'70 LT-1 vs. '70 Z28 Engine

[R N.]

Hello Everyone:

What were the differences between the LT-1 Corvette engine and that of the Z-28 Camaro for 1970. Corvettes were rated at 370 HP and the Z-28's at 360 HP.

I thought these were the same engines. Does anyone know?

Thanks for you help.

Kurt Neiman

[John H.]

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

They were identical except for the exhaust manifolds - the Corvette had "ram's horn" manifolds, and the Z/28 had rear-outlet "log" manifolds.

[R N.]

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

HI John:

Would the difference in the exhaust manifold account for the difference of the 10 HP between to two engines?

Thanks, Kurt

[Duke W.]

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

Yes, the SAE gross rating standard that was used to rate these engines included the production manifolds, but NOT the production exhaust system. The manifold outlets were connected to a large pipe diameter laboratory exhaust system with an evacuation pump, so the difference in rating is purely due to the exhaust manifolds as the configurations in SAE gross trim were otherwise identical.

A question arises once in a while as to the efficiency of the ram's horn manifolds compared to others. This example indicates about 2.7 percent and the Corvette LT-1 was configured with the two-inch outlet versions, not the 2.5" versions that were congifured on SHP/FI engines and the 327/300 with manual transmission from '63 to '65.

Duke

[Joe L.]

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

Kurt-----

I agree with John; the exhaust manifolds were the only difference between the 1970 Corvette LT-1 and the LT-1 used in the 1970 Z-28 Camaro. However, whether the exhaust manifold difference actually accounted for a 10 hp (or, any) actual difference, I wonder about. It seems that beginning with the 1970 model year (the first time that the same SHP small block engine was used in both Corvettes and Camaros) the engines were always rated just a bit lower in the Camaros. Usually, differences in either induction system or exhaust system were cited as the "culprit" in causing the difference. For some reason, though, it seems that the Camaros always "sufferred" from the "more restrictive" induction or exhaust system differences; in no year model did the same engine produce more advertised horsepower in the Camaro than the Corvette.

I believe that "marketing considerations" have a lot to do with the final horsepower ratings assigned to engines in various chassis applications. The manufacturers generally don't want a lower-priced model to have the same or more advertised horsepower than a higher priced model, even if the engines are the same. This is especially true for a "flagship" model like Corvette. If necessary, I think that they will go so far as to make sure that "induction system" or "exhaust system" differences are engineered into the cars to produce the difference. Or, if they can do it with some "sleight of hand" within the legally defensible rating procedure (e.g. no one will have a legal issue if they rate a particular engine at a figure LOWER than its actual performance), so much the better.

[Duke W.]

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

I agree that "marketing" was a consideration in SAE gross ratings, but there were no differences in the induction system since SAE gross did not require the production air cleaner. Also, the production carburetor and spark advance calibration did not have to be used for SAE gross testing. The OEM was free to set them at whatever produced the best power and torque curves and typical production calibrations were more conservative.

Duke

[Clem Z.]

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

did the 70 camaro have true dual exhaust because if the corvette had a true dual system that could make the difference

[William C.]

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

Seems like I remember seeing some of the old "Test 20" curves published in an SAE document in the era when they would have been current, but my Chevy buddy's at engineering always said that no other Chevy would be allowed the horeepower of the Corvette, even if the engines were identical. The 450HP 427 which showed up in the Corvette for a short while when the pass car was 425 may be a case in point.

[Michael H.]

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

Bill,

I think you are correct. The 66 pass car 427 385 HP comes to mind as the same engine in a Corvette was 390 HP. Although, that too may be a result of different exhaust manifolds. And wasn't the 65 Chevelle with solid lifter 396 basically the same as a Corvette but was advertised with less HP? I do remember that GM was allowed to get away with a little more with Corvette than it was with passenger car. I also seem to remember a horsepower per pound formula that applied to pass car but was slightly different for Corvette. Was something like eight or nine HP per pound? Too many years ago, can't remember all the details.

Michael

[William C.]

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

I can never remember the details of the Z-16 Chevelle engine, rated at 375 hp, but in the back of my mind I thought it was a hydraulic lifter engine. I remember the only one at school was a Convertibel bought in the Chevy Engineering Fleet. And of course that year the Full Size pass car high perf 396 was rated at 425 hp just like the Corvette. That is one of the things that makes me think the Z-16 was a unique engine, not just a duplicate of the Pass car engine.

[Michael H.]

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

It does make sense that the Chevelle 396 was different than the Corvette and pass car but I don't remember. That would be quite a difference in HP, from 375 to 425. Must be a different engine as you said. Also, What was a 360 HP Chevelle? Was that a hyd lifter motor also?

The 68 Camaro 375 HP 396 comes to mind. I believe that would be exactly the same engine as a 65 Corvette 425 HP 396, wouldn't it? Same 143 cam, same big port heads and 11.0-1. I don't know near enough about pass car.

[William C.]

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

360 hp engine in '66 was essentially the same as the 350 hp in '67. oval port heads and hot hydraulic cam, but a 600 holley rather than the 780-800 used on the Corvette. The carb on the '65 Z-16 car was a 3310 780 CFM Holley, with an aluminum intake. and I have an old copy of the Chevelle owners newsletter that confirms the hydraulic lifter cam for the Z-16. so those differences would certainly have made for a different HP than the Corvette. I don't have the parts books the check out the camshaft, my '65 book is too early and my '68 book does not cover Chevelle. Maybe Joe L. can follow the Cam in the Chevelles for us.

[Mike McKown]

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

Mike:

The 360 hp Chevelle came out in '66. It was the base 396 with a slightly hotter cam and retained the oval port heads of the base engine.

Unless I have a bad, bad case of brain fade, the Z-16 Chevelle was hydraulic lifter.

The 396/375 Camaro engine was the same as Pass car 425 and '65 Corvette 396/425 and NOva 396/375.

[Mike McKown]

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

I thought the Z-16 came only as a 2 door hardtop. Am I wrong?

[Michael H.]

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

The HP numbers for those engines in Chevelle and Camaro were so confusing. In 68, there was a 325, 350 and 375 HP 396 for Camaro but I still don't know what made the 325 a 350. Different hyd lifter cam?? I know the 375 HP was the same as a Corvette 425 HP but I never knew why the different HP numbers for what was basically the same enging. I'm sure someone that knows those cars will pop in here soon and straighten us out on all this.