Augustus

The 70 I have is a jet, and sounds like a jet literally. (Nice whine noise with the tranny too).. and on the highway it's brutally fast as third gear I can hit over 100mph.
I had the secondaries on my carb adjusted to the way I wanted and know I can hear it wail on full throttle.

Highier compression is the key. I think it's 50HP per 1point in compression.

If it's a 72 and in good shape go for it... These new cams from Comp cams etc.. offer fast ramp design cams which allow dynamic cylinder pressure to be built up and provide usage of high lift cams to work effectively in lower compression motors.
Put a set of headers and you'll like it alot.

Derrick Reynolds

'70s are significantly more expensive than '72s, but I don't think that has much to do with the '70 being higher compression since '71s also seem to be much more expensive than '72s. It looks to me like a substantial portion of the market can't get their brain wrapped around the idea of a change to the rating system for Hp from '71 to '72. They just don't seem to understand that you don't feel that change at the gas pedal.

Lots of people also seem blissfully unaware that when you stomp on the gas, and feel the car pushing you back in your seat, that's not horsepower you are feeling, it's torque. If you are looking for a fun car to drive on the street, horsepower is essentially meaningless, you are looking for torque. '72 Corvettes with a stock 454 have more than enough torque to put a smile on your face every time

BBCorv70

As you say, horsepower isn't what pulls you back into your seat, it's torque. Always loved the big blocks.

I bought my 70 a very long time ago. My reasoning at the time was more a matter of feeling that by 1970 they had most of the bugs out of the C3 design, highest horsepower, and the most gadgets and features. I don't recall all the differences but I think the 70 and 71 were almost identical, little difference. Over the next few years after 1970 I recall the removeable back glass going away, fiber optics, and the wiper door in 73. It seemed Chevrolet was cutting costs where they could.

The downside of 1970 IMO is actually the compression. Harder to buy gas which doesn't make it ping. I'm pretty sure they went to a lower compression in 71 and open chamber heads. The open chamber heads are more desireable. Lower compression should be easier to run on today's gas.

If I were to start all over, I'd probably look for a 70, 71, or 72. My personal preference, chrome bumpers with most of the gadgets. And again, a big block of course... I don't know that I would pay any more for a 70 vs a 71 or 72.

Derrick Reynolds

I agree with everything you posted except the part I quoted here. Today's gas is much better than what we used to get in 1975, and a properly tuned 10.25:1 compression engine should run great on it. I have never heard my engine ping.

BBCorv70

That may be. I'm just now getting this car back on the road after 18 years of being apart. My recollection of pinging comes from the 80's, last time I drove this car regularly.

MEAN72

I bought my 1972 LS5 new with close ratio tran (M21) with 3:55 rear. I was disappointed in the power since my previous vette was a 1967 427/435 hp.

The first thing I did was remove the air pump and change the initial timing. It made a difference. Second thing I did was add headers and side pipes. It made a BIG difference. It now ran like a Corvette is supposed to run. The third thing I did was re-curve the distributor and re-timed it. It will now pass anything but a gas station.

Don't be afraid of the '72 LS5. My changes were modest and can make it run like a Corvette is supposed to run.

joewill

there are several basic differences, most already discussed.

the 70 (2/3rds of them) had the open air cleaner element. the 72 was dual snorkel.. some would say harder to breath = less horsepower.

The 70 had higher compression which almost always equates to higher horsepower ( given using the correct gas)

don't know the difference in Cam configuration of a factory 454 back then, Corvettes were evolving into a luxury car back then and I bet the cam configurations were evolving also into a more lower rpm , lesser emmissions, torque in the low end type of configuration, killing horsepower.

The 70 did not have A.I.R., all 72 big blocks did.

and of course the change in horsepower rating in gross vs net.

depending on the cam and compression and rear end torque multiplication ratio, many people ( including me) , probably can't tell the difference or may see one perform better over the other based on any hop-ups

jr9170

I use Sunoco Ultra 93 in my 70 454 no knocks or pings.

BBCorv70

Sometime in the 80's I recall running a tank of half Cam2 racing fuel and high octane pump gas (for the period). Sounded like I was dropping marbles down the carburetor when I pushed it.

