I saved this from an earlier post either at Corvette Forum or NCRS, dated 2001..
I can provide some info if you understand that virtually all of this is coming from memory and may not be 100 % accurate. But, with that caveat, here goes:
1) All 1970-74 Corvette 454 cid engines were two bolt main configuration EXCEPT 1971 LS-6;
2) Most, if not all, 70-72 Corvette 454 cid engines used a forged steel crankshaft. There may have been some exceptions, though, with those using a cast nodular iron crankshaft;
3) All 73-74 Corvette 454 cid engines used a cast nodular iron crankshaft;
4) All 70-74 Corvettes with 454 cid engines, except 71 LS-6, used the same size intake and exhaust valves which, as I recall, were 2.06" intake and 1.72" exhaust.
5) 1970 LS-5 cylinder heads were unique to that year. For 1971-72 LS-5 engines, although different castings were used for each year, the cylinder heads were, essentially, the same.
* 1973 and 1974 LS-4 engines used cylinder heads specific to each year which were different for each year.
* As I recall, all 1970-72 LS-5 engines used cylinder heads which had about the same intake and exhaust port volumes.
* 1973-74 LS-4 cylinder heads had smaller intake and exhaust ports, although I believe that 73 and 74 were about the same.
* All cylinder heads, except 1971 LS-6, were cast iron material.
* 1970-72 cylinder heads did not use induction hardened exhaust valve seats, including the valve seat inserts used on 71 LS-6 aluminum heads.
* 1973-74 LS-4 cylinder heads used induction hardened exhaust valve seats;
6) All 1970-72 LS-5 engines used the same camshaft, GM #3883986, which was also used on 66-69 L-36 427 engines.
* 1973 and 1974 LS-4 engines used a different camshaft, GM #353040, which was the same for both years. This camshaft was an "emissions profile" camshaft;
7) All 70-74 454 LS-4 and LS-5 engines used the same connecting rods which were forged steel with 3/8", knurled shank rod bolts;
8) All 70-74 LS-4 and LS-5 engines used cast aluminum pistons. The piston dome configuration was unique to each specific year, however, even though compression ratios may have been the same (1972-74).
* 1970 LS-5 used 10.25:1 compression ratio;
* 1971 LS-5 used 8.5:1 compression ratio;
* 1972 LS-5 used 8.25:1 compression ratio;
* 1973-74 LS-4 used 8.25:1 compression ratio.
9) All 1970-74 Corvettes with 454 cid engine used the same oil pan, including LS-6;
10) 70-72 LS-5 engines used unique-to-each-year cast iron intake manifolds. However, all of the manifolds were similar. 73-74 LS-4 intake manifolds were also cast iron but had smaller port size to match the 73-74 cylinder heads. 73-74 manifolds also incorporated provisions for EGR.
11) All 70-74 Corvettes with 454 cid engines used the same side-specific exhaust manifold castings. 1971 with LS-6 and all 73-74 LS-4 manifolds were drilled and tapped for A.I.R. fittings.
12) All 70-74 Corvettes with 454 used the same valve springs except the 73-74 exhaust valve springs which were shorter to accomodate the rotators used during those years.
13) All 70-74 Corvettes with LS-5/LS-4 engines and manual transmissions used a 14" cast nodular iron flywheel with an 11" clutch. LS-6 used a 14" flywheel with a special dual disc clutch;
14) All 70-74 Corvettes with LS-5/LS-4 used the same oil pump.
15) 1970-72 with LS-5 used the CCS (controlled combustion system) exhaust emissions control system. All 1971 LS-6 and all 73-74 LS-4 used the AIR (air injection reactor system) exhaust emissions control system. Many of the horsepower/performance differences, particularly during the 1972-74 period, were the result of emissions control system differences.
Nice post. The 1970-71 block would have been casting number #3963512 while the 1972-74 block would probably have been casting number #3999289.
The #512 block is usually "worth at least 5X--times-more" than a similar #289 block .....
As for the bare block itself, the two are similar with the 1971 block having a tall distributor tower where the 1972 and later blocks have a short distributor tower boss in the intake area.
1972 was also the last year the 454 had an LS5 RPO code, later 454s were RPO LS4.
FWIW, the short block assemblies also differed.
