Assistance requested

[D Wagaman]

Hello to all.

I am new to the LT1 forum. I currently have a 69 coupe, and am interested in obtaining an LT1 convertible. I have been looking on the web to find information regarding the engine components, and other unique LT1 features, to assist me identify whether or not the cars that I am considering are true and/or correct LT1's. For example: I see here and there, in articles I read and in some of the threads in this forum, mention of electronic/transistor ignitions, but cannot seem to find a comprehensive and verifiable listing of components from a reliable source to educate myself with.

In addition, if anyone is aware of a true and correct LT1 convertible for sale, preferably a 70 or 71, I would be interested in hearing about it.

I would be very appreciative of any assistance that could be offered to a "wannabe" LT1 owner.

Thank you!

 

[tomtom72]

Hi & welcome D Wagaman, I did own one and I'm in your position now. Been looking for awhile. You have probably heard this before, I have, but the best thing to do is get books. I joined the NCRS and bought these two books right away: "1970 - 1972 Corvette Technical Information Manual & Judging Guide" and "1968 - 1982 Corvette Specifications Guide". I owned a 72 LT-1 back in the late 70's and had to go thru it mechanically and thought I learned a thing or two. I will say after getting these books I really didn't KNOW much. Especially if you are looking at the 70 & 71 LT-1, they are relatively easy to "fake" cause the VIN doesn't tell you it's a LT-1. The 72 model year chevy started putting the engine code in the VIN so it is easier to tell what motor came with the car. Those two books tell you where all the #'s are and what those #'s should be. Good hunting. Tom

 

[rainman]

I agree with Tomtom72. The best thing to do is get the books he recommended. But here's a list of some things to look for. It's not all inclusive and some things are easier to fake than others.

Engine suffix: 70 CTK or CTU 71 CGZ, 72 CKY
6500 rpm tach (except 72 with A/C)
Transistor Ignition (except 72)
Air Injector Reactor (removed from most cars but should be evidence that it was once there)
Harmonic Damper: 8 inches diameter (common with 70 350hp and 70-72 big block)
No radiator expansion tank
No fuel return line

Hope this helps

 

[D Wagaman]

Thanks.

Hi & welcome D Wagaman, I did own one and I'm in your position now. Been looking for awhile. You have probably heard this before, I have, but the best thing to do is get books. I joined the NCRS and bought these two books right away: "1970 - 1972 Corvette Technical Information Manual & Judging Guide" and "1968 - 1982 Corvette Specifications Guide". I owned a 72 LT-1 back in the late 70's and had to go thru it mechanically and thought I learned a thing or two. I will say after getting these books I really didn't KNOW much. Especially if you are looking at the 70 & 71 LT-1, they are relatively easy to "fake" cause the VIN doesn't tell you it's a LT-1. The 72 model year chevy started putting the engine code in the VIN so it is easier to tell what motor came with the car. Those two books tell you where all the #'s are and what those #'s should be. Good hunting. Tom

Thank you. Good advice.

 

[D Wagaman]

Thank you.

I agree with Tomtom72. The best thing to do is get the books he recommended. But here's a list of some things to look for. It's not all inclusive and some things are easier to fake than others.

Engine suffix: 70 CTK or CTU 71 CGZ, 72 CKY
6500 rpm tach (except 72 with A/C)
Transistor Ignition (except 72)
Air Injector Reactor (removed from most cars but should be evidence that it was once there)
Harmonic Damper: 8 inches diameter (common with 70 350hp and 70-72 big block)
No radiator expansion tank
No fuel return line

Hope this helps

Thanks for the input. Couple of questions:

What is the harmonic damper?

Why no fuel return line?

 

[rainman]

I don't know why there is no fuel return line, but its a good thing to check. All cars other than the LT-1 had the return line. You can see the harmonic damper below the water pump. It's 1 3/4 inches thick on LT-1s, 70 350hp cars, and big blocks. All other cars have thinner, smaller dampers. The harmonic damper or vibration damper is used to control harmonic vibration.

 

[Dave's LT-1]

From what I've read and seen, cars equipped with the LT-1 engine have the aluminum intake and Holley carbs which do not require the fuel return line.

 

[D Wagaman]

Thanks.

I don't know why there is no fuel return line, but its a good thing to check. All cars other than the LT-1 had the return line. You can see the harmonic damper below the water pump. It's 1 3/4 inches thick on LT-1s, 70 350hp cars, and big blocks. All other cars have thinner, smaller dampers. The harmonic damper or vibration damper is used to control harmonic vibration.

Thank you.

 

[D Wagaman]

From what I've read and seen, cars equipped with the LT-1 engine have the aluminum intake and Holley carbs which do not require the fuel return line.

Thank you.