Won't be until spring/summer of next year before I get this car back on the road very often. See how it runs then..

Could be modern formulations are more compression friendly?

Augustus

I have no issues with running Sunoco 93 Octane. LOL... I remember the Big thing about Lead being stripped out of gas.. and everyone changing over to hardened exhaust seats.
I wonder if this new gas does have a different formulation.

If and when an engine rebuild calls for in the future... I'll keep the same compression and try different cam profiles to have some fun..Bigger cam with more exhaust overlap.. but I like keeping everything stock looking in appearance so I won't slap Hedders on it.

When I first got my car I ran it for 2years thinking it was the way it was.
One thing was different was the noise of the Rochester Howling when I floored it like my 455 Poncho.
Then having my buddy do a once over adjustment Carb tuning...that woke up my motor ..If those secondarys don't wail when you punch it your missing alot of untapped Power. LOL

L84s R Us

The heads on the 72 are different from the others. Along with timing they changed the combustion chamber shape just a bit to get the fuel to burn off a little more complete.
To up the horse power enough all you have to do is use a set of closed chamber heads. I do not have the casting number in front of me, but I am sure half you know have it memmorized. My 72 has plenty of pull since the head change. The nice thing is the thing still looks stock. The numbers are under the valve covers as we all know. I have the rectanguler port heads and the LS-6 manifold. The thing was a dog with them on it. Most of that stuff is for the higher spinning big blocks and does no good at the lower end of the RPM range. The 72 just does not have the compression to push those parts.
I put the closed chamber heads on with my original 72 intake and I have to say she runs pretty good.
I have a 63 fulie also. the big block pulls pretty damn hard now, but they are totally different beasts.
Just enjoy your car and make the changes when you get around to it, but for me the heads is all I should have done. I wasted a lot of money to figure that out, but I have some pretty cool parts sitting in the garage now.

7T1vette

The '69 L36 engine (427 w/ 10.25 comp) was rated at 390 hp @ 5400 rpm. The '70 LS5 engine (454 w/ 10.25 comp) was rated at 390 hp @ 4800 rpm. Hmmm. Makes one think that the LS5 still had some 'ponies' left on the table; I'm guessing about 50 more at about 5400 rpm. Why do I think that? Because the '71 LS5 engine (454 w/8.5 comp) was also rated at 390 hp...but at 5400 rpm. {Aha!} Finally, the '72 LS6 engine was rated at a puny 270 hp--but, this hp output was at 4000 rpm! If you took it up another 1400 rpm, one would probably expect the engine to put out another 100 or so HP {just what the '71 would put out}.

So, what you really have is a lot of "smoke and mirrors" from the marketing folks at GM. Tout the HP in '69. Tone it down in '70 so as to not make the LT-1 engine look weak compared to a big block [without all those internal goodies]; GM liked getting the extra dough from LT-1 option sales. Drop the compression in '71, but show that it has the same HP as in '70 (but rate it at 600 more rpm in order to make that 'number'). And, finally in '72, derate the BB so much that the HP rating won't make the new owner's insurance rates go through the roof.

You have to read 'between the lines' on manufacturing specs to understand what was done and why before you can compare engines from different years. Torque output from '70-'72 454 engines is similar, but the '70 will outpull the '71 & '72 because of higher compression making some more torque across the entire rpm range. I sure wouldn't "pass" on buying a '71 or '72 BB because of engine ratings.

L84s R Us

I picked this up off of another thread. I will not take credit and I left the guys names on it. It says a ton without saying much. But, the bottom line truly is the horsepower ratings were rated for insurace and marketing as previously suggested. The information below is good reading though. Sorry, the name did not transfer but the author was from this forum


