1970 454/390hp

[Scott #37632]

I am relatively new to Corvette ownership so here is a basic question: My friend has a '70 with the LS5 454/390hp engine. Is his engine a derivative of the 1969 L36 427/390hp? How do the engines differ other than the displacement? Thanks

[Chris H.]

Re: 1970 454/390hp

Scott,

The 70 454 is basically a stroked 69 L36 with an iron intake manifold versus the aluminum one on the 69. The 70 454 has the honor of having the highest torque rating ever for a Corvette...500 ft-lbs. 70 was also the last year of high compression, so power dropped in 71.

Chris

[Clem Z.]

Re: 1970 454/390hp

the spec look the same,CR,cam lift,roch carb,the 69 has a aluminum intake,just a difference in displacement

[Joe L.]

Re: 1970 454/390hp

Scott-----

Chris and Clem have "hit the nail on the head". The only core-engine differences between the 69 L-36 and the 70 LS-5 were the pistons and crankshaft and the aluminum versus cast iron intake manifold. The configuration of the 2 manifolds were about the same, though; primarily, the material was the only difference. Although outwardly configured about the same, the flywheel and balancer were also different since the 427 is an internally balanced engine design and the 454 is externally balanced, requiring counterweighted balancer and flywheel.

The other differences in engine peripherals were the carburetor and distributor. Although both engines used Rochester Q-Jets, the calibrations for the carburetor and the distributor were quite a bit different. This was because the 70 454 used the "controlled combustion" exhaust emissions control system, whereas the 69 L-36 used the air injection reactor exhaust emissions control.

[Kevin #38315]

Re: 1970 454/390hp "internal" vs "external" balanc

Joe,

Can you elaborate some on the concept of "internal" vs "external" balanced engines? I think I understand that the difference is in the placement of the counterweights (outside the block on the balancer and flywheel vs inside on the crankshaft). Is there an advantage to one over the other? Cost? Performance?

Thanks

Kevin

[Joe L.]

Re: 1970 454/390hp "internal" vs "external" balanc

Kevin-----

In general, an internally balanced engine is SLIGHTLY preferable to an externally balanced. Primarily, it's a question of ease of balancing and getting a good, precision balance. From the standpoint of performance, I, personally, don't think that there's much of a difference.

The reason that Chevrolet used external balance on some long stroke engines (like the 400 cid small block and 454 cid big block) was that the size of the crank counterweights otherwise necessary to balance the engine would not fit in the existing crankcase. The external balance allows for part of the balancing mass to be relocated from the crank counterweights to the flywheel and harmonic balancer.

The only alternative to this for these long stroke engines is to use "mallory metal slugs" in the internal counterweights. "Mallory metal" is a tungsten alloy that has a very high higher specific gravity (i.e. it's heavy). By drilling holes in the counterweights and adding "mallory metal slugs", more mass can be brought into the crank counterweights. This can be done to convert an externally balanced engine to an internally balanced.

The above process is VERY expensive, though. That's why Chevrolet would never consider such a thing for a PRODUCTION engine. For all PRACTICAL purposes, an externally balanced engine is as good as an internally balanced engine. Sometimes, "stroker" or "monster" engines require so much counterweight that a Mallory metal-slugged crank is a must. "If you want to play, you have to pay"

[Clem Z.]

good site for engine specs

http://nhra.com/tech_specs/engine/index.html

[Craig S.]

Re: good site for engine specs

Clem - thx for that site, very nice!....Craig

[Clem Z.]

all you want to know and more. *NM*