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.

[Chevy454]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: old5.0</div><div class="ubbcode-body">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. </div></div>
I think that's too low...I would guess 250-300 @ the wheels, depending on the tune. Our 427/425hp did 370+ to the wheels rebuilt to as close to the way it would have arrived from the factory as possible...10.2:1 compression, didn't cut the heads/block, original crank/rods/manifolds, etc, etc. This would push our 3750lb Camaro to 106-108 mph depending on the air.

[Keith Tedford]

Roger Huntington was a pretty on the ball guy back then.

Auto journalist Roger Huntington wrote an article about what these engines actually put out, and here is the list. The figures are for gross HP though, I have the list of net HP ratings too.


Engine------------------Advertised----Rated----------True
------------------------HP @ RPM---- Torque@ RPM-- HP @ RPM

Buick 455 Stage 1-------360@5000----510@2800------420@5400
Camaro Z/28 302--------290@5800----290@4200------310@6200
Chevelle 396 L-78-------375@5600----415@3600------400@5600
Corvette 427 L-88-------430@5200----450@4400------480@6400
Mopar 340-4 bbl---------275@5000----340@3200------320@5600
Mopar 440-Magnum------375@4600----480@3200------410@5400
Mopar 440 Six-Pack------390@4700----490@3200------430@5600
Mopar 426 Street Hemi---425@5000----490@4000------470@6000
Mustang Boss 302--------290@5800----290@4300------310@6200
Ford 351-4 bbl Cleveland--300@5400----380@3400------340@5600
Mustang Boss 351--------330@5400----370@4000------360@6000
Mustang 428 Cobra-Jet---335@5200----440@3400------410@5600
Mustang Boss 429--------375@5200----450@3400------420@5600
Oldsmobile 455 W-30-----370@5300----500@3600------440@5600
Oldsmobile 350 W-31-----325@5400----360@3600------350@5800
Pontiac Ram Air 400------366@5100----445@3600------410@5600

[XXXGoldL34M20]

What were the stats for the Chevelle 454 L-S6 from Roger?

[old5.0]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Chevy454</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: old5.0</div><div class="ubbcode-body">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. </div></div>
I think that's too low...I would guess 250-300 @ the wheels, depending on the tune. Our 427/425hp did 370+ to the wheels rebuilt to as close to the way it would have arrived from the factory as possible...10.2:1 compression, didn't cut the heads/block, original crank/rods/manifolds, etc, etc. This would push our 3750lb Camaro to 106-108 mph depending on the air. </div></div>

Yeah, I could see something in the 250-260 range. My guess was completely unscientific based on personal observation.

That said, I think these engines are just begging for a custom cam. The square port BBC heads are excellent pieces that still stand up well 40+ years later. I think the power increase an otherwise stock L78 could see with only a modern, custom cam grind would be shocking.

[Chevy454]

The cam isn't the problem, ask any cam company (I've talked to no less than 3 about this very subject), the 143 cam is a pretty darn good piece. the problem (imo) is the huge tolerances from the factory...chambers 10cc+ too big, dome 6cc+ too short, deck clearance all of the place, etc, etc. As i said above, we did an L72 as close to factory as we could get it and it came in at 10.2:1...Scott Tiemann tore into an original L72 out of a Berger copo and it was a scant 9.8:1!

[Salvatore]

No need to dyno a street car and especially a show car motor. Whats the point? If the dyno on your motor says 475 hp, it does not mean much at a car show or on the street. Waste of time and money IMO.

[old5.0]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Chevy454</div><div class="ubbcode-body">The cam isn't the problem, ask any cam company (I've talked to no less than 3 about this very subject), the 143 cam is a pretty darn good piece. the problem (imo) is the huge tolerances from the factory...chambers 10cc+ too big, dome 6cc+ too short, deck clearance all of the place, etc, etc. As i said above, we did an L72 as close to factory as we could get it and it came in at 10.2:1...Scott Tiemann tore into an original L72 out of a Berger copo and it was a scant 9.8:1! </div></div>

Oh yeah, I don't doubt that at all. I know some NMRA Factory Stock class racers that have gone through hundreds of factory E7TE castings before finding a matched set with similar flow numbers and chamber volumes in the same neighborhood as the factory specs. But with the cam, I have to think there's power hiding there.

Look at this way. If you call Comp, for example, and order a custom grind, they'll be happy to sell it to you, but it's still based on lobe profiles already in their inventory. They may be willing to tweek the duration here or the lift there, but it isn't a true &quot;custom&quot; grind. It may be an improvement over an OTS cam, but you're still leaving power on the table. And it may genuinely not be much of an improvement over the factory 143 cam. A true, from the ground up custom is a whole different animal.

A little off topic, and I apologize, but I know of a 347 stroker small block Ford with a set of inline valve Canfield heads, stock 20* valve angle, Super Victor intake, Pro Systems prepped Holley, and a true custom cam that's making close to 700 horsepower at the flywheel. And it's only 10.5:1 compression, totally streetable, and makes a ton of torque, despite the big single plane and small displacement. The key to the whole thing is the camshaft.

I dunno, I'd like to see what an otherwise stock 396, or 427, could do with a true custom designed around the entire car.

