rafalc

I've been in the market for a chrome bumper for some time now. One of the things that I am still a little confused about, don't have a lot of experience with and wondering about is the different HP on a 350 motor going from 68 to 72.

I understand that going into the 70s the way the HP was reported changed, but did the actual HP change as well?

While shopping, what motor should be my "cut off" as in.... I look any weaker and I'll feel like driving a honda? I don't have a lot of experience driving many of these cars so I want to make sure I get a good motor that I will not get bored with (without the need fo going to a bb). Of course a lot of things can be done to increase the power and make it sound better but I would like a good base motor.

Thanks

Easy Mike

68s have 327s; no 350s. 69-up have 350s. For 68-70, advertized gross horsepower figures were determined on a dynometer with no drive accessories. 71 and later horsepower figures were net figures determined with accessories in place. Emissions requirement detuning can also be configured into the mix beginning with 71.

Why limit yourself to a "cutoff" horsepower figure? You could possibly miss some nice cars that way.

Good reading here:

rafalc

Thanks Mike...my mistake on the 68s. How about the second part of my question....is there any base motor in the 69-72 that you would say "stay away" from? Too weak? Not worthy to be in a corvette? Or am I just overthinking this. Again...I haven't driven enough of these cars to really feel the difference or the lack of.

builder

Generally the earlier the better for the 350's in the 69-72 range.

Ganey

They all have "a good base motor" though none are "worthy to be in a corvette". Therefore many have been modified for more power which if someone knows is easy to do & keep a stock appearance.
You will buy an individual car so really you need to drive them to see what works for you.

Emissions equip. started in 68 (earlier in CA).

To me a good cutoff is any less than L-88, which needs headers/exhaust so they all get modified.

69 Chevy

Base motor 350's of 69/70 had 300 horsepower and 11:1 compression. These were the last years of high compression engines. '71 had 9:1...'72 has 8.5:1. You could feel the power loss in the seat of your pants. But, as was said, the fed gov't mandated a change in the way manufacturers measured HP to the SAE way. The 30 HP or so loss in that case was just on paper.

Roughrider

Only three things to say for buying a chrome bumper...4-2-7!

Then again you can add...L-T-1 if you're set on a small block.

gbvette62

There were 2 350's offered in 1969, a 300 horse and a 350 horse version. The difference between the 2 engines were mainly in the cam and heads used.

For 1970, the 300 and 350 returned basically unchanged, and the 370hp LT-1 350 was added to the line up. The LT-1 added a bigger cam, high rise aluminum intake and Holley carb to the 350.

In 1971, all GM engines had their compression ratio reduced, in preparation for the coming use of unleaded regular fuel. The base (L-48) 350 dropped from 300 horse to 270, and the LT-1's horsepower was reduced from 370 to 330. The 350/350 was no longer offered in 71.

Starting in 72, GM changed the way they rated horsepower. After using gross horsepower figures for years, they switched to a net horsepower rating. Gross HP is rated using a bare engine, with no accessories, on an engine dyno. Net HP is a truer rating, basically it's a rear wheel horsepower, with all power robbing add ons in place. Because of this change in ratings, the 72 L-48 went from being 270HP to a rating of 200HP, and the LT-1 rating was reduced to 255HP. The engines are essentially the same as the 71 versions, only the way their horsepower was rated changed.

From a driveability standpoint, there is probably very little difference between a 69-70 high compression 300 horse L-48, and the lower compression 71-72 L-48's. In a quarter mile race, the earlier engines are probably a couple tenths quicker, but in normal driving the difference is probably negligible. The same would be true of the 70 vs 71-72 LT-1's. The difference in performance is much more noticeable when comparing big blocks, especially the 69 400/430/435 versions, compared to 70 and later 454's (except maybe 71's pretty rare LS-6).

As a plus, the 71-72 engines will run happily on today's regular fuels, while the 69-70 350's usually need the plus grade, if not premium.

Mike,

The 71's were still rated as a gross horsepower. The rating changes didn't take place until 1972, for GM cars. If I remember correctly, Chrysler and Ford waited until 72 to drop their compression ratios and may have waited until 73 to update the HP ratings.

Glenn

gbvette62

Actually the 71-72 base motors had 8.5:1 pistons in both years, and 69-70 300HP engines had 10.25:1 CR. The compression ratios for 69-72 350's break down as follows.

