Actual HP for an L-78

[Bill Rose]

I get this question now and then, at car shows. The air cleaner says 375 HP, and GM rated the 69 L-78 at 375 hp. Does anyone have actual dyno numbers for a stock L-78, with manifolds, 4346, 499, 163, etc. I didn't dyno the engine, but was wondering what kind of horse power I can brag about, without lying thru my teeth.

[442w30]

Why brag? Is it you that's fast, or the car?

[Keith Tedford]

As delivered from the factory there certainly wasn't much to brag about. The leaned out carb and slow advance curve, set up for emissions, really killed the performance. Low 15s and high 14s weren't uncommon. The rectangular port heads and relatively mild cam probably didn't help things either. Those heads need a lot of air flow to be effective. With some tuning, perhaps 325-330 at the wheels. There is more to be had if all the tricks are applied. A friend's L78 Chevelle, with a lot more cam and lots of little tricks ran 11.70s, so the potential is there. Put it on a chassis dyno and run it down the track. That will give you the best numbers. The track has the final say.
As a side note, the driver has a lot to do with the ET. A good driver versus a bad one can make a big difference in how well a car ETs.

[olredalert]

----Hey Bill,,,Somebody at GM thought that your basic engine combo was good for 425HP back in 65 in a Corvette. Of course, that was probably under optimum conditions on GMs dyno, but if its bragging, thats as good a place to start as any. After 1965 and early 66 I think GM started to sandbag a bit for two reasons. First; Insurance. Second; Various racing entities.....Bill S

[66 L78 ragtop]

I have GM paperwork dated Aug 65 showing that the L78 produced 425 @ 6200 RPM. The down rated horsepower occurred in 66: 375 @ 5600 RPM

[Bill Rose]

I guess brag wasn't the best word to use. I've had that horse power question a few times, and I wasn't sure how to answer it. Thanks for the help with this guys. Next time I build a motor, it's going on a dyno before it goes into the car. I'd still like to get some numbers from a freshly built stock L-78, and see how it compares to the numbers from GM, 40 yrs ago.

[PxTx]

If you want to talk about HP, just have the car chassis dynoed. They'll be able to help you with a corection factor for drivetrain loss.

I think it would be preety cool if you can get it to make 375 WHP. Just depends on how bad you want it.

[old5.0]

I would guess a showroom stock, assembly line built L78 probably made somewhere between 200-220 horse at the wheels in the real world. That said, pulling 375 to the wheels while maintaining a stock look shouldn't be hard in this day and age.

[SSRSBOB]

Called my engine builder. They vary, he has done many. Usually in the 415-435 range. Many head and block castings are better than others, core shift, etc. That's why no two L78's make exactly the same power. it's generally a range.

Bob

[XXXGoldL34M20]

just tell everyone that it is <span style="color: #CC0000">425 H/P</span>
my buddy with an L78 1970 Chevelle does and no one ever questions him.