71 LT-1 vs. 72 LT-1

[jmp]

Hey all!

Just wondering if someone could fill me in on the differences between the 71 and 72 LT-1s? Or at least point me to a site that describes the differences?

Thanks!

[72LT1Steve]

Joseph;

Differences between the two years is not much. Fiber optics were gone in '72. With the alarm system now being standard. '72 LT-1's engines were rated at 255HP as compared to '71 where they were rated at 330HP. This was not due to any mechanical change, but more because of rating criteria. In '72 horse power was "net" rated at the rear wheels rather "gross" rated at the flywheel. Of course the interior console data plates reflected this different information as well.

In '72 Chevrolet began it's engine designation in the VIN number's. You should find an "L" designator in the 5th position for the LT-1 350. "K" would represent the base motor 350 and "W" for the 454 motor.

'72 was the only year that air conditioning could be ordered with the LT-1 package, and this was for only about 1/2 to the last 1/3 of the year or so, with approximately 240 cars being so equipped. In conjunction with this option, the standard 6500 red line tach was not used, but replaced with a 5600 red line tach. The front turn signal lenses were amber in '72 and clear in '71. I have heard of some '71 cars having amber lenses as well, but have'nt seen a any to date.

And finally paint colors options changed somewhat, with five of them changing (at least name wise).

Hope this gives you some idea.

Take care Steve
'72 LT-1 Roadster

[RalleyRed]

I agree with everything Steve mentioned bar one,

And I maybe wrong, but I don't think so.

Both motor's were rated at the flywheel, the difference was that the 72's up ( all the accessories mounted as were the muffler's )

While the earlier car's had none of this to steal HP.

Both are very nice Vette's.

Rick

[DkBG]

Your both right ! Your saying the same thing in different ways .

[RalleyRed]

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.

:upthumbs

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

Thank's,

Rick

[inferno-vette]

I'm sure that Steve is right because If you dyno an engine at the flywheel and then at the rear wheels you can see a difference of 20-25% loss due to the drive train........in this case 330 gross hp-23%= 255 net hp.
Paul

[rainman]

The 1971 Chevrolet sales broshure for the corvette listed both gross and net hp for all four engine options. The broshure shows the LT-1 for that year with 275 net hp.

[jmp]

I'm a little confused about something... On the plate on the center console of my 72 LT-1, it lists the torque as 360 ft/lbs. But I've seen 72 specs on the web listing the torque as 280 @ 4000 rpm. I'm going with what my car says! And I guess I'll check the heaps of manuals that came with the car when I get home tonight, but if someone else can chime in here...

[jmp]

Ok, it turns out both figures are correct. The 360 number is gross, while the 280 is net. This according to Motor Trend's June 1972 issue. This issue also says that the gross hp rating for the 72 LT-1 is 330 (net 255).

Here's some performance stats:
0-30 2.9
0-60 6.9
1/4 mile 14.3 @ 92 mph
Gas Mileage 9-12 mpg

WTF? The gas mileage for the 454 is 13-15 mpg! That's better than the base 350 too!

[gdh]

I concur with the above stats. and on a long trip last year I averaged about 13 mpg.

[0018]

Originally posted by jmp
Hey all!

Just wondering if someone could fill me in on the differences between the 71 and 72 LT-1s? Or at least point me to a site that describes the differences?

Thanks!

[6 Shooter]

Sounds Like the 71 LT-1 had the Stuff ! :r

[0018]

Originally posted by jmp
Hey all!

Just wondering if someone could fill me in on the differences between the 71 and 72 LT-1s? Or at least point me to a site that describes the differences?

Thanks!

[0018]

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!!!

[0018]

Originally posted by 6 Shooter
Sounds Like the 71 LT-1 had the Stuff ! :r

Yep, it does, until you drive a '70 LT-1!!

[0018]

Originally posted by inferno-vette
I'm sure that Steve is right because If you dyno an engine at the flywheel and then at the rear wheels you can see a difference of 20-25% loss due to the drive train........in this case 330 gross hp-23%= 255 net hp.
Paul

[0018]

Originally posted by 0018


The 1971 LT-1 had more poop than the '72. More horsepower too, however you measure it. Not to mention the Transisor Ignition, and advanced ignition and valve timing. Like the Packard ad used to say "ask the man who owns one." Ive owned 'em all and the 1970 is the fastest. I presently own an original Ontario Orange '72 coupe with 49,000 actual miles, and love every inch and ounce of it!! (But I must admit, its the slowest LT-1) as if it really matters. Its still too fast for a 48 year "kid" after a few cold ones, so I call a taxi. Cab Drivers are more understanding than my wife. So who has a '70 LT-1 Roadster for sale??

[6 Shooter]

330 HP with 10.8:1 compression and a 6,300 RPM Redline . . .

That's why I like the LT4 so much, push the petal down and let them ponies go !!! :_rock

[0018]

Originally posted by rainman
The 1971 Chevrolet sales broshure for the corvette listed both gross and net hp for all four engine options. The broshure shows the LT-1 for that year with 275 net hp.

The 275 net hp seems about right for a '71 LT-1. 1971s are noticeably a tad faster than the '72, which is rated at 255 hp. There are minor differences between the two engines. The '72 had decreased ignition and valve timing to meet the ever tightening government emission regulations. Also the transistorized iginition was discontinued on LT-1s in '72. The big horsepower reduction took place the year before when the high compression '70 engines were detuned to be compatible with the new unleaded fuel which was to replace leaded fuel by the mid '70s. With the introduction of TPI fuel injection in 1985, horsepower started its upward trend, which now is in excess of 400 hp. Way to go guys!!

[wagonmaster]

Ok guys here it is.... The '71 was rated with the old Horsepower method. That was flywheel dyno horsepower with NO loss for water pump, alternator, smog pump, etc. '72 was the very first year that the "net" method was used for torque and horsepower. This was a "real world" figure that all the cars would generally meet that factored in all those frictional losses, but was NOT rear wheel horsepower. We surely DID have chassis dynos then, but they weren't used for this. I sold these new in '71 and '72 and was really crushed about the H.P. rating system.
Kinda makes you understand why the new 350 h.p. Corvette is so much faster that the "oldies" with 350 h.p. doesn't it?
The saddest part of all this to me is that the LT-1 would pass the more stringent '73 emissions, but the feds wouldn't allow Chevrolet to adjust the valves at 50,000 miles, and they tested emissions to that point on the test "mule" vehicles from all the manufacturers. If they had allowed the adjustment, we could've had them two more years anyway. ('75 was too tough even with the adjustment) Hope this helps. :upthumbs :beer
Joe

[jmp]

Originally posted by 0018
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]

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]

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

:_rock

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]

Originally posted by RalleyRed
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.

:upthumbs

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