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Sularus 02-14-2011 09:54 PM

engine swapping
Okay, here is the deal. I own a 2001 pontiac grand prix with a 3.8L v6. I am slowly working on improving the gas mileage as much as possible. I have some plans to work on the aero some. I won't be able to do too much, due to an upcoming deployment in April. I will be gone all summer, but my wonderful wife is getting us out of debt while I am gone.
I am thinking of swapping in a 4cy engine either over the winter or next spring. I was wondering if anyone here has a good amount of expierence with GM products. I am thinking of putting in a GM 4cyl, mainly it would be easier to get the computers working properly in the long run without going to a standalone engine management system.
I know I am going to get the usual response "just by a smaller car". The whole point of getting out of debt is too stay out of debt. I plan on doing most of the swap with parts freshened up from a junkyard or other second hand purchases. If anyone has any ideas, I am open to suggestions. I don't have to stay with GM products, it just makes mating computers up easier.


Varn 02-14-2011 10:09 PM

From what I have read the 3.8 is pretty economical for it's size. A friend had one in a Buick and always got 30+ mpg. Have you gotten a scan gauge type of instrument and gotten your tires up to the max side wall pressure. Narrower tires. Some aero tricks maybe. Drive slower and less. Changing engines is a lot of work once you consider the money and effort you will have to drive thousands of miles to break even.

Thanks for taking your turn the sand box.

texanidiot25 02-14-2011 10:13 PM

From what I remember, the W-Bodies didn't use any 4 cylinders as even a base motor, there's no easy factory solution. And, in the end, you'd spend more in the swap than you'd save in gas money. Engine, trans, mounts, computer, wiring, exhaust, etc etc, you'd be easily looking at 2 grand... Then the troubles of trying to make it emissions compliant.

In this case, selling the car for another would be a better plan, but the 3.8 is a pretty efficient motor, especially for a car it's size.

redneck 02-14-2011 10:34 PM


From what I have read the 3.8 is pretty economical for it's size. A friend had one in a Buick and always got 30+ mpg

I had a 1989 Buick Park Ave with the 3.8 and 30mpg on a trip was no problem.
Probably the best engine GM made. I sold it with 270,000 on the clock still running like new.

I really miss that car...


Jim-Bob 02-14-2011 11:03 PM

The problem is that you are going to spend more money for the swap than you would to just buy a more efficient car to begin with. This does not mean you need to go into debt. You just need to allocate the money you were going to spend on a swap towards buying another car. Swapping engines on a modern car is a very involved process because of the complexity involved. You would need custom drive axles, exhaust work, oodles of wiring, custom engine mounts, etc. Expect to spend $3,000 easy to get an end result that is underpowered and still not very efficient. Instead, go take that money and buy a decent Geo/Chevy Metro with a 3 cylinder/5 speed. It will get 40 mpg city without breaking a sweat and exceed 50 on the highway all day long. Keep the other car for when you need to carry people around and you will likely have a better setup.

mort 02-15-2011 01:20 AM

Hi Sularus,
I did the opposite many years ago, dropping a 3.8 V6 and turbo-hydra into a Chevy that had a 4cyl and a 4 speed manual. Of course the mileage dropped but performance was fine. If you can find the engine you want in a GM of about the same age it shouldn't be too much trouble. I found a Buick at a junk yard that had been sandwiched. I had to cut the drive shaft, this was in rwd days. And there was some motor mount welding and add some front spring spacers to get the front end leveled, but really minor stuff all considered. All told it was a pretty complete drive train swap for about $1000. So I think you can do it, and maybe cheaper too.
I think it is a good idea and in the long run will save you money.


D.O.G. 02-15-2011 01:48 AM

I'll start by admitting I know nothing about American cars, but.....
Have you considered the lower power to weight ratio a smaller engine will give you?
As an example, I used to work at a place that had two delivery utes, same body, but one ran a 4.2 litre V8 and three speed auto, the other, a 3.3 litre Six cylinder with a five speed manual. On paper, the Six should have been better on fuel, but because it had to be pushed hard all the time it was consistently worse.
I'm not saying that's the case here, but it's better to think about factors like this first.;)

NHRABill 02-15-2011 09:50 AM

You just don't drop a motor in and out of a newer car without major complications. if the motor you are choosing was never intended for the vehicle you MUST check your local laws to see if it is allowed first.

