502 block cast.# 12561358 has 454 bore size
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502 block cast.# 12561358 has 454 bore size
just got a core motor from wrecking yard, block casting # 12561358 and heads 12561358.
chevy shows them as 502 crate motor, fuel pump boss and flat tappet cam with provision for roller tappet holder.
The problem is: the bore size is 4.250- 454 size.
Heads have enormous ports, 118 CC chamber, forged steel crank,the exhaust manifolds are almost twice the size of a normal 454.
Don't know what to make of it !!!
chevy shows them as 502 crate motor, fuel pump boss and flat tappet cam with provision for roller tappet holder.
The problem is: the bore size is 4.250- 454 size.
Heads have enormous ports, 118 CC chamber, forged steel crank,the exhaust manifolds are almost twice the size of a normal 454.
Don't know what to make of it !!!
Last edited by Griff; 06-29-2020 at 12:07 AM.
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Are you sure the block isnt 12561357 ? That is a 454. Then again GM has certainly made mistakes in casting numbers. Have seen plenty of them over the years. It would be very unusual to find a 502 engine in a wrecking yard. What is the engine code stamped on the front pad of the block ? That would give you another clue.
Either way if its 4.250 bore then its 4.250 bore. What else is there to say.
Either way if its 4.250 bore then its 4.250 bore. What else is there to say.
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Are you sure the block isnt 12561357 ? That is a 454. Then again GM has certainly made mistakes in casting numbers. Have seen plenty of them over the years. It would be very unusual to find a 502 engine in a wrecking yard. What is the engine code stamped on the front pad of the block ? That would give you another clue.
Either way if its 4.250 bore then its 4.250 bore. What else is there to say.
Either way if its 4.250 bore then its 4.250 bore. What else is there to say.
yes...clearly cast 12561358 and the heads 12562932 (502 head casting), cast crank 10114188, 7.4 liter on side of block, looked in freeze plug and almost siamesed cylinders. I actually did not want a 502, 454 is even too big for the 70 chevelle that's getting restored. Just confused by the casting numbers and size of the ports of the heads.
Could GM use same casting cores and mark 7.4 for the 454 and 8.2 for the other?
oh well...I got what my customer wanted so everybody is happy...just confused!!!!
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Originally Posted by [email protected]
Could GM use same casting cores and mark 7.4 for the 454 and 8.2 for the other?
Originally Posted by [email protected]
heads 12562932 (502 head casting).
.
.size of the ports of the heads.
.
.size of the ports of the heads.
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thanks for the info, it should make a nice smooth motor for the chevelle, would like little more compression but at +.030 over flat top pistons .040 gasket, .020 deck is 8 to one!!! would like 9 to 1.
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I don't understand much of this thread. But I'm quite dumb and don't get much.
502 casting block but no 8.2L markings on outside of block and 4.25" bore ?
'Huge ports in heads' that are oval ports ?
'Exhaust manifolds twice the size of normal 454 exhaust manifolds' ?
502 casting block but no 8.2L markings on outside of block and 4.25" bore ?
'Huge ports in heads' that are oval ports ?
'Exhaust manifolds twice the size of normal 454 exhaust manifolds' ?
#7
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Blocks with incorrect casting numbers are a lot more common than guys realize. When you see them all day every day you stop worrying about it. As far as the manifolds go they are probably just truck manifolds which can be larger than what guys are used to seeing on a 71 Chevelle. I bet the ports are no larger than any other 454 oval port head. Pics would be nice
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SB (06-30-2020)
#8
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Originally Posted by [email protected]
thanks for the info, it should make a nice smooth motor for the chevelle, would like little more compression but at +.030 over flat top pistons .040 gasket, .020 deck is 8 to one!!! would like 9 to 1.
#10
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Originally Posted by [email protected]
the ports on the 12562932 heads are bigger than the big oval heads Gen IV motor, have them side by side.
Now,, you mention a Chevelle. You will REALLY be doing the owner a favor by finding some mid '90s GM Vortec heads w 100cc closed chambers. ZERO deck the block for a .040" quench clearance with the flat tops. You might even find somebody willing to swap heads even with you. The closed chamber and tight squish will give you a lot more compression AND detonation resistance. The throttle response on the street will be MUCH more satisfying than where you are currently headed. Cam it around 220@050 duration. Initial timing 16-18 degrees, 36 total, all in by 2500rpm. Run a vacuum advance - if an auto use ported vacuum. If a stick shift, run the vacuum direct to the plenum.