71 LT-1 vs. 72 LT-1

[jmp]

Having owned all 3 years of LT-1s, the 1970 is without a doubt the fastest. Rated at 370 H.P., this high compression small block put out over 430 horsepower. The 370 H.P. rating was an insurance dodge. Government emission regulations eventually killed the LT-1. The Compression ratio was reduced from 11:1 to 9:1 in 1971 to be compatible with the new unleaded gas. Ignition timing was reduced from 12 degrees advance, to 8 degrees on the '71s, to 4 degrees on the '72. Valve timing was also retarded to meet the new emission laws. The LT-1 was becoming "too tame" to carry on the legend it started in 1970. I personally am glad Zora decided to pull the plug on the engine he wanted for so long. I would hate to see the anemic engines of the mid and late '70s being badged as LT-1s. I have heard of early '71 LT-1s being equipped with leftover '70 high compression engines. All three years are great cars, and worthy of the LT-1 designation. Unfortunately Uncle Sam and the environmentalists had to put a damper on our fun. Maybe its a blessing in disquise, if the LT-1 was to become a common Corvette, like the L-82, that wouldnt be much fun either. Drive 'em. Drive 'em hard! Thats why Zora built 'em in the first place....FUN!!!

OK, I'm bringing this back up again, but with a slightly different slant. Btw, thanks for the info 0018 -- very helpful.

I'm wondering about putting some of the oomph back into my 72 LT-1. I don't want to go aftermarket or even really hybrid, but is there anything I can do to counteract the changes made to the 70 LT-1? Increase the compression? Change the ignition and valve timing back to 70 settings?

Btw, how did they reduce the compression? I think I know of a couple of ways to increase compression, but not really of decreasing compression, unless they -- what? -- changed the block, heads, or pistons??

 

[0018]

Joe, The piston were domed on the '70s. The heads were also different. I have advanced the ignition timing on my '72 LT-1 to 8 degees advance. You may want to keep advancing to the ping point of the gas you are using. Consider an aftermarket electronic ignition system, and rejetting the secondaries 2 numbers richer. These are easy and cheap things to do that will make a difference. Good luck. 0018

 

[LUDS96]

LT-1 -LT-1

Figure it out! My 96 puts out about 287 RWHP 373.5 Flywell 13.4 1/4 mile
http://corvetteactioncenter.com/tech/tools/horse.html

 

[jmp]

hp estimates

Well, given that I don't have a 1/4 mile time, I used the Motor Trend time of 14.3 seconds, plus a weight of 3475 and got:

Your Corvette 72 LT-1 weighs about 3475 pounds and can complete a 1/4 mile in about 14.3 seconds. That means that you've got about 234.87 HP at the rear wheels, and about 305.34 HP at the flywheel. Remember, this is only an approximation!


235 RWHP
305 HP



When I finally get my car to the track (next spring at the earliest) I'll redo this. Or I could just dyno the car... :t

 

[Tom Bryant]

DkGB,

I believe there is a difference between measuing hp at the flywheel and measuring it at the rearwheel's.

Again, I'm rarely sure of anything these day's but I don't think they had chassis dyno back in 72.

Please correct me if I'm wrong.



I'm alway's willing to learn new stuff.

Thank's,


Rick

I was reading an explanation on Chevy Talk, I think, a while back about the differences in rating horsepower. Of course "gross" is at the flywheel with no engine accessories attached. Even the water is pumped externally. "Net" is at the flywheel with all engine accessories attached just as it would be in the car and "rear wheel" is obviously read at the rear wheels. Not sure if this is 100% correct but it seems like I have heard this explanation before.

There have been chassis dynos around for years. They just weren't common outside places like GM testing facilities. The first one that I knew of was at a shop in Fort Wayne in the late '60s.

Tom