L79 or standard 300 hp engine?

[Paul P.]

Got a question in to my Corvette Story web site. A 1966 owner is wondering how it would be possible to differentiate between a standard 327 cu in engine and the L79, a 350 hp engine? The owner states that theirs has double hump heads, and the block was set up for a automatic transmission. Apparently there are differences in the ignition timing.

~paul

[Joe L.]

Re: L79 or standard 300 hp engine?

Got a question in to my Corvette Story web site. A 1966 owner is wondering how it would be possible to differentiate between a standard 327 cu in engine and the L79, a 350 hp engine? The owner states that theirs has double hump heads, and the block was set up for a automatic transmission. Apparently there are differences in the ignition timing.

~paul

Paul------


The most prominent visual difference between the 300 HP and L-79 is the harmonic balancer. The 1966 300 HP balancer is 6-3/4" OD; the L-79 was 8" OD. Both engines use the same cylinder head castings with "double hump".

If the engine was originally equipped with an automatic transmission then it's not an L-79. No L-79 was ever originally equipped with an automatic transmission.

[Paul P.]

Re: L79 or standard 300 hp engine?

>> If the engine was originally equipped with an automatic transmission then it's not an L-79. No L-79 was ever originally equipped with an automatic transmission.

Interesting. Thank you for taking the time to reply.

~Paul

Paul------


The most prominent visual difference between the 300 HP and L-79 is the harmonic balancer. The 1966 300 HP balancer is 6-3/4" OD; the L-79 was 8" OD. Both engines use the same cylinder head castings with "double hump".

If the engine was originally equipped with an automatic transmission then it's not an L-79. No L-79 was ever originally equipped with an automatic transmission.

[Keith B.]

Re: L79 or standard 300 hp engine?

The L79 option for 67 Chevelles could have gotten an auto. But all corvette L-79 got 4 speeds

[Duke W.]

Re: L79 or standard 300 hp engine?

and the block was set up for a automatic transmission.
~paul

I don't understand what you mean by the above statement. Powerglide was not available with the L-79, and the 300 HP/PG has a different engine code stamped on the right front deck than a 300 HP/manual, and L-79 is unique, too.

300 HP engines have a cast iron inlet manifold and stamped steel valve covers. L-79 inlet manifold is aluminum with "Corvette" die-cast aluminum valve covers.

300 HP tach redline begins at 5300, L-79 at 6000.

300 HP idle behavior is 18-19" Hg @ 500 in neutral with a manual trans. PG idling in Drive @ 500 pulls a couple of inches less vacuum. L-79 is 14" @ 750.

Of course on 57 year old car likely with no documented history the engine could be some kind of kluge configuration.

Duke

[Duke W.]

Re: L79 or standard 300 hp engine?

The L79 option for 67 Chevelles could have gotten an auto. But all corvette L-79 got 4 speeds

I expect that was because TH400 was available in the A-body. It wouldn't fit the C2 without mods to the floor plan, and GM was wise not to offer PG with its 1.82:1 first gear on the L-79 . TH400 (2.48:1 first gear) was available in seventies vintage C3s with L-82 that was basically a stroked, low-compression version of the L-79.

Duke

[Keith B.]

Re: L79 or standard 300 hp engine?

I expect that was because TH400 was available in the A-body. It wouldn't fit the C2 without mods to the floor plan, and GM was wise not to offer PG with its 1.82:1 first gear on the L-79 . TH400 (2.48:1 first gear) was available in seventies vintage C3s with L-82 that was basically a stroked, low-compression version of the L-79.

Duke

the 67 L79 Chevelle still had the powerglide

[Joe L.]

Re: L79 or standard 300 hp engine?

I don't understand what you mean by the above statement. Powerglide was not available with the L-79, and the 300 HP/PG has a different engine code stamped on the right front deck than a 300 HP/manual, and L-79 is unique, too.

300 HP engines have a cast iron inlet manifold and stamped steel valve covers. L-79 inlet manifold is aluminum with "Corvette" die-cast aluminum valve covers.

300 HP tach redline begins at 5300, L-79 at 6000.

300 HP idle behavior is 18-19" Hg @ 500 in neutral with a manual trans. PG idling in Drive @ 500 pulls a couple of inches less vacuum. L-79 is 14" @ 750.

Of course on 57 year old car likely with no documented history the engine could be some kind of kluge configuration.

Duke

Duke-----


Yes, the L-79 had an aluminum manifold versus the cast iron for the 300 HP. That's certainly the most obvious visual difference between an L-79 and 300 HP.

[Joe L.]

Re: L79 or standard 300 hp engine?

The L79 option for 67 Chevelles could have gotten an auto. But all corvette L-79 got 4 speeds

Keith------

Yes, the L-79 was used in other models including Chevelle and Chevy II. However, I was only referring to Corvette applications. If the engine in question had come from one of those applications it certainly could not have been original for a Corvette.

I should have mentioned checking the engine suffix code. That would be clearly and easily the best way to determine the origin and engine type.

[Gary B.]

Re: L79 or standard 300 hp engine?

Duke-----


Yes, the L-79 had an aluminum manifold versus the cast iron for the 300 HP. That's certainly the most obvious visual difference between an L-79 and 300 HP.

And the intake is one of the first things someone would change if they wanted to make a 300 HP base motor look like an L79. (Similarly for the valve covers.)

Gary

[Duke W.]

Re: L79 or standard 300 hp engine?

the 67 L79 Chevelle still had the powerglide

I checked the 1967 Chevelle vehicle information package from the the GM heritage Web site and the powertrain chart, page 63 of the pdf, does not show any automatic tranmissions available with L-79, which in that chassis was rated at 325 HP.

Both the 325 and 350 HP 396 engines were available with either PG or TH400.

Duke