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Discussion Starter #1 (Edited)
I am rather new when it comes to restoring classic cars but, I am buying a 1969 Impala with a 400 small block. And in order not to guzzle down my gas money I had the thought of taking out the original engine and replacing it with a more modern engine, say from the 2000's up.
How practical would that be? I f practical what would the best type of engine to outfit it with? How much work would it take roughly? How much could I save in the long run?
 

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Welcome to the Team DJ!

I doubt seriously if you would save enough in gasoline to justify the expense. A modern LS-x engine in a rebuildable condition (that is to say still running at point of sale) will run you $1,200 to $5,700 dollars depending upon size and model (some are more in demand performance wise than others). Add to this the price of a rebuildable 4L65e, a 4L80e or a newer 6L90e transmission and you could be spending $7,800 on just the tranny.. They are not cheap (well the 4L60 or 4L65e might be as they are getting old and are very plentiful in the number of donor vehicles you will find in yards). You are however not done by a long shot in terms of cost. You will need a wiring harness to fit your car that will also control both your motor and transmission which will probably require reflashing at the least. Having a harness that is too big is better than one that is too small as you are going to have pay someone money to cut it down to fit into your car and pull out all of the wiring you will no longer need in the harness (your 1969 Impala doesn't have ASB (brakes) to worry about wheel reluctors; or any of the other dozen or so sensors on a modern car that keeps it from running if something isn't sending the right signal to the controller to make it operate.

You are still not done spending money. The new motor is not a drop in. They are all modular so you can mix and match your choice of accessory positioning to clear your car's chassis. However you are going to be buying a lot of front drive accessories and brackets to get the combination that works best for you. This includes the intake manifold (there are three different ones that all interchange differing in height and positioning of the air inlet, as well as six different oil pans not one of which is an ideal fit. Though if modifying one to fit your car I would use the one from the Camaro. Then there are the problems with the motor mounts not bolting up and the requirement to find headers to fit your car.

In general a BBC used to be considered the most expensive motor option for your car, now the LS-x has surpassed it with the motor costing on par to half again as much depending upon your fabricating skills.

So if you think you are going to save $8,500 (rebuilt motor and tranny all store bought goodies) to $12,000 (new crate engine, and tranny with wiring harness) in gasoline by buying a new LS-x to throw under the hood you must be planning on putting a boat load of miles to justify it.

Worse case scenario with a 450 horse power 406 (a rebuilt 400 with a modern after market aluminum heads, roller cam and four barrel intake with carb) will be about nine to eleven miles to the gallon assuming you drive like a crazed idiot racing to every stop light so you can slam on the brakes before jack rabbiting away again.

I had a 513 horsepower 406 in my Impala, and I got 17.3 miles per gallon because of the use of an overdrive transmission and a lead foot (I'm sure others could have easily improved on that number). A double overdrive with a 0.5 final drive ratio and I can see you easily in the twenties as far as mileage goes, which is comparable to a 283 with a well tuned two barrel (just having nearly three times the power at your command) or your desired LS-x engine as I get 21.8 mpg with my 5.3L LQ-9 motor and my 6L90e transmission now in my Silverado (Once again others may get better mileage).

Big Dave
 

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a 5 speed manual or 4spd OD automatic and a modestly built 283 - 350 could be a happy medium for you.

as many have said before, it's hard to beat a crate motor but you could spend between 1800 - 3500 for that. I think either tranny option could cost 1500 - 2500 if you can find a used one.

like Dave said, you won't recoup your costs in fuel savings, but it would be more enjoyable to drive at any distance!
 

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The SBC 400 is a very desirable motor as they are getting hard to find. Used Chevy two bolt blocks are approaching the price aftermarket 400 blocks are sold for. People build 383 motors because they can not find a 400 block (the only difference between a 400 and a 383 is the bore, cost of a 383 is identical to that of a 406). If you wonder why people spend more to build a 383 over a 355 just read on line the testimonials for the 383.

If you want the best mileage install a 250 cubic inch six cylinder. It is a 283 missing two cylinders for better mileage. There exists a 153 cube four cylinder that will bolt in but the engine running flat out all the time will burn more than the six as it is constantly straining.

As a personal testimonial I had a four wheel drive three quarter ton Suburban with a 350 under the hood. It got 9 miles per gallon with 4.56 gears. I removed the 350 after it had already been replaced once before under warranty after blowing it up trying to climb a hill in NC while towing a 6000 pound trailer. I replaced it with a 454, and my mileage improved to 11 miles per gallon. Bigger motor yet it got better mileage because the 350 was always running flat out to get that amount of GVW down the road.

The 400 was developed by Chevrolet engineers in 1970 primarily to allow Impala and Caprice owners the performance equivalent of a Cadillac with an increasingly heavy car. Cadillac had to go to a 500 cube motor to motivate their lead sleds (which is essentially an Impala that has ten extra inches in the rear seat room for passenger comfort). The heavier the car the bigger the motor has to be to move it. That is why the 327 was stroked out to a 350 in 1968, just to move the Impala around as the cars got heavier every year as more options became standard equipment on the car.

Big Dave
 
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