L72 engine

[68-427]

I see that Barrett Jackson will be selling a 68 Yenko Camaro this January. They describe the engine as 450 HP. I thought the L72 engines for 68 were 425 HP. Which is correct? Were there any significant differences between the 425 HP L72 and the 450 HP L72?
Any thoughts on what this car will bring at the sale??Thanks.

[Keith Tedford]

People love to use the biggest numbers that they can. With headers and tuning an L72 might make the 425 hp and the L78 375. Forget the big numbers. They just won't happen with an as factory built engine.

[68-427]

I was just wondering which HP number is correct for a 68 Yenko 427. In other words, what should the air cleaner decal say?
Is the 68 Yenko Camaro that is listed at B-J correct when the air cleaner decal says 450 HP? I assume this car is the real thing and some of the members here are familiar with the car.
Thanks.

[WILMASBOYL78]

The L72 engine was rated at 450hp for a short time at the beginning of the 66 model year and then "downsized" a little. Most assume it was for insurance purposes, or maybe to balance out the presentation between the L78 and L72.....as for real horsepower....blueprinted L72 with tuning and headers will probably produce 450hp or more...the L78 version can make 415-425 with similar prep.

I seem to remember the article about the Harrell prepared 427 cars being rated at 450hp...you can have any horsepower you want for about $3.00...just buy the sticker! http://www.yenko.net/ubbthreads/images/graemlins/grin.gif

wilma

[3macs1]

Hi Keith:
I'm suprised that the big engines would not make the rated HP. The dyno graphs Gm published for them at the time clearly show they did and if anything GM derated the actual HP.
I have only had one BB ever on a dyno a oval port 427 390 hp and it produced 431 Hp . I know it was bored 30 over and the engine rebuilder was told to do what they want inside to get the max HP but it has to stay original outside and not be decked to keep the vin. It did have headers installed but it's original reworked quadrajet and points.
Same time the brothers that built it are well known in Nova Scotia for their ability to produce HP. Those who know them will remember their 10 second white camaro with the 292 chevy 6 cylinder which they raced across canada and the US for years.
Great guys. I Really don't know what they did vs stock nor did I ask at the time.
Same time these guys could probally pull 50 hp out of a craftsman lawn tractor.

[Keith Tedford]

I was referring to "as factory built" meaning as delivered from GM. One of the guys on this site had an L72 on an engine dyno and it made something like 429 hp. It had a 2" carb spacer which won't fit under a Chevelle hood. It had dyno headers which don't come on the factory cars. It was running racing gas which isn't practical for the street if you run 3K+ miles a year like I do. I would assume that the carb and timing were also optimized.
Our L78 Chevelle is factory stock except for tuning and headers. It is capable of 13.3s. It has no options to add any substantial weight. That might equate to 320 hp at the rear wheels. There are formulas on the internet where you can roughly figure hp and et. With flowed heads, good streetable cam, headers, and lots of little tricks, a friend's '70 L78 Chevelle runs 11.70s. There is a big difference between "as delivered" and tuned. Not that I have a lot of faith in the old magazine road tests, but the L78 cars were usually mid 14s in the quarter. I road in a few of these back in the day. Our COPO Chevelle came with#68 primary jets and lean surge at highway speed. The advance curve was also for emissions. On top of that 5 cylinders had rings that didn't seat. It was a dog. A re-ring, good valve job, headers and some tuning and it was night and day difference.
I believe that GM tested their engines on an engine dyno without accessories. These numbers will not be indicative of what the engine will produce in a car through the drivetrain. Plenty of losses there.
In the end, the quarter mile is the real test.
http://www.yenko.net/ubbthreads/images/graemlins/burnout.gif http://www.yenko.net/ubbthreads/images/graemlins/3gears.gif

[Chevy454]

I tried to emulate an *as delivered* L72 as best I could and it hit just over 425hp on the dyno...crappy TRW pistons, rods, cam/lifters, rockers, etc...no internal tricks, just slammed together like in '69...the only thing that wasn't as it left Tonowanda was the .030" bore. I dyno'd it through the stock exhaust manifolds and air cleaner and points ignition...I later found out the 780cfm Holley I had ran was junk, and when I switched to a decent one I picked up ET/MPH, so there was a little more in the engine...put it in front of an automatic, and it pushed our 3700-3800 pound Camaro to 12.7s @ 108+ [on pump gas], and would have picked up a tenth had I known then what I know now about getting the car to hook.

Our blueprinted L72, on the other hand, put 75+ horsepower onto that number, and has gone, ummm, let's say "really low" 12s @ well over 115, in the same car as above...

