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The car's VIN will also have a character indicating the engine installed with that VIN. The 5th character from the left will be a K for the base engine, L for LT-1, and W for LS-5.
So a ZR1 wuld be a radio delete and the J56 Brakes.
As mentioned, radios were an option, lack of one was standard. The restriction for ZR-1s (as well as others) was that a radio could not be ordered.
Can I visually tell by looking at the calipers if they are J56?
The front calipers will have twin pin pad retention, the rear calipers remain standard single pin. If you are able to look at the caliper with the wheel off, you can check the casting numbers as well as look for the phenolic insulators at the end of the pistons on all calipers.
If you are looking at buying an LT1 or a ZR1 I would enlist the help of a knowledgeable corvette expert pre purchase. Also, there is a lot of knowledge here on the forum so if you post up pictures you will get some valuable feedback.
If you are looking at buying an LT1 or a ZR1 I would enlist the help of a knowledgeable corvette expert pre purchase. Also, there is a lot of knowledge here on the forum so if you post up pictures you will get some valuable feedback.
Stan F is about one of the most knowledgeable person to help with this question.
For a ‘72, as mentioned “L” in the VIN is the key item to distinguish if it’s a factory LT1. Here is a list of factors I copied from a previous forum post on identifying LT1s and differences between years. More important when Looking at 70 and 71s since no vin verification. It does not talk about ZR1s per se. Long post. 70-72 LT-1 Differences
1st. No 1970 or 1971 LT-1 had A/C
2nd. Emmission sticker on fire wall behind master cylinder should have letters AX on upper left corner for a 71.
3rd. All LT-1's are 4 speeds. (M20 was std , M21/M22 were optional)
4th. Tach has 6,500 RPM red line on 1970 & 1971 and on 72's w/o AC . 5600 for 72 with a/c
5th. All 71 LT-1's came with A.I.R. system. If removed should still have manifolds with holes for the tubes, Car may have headers and if so ask to see old manifolds.
6th. LT-1's had copper radiator W/O a overflow canisiter on the passanger side fenderwell. There should also be no holes whers one had been mounted.
7th. All 70 / 71 LT-1's had Tranisitor Ign. system. That may have been removed. But if it is removed look for the 3 holes on the front face of the driver side inner fender well where the Amplifer box was mounter.
Take a flashlight and look in front of the front wheel or open hood and look at it from the front side. 2 holes on bottom and 1 on top. No TI on the 72 LT-1
8th. Should have a Winters snowflake intake manifold with casting # 3959594
for 1971 and 1972, per NCRS, 1970 should be #3972110. Both manifolds are aluminum (my addition).
9th. LT-1's had a Holley carb. so there is only 1 fuel line , no return line like a quadra-jet carb. Look along frame rail on passanger side for the single line. Also the fuel tank is different. There should be no nipple on the passanger side, side wall for a return line.
If you lay on your back under the rear wheel you can reach your hand up and feel for an indention on the passanger side. If there is a nipple that is capped off , then beware.
Also the single fuel line on a LT-1 was not the same line that was used to feed fuel on the 2 line set up. So if someone removed the return line the look of the 3/8 line is still different. Not a big difference but if you can look at a car with a 2 line set up then you can see what you do not want to find.
10th. LT-1's had solid lifters , but if the car does not then that is not to big a red flag. Many people do not like them and may have replaced with HYD. lifters during a rebuild.
11th. The hardest to fake and most expensive would be the 4 bolt main block. No # on the outside of the block can verify this.
Only way to verify is to remove the pan or have a lighted optical viewer and remove the drain plug.
12th. LT-1's use 2.5" exhaust pipes like the big block cars. But the manifolds were still 2" set up. So the pipes flair from 2 to 2.5" about 6 inches from the manifold. The exhaust hangar at the trans is also different. Look on line at the Corvette Central site and you can see both 2" and 2.5" hangars.
13th. As I recall the highest rear end gear was 3:36 if trans was a M20
And id Trans was a M21 or M22 the 3:55 was highest gear
M20 3:36 Economy
3:55 Standard
3:70 Performance
M21 / M22
3:55 Economy
3:70 Standard
4:11 Performance
14th. The 71 /71 LT-1 Aluminum valve covers should have a rubber oil cap not a twist in. These covers are very hard to find. All the catalouges sell the twist in cap style.
