'70 LT-1 vs. '70 Z28 Engine

[Michael H.]

Re: '70 LT-1 vs. '70 Z28 Engine

That sounds right on the 360 HP Chevelle. Was there a 375 HP 396 Chevelle in 66 or was that not available until 67? I always thought there was but can't remember. I sure do remember some fast brand new 66 396 Chevelles tho.

[William C.]

Re: '70 LT-1 vs. '70 Z28 Engine

One convertible was delivered from baltimore to Chevy Engineering and converted to a Z-16 for evaluation. The car was then sold including the Z-16 package in the company fleet sale. Was purchased by a GMI student. Nobody thought a thing about it being unique back then, the z-16 was scarce period, so why not a convert? The later 325/350 hp engines were a camshaft change only. late '66 Chevelle did offer the 375 hp engine with the same configuration as '67-69 chevelles and Camaros.

[Mike McKown]

Re: '70 LT-1 vs. '70 Z28 Engine

I wonder where that $500,000 convertible is now?

[William C.]

Re: '70 LT-1 vs. '70 Z28 Engine

I talked to the fellow who bought it out of Chevy around 1985, he was still working for GM then, He said he sold it to a fellow who "rode 'em hard and Put em away wet" Said he had tried to track it down around 1980 but had no luck.

[Mike Cobine]

Re: '70 LT-1 vs. '70 Z28 Engine

Chances are like most '65 Chevelle convertibles, it rusted out completely and was junked. the worse part is that once many of these convertibles got a hole in the top, they were in mortal danger. Too many ignored it if it wasn't over a seating position and then when they decided it was time to "restore" or "save" the car, they tossed plastic over the car to "protect" it from the rain.

BIL bought one like that years ago, and it was at the point that he was in a mad dash scramble to try to keep up with the rust. He finally gave up and sold it.

[Duke W.]

Re: '70 LT-1 vs. '70 Z28 Engine

What do you mean by "true dual exhaust system"?

Duke

[R N.]

Re: '70 LT-1 vs. '70 Z28 Engine

Duke:

I think the Camaro had dual pipes back to the axle, both pipes feed into a single muffler tucked up between the gas tank and axle with dual pipe exiting the muffler with dual exhaust tips, as apposed to dual pipes with thier own mufflers.

Kurt

[Joe L.]

Re: '70 LT-1 vs. '70 Z28 Engine

Bill, Michael, et al-----

The 396 375 hp had 2 "versions". The first was used for 1965 with Z-16 only. This engine used a hydraulic lifter camshaft of GM #3873844 which was unique to this application. This engine had no "L" prefix RPO designation that I've ever been able to verify. It was supplied with the Z-16 package only, much like the 67-69 302 was a non-"L" designated engine and supplied with the Z-28 package only. Otherwise, the Z-16 engine was very similar to the L-78 engine used in 1965 Corvettes and full size passenger cars.

For 1966, the L-78 was dropped for Corvettes and replaced by L-72. However, the L-78 continued and was used in Chevelles and Camaros. For Chevelles its use began for the 1966 model year (I had a friend that bought one new in 1966) and it was rated at 375 hp. Incidentally, like the L-72 used in Corvettes, the L-78 for 1966 Chevelles destined for California did NOT have K-19. Somehow, it was exempt. For 1967 L-78s, the California-bound cars did get the K-19, though.

The L-78 was used in Chevelles and Camaros through the 1970 model year, although for 1970 only it "morphed" to 402 cid. The L-78 used from 1966 through 1969 was exactly the same engine, internally, as the 1965 Corvette L-78. The only differences were the exhaust manifolds, distributor (non tach drive for Chevelles and most Camaros) and Holley carb list number. Did the exhaust manifolds account for the 50 hp difference? No, they didn't. The big difference was that the 1965 Corvette L-78 was rated at 425 hp at 6,400 RPM; the later L-78 was rated at 375 hp at 5,800 RPM. This was a horsepower rating "strategy" just like that used for L-88 and ZL-1.

[Clem Z.]

true duals

a lot of late model camaros have a single pipe off of the "Y" pipe at the engine thru a single cat convertor to the muffler and the muffler had 2 outlet pipes where the corvette has 2 pipes from the engine manifolds back

[Joe L.]

Addendum

Also, I should have added info on the 325, 350 and 360 hp engines used for the 1965+ period.

The 325 hp aka L-35 used a mild hydraulic camshaft of GM #3874872. However, this camshaft was used for 1966 only. 1967-69 used camshaft GM #3904365 which had very similar specs, but no groove for the rear camshaft journal. 1966 L-35 engines all used a Holley carb. However, 1967 and later used a Rochester Q-Jet.

1966 360 hp aka L-34 used camshaft GM #3883986 which was the same as that used for 1966 Corvette with L-36. For 1967-69 this was changed to GM #3904359. Once agin, very similar specs but no rear journal groove. 1966 was the only year for the 360 hp rating for the L-34; for 1967 and later it was changed to 350 hp. I think that this was likley because, for 1966, the L-78 was kind of a "secret" engine. So, Chevrolet wanted to have a pretty good hp spread between the base 325 hp and the up-rated 360 hp. For 1967, the L-78 "came out into the open" so Chevrolet decided that they wanted the L-34 spaced somewhere in the middle as far as advertisded HP was concerned. For 1966 and 1967, the L-34 was equipped with a Holley carburetor; for 1968 and later it changed to a Q-Jet.

All 1965-66 L-35, L-34, and L-78 used forged steel crankshafts. Some 1966 with L-34 MAY have had 4 bolt mains, but I've never been able to confirm that. L-35 and L-34 used oval port heads and 10.25:1 cast aluminum pistons.

[Duke W.]

Re: true duals

That didn't apply prior to the adoption of catalytic converters. Kurt's post jogged my memeory of the Camaro exhaust systems. I now recall they may have had separate resonators with the single muffler. The single muffler would have effectively acted as a crossover, which alters the exhaust note, and might, depending on muffler volume and number of passes have less restriction than the Corvette system, but I doubt it.

Duke

[Barry Chappell]

Re: '70 LT-1 vs. '70 Z28 Engine

If I remember correctly, the "Advertised Horsepower @ RPM" was different from the Corvette engine vs the Camaro engine.

I think the '70 LT-1 was rated 370@6000 rpm, and the '70 Z-28 was rated 360@ (approx. 5000).
I don't remember the exact figure.

GM did this with the Nova in '68 with the 327/350. In the Nova it was a 327/325. The HP@rpm was lower.

[Michael H.]

Re: '70 LT-1 vs. '70 Z28 Engine

Thought so. Thanks Joe. I was sure the 396/375 and 396/425 engines were the same for Corvette and Chevelle but didn't know why the difference in advertised HP numbers. I remember some pretty fast 66 Chevelle's from that era.

[Verle R.]

Re: '70 LT-1 vs. '70 Z28 Engine

Bill,

What color was that convertible?

Thank you,

Verle

[William C.]

Re: '70 LT-1 vs. '70 Z28 Engine

Tan metallic with a brown interior as I reacall (40 years ago is a long time)