1966 Question

[Marvin B.]

Hello! I am trying to help a friend of mine (who is not a NCRS member) to determine what engine his car was born with. As I dig into the information he has provided to me, I find that his engine is not original to the car. This car is a 1966 Corvette 2-dr convertible equipped with a replacement 427 cu in big block engine built to 425 HP specs with a 0.30 overbore and with a stock cam, but it is not a numbers matching engine to the car. The owner states that the previous owner insisted the car came with a 427/425, but when the previous owner bought the car, it had a small block in it. The previous owner then put the 427 in it. The block has been decked and information onpassenger front pad has been shaved off. The engine casting number is 3869942, which is consistent with a 427 bigblock either 390 hp or 425 hp. The VIN and trim tag are consistent with the vehicle being built in February 1966. The owner does not have any documentation.

My question is this: I know that the engine is likely not original, but without the original engine, is there any way that I can determine what engine the car was born with? Thanks in advance for your help.

[Bob R.]

Re: 1966 Question

It's not that difficult to make a big block out of a small block if you are willing to spend a little money and you can recoup that money when you sell the car as a big block so I'm sure this happens. If the car was originally a 425 it would have a high horse tach and a rear sway bar of course these things can and have been added or changed but it gives you something to look for.

[Bill M.]

Re: 1966 Question

Couple of things come to mind. the red line on the tachometer, oil pressure gauge, check the caps on the rear that hold the drive shaft universal, size of sway bars, check size number of coils on front springs, I am not sure but maybe location of voltage regulator. these wont tell you HP but may help in finding if big or small block. Get a hold of Nolans book and compare pictures.

[Richard G.]

Re: 1966 Question

Manual transmission would have been a mandatory options. Look for evidence of any other transmission.
Inspect for the mounting holes for the TI box. It was a mandatory option with the 425hp motor.
It would also been possible to have been a 390 hp 427 with the optional TI but that would be a rare dog.
No method to exactly identify a 425 hp motor option, without a history or documentation, but you can go with the best odds.

[Jim D.]

[Larry E.]

Re: 1966 Question

FWIW: If you can get copies of the the previous titles the "taxable horsepower" is indicated>

Taxable HP = (bore squared x number of cylinders)/2.5

So a 4-inch bore V-8 is 51.2 and a 4.25-inch bore V-8 is 57.6.

[Marvin B.]

Re: 1966 Question

Thank you to all of you for responding so quickly on my request. I've made an appointment to see the car to document many items, all of which can't prove to a certainty what engine the car was born with. This will be a learning experience for me.

Bob R: Back in the day I have removed engines and replaced them with either SB or BB engines because of various reasons, so I agree that in today's world if someone wanted to replace a SB with a BB and do it "right", it could be very hard to determine originality. The tach and rear sway bar will be photographed and sway bar measured.

Bill M: As noted to Bob, I'm going to check the tach. The oil pressure gauge should be 80# The sway bars and coil springs will be measured for size. I don't have Nolan Adam's book but do have M.F. Dobbins Fact book. I gathered some information from there.

Richard G: I'm hoping to be able to get numbers from the 4-spd tranny and rear axle data. Also will check the TI box or the evidence that it may have been there.

Jim D: Hopefully the fuel line will still be original. I don't have a judging guide, but got a few more leads from Corvette Forum.

Larry E: We don't have taxable horsepower in Wisconsin, but I'll put the formula my file! Thanks!

In visiting with the owner, I found that the previous owner may have information useful to this search. I also know the mechanic that does all the repairs, so hoping to be able to get info from him. With many pieces of the puzzle coming together, I still may not be able to make a determination what the car was born with, but the journey may be more interesting than the final destination!

Thank you all again!!! You have given me several things to consider. Marv B

[Marvin B.]

Re: 1966 Question

Okay. I have seen the car and agree that the car is now equipped with a replacement 427 cu in big block engine, but it is not a numbers matching engine to the car. However it has a casting number of 3869942 and suffix of IP. My research shows that it is a later 1966 Corvette block.

What would the judging criteria be on the vehicle with a replacement block as described? The vehicle tags are consistent with the vehicle being built in February 1966.

Thanks in advance for your help.