[olredalert]

------Big thumbs up on the deck height variations, Rob. Theres a reason that so many chevy engines have been decked and it wasnt for higher than stock, as advertised, compression. Racers were just trying to get all the compression they were legally allowed to run. Bob H told me one time that when they checked the deck height on Red Alerts original LS6 engine that it was off substantially. Actually, he gave me a figure, but that #s gone. My old memory just isnt that good.......Bill S

[YENKO DEUCE REGISTRY]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Chevy454</div><div class="ubbcode-body">The cam isn't the problem, ask any cam company (I've talked to no less than 3 about this very subject), the 143 cam is a pretty darn good piece. the problem (imo) is the huge tolerances from the factory...chambers 10cc+ too big, dome 6cc+ too short, deck clearance all of the place, etc, etc. As i said above, we did an L72 as close to factory as we could get it and it came in at 10.2:1...Scott Tiemann tore into an original L72 out of a Berger copo and it was a scant 9.8:1! </div></div>

Agreed - had I known how wide the tolerances were back when I was putting my deuce engine together I'd have checked it more closely, I doubt I'm anywhere near 11.0:1 with my TRW's!

[COPO PETE]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: [email protected]</div><div class="ubbcode-body">No need to dyno a street car and especially a show car motor. Whats the point? If the dyno on your motor says 475 hp, it does not mean much at a car show or on the street. Waste of time and money IMO. </div></div>
Quess I'm wasting all my time and money!
Peter

[Chevy454]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: old5.0</div><div class="ubbcode-body">
Look at this way. If you call Comp, for example, and order a custom grind, they'll be happy to sell it to you, but it's still based on lobe profiles already in their inventory. They may be willing to tweek the duration here or the lift there, but it isn't a true &quot;custom&quot; grind. It may be an improvement over an OTS cam, but you're still leaving power on the table. And it may genuinely not be much of an improvement over the factory 143 cam. A true, from the ground up custom is a whole different animal. I dunno, I'd like to see what an otherwise stock 396, or 427, could do with a true custom designed around the entire car. </div></div>
Yeah, we're talking about the same thing...I had a place on the east coast recently cam doctor and log one of our blueprint camshafts, and we had this very conversation. Being the good salesman that he is he of course told me he could do a cam for me [just shy of a grand for dual lobe design + blank] and pick up a little power, and he's probably right...but he was quick to admit that the stock 143 camshaft was a pretty good piece for what we do. I doubt the gain would be some mind numbing amount, because the constraints of a stock engine and it's parts [that's what this discussion was in reference to] are pretty tight. Limited exhaust flow versus headers, limited ramp velocity of solid cam, limited induction from dual plane + 780 vacuum carb, etc, etc. On a full blown race engine where parts can be taylored to fit, then it's a different story, of course.

And I will say this: by simply adding some compression and pulling the retarding the camshaft 6 degrees, the stock 143 will peak higher and hang onto power a lotbetter than most would think... <<GRAEMLIN_URL>>/wink.gif

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: olredalert</div><div class="ubbcode-body">------Big thumbs up on the deck height variations, Rob. Theres a reason that so many chevy engines have been decked and it wasnt for higher than stock, as advertised, compression. Racers were just trying to get all the compression they were legally allowed to run. Bob H told me one time that when they checked the deck height on Red Alerts original LS6 engine that it was off substantially. Actually, he gave me a figure, but that #s gone. My old memory just isnt that good.......Bill S </div></div>
Most folks would be surprised at just how much diffeerrence there is from front to back on each bank! <<GRAEMLIN_URL>>/sick.gif

[JRSully]

fwiw, when I had my 70 L78 engine rebuilt, it was comprised of the following: stock, orig block .30 over (now 408 CI),crank, dot rods, stock configuration 11:1 speed pro pistons, NOS 143 cam, uncut 291 heads/orig valve size, uncut 569 intake, stock 4557 holley, orig 2000 distrib (36 degrees all in @ 3k, headers,100 octane fuel: 421 hp @ 6k on the dyno

[COPO PETE]

I think that sounds resonable. If you had retarded the cam 6 degrees, put 40 degrees timing in and took it to 7000, you would have found the peek at around 6300 rpm, but maybe not with the 70 intake. Also, every dyno is different, and a hugh difference if you dyno in the winter or in summer on a hot hot day.
Peter

[Chevy454]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: COPO PETE</div><div class="ubbcode-body">I think that sounds resonable. If you had retarded the cam 6 degrees, put 40 degrees timing in and took it to 7000, you would have found the peek at around 6300 rpm, but maybe not with the 70 intake. Also, every dyno is different, and a hugh difference if you dyno in the winter or in summer on a hot hot day.
Peter </div></div>
Just as an FYI [your mileage may vary!]...our L72 liked 38 total, but you nailed the 6300 peak! <<GRAEMLIN_URL>>/biggthumpup.gif

[JRSully]

Those '70 569 pancake intakes aren't as bad as everybody thinks and I think this has been hashed about in another thread. Interesting concept on retarding the cam 6 degrees and bumping timing to 40.? Might be time to shelf the orig engine and build that CE block I got laying around...

[Chevy454]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: JRSully</div><div class="ubbcode-body">Those '70 569 pancake intakes aren't as bad as everybody thinks and I think this has been hashed about in another thread. Interesting concept on retarding the cam 6 degrees and bumping timing to 40.? Might be time to shelf the orig engine and build that CE block I got laying around... </div></div>
Search this site for &quot;compression map&quot;...that is how you propertly determine your cam timing [particularly IVC]...ignition timing is determined by burn rate [chamber design, port velocity, dome height/design, etc], ie, the slower the burn rate the more ignition advance you need.

Just for grins, I've attached a dyno sheet from last week of our Pure Stock L72...stock untouched intake/exhaust manifolds, Crane blueprint Gm143 cam [retarded 6 degrees]. There's a slight *lull* down low where the carb is transitioning, but we're running out of time so it will just have to do.