C56spd

Does anyone know the differences between the three above 454ci. engines besides the LS6 having aluminum heads?

According to the Corvette Black Book, the LS6 was rated at 425hp, the LS5 was 365hp in 71 and 270hp in 1972, and the LS4 was rated at 275hp in 1973.

Apparently horsepower ratings changed from the gross hp to net hp in 1972. That is why the LS5 is different in 71 vs. 72. Still, the LS6 had 60 hp more than the LS5. I can't believe it was all due to aluminum heads.

Anyone have info on these three engines?

Thanks,

zwede

LS6 had a better intake (aluminum). Holley carb. LS5 had a more restrictive iron intake and QJET. Camshaft was different on LS6. Much more rumpity-rump. LS5 cam was mild and everyday driver friendly.

Solid LT1

The LS6 has aluminum "open chamber" square port hi performance heads (same heads as the 1969 ZL-1/L88 motors), a Holley carb, a solid lifter cam, dual disk clutch (check option MA6 for information) and a really ROTTEN intake manifold! The LS5 in 71/72 are the same except the 72 was rated in SAE net rather than gross power ratings (just like the LT-1, went from 330HP to 255HP in 72.) The LS4 has an EGR emissions system on it that allowed some tuning changes for better power.

JJMURFS

There are MANY differences between the engines you mentioned. The compression ratios were different, the cams all had different profiles (the LS6 was solid lifter), and the intakes were different LS6 had aluminum intake and big Holley carb the others had cast iron intakes with Q-jets. The blocks were also different the LS6 had 4 bolt mains the lower performance engines had 2 bolt mains. The LS6 had ALL the good parts high flowing square port heads, high performance intake, higher compression forged pistons, high revving solid lifter cam. The LS4 is a good running BB, the LS5 is a good running powerful BB, but the LS6 is a true high performance BB on steroids!!!

Tom73

I had asked the same basic question over on the NCRS forum and got this response from Joe Luca:

1) All 70-74 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. 73-74 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 71 LS-6, were cast iron material. 70-72 cylinder heads did not use induction hardened exhaust valve seats, including the valve seat inserts used on 71 LS-6 aluminum heads. 73-74 LS-4 cylinder heads used induction hardened exhaust valve seats;
6) All 70-72 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 (72-74). 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 accommodate 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 72-74 period, were the result of emissions control system differences.

tom...

zwede

Just a small correction: Many LS5's had 4 bolt mains. I'm not sure ALL of them had 4-bolts, but my '71 LS5 came with 4-bolt mains. The LS5 also has a very strong forged crank. It's a good short block, if you can get around the flat top pistons and get some compression. I'm still running an all stock short block. Rear wheel hp went from 250 stock to 390 with heads/cam/intake/headers and it is 100% street friendly.

Tom73

Joe put the disclaimer on his response that he was doing it from memory. But my understanding was that the specs for the LS5 was a two bolt main but some did end up with 4-bolt mains. Also my Chevy specs for the '73 LS4 states that the 4-speed cars used a forged crank while the automatic cars had a cast crank.

tom...

Tex71BB

Also, Chevy quoted both gross and net hp in '71 - 285 net hp for the '71 LS-5 vs. 270 for the '72 LS-5. No doubt due to the 1/4 point drop in compression noted above.

Glenn454

My 71 LS5 has a 4 bolt main block also, and 3521 casting steel crank.

C56spd

Do you know if what the torque was for the LS4-6?

73 LS-4

Been a while since I looked at my console plate but I think it was 395 ft/lbs net for the 73 LS-4, I believe the 72 LS-5 and 74 LS-4 are both within 5 ft/lbs plus or minus, I don't remember seeing the net torque ratings for a 71 LS-5 however, but I'd imagine it would be similiar.

:cheers:
Pat Kunz

greg454

The console plate on my 72 LS5 lists 455 ft/lbs.

73 LS-4

I just looked back through one of my books, 72 lists at 390 ft/lbs net at 3200 rpm. now a 71 LS-5 lists at 465 ft/lbs gross at 3400 rpm. The 71 LS-6 was rated at 475 ft/lbs gross at 4000rpm. This book is however not gospel as I do find a few mistakes in certain specs listed. I wouldn't doubt that 455 would rate close to the gross numbers for a 72 on torque.

:cheers:
Pat Kunz