NMT1957

What is the reason for the drop in horsepower from 1970 vs 1972 Big block? Was it just the different way of rating Horsepower or was it due to the compression difference? Or were there other factors as well?

AzMotorhead

Drop in compression was one reason. Prior to 71 HP ratings were in gross HP.After 70 all HP ratings were in net HP.

HamadUP

combination of both, in '71 the HP was 365 gross, 25 HP less than the '70s 390 gross, due to lower compression (from 10 to 8.5), and in '70 the the same gross 365 HP was converted to 270 HP, but technically, they are the same engines, well, still there are some people that they will say in '71 it was 285 net due to a better cylinder head flow.

Ironcross

Because the 454`s are actually smog engines and they started in 1970 reducing HP available in the 70 BB Vettes. In 1972, it was actually worse to finally where the BB`s were dropped completely except for over the counter off road LS7 454`s. That particular engine was sup post to have been available for the 70 model run. It never happened. The exception was a one year high HP LS6 454 but only available in a Chevelle. Fuel, omissions, and foreign oil {Arabs} screwed the 70`s right up. And the GD "greenies' are still at it today..

xCCTer

454s were dropped after '74.

early shark

NMT1957,

The reason for the difference in net horsepower ratings between the '71 model at 285 hp and the '72 model at 270 hp is two fold. Further recalibrations were done to the quadraject carburetor and retarding of the ignition timing further from 4 degrees to 8 degrees.

The gross rating for the 1972 Corvette LS5 is 350 hp.

darkmercury

Using the matching block/heads/intake...
What Mods could be done to increase the HP on the 72-454 with today's available parts?

Maybe a 770cfmStreet Avenger Holley Carb probably will help...
Then what???

Nothing radical.... just a reliable increase for fun driving and strong running.

zwede

Not much you can do unless you're willing to go into the motor. The stock Q-jet has more than enough flow, no gain by going to a holley. Headers will help, that's about it. Some gains by swapping the cam but you don't have the compression to support anything radical.

The LS4 & LS5 need compression and a good intake to come alive. After that a decent set of heads and cam and you'll easily pass the 500hp mark.

NMT1957

I had my heart set on buying a 1970 Big Block because of the 390 HP rating, but due to limited availability and higher price I may go to a 1972 Big Block 270 HP. It kinda breaks my heart so I just wanted to know how much difference there really was between the two motors. Im sure the 1972 will have plenty of HP , its just the idea of it I have to get used to. Thanks.

darkmercury

Slowly save up for some engine work... or go heads and cam for the HP.
I'm considering a 72 BB too... In due time, I'd potentially be willing to let a qualified person do a lil' engine work for more HP without breaking up the matching numbers or damaging the original parts. Nothing radical but better than 72's stock setup numbers.

I'm never racing or running the car down the strip anyway... but it would be cool to know you have created a better HP situation for the car. The sound of power and feeling when BB drives by is just kickazz.

early shark

NMT1957,

The 1972 Corvette LS5 engine has a net torque rating of 395 ft lbs. The strongest L78 396 engine only had 410 ft lbs of torque, and thats at the gross rating!

You just need to buy a '72 Corvette LS5 WITHOUT a/c, look for a M20, 3:36 ratio drivetrain, the car will feel plenty strong. If you can find an M21, 3:55 even better! You won't need to get into the engine.

CCrane65

My 1972 shifter console plate says the torque is 455 lbs ft.
and 8.5:1 compression.

And it has A/C, 3.08 rear and M20. Cruises down the highway at 70 running 2500 rpm.

And I can smoke the tires (radials, not bias ply) anytime I want. Completely stock.


cc

CCrane65

Be careful about intake manifold changes. Many others on the forum have learned the hard way that there are very few that will clear the stock BB hood and those that do don't offer much improvement if any. The most common suggestion is to go with a factory intake such as an earlier aluminum from either an LS6 or a 427.

You could also consider having the stock intake ported. Most standard hot rodding tricks will work as long as you keep in imnd the clearance issue.

cc

nutsy

my 72 big block is definitly faster than my 70 bb was. maybe because i got 68 heads that have more compression. anyone know more about this? also my 72 is a auto, 70 was a 4 speed. with a newly rebuilt engine.

Chris Farrer

I would say my '72 BB Auto will set you back in the seat off the start but the acceleration is not startling as is not the top speed.
The new Nissan Skyline GTR now that's something else.
I didn't buy my car to goof off, just for cruising.
You just can't beat the rumble of a Big Block with that unique sound.

Ironcross

A actual quote from 'Bill Thomas racing engines' for a L78 396 is 415 on the torque side but at only 4000 RPM and the Horsepower is 425 at 6500 RPM.....

73, Dark Blue 454

450-500 HP is child's play with a 454 if you'll up the flow and compression with some aftermarket heads (Brodix RR-BB-O?) and add cam in the 230 - 240 @ .50, then run some 1-7/8" long tubes. Your cam choice will be determined by rear gear, tranny, and your goals.

Now the bad news. I'm not sure the stock IRS will hold up to 500 HP especially if you run sticky tires.

Good luck!

SoonerBJJ

Sorry for the necropost but this thread is relevant for my own plans.

This and other references in this thread to increasing compression in the LS5 to gain HP. Is this referring to the 71 and beyond LS5 wherein compression was dropped from that of the 70 454?

I wouldn't imagine that you could squeeze much more in the 70 if you're running 93 octane?

Without sending the original block to a machine shop or opening up more room under the hood, it seems the options for improving the intake and cylinder heads on the 70 BB are limited if I'm interpreting all this correctly.

jr9170

Love my 70 454 lots of torque and plenty of power.

BBCorv70

Is the 70 really that much harder to find or more expensive than the 72? They're quite similar.

So far as max compression goes, I thought I read somewhere that you can get around some of this with a modern cam?

The 70 has a closed chamber head. I think they went to open chamber in 71. Many people prefer the open chamber anyway.