Possible 1970 LT-1; need help for verification.

[Brian A.]

Hello all!

First time poster in need of some 1970 LT-1 aficionados. I found a 1970 Corvette that the owner claims to be a real LT-1. There are some things that point towards it possibly being true, but nothing really for certain. Here's the facts:

The car has a GM power bulge hood. It has the '370hp' plaque under the gear shift(could have been changed in the past). It doesn't have the TI ignition any longer but I know the amplifier(is that the proper word?) is supposed to go on the drivers side fenderwell. There are two small holes that look factory there. Is that where it would go?

There is an emissions sticker on the cowl right above the power brake booster with reference to 360/370hp motors and tuning instructions. It looks like it has been there for a long time but I didn't think they really got into emissions until 1971(lower compression, AIR, etc); could be wrong there. It has the correct 4555a carb and intake(easily changed). The heads are the '186' but that could be for a 300/350 according to the NCRS books. The block is a period '010' but I couldn't make out the date on the pass rear side of the block.

Some things not so easily changed: It has the 'big' harmonic balancer(I don't think the 300hp version would have that) and deep oil pan. We got it running and even running on 6 cylinders(needs new plugs/tune up) you could hear the solid lifters. It has the original M21 close ratio trans and 4.11 rear gears.

Bottom line: Are there any telltale things I could be missing that might authenticate this as a real LT-1??? Any pictures that you guys may have of a restored LT-1(detailed engine shots) might help for a comparison. If you could please reply *directly* to me in addition to this board it would be great(balspaug@indiana.edu); I don't check it that often. Thanks in advance!

[Jim T.]

Re: Possible 1970 LT-1; need help for verification

Check the fuel line. The LT-1 had only one fuel line coming from the tank and no return line running along with it. I have a 70 350/300 and it has the return line. A LT-1 and the 350/350 had the air injection system with the fresh air tubes going into the exhaust manifolds. 70 350/300 did not come with the air injection pump and fresh air tubes from the factory.
The emissions on Corvettes started earlier than 70, my 68 327/350 L79 has the original air injector pump and fresh air tubes.

[Jim T.]

Re: Possible 1970 LT-1; need help for verification

You know the head and block casting numbers, what were the numbers on the front of the block? CTK,CTR, and CTU=transister ignition. CTV is the ZR1. All 350/370 hp.

[Joe L.]

Re: Possible 1970 LT-1; need help for verification

Jim-----

One small correction: for 1970 Corvettes only the LT-1 used the air injection reactor (AIR) exhaust emissions control system. All other engines, including the L-46, used the controlled combustion system (CCS).

[Brian A.]

Re: Possible 1970 LT-1; need help for verification

Hey all!

Sorry for not saying that originally. It seems the block was decked as there are no numbers on the pad. I remembered reading about the LT-1 not having a fuel return line and am not 100% sure but think this car *does* have a return line. Does that mean with 100% certainty(I know that stranger things were probably done by the factory way back when) it was not an original LT-1? Thanks!

[Joe L.]

Re: Possible 1970 LT-1; need help for verification

Brian------

If it has the fuel return line, it's very unlikely that it's an original LT-1. I really don't think that the factory would have installed an unused fuel return line.

The "decked" or otherwise unstamped block is also cause for suspicion, here. That's because, in combination with the other attributes of the car, the engine suffix code would have pretty much settled the issue.

There are other documentation "avenues" still open, though. Check to see if the tank sticker is still present on the top, left side of the tank. This can be determined by pulling pack the fuel filler rubber seal and looking to the left with a flashlight. If present, though, I wouldn't attempt to remove it through the filler door opening. For that, you'll need to drop the fuel tank. If it's readable, it will settle all contentions.

Also, check to see if the Protecto-Plate Warranty Booklet just might still happen to be with the car or in the owner's possession. That will settle the issue, too.