[68-427]

So, is the B-J 68 Yenko the real thing? Anybody brave enough to guess what the car might sell at?

[nuch_ss396]

[ QUOTE ]
Hi Keith:
I'm suprised that the big engines would not make the rated HP. The dyno graphs Gm published for them at the time clearly show they did and if anything GM derated the actual HP.
I have only had one BB ever on a dyno a oval port 427 390 hp and it produced 431 Hp . I know it was bored 30 over and the engine rebuilder was told to do what they want inside to get the max HP but it has to stay original outside and not be decked to keep the vin. It did have headers installed but it's original reworked quadrajet and points.
Same time the brothers that built it are well known in Nova Scotia for their ability to produce HP. Those who know them will remember their 10 second white camaro with the 292 chevy 6 cylinder which they raced across canada and the US for years.
Great guys. I Really don't know what they did vs stock nor did I ask at the time.
Same time these guys could probally pull 50 hp out of a craftsman lawn tractor.

[/ QUOTE ]

431 hp on a Q-jot! http://www.yenko.net/ubbthreads/images/graemlins/eek.gif SWEET! http://www.yenko.net/ubbthreads/images/graemlins/3gears.gif

[3macs1]

Not saying it was not worked Steve. Q-jets are usually ok in the right hands under 500Hp, lose some top end but this motor was not built for racing.
Had no choice had to put the original carb back on.

[Keith Tedford]

We have a 455 powered '72 Lemans. The Q'jet is from a '70 Ram Air III engine. The car is quicker than our L78 and satin smooth to drive. I've had lots of Holleys that worked fine. The 4346 on the Chevelle for one. I've had Q'jets the same. I've also have one of each on the shelf that absolutely won't work. Seems like they both have some kind of internal problems. Perhaps casting flaws? None of my usual cures have worked. A well set up carb can make the difference between a car you love and one that you hate. Jim Hand, the Pontiac guru, sure knows how to make them work.

[nuch_ss396]

[ QUOTE ]
We have a 455 powered '72 Lemans. The Q'jet is from a '70 Ram Air III engine. The car is quicker than our L78 and satin smooth to drive. I've had lots of Holleys that worked fine. The 4346 on the Chevelle for one. I've had Q'jets the same. I've also have one of each on the shelf that absolutely won't work. Seems like they both have some kind of internal problems. Perhaps casting flaws? None of my usual cures have worked. A well set up carb can make the difference between a car you love and one that you hate. Jim Hand, the Pontiac guru, sure knows how to make them work.

[/ QUOTE ]

A '72 455 Lemans quicker than an L/78?! OK, some day
maybe we can all sit down and figure-out which cars really
were the fastest. I've spent so many years amassing BBC
SHP components thinking they represented the fastest of the
fast. NOW, you guys come along with your Pontiacs & Oldsmobiles
and ruin everything for me.... http://www.yenko.net/ubbthreads/images/graemlins/crazy.gif

Steve http://www.yenko.net/ubbthreads/images/graemlins/frown.gif

[Keith Tedford]

I just speak from personal experiences, about 200K miles with the L72 and about 40K with L78 cars. In '68 I had a Ram Air Firebird with all the tricks of the day done to it. I have also had a '68 L35 Chevelle and a '69 GTO with the 350 hp 400. All fun cars. All with different characteristics. I think what I've seen is that the average muscle cars from the factory with the smaller ports worked better in the milder factory configurations. .500" lift and 240 degree duration was a fairly stout factory cam in the '60s. The factories couldn't go too crazy on wild cams and still have a 5-50 warranty. Look at drag strip performance figures (Stock and Super Stock) and things are a little different. Chevies tricked out for racing do very well as their full breathing capacity is being utilized. At one time 302s were running against 428 CJs in the same class. Our 455, while no race engine, works pretty well for such a mild combination. 230 degree .480 lift cam and headers. The port cross section is very similar to that of a 350 Chev. The L78 cars that I have/had wouldn't even come close to our old L72 in stock form. The 31 extra cubic inches don't, in themselves, account for all the difference in power although they do create quite a bit more toque as well as horsepower. The combination just seems to work quite a bit better with the extra air flow. Don't throw your L78 stuff away though. A friend's L78 Chevelle, with lots of tricks, runs 11.70s and the car is very streetable. Chevies do have more potential than most. http://www.yenko.net/ubbthreads/images/graemlins/smile.gif

[427freak]

L72 should be a posted 425hp in 68. Last 2 cars I have seen sold in last 12 months went 350k +. Haven't seen the BJ car, have no idea what it will go for.
Plane ticket to Ariz. $400. Bidder registration $400. Free drinks, TV coverage and blonde on arm, priceless.