Is this car devalued by a non-matching motor - Impala Tech
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post #1 of 6 (permalink) Old 08-25-2018, 04:29 PM Thread Starter
Join Date: Aug 2018
Location: Waukesha, WI
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Is this car devalued by a non-matching motor

I am interested in purchasing a Triple Black '66 Impala SS convertible. This car was originally a 427SS with a 4 speed manual transmission, and is badged as such. Someone stole the car and removed the engine and transmission from it. The car was recovered by the police, and the owner put a 396 in it, with a manual 4 speed transmission. The overall car only has 38k miles on it, and is in A+ shape. Not sure about the mileage on the 396 and transmission. The owner wants 42K for the vehicle. How much does the current engine and trans setup devalue the car, if at all? What would be a fair price for this car in its current condition?
How hard would it be to find a date code correct 427 and transmission for this car? Approximate cost of such a find?

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civman is offline  
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post #2 of 6 (permalink) Old 08-25-2018, 05:17 PM
Join Date: Jul 2009
Location: Canada
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Yes, the wrong engine seriously hurts the value. Check the Hagerty website for values. It's not just about a date coded engine, the engine is VIN-stamped as well, so the car will never be numbers matching.

Two doors, four doors, wagons, and ragtops.
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post #3 of 6 (permalink) Old 08-25-2018, 06:06 PM
Join Date: Jan 2006
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Date code won't apply because all big blocks from 1963 forward were stamped with a partial VIN number on the engine itself. Same for the tranny. You could find a two bolt main 390 horse 427 (passenger version), but it will be stamped with a VIN different from your car's VIN.

Personally, I think that the guy selling the car has been watching to many TV auctions. It isn't worth that much in my opinion but then I have a low opinion of factory SS vehicles or numbers matching; having built most of my cars from junk yard parts installed in an old unloved used car.

That said you can install a 1976 454 (used the same block as the 427) and it will have the same date code as your missing engine because GM recycled the date codes every ten years. On a rebuild, deck the block and bore it thirty over then install a quarter inch stroker crank to make a 496 cube motor. Casting numbers may be different, I can not recall when they changed, and I am too lazy to look it up in my Chevrolet by the Numbers book (Alan Colvin 1965-'69 edition).

You could restamp the 454 block by hand with your VIN (used a 3/16" Gothic Normal), and make up a fake date code ( 1/8" Bookman) based upon your car's build date (should be 10 to 18 days before the build date depending upon how far your assembly plant was located from Tonawanda, NY; were your motor was cast, machined, and assembled).

GM bought their dies from three different sources. I think the only one still in business today is George T. Schmidt & Co. (Chicago).

I believe that you wouldn't be the first to fake a numbers matching car to justify an inflated purchase price. Most enthusiast (especially those who think numbers mater) consider this to be fraud, but I have restamped many 396 blocks for customers that blew up their born with motors in their Camaros (I put the same numbers from the old block on the new rebuild). I often wonder if any my old motors were ever sold by Mecum as a numbers matching original.

Big Dave
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post #4 of 6 (permalink) Old 08-25-2018, 07:59 PM Thread Starter
Join Date: Aug 2018
Location: Waukesha, WI
Posts: 5
Thanks for the information.
I was just interested in the buy pricing for this vehicle. I'm thinking somewhere around 28k, all in. I was just wondering, if I put a 427 (L72 or L36) back in the car, would it add value. I just think the 396 under powers the car a bit. The 427 would give it balls again. My journey in this project continues....

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post #5 of 6 (permalink) Old 08-25-2018, 09:04 PM
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In 1966 there were 1,856 L-72 427's installed in a Biscayne and the Impala (though most were in the lighter Biscayne two door sedan than an Impala). There were 568 1968 427 SS impala and 546 1969 427 SS Impala cars built which was the entire record of L-72's in a full size Chevy. It bears noting that these were their own model, and didn't count the number of 390 horse 427's and 350 horse 396 Impala SS cars that were built. (I could find documentation for only 11 1967 427 Impalas built, but I have to believe there was more than that made).

This also needs to be brought up. The L-72 425 horse 427 had 11:1 compression with cast iron closed chamberd heads. You can not run above 9.2:1 compression with cast iron heads on a SBC or 8.7:1 with a BBC with today's 93 octane pump gas. It will send the motor into detonation if you try.

To run on the street (pump gas) you need lots of cubes to make a BBC work. A 496 is a good start, though most have a 540 or bigger motor. They all look alike so you can not believe the decal on the air cleaner. 582 is as big as you can go with a standard deck block (and expect anyone not to laugh at your 396 decals).

With a truck block a 632 is a good start though the current max is over 905 cubes in a "Chevy BBC" even though there are no Chevy parts used in that motor made by Pat "Popeye" Mussi.

A 396 is like running a 305 SBC instead of a 350. Like the 305 the bores of a 396 are too small to prevent the cylinder walls from shrouding the valves and killing breathing capability. Nothing personal but a 400 cube SBC will double your power and take 140 pounds of ugly weight off of your front axle while doing it. The only restriction on a SBC 400 is the Chevy block. Above 500 horsepower you will break the block. (I had a 513 horse power 406 in my '89 Caprice and loved it for seven years, until I split the block in two). If you are going for more than 500 horsepower with any SBC; buy a Dart Little M block to build it with.

Big Dave
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post #6 of 6 (permalink) Old 08-26-2018, 07:41 AM
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Location: Coopersville, MI
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Value is based on the individual and purpose of the car. A true collector who wants a trailer queen will be all over the numbers matching car for their collection and due to the rarity of a car its value can be pretty high.

The next tier for those that can't afford the real thing are well done clones. These cars look like the real deal and have a drive terrain that matches the real deal, but the numbers and date codes don't all add up. Depending on the rarity of the real deal these clones can be a real deal for someone that plans on doing a little driving. They may sell for half the price of the real deal.

Then you have the next level which look like the real deal, but instead of a stock motor it may be stroked out or instead of a 427 it has a 454. And from here it just keeps getting further from stock with things like swapping in overdrive transmissions and such, but at some point as you make your changes the cars value starts to increase. As I have seen some totally custom cars running modern drive terrain with modern suspension and all kinds of body tweaks sell for more than a numbers matching less desirable car.
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