I have a question I hope doesnt sound to dumb. I am a novice at this engine stuff. Can someone explane something to me?

Back in 1969 Chevy had offered a 300hp 350 in the corvettes, they also offered a 350hp 350, What was the differance between the 2 what changes did they do to get 350hp.

Thanks and I hope this isnt to dumb of a question.

 

i'm not sure, but two popular heads back then were the camel or double hump heads or fuellie heads and they had two different valve sizes so my guess is the more powerful one used the big valve, probalby a different cam and maybe even a different compression ratio....

 

The 350-350 engine used domed pistons and a compression ratio of 11.00:1 with solid lifters

The 350-300 engine used flat top pistons and had a compression ratio of 10.25:1 with hydraulic lifters

 

I've wondered much the same thing, but on a broader scale:
From 68-73 (the last year I care about, since I own a 73!) the 350 engine went thru HP reductions each year. Basically the same engine but with different mods to reduce HP and I'm guessing reduce smog. But what was really done, and can those changes be reverse-engineered? Or would it be smarter/cheaper to just start fresh with a new crate engine with more HP?
What would it take for a wimpy ol' 73 small block to act like a late 60's small block?

 

[QUOTE=johnnybrewmeister]I've wondered much the same thing, but on a broader scale:
From 68-73 (the last year I care about, since I own a 73!) the 350 engine went thru HP reductions each year. Basically the same engine but with different mods to reduce HP and I'm guessing reduce smog. But what was really done, and can those changes be reverse-engineered? Or would it be smarter/cheaper to just start fresh with a new crate engine with more HP?
What would it take for a wimpy ol' 73 small block to act like a late 60's small block?[/QUOTE

In my opinion 1970 was the peak year for the small block engine. The LT-1 engine had 370 gross hp (gross-engine being tested for output without accessories) It was an improvement of the 350-350 engine by using a more radical cam, transistorized ignition, 850cfm carb
a high rise intake along with solid lifters. This engine was a monster in it's day!!!!

To tone down HP GM cylinder heads with a larger chamaber volume (thus lowering the compression ratio) to allow the vettes to run on unleaded feul. On paper, GM began using net HP ratings (net-engine tested for output with accessories) the The 73 in it's stock configuration still had some pep but not as much as the small block vettes of the late 60's-1971(my pick for the last of the high performance vettes of this generation)

To answer the last part of the question, good cylinder heads, a nice cam, and a good ignition system and what your money can afford. Hope this helps.

 

The 350 Hp engine used a little bit more cam than the 300 HP motor. It was a Hyd. cam not a solid cam. It used 11 to 1 domed pistons vs the 10.25 to 1 in the 300 motor. . The only solid lifter cam in a SB C3 was in the LT1 motors. The LT1 motors used a 780 vacuum secondary Holley not an 850.

 

Thanks everyone, I'm just trying to get educated on the C3 and a little on the history of the small block. I appreciate all the input. Thanks again.

 

Tetra-Ethyl Lead was being phased out and catalytic converters were being phased in during these years.

There weren't sophisticated enough engine management systems available to deal with the onset of detonation, so the manufacturers were forced to drop compression ratios as the octane of the available fuel dropped to provide any measure of reliability.

Since that time, knock sensors and computing power of engine management systems have been developed, witness the LS-7, 505 HP Net.

Fuels have also become more engine friendly, gone are the days of 104 Octane at the local Sunoco, but the new 91-93 octanes are remarkably engineered and clean, capable of supporting around 10.5:1 Compression Ratio.

 

You can duplicate (+\- some) the specs of the 350hp engine by adding better heads and cam.

Converting your flat top piston 350 to Vortec L31 heads (PN: 12558060) and the L46\L82 Cam (PN: 3896962) will get you close.

Compression will be close to 10.25:1, you will need the Vortec style intake manifold.

With headers and good tuning, you will be well over 300hp.

Audie

 

That sounds about right. May have also had different carb jetting and timing settings due to the compression, cam and head differences.

 

The L-46 350/350 had upgraded internals for the added HP. Forged pistons, steel crank, 4 bolt main, windage tray, same heads as the 300 HP engine but the chambers were unshrouded and the valve sizes were increased, the cam was hydraulic and was the same one used in the L-82 which was sold through 1980. The carb and distributor had different calibration. A very flexible combination that was designed from the start as a HP Vette engine. Not used anywhere else.

The L-82 is a low compression version of the 350/350 with added pollution controls and heads that are less than desireable from a flow/hp and relaibillity standpoint. If you swap the heads and fix the smoggy exhaust system you can backdate your L-82 to get close to L-46 specifications. It makes for an easy to live with upgrade combo. Lots of RPM potential with great street manners and decent mileage.

-Mark.

 

Excellent words and I totally agree, this is an great upgrade for any pre 1987 low HP 327\350\400ci V8s...

Audie

 

I have a 68 300 hp numbers matching and I can attest, that the heads and block are identical to the 350 hp version. I read on this and found it to be only the cam, carb and manifold that are different, both have identical torque values (360 ft lbs)

 

WRONG! the 350-350 was a all forged bottom end with a BIG hydraulic cam. The bottom end is essentially the same as the LT-1. The heads had 2.02/1.6 valves but pressed in rocker studs. Intake was Q-jet. 350-350 has bottom end good for 7K RPM if you upgrade valvetrain and cylinder heards. Good motor for the "Mechanically Disinclined" who cannot adjust valve lash.

 

WRONG your 300HP engine has cast crank, cast pistons and standard connecting rods. The heads are the same casting BUT 350HP heads have a machined combustion chamber relief for flow and 2.02/1.6 valves. I wouldn't rev your 300HP motor much past 6K RPM but wouldn't have a problem running a 350HP to 6500 RPM. Also the 350HP blocks while having the same casting numers are made with high Nickle/Tin content Iron while you block is standard Iron (010/020 nubers under timing cover and other locations but, if I told you, I would probably never find a good core for my LT-1 again.)

 

Does anyone have complete engine build specs for both of these motors?

 

I have been trying to pull together the informaiton on the L46 350\350.

I have never read about the high tin block before, can this be verified?

Also have not been able to verify that the L46 186 heads had pressed in studs vs screwed in w\guide plates? And the machined combustion chamber relief, can this be verified?

I have never found the specs on the rods other than the forged "pink rods" were used. Part number?

I am also still looking for the piston part number and dome spec?

If we can verify this I will post what I have compiled...

Audie

 

Got that message several posts before yours.....Thanx for the edumuhcation

 

Wow, Thanks everyone. This makes for good reading. Like I stated before I am trying to get educated and everyone is helping a lot. Thanks again.

Mine is the 300hp and the previous owner made upgades not sure what but things were done for the better.

 

73 and 74 specs, the others are also on the site: http://www.nastyz28.com/camaro/z28l82.html