1) All 70-74 Corvette 454 cid engines were two bolt main configuration EXCEPT 1971 LS-6;
2) Most, if not all, 70-72 Corvette 454 cid engines used a forged steel crankshaft. There may have been some exceptions, though, with those using a cast nodular iron crankshaft;
3) All 73-74 Corvette 454 cid engines used a cast nodular iron crankshaft;
4) All 70-74 Corvettes with 454 cid engines, except 71 LS-6, used the same size intake and exhaust valves which, as I recall, were 2.06" intake and 1.72" exhaust.
5) 1970 LS-5 cylinder heads were unique to that year. For 1971-72 LS-5 engines, although different castings were used for each year, the cylinder heads were, essentially, the same. 1973 and 1974 LS-4 engines used cylinder heads specific to each year which were different for each year. As I recall, all 1970-72 LS-5 engines used cylinder heads which had about the same intake and exhaust port volumes. 73-74 LS-4 cylinder heads had smaller intake and exhaust ports, although I believe that 73 and 74 were about the same. All cylinder heads, except 71 LS-6, were cast iron material. 70-72 cylinder heads did not use induction hardened exhaust valve seats, including the valve seat inserts used on 71 LS-6 aluminum heads. 73-74 LS-4 cylinder heads used induction hardened exhaust valve seats;
6) All 70-72 LS-5 engines used the same camshaft, GM #3883986, wrong: 1972 is the year they changed the cam to the “emissions profile” grind. which was also used on 66-69 L-36 427 engines. 1973 and 1974 LS-4 engines used a different camshaft, GM #353040, which was the same for both years. This camshaft was an "emissions profile" camshaft;
7) All 70-74 454 LS-4 and LS-5 engines used the same connecting rods which were forged steel with 3/8", knurled shank rod bolts;
8) All 70-74 LS-4 and LS-5 engines used cast aluminum pistons. The piston dome configuration was unique to each specific year, however, even though compression ratios may have been the same (72-74). 1970 LS-5 used 10.25:1 compression ratio; 1971 LS-5 used 8.5:1 compression ratio; 1972 LS-5 used 8.25:1 compression ratio; 1973-74 LS-4 used 8.25:1 compression ratio.
9) All 1970-74 Corvettes with 454 cid engine used the same oil pan, including LS-6;
10) 70-72 LS-5 engines used unique-to-each-year cast iron intake manifolds. However, all of the manifolds were similar. 73-74 LS-4 intake manifolds were also cast iron but had smaller port size to match the 73-74 cylinder heads. 73-74 manifolds also incorporated provisions for EGR.
11) All 70-74 Corvettes with 454 cid engines used the same side-specific exhaust manifold castings. 1971 with LS-6 and all 72-74 LS-5,LS-4 manifolds were drilled and tapped for A.I.R. fittings.
12) All 70-74 Corvettes with 454 used the same valve springs except the 73-74 exhaust valve springs which were shorter to accommodate the rotators used during those years.
13) All 70-74 Corvettes with LS-5/LS-4 engines and manual transmissions used a 14" cast nodular iron flywheel with an 11" clutch. LS-6 used a 14" flywheel with a special dual disc clutch;
14) All 70-74 Corvettes with LS-5/LS-4 used the same oil pump
15) 1970-72 with LS-5 used the CCS (controlled combustion system) exhaust emissions control system. All 1971 LS-6 and all 73-74 LS-4 used the AIR (air injection reactor system) exhaust emissions control system. Many of the horsepower/performance differences, particularly during the 72-74 period, were the result of emissions control system differences.

jr9170

texas jim

That's it! You can't make good hp w/o good compression. After '70, the compression was gone and the engines were dogs. That simple.

Clue

What about this 8.75 to 1 compression ratio engine :

http://www.gmpartsdirect.com/results...umber=12568778

LancePearson

so....simply advancing the timing again could give back some h.p?

LancePearson

just out of curiosity, what mpg did those huge blocks with heavy horsepower get on the highway? I know many were used as drag cars probably so that didn't matter but just in case you got one and drove 100 miles how much fuel would you likely get? Curious is all.

72ragtop

Lance, my 72BB with auto and 3.08s. Stock motor with A.I.R. hooked up gets about 8 around town and 13 on highway if i keep it under 70.

gdh

That's pretty good as my old stock sb got about that. With the stroker rebuild when fresh I was up just over 19 highway. I love driving bb's but really hate being a passenger in one. My neck hurts and it usually get bounced off something hard in behind the seat - so while driving as a passenger and don't even want to talk about the heat on the floor.