small block 400 or 377 c.i. stroker?
03-11-2014, 06:06 PM
#1
Cruising
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small block 400 or 377 c.i. stroker?
Hello, I recently purchased my first C3 Corvette Stingray, year 1976. I was told by the previous owner that it was a numbers matching L48 car. I checked the casting numbers on the driver side rear of the engine block and it should have been stamped 3970010 which makes it a 350 sbc, instead this is what I have. Casting #3951511 This comes back to a small block 400, and the suffix code on the right front pad of the engine is CPK. This comes back to a 1972 Caprice 400 4-bolt main. What really amazes me is that the harmonic balancer does not have the cut-out groove on the back side of the damper like a 400 sbc should have. This damper is smooth all the way around, and looks like a 350 sbc damper. The engine runs very strong, has lots of power and endless torque! The heads appear stock, and it sounds like it has a RV cam, nothing radical. Cast iron 4-barrel intake and Rochester Quadra-Jet carb. I'm trying to figure out if this engine was destroked to a 377 small block? Any help is greatly appreciated. Thank you
03-11-2014, 06:44 PM
#2
Race Director
Hello, I recently purchased my first C3 Corvette Stingray, year 1976. I was told by the previous owner that it was a numbers matching L48 car. I checked the casting numbers on the driver side rear of the engine block and it should have been stamped 3970010 which makes it a 350 sbc, instead this is what I have. Casting #3951511 This comes back to a small block 400, and the suffix code on the right front pad of the engine is CPK. This comes back to a 1972 Caprice 400 4-bolt main. What really amazes me is that the harmonic balancer does not have the cut-out groove on the back side of the damper like a 400 sbc should have. This damper is smooth all the way around, and looks like a 350 sbc damper. The engine runs very strong, has lots of power and endless torque! The heads appear stock, and it sounds like it has a RV cam, nothing radical. Cast iron 4-barrel intake and Rochester Quadra-Jet carb. I'm trying to figure out if this engine was destroked to a 377 small block? Any help is greatly appreciated. Thank you
03-12-2014, 12:50 PM
#3
Pro
My opinion is it is neither.
The number of wrong flexplates or balancer stories is overwhelming.
Ken
03-12-2014, 02:25 PM
#4
Team Owner
I will bet you $100 that it isn't a 377
It was a very rare mod only done by racers in the 70's and early 80's. Back then you didn't have Summit Racing or jeg's where you can just about buy any part.
the 400 block has bigger main bearings. So you had to machine your own bearing spacers for a 350 crank. But stupidity was that forged cranks, rods, and valve train was not up to the potential like today.
Back then the "Pink" forged rods and bolts are weaker than modern junk forgings from SCAT and eagle.
As to your comment about single planes. I have run the biggest single planes and tunnel rams with dual 4 barrels in all my street rods and Vette since the 80's. I always had big head ports and the majority of the dual planes 20+ years ago were not tuned engineering
At streetable rpm the biggest ci always wins. 30 years ago I was very proud of my 337 ci 4.060 X 3.25 with a tunnel ram in a dragster and later in my street rod. So what if you could run it to 8000 rpm. It would still have less TQ and slower ET that throwing just a 3.75 stroker crank in making a 385 ci and lowering the red line to 7500
It was a very rare mod only done by racers in the 70's and early 80's. Back then you didn't have Summit Racing or jeg's where you can just about buy any part.
the 400 block has bigger main bearings. So you had to machine your own bearing spacers for a 350 crank. But stupidity was that forged cranks, rods, and valve train was not up to the potential like today.
Back then the "Pink" forged rods and bolts are weaker than modern junk forgings from SCAT and eagle.
As to your comment about single planes. I have run the biggest single planes and tunnel rams with dual 4 barrels in all my street rods and Vette since the 80's. I always had big head ports and the majority of the dual planes 20+ years ago were not tuned engineering
At streetable rpm the biggest ci always wins. 30 years ago I was very proud of my 337 ci 4.060 X 3.25 with a tunnel ram in a dragster and later in my street rod. So what if you could run it to 8000 rpm. It would still have less TQ and slower ET that throwing just a 3.75 stroker crank in making a 385 ci and lowering the red line to 7500
03-12-2014, 02:45 PM
#5
Race Director
It would be noticeable if it was the wrong damper. It would shake like an out of balanced washing machine load, increasing with RPM. Best bet is it was a 400 block rebuilt with an internally balanced 400 rotating assembly if it runs strong and smooth at rpm. You can buy a 400 main 3.48 crank to destroke it or the main bearing spacers but if someone went through choosing a 400 block to rebuild and used the existing external parts likely they bought the internally balanced 400 rotating assembly to make it all work if they had a clue. It is only a couple hundred more.
03-12-2014, 02:48 PM
#6
Race Director
I will bet you $100 that it isn't a 377
It was a very rare mod only done by racers in the 70's and early 80's. Back then you didn't have Summit Racing or jeg's where you can just about buy any part.
the 400 block has bigger main bearings. So you had to machine your own bearing spacers for a 350 crank. But stupidity was that forged cranks, rods, and valve train was not up to the potential like today.
