Corvette "mongrel" motor question
Thread Starter
Drifting
Joined: Jul 2015
Posts: 1,765
Likes: 254
From: Catlett VA
Corvette "mongrel" motor question
We have all heard the SB and BB motors referred to as mouse and rat. I think I have one that should be called a mongrel- combination of a couple types. Just love getting a car with little or no info on the motor. I got this 68 convert in July with a "454" motor. Obviously, swapped out the 427 for the later production 454. I checked the engine code stamped on the block and found it was from a 1968 two door full size Chevy- probably that fancy Caprice sport coupe they made. I just ordered spark plugs, based on the assumption that I needed for a 68 454 engine. (it did not occur to me that they increased the Mark IV engine to 454 cu in in 1970) Plugs arrived and they are not correct for the heads on the car. Plugs on the car are the smaller 5/8 inch size. Plugs ordered came as the larger (think 13/16?) size. So- heads on the car do not match the block. I did not check head casting numbers to see what year they are Does anyone know when Chevy switched to the smaller spark plugs? I'm thinking about 1974. So- back to the engine code lists, but I think I may have a 427 block made in 1968 with 454 heads made in ????. Does that make sense?
Safety Car
Joined: Sep 2007
Posts: 4,458
Likes: 331
From: Indy Indiana
sometimes you can see the date code for the head after removing the oil filler cap.. otherwise you have to remove a valve cover to get the casting code and the date code.. let us know what you find.
a 454 is just a 427 with a 454 crank in it.. but due to the longer stroke there have to be reliefs cut into the bottom of the cylinder walls to keep the rods from contacting the cylinder walls due to the longer stroke. the 69 512 block was machined to support this since gm was future engineering the 69 block to support the 454 in 1970.
you most likely have a 427 block..
check the date code in the back of the block behind the distributor and the casting code also. this will tell you what you have.
my book states that the 68 big chevy 427 engine is pretty much the same as the corvette 427/390HP engine so you have a stout engine.
the heads may be a different story, if you have later big block heads they are probably the open chamber heads vs closed chamber for the earlier heads and this will lower your compression and perhaps not be properly mated correctly to your pistons.. dropping your potential power. other opinions may vary...
a 454 is just a 427 with a 454 crank in it.. but due to the longer stroke there have to be reliefs cut into the bottom of the cylinder walls to keep the rods from contacting the cylinder walls due to the longer stroke. the 69 512 block was machined to support this since gm was future engineering the 69 block to support the 454 in 1970.
you most likely have a 427 block..
check the date code in the back of the block behind the distributor and the casting code also. this will tell you what you have.
my book states that the 68 big chevy 427 engine is pretty much the same as the corvette 427/390HP engine so you have a stout engine.
the heads may be a different story, if you have later big block heads they are probably the open chamber heads vs closed chamber for the earlier heads and this will lower your compression and perhaps not be properly mated correctly to your pistons.. dropping your potential power. other opinions may vary...
Thread Starter
Drifting
Joined: Jul 2015
Posts: 1,765
Likes: 254
From: Catlett VA
motor
When I complete all of the annoying other repairs needed, maybe I will pull the cam and add one I like and know about. Old Corvettes- love them or hate them, depending on the day of the week.
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
Pull a valve cover and get the head casting number.
Look it up here:
http://www.mortec.com/bbc.htm
Buy plugs for the description.
Jebby
Look it up here:
http://www.mortec.com/bbc.htm
Buy plugs for the description.
Jebby
Thread Starter
Drifting
Joined: Jul 2015
Posts: 1,765
Likes: 254
From: Catlett VA
motor
Sayfoo- that would be my guess also. The 454 can also chug along at low rpm without fouling the plugs.
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Thread Starter
Drifting
Joined: Jul 2015
Posts: 1,765
Likes: 254
From: Catlett VA
engine numbers
well, I went back and re-checked the numbers. found I was reading one of them upside down.
stamped number front of block above timing cover: T0601TST (Tonowanda, June 01, TST is suffix for 454 truck engine in 1978. Should be LF-8)
casting numbers. Passenger side D21 78
casting numbers driver side 861959
Any other info from thee numbers? Is the passenger side number showing 78 as the production year 1978? Is D21 April 21?
My list for the LF-8 shows 20 and 30 for 3/4 an 1 ton. I'm hoping that also means a four bolt block.
stamped number front of block above timing cover: T0601TST (Tonowanda, June 01, TST is suffix for 454 truck engine in 1978. Should be LF-8)
casting numbers. Passenger side D21 78
casting numbers driver side 861959
Any other info from thee numbers? Is the passenger side number showing 78 as the production year 1978? Is D21 April 21?
My list for the LF-8 shows 20 and 30 for 3/4 an 1 ton. I'm hoping that also means a four bolt block.
Last edited by ronarndt; Dec 17, 2015 at 10:44 PM.
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
861959 is actually 361959
73-90 454 2 or 4 bolt
Unless it an original application....the 4 bolt means almost nothing in a street application other than conversation. A 2 bolt block is stronger than most will ever use or build.
Jebby
73-90 454 2 or 4 bolt
Unless it an original application....the 4 bolt means almost nothing in a street application other than conversation. A 2 bolt block is stronger than most will ever use or build.
Jebby
Last edited by Jebbysan; Dec 17, 2015 at 10:51 PM.
Thread Starter
Drifting
Joined: Jul 2015
Posts: 1,765
Likes: 254
From: Catlett VA
engine numbers
"861959 is actually 361959" Jebby- you can not believe how much time I spent trying to decipher that casting number. Part of the raised characters of the numbers were missing from rust or wear. I still would not mind having a four bolt. I re-built a 2 bolt for my truck a couple years ago and you are right- the 2 bolt is a stout engine.