L72 engine

[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! SWEET!

[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....

Steve

[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.