[robert leazenby]

Re: Possible 1970 LT-1; need help for verification

Even though the TI had been "removed" the harness plug should still near where the other wiring goes from the driver's fender through the radiator support. This might tell if it ever had the TI. There are other wiring items that you can check if you wanted to take the time.

If it has the original alternator, the pully should be machined from a solid stock as opposed to a stamped unit. Also being a 70, there should be indications that it does not, nor ever had air conditioning.

I agree with the other posts, the tank sticker would be the best way, barring that, I would make sure there are not two fuel lines.

[Chas Kingston]

Re: Possible 1970 LT-1; need help for verification

Look for copper radiator; no expansion tank. Check my web page (below) for other numbers. (Dig through several screens; I don't remember the URL to the specific page)

Geezer


Geezer's Hobbies

[Roberto L.]

Re: Possible 1970 LT-1; need help for verification

Hello, check the tachometer (redline), it is more difficult to replace than the power plate. Add to the other clues.

Roberto, NCRS #30019, RMC

[Robert C.]

Re: Possible 1970 LT-1; need help for verification

Brian, Check the red line on the tach-6500 for 350 and 370 hp

The carb is very rare if it's a 4555-make sure it has the three digit date code, not 4 digits(remanufac'd)

The fuel line splits before it goes to the front and rear bowls joined by a brass "T". (70 and 71 LT-1s)

The fuel pump is a 40709 (70 and 71 LT-1s)base is a 40769

Check the coil, should be a 272, very rare

Distrib.-1111491 (LT-1 only)check band at the base for part# and date.

Vacuum advance part #- 201 16 (70 LT-1 only)

Exhaust manifolds should have plugged A.I.R. holes if the system is gone.

Alternator should be a 1100884, 61 amp (all air cond. cars or LT-1 70's)

8" diameter harmonic dampner (LT-1s and BB)plus they are thicker

White emission label with "CL" or "CT" code

TI harness is wraped with DULL BLK CLOTH tape, not the gloss black

tape on the main harness.

[Duke W.]

Tach redline

The LT-1 tach redline begins at 6500. The 350 HP engine was lower - either 5800 or 6000 I think, maybe 6200, but definately below 6500.

Since the LS-6 mechanical lifter big block never was installed at St. Louis in '70, the LT-1 would have been the only engine that used a tach with a red zone beginning at 6500.

I believe that all mechanical lifter engines from at least '63 to the last available in '72 had a red zone that began at 6500. Hydraulic lifter engines, including SHP engines with hydraulic cams has lower redlines.

Duke

[Jim T.]

Re: Possible 1970 LT-1; need help for verification

Joe
Thanks for the correction on the 350/350 not having the AIR system. For some reason I thought that 350/300 was the only small block in 1970 that did not have the AIR.

[John C. Woods]

Re: Possible 1970 LT-1; need help for verification

Brian: You can also check the stub axles on your rear end. LT-1's have the heavy duty end caps, just like the 454's and T400 small blocks.

I don't think anyone mentioned oil pressure. LT-1's have high pressure oil pumps, but someone putting together an engine with LT-1 like performance would be sure to do the same.

Someone mentioned checking the alternator. '70 LT-1's used an 884, which is a tough find and expensive. It's rated at 61 amps and in '70 was only used on LT-1 and C-60 (air conditioning) cars. Someone could have purchased an 884 with the appropriate date code and installed it on the car, so the presence of an 884 does not really prove anything for certain. But what if the alternator is a 901 or 900? Those alternators were used on 300 and 350 HP cars. If your car has one of those alternators, then what is the date code? If it matches the build date of your car (a few weeks or a month or two prior of the assembly date of the car) then it's reasonable to assume that it is the original alternator. That could provide a meaningful clue as to what the original configuration of the car was.

My sense is that the presence of the fuel return line carries the day with respect to the question of factory authenticity. I hope this helps you in your search for the answer. Regardless of what you find out, with that engine and those gears, I'll bet that is one kick of a car to drive!