Truck Shop
Senior Member
Procrastinated about posting but what the heck.
Started on one of two identical 454 chevy rebuilds for one ton 4x4 tow trucks, outside work I guess.
Both are old LS-5's gen IV, early 70's, 1974's to be exact, low power/torque engines built during the
oil embargo of 1973. Chevy detuned the 454 which came out in 1970 rated up to 450 hp and was
said it was a conservative figure put on it for insurance reasons, although no dyno proof it was 500 hp.
1974 versions were rated at 215 & 235 horse power and 360 torque. With a compression ratio of 8.2
and 7.8 depending on cylinder head combustion chamber CC's, chevy made closed and open chamber
heads ranging from 99 to 122 CC's using flat top 2 & 4 valve relief pistons and a steel shim head gasket.
Camshafts were really small, 196 intake & 200 duration @ .050 lift which was 215 & 230 advertised
duration. Lift was really low 398 and 415 advertised. The real low profile intake manifolds were basically
nothing more than a place to mount a 4 barrel, and the Quadrajet was 600 to 650 cfm but wasn't a
real problem. There were 750 & 800 CFM Q-jets which can be distinguished by a small bump inside
bottom of primary venturi's. Heads were either 2.07 or 2.19 intake valves, but 2.07's work just fine
for mild power gains.
----Both of these engine will get a compression ratio bump to 9.1 with 100 thousands tall hypereutectic
dome pistons. To figure that a formula of bore and stroke with compression height, a dome volume of
-10.50 and deck clearance with head gasket figured in gives compression ratio. Hypereutectic pistons
reflect allot of heat back to combustion chamber so a real critical step is ring gap, wider by double for
top ring and a few thousands for second ring. A standard gap for a bore over 4" is .004 for inch of bore
diameter. The gap for towing is figured @ .008, so 8 x 4.25 = .034 top ring gap and .018 for second.
Reason--the heat transfer to top ring can close the gap breaking piston ring lands destroying pistons
and scratching the bore. Plus a little extra piston skirt clearance @ .004 will have it run well.
---Cylinder heads are 241 castings with 113 CC chambers 2.07 valves, oval ports. a common head
back then. With stock ratio-stock sled rockers and 3/8" diameter pushrods, Chevy also made them with
5/16 pushrods. Roller rockers or roller tip rockers really add {zero hp gain} unless a higher ratio &
combined with a roller cam, stock ratio is 1.7.
---Camshaft I will use will be a Comp Cams 260 flat tappet. Single pattern @ 112 lobe center 206* duration
@ .050 lift both intake and exhaust which is 260* duration advertised and .475 lift. Would like use a
Howards Cam 263*/.488 lift but none in circulation and would be a 3 month wait. Anything over 268*
duration and vacuum drops and makes for lousy power brakes and around town drivability. Plus a cam
for this application needs to have a working range of 1000 to 4500 rpm, with a fairly smooth idle.
---Carb will be a Edelbrock 650 AVS-{air valve secondary} mechanical. With this configuration for street
it only requires 610 cfm. With a medium rise aluminum intake and 1 5/8 headers.
---Should produce 390 hp and roughly 450 lbs torque. Will have a few photos when assembling.
One I built some years back---485 hp below.
*
Started on one of two identical 454 chevy rebuilds for one ton 4x4 tow trucks, outside work I guess.
Both are old LS-5's gen IV, early 70's, 1974's to be exact, low power/torque engines built during the
oil embargo of 1973. Chevy detuned the 454 which came out in 1970 rated up to 450 hp and was
said it was a conservative figure put on it for insurance reasons, although no dyno proof it was 500 hp.
1974 versions were rated at 215 & 235 horse power and 360 torque. With a compression ratio of 8.2
and 7.8 depending on cylinder head combustion chamber CC's, chevy made closed and open chamber
heads ranging from 99 to 122 CC's using flat top 2 & 4 valve relief pistons and a steel shim head gasket.
Camshafts were really small, 196 intake & 200 duration @ .050 lift which was 215 & 230 advertised
duration. Lift was really low 398 and 415 advertised. The real low profile intake manifolds were basically
nothing more than a place to mount a 4 barrel, and the Quadrajet was 600 to 650 cfm but wasn't a
real problem. There were 750 & 800 CFM Q-jets which can be distinguished by a small bump inside
bottom of primary venturi's. Heads were either 2.07 or 2.19 intake valves, but 2.07's work just fine
for mild power gains.
----Both of these engine will get a compression ratio bump to 9.1 with 100 thousands tall hypereutectic
dome pistons. To figure that a formula of bore and stroke with compression height, a dome volume of
-10.50 and deck clearance with head gasket figured in gives compression ratio. Hypereutectic pistons
reflect allot of heat back to combustion chamber so a real critical step is ring gap, wider by double for
top ring and a few thousands for second ring. A standard gap for a bore over 4" is .004 for inch of bore
diameter. The gap for towing is figured @ .008, so 8 x 4.25 = .034 top ring gap and .018 for second.
Reason--the heat transfer to top ring can close the gap breaking piston ring lands destroying pistons
and scratching the bore. Plus a little extra piston skirt clearance @ .004 will have it run well.
---Cylinder heads are 241 castings with 113 CC chambers 2.07 valves, oval ports. a common head
back then. With stock ratio-stock sled rockers and 3/8" diameter pushrods, Chevy also made them with
5/16 pushrods. Roller rockers or roller tip rockers really add {zero hp gain} unless a higher ratio &
combined with a roller cam, stock ratio is 1.7.
---Camshaft I will use will be a Comp Cams 260 flat tappet. Single pattern @ 112 lobe center 206* duration
@ .050 lift both intake and exhaust which is 260* duration advertised and .475 lift. Would like use a
Howards Cam 263*/.488 lift but none in circulation and would be a 3 month wait. Anything over 268*
duration and vacuum drops and makes for lousy power brakes and around town drivability. Plus a cam
for this application needs to have a working range of 1000 to 4500 rpm, with a fairly smooth idle.
---Carb will be a Edelbrock 650 AVS-{air valve secondary} mechanical. With this configuration for street
it only requires 610 cfm. With a medium rise aluminum intake and 1 5/8 headers.
---Should produce 390 hp and roughly 450 lbs torque. Will have a few photos when assembling.
One I built some years back---485 hp below.
*