The LS5 had a compression ratio of 9.00:1 where the LS4 dropped to 8.25:1 and had a milder camshaft, .2741/.2824 I/E to the LS4s .2588 on both intake and exhaust. So it's not just the heads, carburetion and other minor items that accounted for the change. 1972 also saw hp ratings change from gross hp to net hp.
That's one big reason you see a drop from the 365hp LS5 in 1971 to the 270hp LS5 in 1972.
LS5 camshaft - lobe lift = .2741/.2824 I/E
LS4 camshaft - lobe lift = .2588/.2588 ....... on both intake and exhaust.
The cam specification for the stock 1970 SS 454 LS-5 cam is as follows; MILD
Valve lift - intake .461"
Valve lift - exhaust .480" - using stock 1.7:1 rockers
Duration: all measured @.050 deg
intake open (3) ATDC
intake close (37) ABDC
peak @ 110 deg
total intake duration @.050 = 214*
exhaust open (49) BBDC
exhaust close (11) BTDC
peak @ 120 deg
total exhaust duration @.050 = 218*
The camshaft specification for, Comp Cams XE274-H cam [#11-246-3] is as follows;
Basic Operating RPM Range 1,800-6,000
Duration at 050 inch Lift 230 int./236 exh.
Advertised Duration 274 int./286 exh.
Valve Lift with Factory Rocker Arm Ratio 0.552 int./0.555 exh.
Lobe Separation (degrees) 110
Valve lift - intake .552"
Valve lift - exhaust .555" - using stock 1.7:1 rockers
Lobe lift - 0.325 intake
Lobe lift - .0327 exhaust
Duration: measured @.050 deg
intake open (31) BTDC
intake close (63) ABDC
total intake duration @.050 = 230*
exhaust open (77) BBDC
exhaust close (29) ATDC
total exhaust duration @.050 = 236*
Here's my 1970 Chevelle SS454 combo, TH-400, w/3.31 12bolt posi.
#L2377F+.030 Speed Pro flattop forged pistons.The compression is supposedly, about 8.0:1.
#11-246-3 Comp Cams XE274H camshaft.[230/236 duration]-[.552/.555 lift] w/60* overlap.
#924-16 Comp Cams valve springs. retainers. locks. lifters. guide plates.
#1411-16 Comp Cams Magnum 1.72 roller rockers, w/Comp Magnum chromemoly pushrods.
#7110 Comp Cams billet timing set. GM HEI w/#990 module and timing set at 39*-40*.
#7161 Edelbrock RPM Q-Jet intake manifold, w/Cliff Ruggles built 750 Q-jet.
#343772 Large oval port heads, w/ Ferrea 2.19 Intake/1.88 Exhaust valves.
Hastings moly rings. Clevite bearings. Melling oil pump. ARP rod bolts. Fel-Pro gaskets.
1 3/4" Hedman mid-length Hedders,
11" Coan 2600-rpm convertor, 26" tall tires w/stock 1970 SS wheels, ect........
I believe most 1980's model, 454 engines were rated at 240hp & 385 #torque .....
(example)-a 1979 model 454 = 7.6:1 comp ratio = 245 hp @ 4000rpm ... 380 #torque @ 2500rpm.
Judging from my 1986 model low-compression 454 experiences, if GM had just put a little more camshaft in both the LS5 & LS4 big blocks, results could have seemed HUGE, especially seat-of-the-pants .... of course, the use of 1 more point compression and aftermarket heads, bigger camshaft, headers, torque converter, rearend gears could make a REAL TORQUE MONSTER MOTOR, out of any mild mannered big block .....
You don't need 9.5 to 1 compression to use the 60203 Voodoo cam ....
To factual cases in point:
1. I put together a combo using an 8 to 1 .... 454 that uses a 238/248 @ .050 cam.
Runs great and turns low, low 13's with 3.07 gears and runs on 87 octane.
2. The 1971 454 LS6 engine that only came in Corvettes has 9.0 to 1 compression and uses the the 143 solid cam (L78, L72 and LS6) that has 242 @ .050 duration.
In 1970, the LS6 used 11.25 to 1 compression. Same motor, just less compression due to the open chamber aluminum heads.
I will say it again, you don't need much compression to run a 230ish-240ish @.050 cam in a 454
Basic Operating RPM Range 1,800-6,200
Duration at 050 inch Lift 227 int./233 exh.
Advertised Duration 268 int./276 exh.
Valve Lift with Factory Rocker Arm Ratio 0.542 int./0.554 exh.
Lobe Separation (degrees) 110