have never driven a rwd 3800, so I don't know. That's why the question of what others might think. And also why advice outside of those three choices is not what I needed, since I cannot afford any of the suggestions outside of the admitantly lame 3 choices I have. I have not meant to offend anyone. But will answer anyone, as well.
