L78 horsepower

[VintageMusclecar]

Originally Posted by luzl78

How much do you think headers add over manifolds? Eric is gonna build my 402 for me and I am going back and forth. It's in my Monte Carlo.

When I built Donnie Cornelis' `69 L78 it made 462 HP and 439 lb.ft through headers (which were too big for that engine but were all I could get my hands on in time to test with) and ~430 HP and 411 lb.ft through the manifolds. However, the peaks don't tell the whole story. The engine lost 60+ lb.ft down low with the manifolds in place, and that you will definitely notice.

[markjohnson]

When they were 425hp in 1965, that was with the more streamlined Corvette exhaust manifolds that also fit & were used on full-size L78 cars that year. They became 375hp when fitted with Chevelle, Nova, Camaro log-style manifolds. It would interesting to see an exhaust manifold comparison on the dyno.

[VintageMusclecar]

What were the final numbers?

[jerry j]

For comparison here is an original 1969 L/78 restoration engine I rebuilt last year. All stock except Comp/Cam replacement cam, EDM lifters,+030 TRW pistons and run with shop headers. Fifteen minute break in & one dyno pull 38 deg timing pump 92 octane. We did not jet or do any other tuning as this is the original motor from a SS 1969 Chevelle.

[bergy]

Yikes! Thanks for all of the input. We were able to coax a few more HP after re-jetting. Then we put the shop carb on and it woke up! 446 hp at 5700.

[L72Biscayne]

I built a 66 L78 all stock except for a little head work. It made 444 @ 6000 rpm with headers and a 3247 Holley carb.

[WILMASBOYL78]

Impressive numbers from the "baby rat'...especially some of the torque figures. So, this begs the question...'if the L78 makes those numbers...what does it's big brother, the L72 really make? I would assume well north of 450hp...

-wilma

[sixt9rsx33]

That is a very impressive torque curve from a stock L78 IMO.

[bergy]

every 427/425 that I have had done developed between 490 and 505 hp through headers with stock carb & dist.

[VintageMusclecar]

Originally Posted by bergy

Yikes! Thanks for all of the input. We were able to coax a few more HP after re-jetting. Then we put the shop carb on and it woke up! 446 hp at 5700.

Sounds about right.

I installed a 3910 on my 496 for the initial dyno tests and the engine picked up somewhere around 20 when I swapped to a 3418 (`67 L88 855 vacuum secondary). During the last series of tests, the engine picked up another 30+ when I replaced the L88 carb with a 4781 850 double pumper, and another 20 when I switched to a 1000 HP (I built & calibrated myself). That's over 60 HP just in the carbs.

The factory carbs are good, but they do leave room for improvement. Comparing them to a newer "race" type carb really is an apples to oranges comparison.