If you are a city driver then a 4 banger in a GP is a total waste you will get worse mileage in my opinion. I believe you will never recover the cost in doing the swap just for the cost of materials.

Ask anyone who has done such a swap it is almost always low dollar for vanity saying that they did it or a combination of the 2. As stated earlier there 3.8 is a great engine and could make a great reliable car if you do some mods and maintain the car properly. if you want a gas miser don't reinvent the wheel look at some other peoples setups and work off that. Many people in here have been working on their cars for many years and have come up with great positive and negative results we all can learn from. Keep reading the forums and I wish you luck.

Sularus 02-15-2011 06:36 PM

Well, lets see if I can answer some of these replies.
Varn - I am hoping to get an Ultraguage soon, and my tires are up to 50psi. The tires only have for 20,000 miles and are still looking real good, so getting new ones that are narrower and have less resistance will be a while and would cost approx 400 - 500 for a new set. The only way I can get 30+ mpg back and forth to work (primary use of car. 50 miles each way) is to drive 5 under the speed limit most of the way.

texanidiot25 - There were 4 cyl turbos used back in the late 80s and early 90s, but they weren't that great. The swap doesn't have to cost over 2grand. That is where getting an entirely wrecked vehicle comes in and using everything possible. As far as emissions, as long as the engine is from a 2001 or newer vehicle (must be to be legal) then I can use the items from both vehicles to make it compliant with little difficulty.

redneck - the main reason I have problems with gas mileage is pontiac did a final gearl ratio for the GTs at 3.29 where the GTPs had 2.93. My wifes 03 Impala has 3.05 and gets awesome gas mileage. I like the 3.8L, but cruising at 50 - 55 mph would be easier to feed 4 cyl instead of 6cyl. Not to mention it is solid cast iron except the accessory brackets. There is some serious weight to be shed up front.

Jim-Bob - It really doesn't have to cost that much. I have most of the tools needed to do custom fab, and what I don't have I plan on getting anyway. The hardest part will be figuring out wiring (accomplished by pinout diagrams and a software suite to rewrite some computer code) and the axles (not too difficult if measured correctly, and getting cheaper for high quality custom made ones). I toyed with the idea of getting a metro, but I am 6 feet tall and have had quite a few back injuries. The Grand Prix is really good on my back, especially with the heated seats.

D.O.G. - thanks for the heads up, It is something to consider. The main reason I got this idea was the new buicks. The new lacrosse and regal both have 2.4L 4cyl and are rated at 30 mpg highway. Granted they are using direction injection motors (can't afford those :( ) I did read there was a version of one of them with a turbo and a 6 speed manual tranny. Both of those buicks weigh more than my GP.

NHRABill - As long as I use a engine/tranny from a car at least 2001 or newer. It has to be able to pass an inpsection and emissions, if it is required in that state. As far as recouping cost, the primary reason is to save money on fuel. NO matter what I do, the 6cy will never be as efficient as a 4cy. The other part is like you said, to be able to say I could do it. I find it amussing you talk about reinventing the wheel. The GP is a mid size sedan. One of the few that did not offer a 4 cyl base model. If you look at current manufacturing trends, most of them are using 4cyl and turbo 4cyl in their mid size sedans.

I think this would be an interesting project. Of course I would have to do some serious shopping around to find the right engine/tranny combo at a decent price. There will be some fab work required for motor mounts, exhaust, and custom axles. The other upside is it would reduce weight up front. That would help balance and handling along with lowering the overall vehicle weight. AT 3500lbs, the GP is a hefty car. I appreciate the comments, keep them coming it helps to make sure I am thinking along all avenues.


Frank Lee 02-15-2011 06:53 PM


the main reason I have problems with gas mileage is pontiac did a final gearl ratio for the GTs at 3.29 where the GTPs had 2.93. My wifes 03 Impala has 3.05 and gets awesome gas mileage.
If this is the case then you have answered your own question. Swap transmissions or just the final drive gears instead.

Add me to the chorus saying a swap away from a 3.8 likely will be more trouble than it's worth.

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