VetteRock89

Hi
I have a 71 vette with a 72 stock 350 in it. I have realized that from 71 to 72 they changed the way they measured the horsepower. I would like to know, is there a difference between the power of a 71 350 and 72 350 standard engine? Is the 72 actually less or is it rated that way? And also, are the horsepwers on paper the actual amount or were they more? My main question is: is a 72 350 the same as a 71 on terms of power and horse? and what is that horse if the same? If not the same, then what are the actual amounts?
Thanks

7T1vette

no difference at all............

'71 base engine was 270 hp (gross); '72 was 220 (net).

Revi

Yep, the same.

In 71 the base engine was rated 270hp gross/210hp net.
In 72 the base engine was rated 200hp net. (IIRC they may have recurved the distributor a bit, explaining the 10hp loss.)

Alan 71

Hi vr,
Here's a picture of a chart that appeared in Corvette News when the 1971 car was introduced.
It lists the 'net' horsepower ratings along with the gross ratings.... and there are a couple of interesting numbers.
Regards,
Alan

VetteRock89

Alright than guys! I was really hoping my car had 270 horses....do any of you know if that is true or just on paper. For example, a 69 z28 is rated at 290 but really has almost 400. Now I understand that vetted were not necessarily for power they were for performance but I still would like to know. And if my car had some headers, what would the horse be up to? Everything is stock except headers
Thanks

Mike Ward

Although the HP ratings are stated in black and white, the RPM it was measured at is not mentioned. Without knowing if the two years were measured at the same speed and if this represented the HP peak, it's impossible to say whether the two years are the same or not.

zwede

Not as delivered from the factory! An all stock 69 Z/28 was a mid-high 14 second car. It made maybe 250 real hp. It responded real well to headers, free flow exhaust, recurved distributor etc, but that doesn't change that it wasn't a particularly fast car off the showroom floor.

As for your vette, I'd expect 20-30hp gain from headers on an otherwise stock engine.

7T1vette

...and another 25-30 hp with distributor recurve for 'performance'.

ClassicGlass63

Alan,
The chart you posted is really interesting. It was the first sign of things to come.
That page along with the same page for the 72 Corvette is in the Service manual.
I will see if I can figure out a way to post the 72 page. It is the one with the really interesting number as far as I am concerned.

The 1972, LS-5 was rated at 270 HP net and had the (350 HP*) off to the side. But it still let us know.

Most of it was done with timing and the cam. A cam is where a huge amount of horsepower comes from. If you also notice the horsepower rating was taken at a much lower RPM than the 1971.

Bottom line really was if you set-up the timing the way it could be you had very minimal horsepower loss in the 1971 to the 1972 changeover.

One point in compression does a lot too.

Truth is, the 72 still had a few pony's tucked under the hood if you set-up the timing right and took off the TCS. The TSC was the biggest preventer of horsepower. It prevented your vacuum advance from functioning except in 4th gear.

I have popped that off of a few friends cars and it is a day and night difference when you put your foot into it. And that should be often. If not you do not belong here.

Revi

The 71 & 72 base engines are the same. They both make approx. 270 gross hp. (Advertised at least.)
Gross HP is measured on an engine dyno with a velocity stack (no air filter), no accessories installed, and open headers.
Net HP is measured (or estimated) with the engine installed in the car, with an air filter, accessories, and OEM exhaust installed.

If you set up your timing per Lars and install headers, you'll probably pick up another 30 gross hp.

My 70 L-46 350/350 (Advertised HP) made 341hp/387tq (Gross) on an engine dyno after a rebuild with ported heads and a slightly larger than stock cam. In reality this means that a 1970 production L-46 probably made in the low 300hp range and not the advertised 350hp.

So your 270/200 may not be as accurate as advertised.

Mike Ward

Net HP is measured on a dyno (same as gross HP) with engine accessories attached.

ClassicGlass63

When I went to clean out the engine compartment on my 1969, 350/350, we cleaned up the engine bay and then went on to doing the engine.

We popped off the heads, cleaned all the carbon off the pistons, the ridge of carbon on the top of each cylinder and did what we could to the heads as far as cleaning.

When I put that motor back together it dynoed at just over 350 Horsepower with 33,000 miles on it.

I am in the process of building my 1972 LS-5 right now. I will let you know how she ends up doing on the dyno. I would be very surprised if it under 350 Horsepower. Very surprised.

It is impossible to tell anything from just driving a car. The trans, the driver, and the rear diff is makes all the difference.

You have to push the car really hard to tell what is really there. If all you want is to feel like you have horsepower, put 4:11 in it. You will beat most things on the street from short stop light to stop light. Even with 200 HP.

My 454 car has 3:08. Of course I like messing with guys from a roll. The higher speed we started the faster I put them away. But from a stop, I got my *** kicked all the time. If there was enough room I would go flying by with that big block pushing those 3:08's.

It is all fun, but honestly, How many of you guys are really driving your car like you should be.

I have so many friends with their high horsepower trailer queens. I have one to trailer around that I still pound on from time to time, but the other one has the pedal on the right used as often as possible.

Just enjoy them the best you can. Does 20 or 30 horsepower really matter very often in today's Corvette world?

Again, just have fun.

ClassicGlass63

The Net horsepower was not actually measured with the engine in the car.

Gross power was measured with nothing that drained any horsepower, where the net was done with everything that drained horsepower.

The belts, timing set to emission standards, air cleaner, A.I.R. pump if so equipped. The cars actual exhaust was used instead of a free breathing set-up.

Gross was taken right off the back of the crankshaft, where the net had a clutch, a transmission drive shaft, rear diff, and it was taken at the axle.

Quite a difference. In the days of gross, they played with it to get the most they could, UNTIL, they started lying anyway.

It was not long before the insurance company's rates went through the roof on the high horsepower cars. So, now you have a 400 HP small block that is rated at 210 HP so they can still sell them.

This is where it got really confusing for a lot of people.

Including me.

Mike Ward

Again, not true. It's measured at the flywheel.

Revi

Can you post the engine/lab dyno sheets for this? Have you run it on a chassis dyno?

lars

Mike is correct. Both gross and net dyno data is taken on an engine dyno, measuring output right at the crankshaft. Net runs the engine with accessories, such as the water pump, etc. The Gross rating is a very deceptive number, and you’d have a very hard time duplicating it on a dyno measuring net power: The Gross not only deletes all engine accessories, but compensates for rotational and friction losses as well, producing an artificially high number.

The Net rating on your engine is probably pretty close to correct at just over 200 horse. The stock, as-delivered 69 302 had nowhere close to 400 horse – probably closer to mid- to low-200’s. Adding headers to your engine will likely add about 15 horsepower, but that’s assuming that you correctly re-tune the carb to compensate for the lean-out condition that the headers will induce.

Lars