L-78 engine Birth date

[zl12iv]

Hi
Do you know the date this motor was produced?
will 65 corvette come with L 78 engine option?
is there a true 65 corvette L 78 425 hp car?
your effort is appreicated. Joe 69 camaro 427

[PeteLeathersac]

Approx. Feb. '65 on
Yes
Yes

[nuch_ss396]

This brings up a good point.

How did the '65 396 go from 375hp to 425hp ( Vette only )?
It could not have been just the Vette header-like exhaust
manifolds. Was it a combo of exhaust & ignition? I'm
positive the '65 396-425hp & the '66 396-375hp as well as
the '66 427-425hp all used the 3863143 camshaft.

So, where did those extra 50 hp come from http://www.yenko.net/ubbthreads/images/graemlins/hmmm.gif http://www.yenko.net/ubbthreads/images/graemlins/dunno.gif

I remember a Vette owner telling me that some of the SHP
full sized cars came with Corvette exhaust manifolds on
them. Funny, I can't ever recall seeing one of them like
that back in the day.

With GM's interest in making the Camaro the "brute of the
street", you'd think they would have come up with a better
exhaust manifold setup for the F-bodies. http://www.yenko.net/ubbthreads/images/graemlins/rolleyes.gif

Anyone got any ideas?

Steve

[3macs1]

One actually sitting in a barn about two miles from me all apart. Been there apart since 1981. Red conv, red and white interior, side pipes and knock offs, 4spd. Original l-78 /425 motor had a noise in it but original. He paid 2500 for it in 81. Reason I remember was I looked at it first and wanted the motor out of it for my chevelle but backed off when I heard it running. Imagine DAAAAAAAAA. Must have been the beaver also Pete that hit me. Joking aside I was just a kid working for 2.00 per hour that was a lot of money to me.
It was out sitting in three feet of snow that day.I actually told him about it and he bouight it. He has a few cars all of which he eventually does the pro stock thing to like his 57 chev, 69 GTO. 40 Ford pick up and some year essex?? 30 maybe. So far he has not seen the vette in that light, hope he never does while at the same time will never sell it or restore it.

[COPO_Anders]

I have an article somewhere in which Joel Rosen says that the 375 hp L-78 engines are identical to the 425 hp Corvette 396 engines made in 1965. Not counting the exhaustmanifolds.

[PeteLeathersac]

I believe they differ only in camshafts and lifters between the 425 and 375's? .

Sad about the car in your story Mac...a coupe as an '65-L78 or '66-L72 has been my #2 favourite car for years...2'nd only to a Canadian '61 409 Strato-Chief utility post! .

http://www.yenko.net/ubbthreads/images/graemlins/beers.gif
~ Pete

[nuch_ss396]

Pete,

My research shows that they used the same camshaft between
the two years I mentioned above.

Anders,

I expect that the exhaust has maybe 20-25hp gain. Does the
TI ignition add the remainder of the hp gain?

Steve

[3macs1]

Here is what I got one time when I asked this question.
Insurance concerns plus General Motors Corporate policies resulted in the use of a lower RPM rating resulting in decrease from 425 HP to 375 HP as a running change for all models except corvette. The L-78 was released for sale in the 1966 SS-396 Chevelle in March 1966 with a rating of 375 HP due to this lower RPM rating and somewhat more restrictive exhaust manifolds, it was otherwise identical to the 425 HP '65 Corvette.( same cam)
The 1965 Z-16 396 Chevelle had the same engine except the Z-16 used a hydraulic camshaft which effectively limited RPM to the lower 375 HP rating.(L-37)
Also all of my 66 Impala/ Biscayne l-72 427's came with the
3880827 and 828 vet exhaust manifolds originally.

[Paul D]

My '66 Impala SS L72 also came with the Corvette cast iron exhaust manifolds.

[Stefano]

I have never Dynoed the different exhaust manifolds side by side but it would be no where near a 50 hp difference.

The top dog prior to the mystery motor was the 409/425. GM could not go backwards in the public eye/marketing, at least at the initial release of their new solid lifter engine.

Some early '66 L78 Chevelles have been documented as showing the L78 option rated at 425hp.

