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Old 12-29-2010, 08:28 PM   #1
84 400
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What have i got in this small block v8?

Got this motor out of a plow truck said to have vette heads and 4 bolt mains. Had a edelbrok preformer intake and holley 750 carb and hei distributor. A bit too much carb if you ask me ... Anyways Was going to do a simple reseal and paint it and put it in my 1956 Willys wagon but ran into some issues. First was snapped off header bolts. Used the welding a nut on trick and got them out. Now the damn spark plug broke off in the head. Tried welding a bolt to it but no dice. So I pulled the head and am gonna take it to the machine shop tomorrow. Anyways I am trying to run the numbers and figure out exactly what i have and if it is any good.

The back of the block has GM 6.7 stamped in it.
It has a one piece rear main seal and a pass side dipstick so it has to be 86 and up
Have not dropped the pan yet but since it was in a truck I am guessing/ hoping it has four bolt mains

On the stamping pad it says 70707FBM and THF58

After running the engine code i found it was built at Tonawanda on July 7th but have no clue what FBM means

On the cylinder heads it says 3927188 J20

After running the numbers online I found that the heads are 1969 327 heads with 74CC

Is this information correct? Are these cylinder heads decent? good? Garbage?

Thanks for any and all info.
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1984 chevy c10, built 400sb,.(SOLD)
77 K10 Project / daily driver "The Grinch" http://67-72chevytrucks.com/vboard/s...d.php?t=318363
1956 Willys Wagon (327 chevy) Project (Now Buick 225)
1980 Corvette L-48 4 speed
1992 Mustang GT built 5.0 5 speed

1985 C10 LWB Sold
1982 K10 SWB plow truck Parted out
1986 D30 M1028 fire brush truck Parted out
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Old 12-29-2010, 08:41 PM   #2
ka_jd7and1
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Re: What have i got in this small block v8?

What casting number are the heads?

FBM is the suffix code for an '87 350 out of a truck, 170HP with TBI.

I would bet somebody changed the top end for some more power and a carb.
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Old 12-29-2010, 09:25 PM   #3
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Re: What have i got in this small block v8?

IM gonna guess that the back of the block says gm 5.7. denoting a newer 1 pc seal block. The block is 86-up. roller cam capable. Heads are junk either 307 or 327 low performance small valve heads. Its funny how many sets of corvette heads there are. probably 100 times more than there were corvettes made.You would have been better off with the heads that orginally came on the block at least they would have had 1.94 valves instead of the 1.72's your heads have. If you plan on even attempting to make any power you need to look into some different heads. The carb is way too big for the application. Especially considering those heads arent gonna make any power past 4500rpm or so.
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Old 12-29-2010, 11:32 PM   #4
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Re: What have i got in this small block v8?

yeah the heads have been completely rebuilt by the looks of it (said motor was built 10years ago???) They have different springs on them and it may have had valve work done.... If it is an easy fix on the spark plug I am gonna continue with a respray and reseal. The willys still has stock drive train with 488 gearing so I do not need a screaming small block.

Now I am wondering what type of cam it has... I am surprised someone went threw all the work to redo the heads and they are not worth much. On a carb would I be better off in the 600 and down cfm range? I don't have much money right now and the unexpected expense of the 1 piece rear main needing a different flywheel is hurting my budget. I will probably stick with the holley until i can afford a smaller carb.

Thanks for the info.
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1984 chevy c10, built 400sb,.(SOLD)
77 K10 Project / daily driver "The Grinch" http://67-72chevytrucks.com/vboard/s...d.php?t=318363
1956 Willys Wagon (327 chevy) Project (Now Buick 225)
1980 Corvette L-48 4 speed
1992 Mustang GT built 5.0 5 speed

1985 C10 LWB Sold
1982 K10 SWB plow truck Parted out
1986 D30 M1028 fire brush truck Parted out
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Old 12-29-2010, 11:42 PM   #5
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Re: What have i got in this small block v8?

I've got a set of those heads... I pulled them off of my Impala years ago and put on better heads. I still have them in the garage, but only because I save all the stock parts from that car. Otherwise, they would have been scrap about 12 years ago.
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Old 12-30-2010, 01:57 AM   #6
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Re: What have i got in this small block v8?

was looking at these more and noticed they have the "double hump" on them and have comp cams push rod guides. Was looking on the casting number site and saw that the
number i read as 3927188 might be 3927186 which is
302/327/350
68-72
1.94/1.50 2.02/1.60
64cc Doubble humps Bolt holes


Hey USSkoval do your old heads have the double "hump" on them?
who knows maybe just wishful thinking ........ but it would make more sense and be inline with what the PO told me
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1984 chevy c10, built 400sb,.(SOLD)
77 K10 Project / daily driver "The Grinch" http://67-72chevytrucks.com/vboard/s...d.php?t=318363
1956 Willys Wagon (327 chevy) Project (Now Buick 225)
1980 Corvette L-48 4 speed
1992 Mustang GT built 5.0 5 speed

1985 C10 LWB Sold
1982 K10 SWB plow truck Parted out
1986 D30 M1028 fire brush truck Parted out
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Old 12-30-2010, 08:27 PM   #7
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Re: What have i got in this small block v8?

Mine are not double humps, but I don't remember the casting number. They are the low po 235 horse 327 heads with the small valves.

If they have the double humps on them, they are the good heads. Not fantastic by today's standards, but if they are in good shape, go ahead and run them.
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Old 01-02-2011, 02:08 AM   #8
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Re: What have i got in this small block v8?

had to pull them off because of 2 broken spark plugs (damm rusty plow truck). brought them to the local machine shop and he is gonna check them over and remove the ****ty plugs. They are 1969 heads with the accessory holes. they have different valve springs and comp cams valve guilds. some one did some work to make the guilds fit and that caused the casting numbers to be shaved down. machinist thought maybe someone was trying to run them on a numbers matching engine and cheating or something....

They are double humps with the smaller 194 valves

here are some pictures.




Thanks for all the help!
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1984 chevy c10, built 400sb,.(SOLD)
77 K10 Project / daily driver "The Grinch" http://67-72chevytrucks.com/vboard/s...d.php?t=318363
1956 Willys Wagon (327 chevy) Project (Now Buick 225)
1980 Corvette L-48 4 speed
1992 Mustang GT built 5.0 5 speed

1985 C10 LWB Sold
1982 K10 SWB plow truck Parted out
1986 D30 M1028 fire brush truck Parted out
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