1970 350/300 or 350/350 ?

[Jim Ruggieri]

I haven't had my a week yet. Currently I'm identifying what I have and what I need. First, how can identify a 350 horse car from a 300 horse? Second, I'm trying to figure out if i'm supposed to have an expansion tank. for reference u have a small block, 4sp, A/C and a heavyduty radiator shroud. My car also has the bracket on thei nner fender for the expansion tank. Here's a pic and link to my corvette forum thread...

Thanks,
Jim




corvette forum thread

[Kent K.]

Re: 1970 350/300 or 350/350 ?

FWIW, Jim, my '71 base engine, auto with A/C car had an expansion tank. First, I'd suggest you try to confirm, or get a close idea, of what the original engine horsepower was in your Corvette before proceeding too far with other irregularities. The expansion tank issue will either resolve itself or help this detective work.
Kent #6201

[Jim Ruggieri]

Re: 1970 350/300 or 350/350 ?

Ken, thats what I'm trying to do. My tank sticker is mostly unreadable so I'm using what I have to solve the puzzle.

[andrew strauss]

Re: 1970 350/300 or 350/350 ?

I had the same problem with my tank sticker.I found a second copy neatly folded and stuck between the instrumnet cluster and the steering column.This copy was in near perfect condition and perfectly readable

[Duke W.]

Where does the tach red zone start? *NM*

[Jim Ruggieri]

Re: Where does the tach red zone start?

Duke, The red zone starts at what appears to be 5400rpm. The center console plate reads 350/350. I know I shouldnt put to much faith in that but everything else, aside from the engine and radiator, is original. Heck, this car has the original shocks...

[Dick W.]

Re: Where does the tach red zone start?

300 hp has 5,300 red line 350 hp has 6,000 red line All this information and lots more are in the newest edition of the '70-'72 Technical Information Manual and Judging Guide available at the NCRS store located at the top of this web page

[Duke W.]

Re: Where does the tach red zone start?

That would indicate 300 HP. I'm certainly no expert on '70s, but I had a buddy back in that era who had a '70 L-46. It ran dead even with my '63 L-76.

Other things to check out are the torsional damper and valve covers. The torsional damper should be the 8" diameter SHP type secured with a center bolt.
Also, IIRC the L-46 has aluminum valve covers.

Idle quality should also be a clue. The 300 HP should be smooth at about 600. The L-46 has a little lope at about 800.

Duke

[Chuck S.]

Re: 1970 350/300 or 350/350 ?

According to the 70 Assembly Instruction Manual, only the LS5 has an expansion tank with the C60 option. I believe both the 350/300 (base engine) and the 350/350 (L46) used the same heavy duty copper radiator with overflow hose secured down the passenger side tank when air conditioning was ordered. I didn't see a picture of the bracket, but it's probably not the expansion tank bracket, or the AC was added later.

Note in the second post of your CF thread, the 71 has the bracket for the expansion tank riveted to a rectangular raised boss on the rear of the passenger side inner fender; on an air conditioned 350/300 or 350/350 car there should be no bracket on that boss...there should be four shallow undrilled dimples where the bracket would have been riveted.

The easiest foolproof way to determine which engine you have is to check the suffix oode in the engine identification stamp. Look at the stamp pad on the block located just in front of the passenger side head; the engine stamp will be something like VMMDDCTL where V is for Flint, MM is the month, DD is the day of the month, and CTL is the engine suffix code.

For base engines, the suffix code would be either CTL (early), or CTD (late).
For L46 engines, the suffix code would be either CTN (early), or CTH (late).

As Duke says, the base engine will have orange painted sheet metal valve covers, and the L46 has finned cast aluminum valve covers like those on the LT1.

[Chuck S.]

Re: 1970 350/300 or 350/350 ?

Jim, I went down further into that CF thread (must be a record for misinformation), and saw your picture of the bracket.

That is definitely an expansion tank bracket, but because of the poor photo, I can't see the area where the AC hose stubs go through the front bulkhead. As much as I can see, that area doesn't look quite right. I also saw you have orange painted valve covers...you almost certainly have the base engine (350/300). Nobody added the orange valve covers to an optional engine; it was always the other way around.

I'm thinking the car either had the fender replaced with an expansion tank car fender as suggested in the thread, or the car has been retrofitted for air conditioning.

[Joe L.]

Re: 1970 350/300 or 350/350 ?

Kent-----

That ABSOLUTELY AMAZES me. The 1971 with base engine with EITHER C-60 or M-40 used a copper brass radiator with an integral filler cap; no external supply tanks was used. I've never seen any exceptions to this.

[Joe L.]

Re: 1970 350/300 or 350/350 ?

Jim-----

I would not absolutely rule out the possibility that some 1970 L-46 were built with an aluminum radiator using an external supply tank. I seriously doubt it, but it's possible; some 1969's were. However, what I do know for virtual certainty is that no L-46 with C-60 would have been originally built that way. So, whether, ot not, any 1970 L-46 were built with an aluminum radiator and external supply tank is moot in your circumstance. Your car should use a copper brass radiator of GM #3018803 which uses NO external supply tank and an integral filler on the right side tank. I don't see the possibility for any exceptions on this. Also, 300 hp engines with 4 speed and C-60 would have used the same radiator. So, with respect to originally installed radiator, it doesn't matter whether the engine is a 300 hp or a 350 hp; the same radiator would have been installed with either since the car has C-60.

As far as what engine, the easiest way to tell is via the engine suffix code stampings as Chuck described. Just inspect the stamp pad. If it's an original pad, you'll find the VIN code derivative and the engine code, including suffix. That "nails it".

The 1970 300 hp and 350 hp (L-46) are very similar externally. The differences involve the valve covers and the harmonic balancer. The 300 hp has steel valve covers; the 350 hp has cast aluminum valve covers. However, the cast aluminum are OFTEN added to 300 hp engines. In fact, that was one of the first things that I did to my original owner 1969 300 hp just a few months after I got it. A LOT of other folks did, too.

The other difference involves the balancer. BOTH 1970 300 hp and 350 hp used 8" balancers. However, the thickness was different. The 300 hp balancer was 1-5/16" thick; the 350 hp balancer was 1-11/16" thick.

[Kent K.]

Sufferin from NCRS

Joe and others,
I owned that '71 a long time ago and confusion between its engine compartment and my '67 could occur (and probably has) on expansion tanks. Sorry for the bad memory and my error.
Kent #6201

[Jack H.]

Agree with Joe...

When heat producing options were introduced (AT and/or A/C), they stepped up to the larger brass radiator from the base Harrison aluminum radiator with expansion tank to get increased thermal dissipation design safety margin...