 

[tomtom72]

Fuel return line

Hi all, I was thinking about why LT-1's had no fuel return line. I came up with this stupid explaination. Quote from Zora..."the LT-1 corvette does not have a fuel return line because the motor does not have any left over fuel after you put your foot in it! In fact it will eat as much 100 octane fuel as you can afford to give it!" I know that's silly, but if my memory serves me right that explaination sure fits my LT-1. God I miss that car. Tom

 

[ddbjr]

Here is my list to insure it may have been a true LT1


The 70-72 LT-1s did indeed use the HD u-joint caps normally reserved only for big blocks. The LT-1s also used a copper radiator and no expansion tank, so the presence of a tank (or holes on the psgr side fender) would mean a base engine no A/C car. The carb was actually a 780cfm vacuum secondary dual feed Holley and a single metal fuel running from the tank to the near the pump should be present. The 70-71 LT-1 also used Transistor pointelss ignition, so look for the amplifier box (or holes where the box was) on the left front side of the radiator (easiest seen by opening the hood and looking from the front of the car through the opening in the hood). Also, there was no Power Steering availalble on the 1970 LT-1 until about May of 70, so an early build car with PS would be suspect since the early 70 LT-1s used a larger 6 quart oil pan that would absolutely not fit with PS (the later cars went back to the normal 5 quart pan). The exhaust pipes on the LT-1 was also 2 1/2 inches whereas all other 70-72 small blocks used 2 inch (same manifolds used on all engines however). The tach redline for is 6500, the L-46 was 6000 and the base is 5300.
Now on the tranny, the LT-1 was just like any other small block Corvette. The car came standard with the M-20 Wide Ratio 4-speed, and the standard rear axle ratio was 3.55 to 1. Unless the buyer checked the M-21 Close Ratio box or another optional ratio with the M-20, the car was delivered with the M-20 and 3.55. Keeping the M-20, you could also order the Performance 3.70 ratio, or the Economy 3.36 ratio. The M-21 Close Ratio 4-speed was availalbe at no extra cost, and this combination gave you the 3.70 axle as standard, along with the Performance 4.11 or Economy 3.55 as options. The majority of LT-1s do indeed have the M-21 with the 3.70 or 4.11s, although many were built with the M-20. In 1972, when A/C was made availalbe in the middle of the year, you were not allowed to order the M-21 on the LT-1 in combination with the A/C, but had to keep the standard M-20 along with the 3.55 axle, and although the 3.36 axle could be had, the 3.70 could not be ordered with A/C. The M-22 tranny was technically an LT-1 option only in 1971 although some debate rages on this. In 1970, it is generally accepted that the M-22 tranny was included and only availalbe as part of RPO ZR-1 and could not be ordered as a seperate option on a standard LT-1. Again, you will hear differing opinions on M-22 usage, but with Chevrolet records showing 25 ZR-1s and 25 M-22s for 70 makes it pretty clear that all 25 M-22s went into the ZR-1s. In 71, it is the LS-6 engine that makes the picture a little foggy. For only the second time (the other year was 66), the M-22 tranny was on the books as a seperate option. Some guys say that it was only availalbe on the LS-6, but some say it could also be had on a standard LT-1. Since the M-22 equipped cars, used a special 12 3/4 inch lightweight flywheel and unique clutch, this would have required many different parts to use the M-22 on the LT-1, this would have complicated the build issue and seems like something Chevy would not have wanted to do, but it is possible. For 72, the only Corvettes to use the M-22 was the ZR-1.
The suspensions on all LT-1s was exactly like the base engine cars, except for 71 where the stiff F-41 setup could be ordered as a stand alone option without having to buy the complete heavy duty car (ZR-1).

donald

 

[early shark]

Donald:

I enjoyed your reply.

I thought I would enlighten you a little bit more on a survey conducted on LS-6 cars. We have accounted for 1/3rd of the total production of these cars, so far. Transmission breakdown is as follows: M22 cars 43, M21 cars 11 & M40 cars 10.

Coupes 44 cars, convertibles 23 cars.

Should the ratios continue for the remaining 2/3rds of production, we should see approximately 2 coupes to 1 convertible for the 188 production figure.

The 130 M22 production figure can be broken down as follows. 20 units for the ZR-2 & ZR-1 packages, leaving 110 units left. It is most likely that these remaining units all went into the balance of LS-6 production. I have not been able to confirm any '71 LT-1's outside of the 8 ZR-1's that were factory equipped with an M22 trans, STILL looking tho.

A '70 or '71 LT-1 car will be my next purchase as well, never owned one, but I have heard they are a BLAST!

 

[rainman]

Donald,

Very good post with lots of good info. As you pointed out LT-1s could come with M-20 and 3.36 rear gears. In fact I owned a documemted 70 LT-1 vert with the 3.36 gears until about 4 months ago.