I believe Bill Thomas' Blue printing guide/book has a dyno chart or info showing that the L78 could produce 425hp if brought to exact specs.

The First 427/L72s were factory rated at 450hp.

[WILMASBOYL78]

Wasn't the L72 rated at 450hp initially and then lowered to 425hp....??? Read an interesting article the other day about a dyno test on the original 65 L78 and then revised results following a blueprint by Bill Thomas...these motors seemed to need a little help to achieve the factory ratings...

Neat stuff..wilma http://www.yenko.net/ubbthreads/images/graemlins/burnout.gif

[3macs1]

Yes sir it was on the l-72. I have never heard of a 66 chevelle however even the early ones being rated at 425.
learned something new today

[Salvatore]

I think GM changed ratings at times with a stroke of a pen. A lot depended on insurance companies back in those days and the cars they wanted to promote. http://www.yenko.net/ubbthreads/images/graemlins/dunno.gif

[JRSully]

I recently had a 70 L78 rebuilt dead stock except for a .030 overbore (70 396'a started life as a 402) 11:1 compression (verifed) nos 143 cam, 569 intake, 4557 holley, stock distributor, stock, uncut heads (hardened seats)stock valve size. Motor was pretty much clearenced and balanced. 422 hp @ 5900 WITH headers, 400 lbs torque on the Dyno. Everything is essentially the same as the 65-69 L78 except the intake (flatter, slightly lower performance) and the I think the 291 heads (70) may have had slightly larger valves vs. the 840 and also what equates to a .060 over bore over an actual 396 inch motor WITH headers, so who knows for sure..

[@wot]

GM also had a marketing dilema. The L78 was originally listed as making 425 hp at 6400 rpm in 1965. Then the L72 came along and that made 425hp at 5600 rpm. So the L78 was dynoed and became a 375hp motor at 5600 rpm. This arrangement gave Chevy two distinct levels of hp they could offer the public.

[olredalert]

-----If you guys are talking strictly about 1965 Chevelles and 1965 Corvettes the difference is the cam, I believe. I dont have the specs in front of me, but the 201 Chevelles all came with a hydraulic cam and lifters while the 425 Corvette came with a solid cam and lifters. The 65 Chevelle 396 was the only instance in the history of rat-motors from Chevy that they put big-port heads and intake together with a hydraulic cam.
-----After 1965 alot of what you all are saying above is true.....Bill S

[WILMASBOYL78]

[ QUOTE ]
I recently had a 70 L78 rebuilt dead stock except for a .030 overbore (70 396'a started life as a 402) 11:1 compression (verifed) nos 143 cam, 569 intake, 4557 holley, stock distributor, stock, uncut heads (hardened seats)stock valve size. Motor was pretty much clearenced and balanced. 422 hp @ 5900 WITH headers, 400 lbs torque on the Dyno. Everything is essentially the same as the 65-69 L78 except the intake (flatter, slightly lower performance) and the I think the 291 heads (70) may have had slightly larger valves vs. the 840 and also what equates to a .060 over bore over an actual 396 inch motor WITH headers, so who knows for sure..

[/ QUOTE ]

Is that with the turbo on high???

wilma http://www.yenko.net/ubbthreads/images/graemlins/beers.gif

[JRSully]

Headers is the key there Thomas, I expect new upholestry in the Black Beater next time around, fun time though, I must say SULLY

[nuch_ss396]

Hey guys,

This was posted over on the NCRS forum in regards to this topic:

The 1965 Corvette L-78 and the 1966-69 L-78 used for Chevelles and Camaros were, basically, the same engine. All internal parts were exactly the same or, essentially, the same. Ignition and carburetion was different but, essentially, the same (e.g. obviously the Corvette and Chevelle/Camaro applications would use a different distributor since, with just a few very minor exceptions, only Corvette used a tach drive distributor). Intake manifolds were different but, essentially, the same.

The real differences between the applications was, as has already been mentioned by others, the exhaust manifolds AND the RPM that the engines were rated at. The latter was the biggest factor in the horsepower rating difference.

By the way, the 1965 L-78 used in passenger cars was exactly the same as the L-78 used in Corvette EXCEPT for the distributor. The exhaust manifolds were the same and the engines were rated at the same RPM.