15th. LT-1's have the same heavy duty half shaft retainers as big block cars. look at the rear end side yokes, there should be caps with bolts. Base cars used U bolts with nuts.
16th. The rocker arms have a letter O stamped in them.
17th. The balancer on the crankshaft is an 8" unit not a 6"
Dino my friend who has a 72 LT-1 w/ Air Car aznd checking the black book said that:
LT-1 came with aluminum radiators & puke tank.
Are you saying no 72's has transistorized ignition?
Thanks agin for all of your info.
Yes. 72 LT1s could be ordered with AC. Only 20 were verts. Had lower redline tachs. No TI in 72. As far as I know no aluminum rad or puke tank on LT1s. Only base engine 4 speed cars came with aluminum rad and overflow tank.
Yes. 72 LT1s could be ordered with AC. Only 20 were verts. Had lower redline tachs. No TI in 72.
True for most of what you posted… Yes, 1972 LT-1s were the only LT-1s available with air conditioning (from about February 1972 until the end of 1972 production), they did have lower red line tachometers (5600 rpm vs. 6500 rpm for non a/c LT-1s), and of course no transistorized ignition in 1972 as it was discontinued after the 1971 model year. But where did the 20 1972 LT-1/C-60 convertible number come from? I’ve seen 240 and 286 total 1972 LT-1/C-60 Corvettes, but never a breakdown coupe/convertible. Even if you extrapolate the number, it’s more than double what you posted.
As far as I know no aluminum rad or puke tank on LT1s. Only base engine 4 speed cars came with aluminum rad and overflow tank.
Except for the ZR-1s of course… All 53 from 1970 to 1972 had aluminum radiators with aluminum overflow tanks. The aluminum radiator WAS different between the ZR-1s and other small blocks.
But where did the 20 1972 LT-1/C-60 convertible number come from? I’ve seen 240 and 286 total 1972 LT-1/C-60 Corvettes, but never a breakdown coupe/convertible. Even if you extrapolate the number, it’s more than double what you posted.
Stan Falenski
Hi Stan. I am by no means an expert. The 20 convertible number is a number that is often put out there. Who came up with it. I don’t know. Just some sort of extrapolation I assume. Sometimes you see 30 as well. . As you are aware Chevrolet never released any records with breakdowns by engine and body style along with color. So it’s all an estimate. Regardless. An AC 72 LT1 would be pretty rare. The only argument to support a 20 number could be that most LT1 buyers would be more likely opt for a coupe with no AC in keeping with a more performance package in mind. Again. All just guesses. The true exact number in reality is unknown. Thanks for your info on ZR1s. Info I did not know before. I always thought all ZR1s came with M22 tranny, is this correct?
I had never heard that number before, which is why I was asking. As mentioned, I’ve heard total 1972 LT-1/C-60 production as either 240 or 286 (I saw the GM letter years ago stating 286, so I’m inclined to believe that). Considering how many LT-1/C-60 Corvettes that I’ve seen over the years I would think that number was a lot higher as I’ve seen a lot of real cars. In any case, until hard evidence is presented, any thoughts on how many of each body style were built is (as you stated) just a guess.
As far as the ZR-1s, yes, they were all M-22 equipped. I’ve never seen any real 1970 - 1972 ZR-1 with anything less than a 3.55 to 1 rear axel ratio… Most were 3.70 or 4.11 though with at least four 1970 ZR-1s with 4.56 to 1 rears.
Was the dual disc clutch an option, standard or not even available on either LT-1s or the ZR1?
Leigh,
That’s a great question…
I can say with a good degree of certainty that no “regular” LT-1 received the dual disc clutch. It was dropped after the 1969 model year (coarse spline) and brought back again in 1971 (fine spline) for LS-6 Corvette and Oldsmobile 442 applications. As far as I’m aware, it was always a big block option anyway.
As far as the ZR-1… If pressed, I’m going to say that these were set up the same as the L-88s. That would be the 3991406 12.75” flywheel, 3886059 (coarse)/3991428 (fine) 10.4” clutch, 3858403 bellhousing, and 1108351 starter. All of the GM parts books show this to be the case as well. Every original ZR-1 I’ve seen has had the 403 bellhousing and 8351 starter (which would infer the small flywheel and clutch) and the one ZR-1 I’ve restored (a 1972) used this setup as well. This was a lightweight flywheel/clutch package that was intended to reduce rotational inertia and make the engine more responsive (on the race track). The draw back was that it took a little bit of slipping the clutch from a dead stop to get the car moving, but you’re not going to see a whole lot of that in road racing so it wasn’t considered a problem.