69-70 base 300HP L-48 had 10.25:1 CR
69-70 optional 350/350 L-46 had 11.0:1 CR
70 350/370 LT-1 had 11.0:1 CR
71-72 base L-48 had 8.5:1 CR
71-72 optional LT-1 had 9.0:1 CR

Mike Ward

One small correction- Net HP is still measured on a dyno and does not equate to rear wheel HP. There are no driveline losses taken into account.

Easy Mike

No. Including the 68 300hp. Are there any you want to stay away from? My point is you may find some awfully nice base engine cars. No sense passing up what otherwise might be a nice Corvette just because it has a base engine.

Maybe. Have you actually looked at any cars? Driven any yet?

Good luck.

rafalc

Thanks for the info guys!

So looks like I'll be going to Carlisle concentrating on the 68-70 years unless of course 71-72 is not original under the hood.

Then again....there are a lot of other things to consider than just the motor when looking at these 40 yr old cars. In the end...I don't think the motor will be a deal breaker but it would def help if I got something on the stronger side....

rafalc

Mike, yes I've looked at about a dozen of cars in the past few months. Drove most of them as well. Last one I drove was a 71 (owner said the motor was replaced by previous guy and was not sure what was in it) and it just felt sluggish.... this is why my concerns came into existance...

gbvette62

I guess that I should say that "basically it's a truer horsepower", instead of rear wheel horsepower, that's my bad!

On the subject of gross and net horsepower, a funny thing turns up when you compare the 71 and 72 Corvette sales brochures.

The 71 brochure has an asterisk next to the horsepower in the power train chart, with a note stating the following: "*SAE net (as installed) horsepower rating". Then the 72 power train chart has this note: "*Net horsepower ratings, in accordance with Society of Automotive Engineers Standards, represent the power of engines as installed in the automobile". The 1970 Corvette sales brochure makes no mention of how the horsepower figures were reached.

It's interesting the Chevrolet chose to refer to both the 71 and 72 horsepower ratings as net, when obviously the 71 wasn't!

gbvette62

I wouldn't right off a 71 or 72, especially based on driving a car that admittedly you don't know what engine was in the car. It could be 283, 305, 307, it may be in a poor state of tune, or in need of a rebuild.

If the budget was there, my first choice would be a 70-72 LT-1 car. If high performance is a big concern, than the second choice would be a 69 or 70 350/350. In spite of what others have said, if your looking at an L-48, base engine car, from my experience the difference isn't all that much between a 69-70 and a 71-72 L-48.

From some old car life magazines, I found the following road test results. In the June 69 issue they compared 4 different 69 Corvettes, the base engine 350/300 with a 3 speed automatic and a 3:08 rear, ran a quarter mile of 16.12, and a top speed of 126. In June 71, they tested 4 71 Corvettes. The 71 base engine, 350/270 automatic with a 3:08, turned in a best quarter mile time of 15.55, and had a top speed of 132. Now some of the difference could be attributed to the drivers, location, the added weight of optional equipment and the weather when the tests took place, but in these particular tests, the 71 was quicker!

For reference, the other times and cars in the tests were:

69 350/350, 4 speed, 4:11 rear - 14.55
69 427/390, 4 speed, 3:08 rear - 15.02
69 427/435, 4 speed, 4:11 rear - 13.94

71 350/330, 4 speed, 3.70 rear - 14.57
71 454/365, 3 sp auto, 3.08 rear - 14.20
71 454/425, 4 speed, 3.36 rear - 13.80

Sunstroked

I've also read that the magazines that tested these cars back in the day saw very little performance difference between the 70-72 cars. Those quarter mile times seem awful slow, but look at the top end speeds! Bias ply tires obviously did not help the e.t.

gbvette62

The top speeds given are the car's top speed attainable, not the 1/4 mile MPH. Sorry I confused you.

As an FYI, I still have the 6-71 issue sitting here, and the 1/4 mile speeds were as follows: L-48 - 90.36 mph, LT-1 100.55 mph, LS-5 100.33 mph & LS-6 104.65.

I think the ET's are pretty typical of what I remember from "back in the day".

Yeah, those old, rock hard, bias plys; weren't the best for starting line traction!

gq82

Very interesting....thanks for the historical statistics. I always enjoy reading comparison road tests from back in the day when our cars were brand new.

indydoug

I wouldn't worry about feeling like you are driving a Honda, especially in a pre-smog-era 'Vette - I have a 1980 that I know needs timing/tuning work, and there is still no comparison to my wife's or daughter's Hondas!

Schaggy

I don't suppose you have those numbers into '72, do you? I'd love to see that.