Back then the "Pink" forged rods and bolts are weaker than modern junk forgings from SCAT and eagle.
As to your comment about single planes. I have run the biggest single planes and tunnel rams with dual 4 barrels in all my street rods and Vette since the 80's. I always had big head ports and the majority of the dual planes 20+ years ago were not tuned engineering
At streetable rpm the biggest ci always wins. 30 years ago I was very proud of my 337 ci 4.060 X 3.25 with a tunnel ram in a dragster and later in my street rod. So what if you could run it to 8000 rpm. It would still have less TQ and slower ET that throwing just a 3.75 stroker crank in making a 385 ci and lowering the red line to 7500
It was a very rare mod only done by racers in the 70's and early 80's. Back then you didn't have Summit Racing or jeg's where you can just about buy any part.
the 400 block has bigger main bearings. So you had to machine your own bearing spacers for a 350 crank. But stupidity was that forged cranks, rods, and valve train was not up to the potential like today.
Back then the "Pink" forged rods and bolts are weaker than modern junk forgings from SCAT and eagle.
As to your comment about single planes. I have run the biggest single planes and tunnel rams with dual 4 barrels in all my street rods and Vette since the 80's. I always had big head ports and the majority of the dual planes 20+ years ago were not tuned engineering
At streetable rpm the biggest ci always wins. 30 years ago I was very proud of my 337 ci 4.060 X 3.25 with a tunnel ram in a dragster and later in my street rod. So what if you could run it to 8000 rpm. It would still have less TQ and slower ET that throwing just a 3.75 stroker crank in making a 385 ci and lowering the red line to 7500
03-12-2014, 04:06 PM
#7
Team Owner
No he brought it up in that other thread that nobody uses single planes on the street.
I can't say this for sure, but if it really is a 400 small block and externally balanced. I saw a damper that was just factory weighted on one side. Not drilled like a balance job and who ever had balanced the motor by welding lots of metal to the flex plate.
I just think destroking is dumb. Modern metals and designs have far exceeded the piston feet per minute of yesteryear.
What fails more often is the valve train. So it is not that hard to build sub 7000 rpm motors clear out to 4.250 inch strokes. So you are losing TQ not going with the longest stroke practical. that is why I gave up on building 383's and went to the longer 3.875 to make 396 ci small blocks Or 415 - 421 ci from 400 blocks
I can't say this for sure, but if it really is a 400 small block and externally balanced. I saw a damper that was just factory weighted on one side. Not drilled like a balance job and who ever had balanced the motor by welding lots of metal to the flex plate.
I just think destroking is dumb. Modern metals and designs have far exceeded the piston feet per minute of yesteryear.
What fails more often is the valve train. So it is not that hard to build sub 7000 rpm motors clear out to 4.250 inch strokes. So you are losing TQ not going with the longest stroke practical. that is why I gave up on building 383's and went to the longer 3.875 to make 396 ci small blocks Or 415 - 421 ci from 400 blocks
03-12-2014, 06:07 PM
#9
I will bet you $100 that it isn't a 377
It was a very rare mod only done by racers in the 70's and early 80's. Back then you didn't have Summit Racing or jeg's where you can just about buy any part.
the 400 block has bigger main bearings. So you had to machine your own bearing spacers for a 350 crank. But stupidity was that forged cranks, rods, and valve train was not up to the potential like today.
Back then the "Pink" forged rods and bolts are weaker than modern junk forgings from SCAT and eagle.
As to your comment about single planes. I have run the biggest single planes and tunnel rams with dual 4 barrels in all my street rods and Vette since the 80's. I always had big head ports and the majority of the dual planes 20+ years ago were not tuned engineering
At streetable rpm the biggest ci always wins. 30 years ago I was very proud of my 337 ci 4.060 X 3.25 with a tunnel ram in a dragster and later in my street rod. So what if you could run it to 8000 rpm. It would still have less TQ and slower ET that throwing just a 3.75 stroker crank in making a 385 ci and lowering the red line to 7500
It was a very rare mod only done by racers in the 70's and early 80's. Back then you didn't have Summit Racing or jeg's where you can just about buy any part.
the 400 block has bigger main bearings. So you had to machine your own bearing spacers for a 350 crank. But stupidity was that forged cranks, rods, and valve train was not up to the potential like today.
Back then the "Pink" forged rods and bolts are weaker than modern junk forgings from SCAT and eagle.