I can’t speak for the ZR-2s as all of the known cars have been “massaged” or outright restored so there are no truly original cars to base any opinion on.
Having said all this, I know that Gary (gbozz on this site) is probably one of the few people I know that has seen (and certainly worked on) more ZR-1s than I have. I think that he may have a different opinion than mine on this.
Great info.
Yes I asked about the dual disc because this is what is posted by GM in their 1972 Historical Data document available online. It looks like correct data on the dual disc, it is just the LT-1 application that seems "off" It just didn't make any sense to me, as there is no listing for a standard size clutch for an LT-1. If this was chart was in fact true we would have heard about it by now.
Another interesting tidbit that I do not know the answer to. Did all the ZR-1s came with the F41 suspension but the std LT-1s did not? (springs & both sway bars). I am not even sure if the F41 suspension could be ordered on a SB, even an LT-1, unless it was a ZR1.
Then I have read that some SB F-41 cars got the rear sway bar and some did not. NO idea which of these stories is true. Did they use the BB rear sway bar?
Yesterday David Howard and I were measuring his collection of rear sway bars (for Carlisle) and got one neither of us knew existed. He has both .44 and .54 dia rear sway bars. (7/16" & 9/16") I know the 9/16" one is the BB rear bar. But we are not certain what the 7/16" rear bar is. My only thought is maybe a late model Gymkhana car Unless it is a SB/ZR1 F41 bar. Any ideas on this?
I was told that there were only 20 ZR1 made in 72?
This is true. There were 53 built in total from 1970 to 1972; 25 in 1970, 8 in 1971, and 20 in 1972.
If that is true is there a list of serial numbers for those 20 cars?
Unfortunately, no.
Originally Posted by leigh1322
Great info.
Yes I asked about the dual disc because this is what is posted by GM in their 1972 Historical Data document available online. It looks like correct data on the dual disc, it is just the LT-1 application that seems "off" It just didn't make any sense to me, as there is no listing for a standard size clutch for an LT-1. If this was chart was in fact true we would have heard about it by now.
Leigh,
I don’t know where that information came from, but it’s not correct. The “regular” LT-1 used a 14” flywheel with an 11” clutch… That’s pretty much a known quantity. The only difference would be the clutch plates which would have changed from coarse spline in 1970 to fine spline in 1971-1972. The only difference would be for the ZR-1 cars that I laid out in a previous post.
Another interesting tidbit that I do not know the answer to. Did all the ZR-1s came with the F41 suspension but the std LT-1s did not? (springs & both sway bars). I am not even sure if the F41 suspension could be ordered on a SB, even an LT-1, unless it was a ZR1.
F-41 was included as part of the ZR-1 option for 1970-1972. F-41 was made available for the 1971 model year (for all Corvettes apparently), but I don’t know that I’ve ever actually seen one in person.
Then I have read that some SB F-41 cars got the rear sway bar and some did not. NO idea which of these stories is true. Did they use the BB rear sway bar?
No 1970-1972 small block Corvette (ZR-1/F-41 or not) ever used a rear sway bar. I know that the option description for the ZR-1 states that there is a rear bar, but in practice, none was ever installed.
Yesterday David Howard and I were measuring his collection of rear sway bars (for Carlisle) and got one neither of us knew existed. He has both .44 and .54 dia rear sway bars. (7/16" & 9/16") I know the 9/16" one is the BB rear bar. But we are not certain what the 7/16" rear bar is. My only thought is maybe a late model Gymkhana car Unless it is a SB/ZR1 F41 bar. Any ideas on this?
The only application that I see for the 7/16” rear bar is for 1975-1982 Corvettes. Perhaps someone else can shed some light on this as I am not familiar with the later cars.
The chart I clipped from the 1972 downloadable file from the GM Heritage site.
It made no sense to me as I do not believe the dual disc was available at all in 72, so it must have just been left over data that did not get edited out after the LS6 got dropped.
Another interesting tidbit is that the 72 454 is listed there as not having an air pump, when in fact they all do. So the air pump I believe was a last minute running change due to emissions, to get it Fed certified, yet it still could not pass Calif emission stds, so the BB were not avail in CA in 72.
07-20-2023, 07:26 AM
How to Verify an LT1 / ZR1 car