As to your comment about single planes. I have run the biggest single planes and tunnel rams with dual 4 barrels in all my street rods and Vette since the 80's. I always had big head ports and the majority of the dual planes 20+ years ago were not tuned engineering
At streetable rpm the biggest ci always wins. 30 years ago I was very proud of my 337 ci 4.060 X 3.25 with a tunnel ram in a dragster and later in my street rod. So what if you could run it to 8000 rpm. It would still have less TQ and slower ET that throwing just a 3.75 stroker crank in making a 385 ci and lowering the red line to 7500
03-12-2014, 09:16 PM
#10
Cruising
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Something like this is what I would guess they used. http://www.summitracing.com/parts/es...make/chevrolet
03-12-2014, 09:45 PM
#11
Race Director
63mako, Are you saying that some 400 sbc came from the factory with the damper weighted on the inside without the groove cut-out as seen on most 400 dampers? If so, then it's quite possible this is what I have. I just noticed that the damper did not have the cut-out groove in the rear of the damper when I was installing a new water pump. There is no vibration coming from the engine when being driven, and if the 400 received a internal balanced rotating assembly in the past, my question is why? The way the engine originally came from the factory, I simply don't see any reason why rebuild, if there wasn't anything wrong with it. So, my bet is that it's not been destroked, just a damper weighted like the original damper with the cut-out in the rear. It is a true 400, as the casting number doesn't lie. #3951511 suffix code CKP which is a 1972 400 4-bolt main. 1973-80 were all 2-bolt mains. Thank you for your input.
http://www.speedwaymotors.com/Small-...teel,7812.html
Some aftermarket dampers have a weight attached at the back inside of the damper. You will feel it if you put your fingers back there and slide them around the rear of the damper.
Last edited by 63mako; 03-12-2014 at 09:53 PM.
03-13-2014, 12:33 PM
#12
Hello, I recently purchased my first C3 Corvette Stingray, year 1976. I was told by the previous owner that it was a numbers matching L48 car. I checked the casting numbers on the driver side rear of the engine block and it should have been stamped 3970010 which makes it a 350 sbc, instead this is what I have. Casting #3951511 This comes back to a small block 400, and the suffix code on the right front pad of the engine is CPK. This comes back to a 1972 Caprice 400 4-bolt main. What really amazes me is that the harmonic balancer does not have the cut-out groove on the back side of the damper like a 400 sbc should have. This damper is smooth all the way around, and looks like a 350 sbc damper. The engine runs very strong, has lots of power and endless torque! The heads appear stock, and it sounds like it has a RV cam, nothing radical. Cast iron 4-barrel intake and Rochester Quadra-Jet carb. Thank you
I would definitely be jumping for joy if I found out my 76 had a 400 in it instead of a 350. 
03-13-2014, 04:03 PM
#13
Cruising
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At first I thought it was a destroked 400sbc, since the damper did not have the cut-out groove in the back. Instead, the 400 was rebuilt at some point with a internal balance rotating assembly, which is why the 400 does not have the stock damper. It's a 4-bolt main, came out of a 1972 Caprice. Actually, I am happier that my Vette has the 400 instead of the L48 350, in which the 400 has much more power and torque over the L48 engine that was in it. The previous owner must have blown the L48, and didn't want to deal with it and probably just had the 400 as a back-up engine, who knows. the guy a bought the Vette from told me it was a matching numbers car. But I was really surprised that it had the 400, although the value of the car depreciated a little since the factory L48 is long gone. No big deal, I am happy with the car anyway.
05-07-2014, 04:30 PM
#14
Racer
Guess people like putting 400 sbc in the 76s, I also have a 76 with a sbc 400 (511) but the car is more of a parts car(rusty). I been debating taking out the l48 in my stock 76 and putting this in there instead since it is a solid car. I feel a corvette should be able to spin the tires maybe that's just me
76 stock l48 = cant spin tires
76 400sbc = spins tires
76 stock l48 = cant spin tires
76 400sbc = spins tires
05-07-2014, 04:43 PM
#15
Safety Car
Are you sure it's a GM balancer? Aftermarket balancers have a weight that can be bolted in the inside groove for the external balanced 400. Also, have you checked the flywheel for a plate of steel welded to the inside of the ring gear?
Don't forget to look for the 3 freeze out plugs on each side of the motor.
I have a 406 sitting on my engine stand just waiting to be installed but the 350 L83 just won't blow after 130,000 miles
Don't forget to look for the 3 freeze out plugs on each side of the motor.
I have a 406 sitting on my engine stand just waiting to be installed but the 350 L83 just won't blow after 130,000 miles
05-07-2014, 07:01 PM
#16
Le Mans Master
Hello, I recently purchased my first C3 Corvette Stingray, year 1976. I was told by the previous owner that it was a numbers matching L48 car. I checked the casting numbers on the driver side rear of the engine block and it should have been stamped 3970010 which makes it a 350 sbc, instead this is what I have. Casting #3951511 This comes back to a small block 400, and the suffix code on the right front pad of the engine is CPK. This comes back to a 1972 Caprice 400 4-bolt main. What really amazes me is that the harmonic balancer does not have the cut-out groove on the back side of the damper like a 400 sbc should have. This damper is smooth all the way around, and looks like a 350 sbc damper. The engine runs very strong, has lots of power and endless torque! The heads appear stock, and it sounds like it has a RV cam, nothing radical. Cast iron 4-barrel intake and Rochester Quadra-Jet carb. I'm trying to figure out if this engine was destroked to a 377 small block? Any help is greatly appreciated. Thank you
