1969 350 300hp Differance?
 

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

The '69 350/350 had 380tq.

It sure was. I remember a new 70 1/2 Z/28 with open headers and slicks and a a sticker still in the rear window beating almost everything where we used to race.

Yea been there, done that, just like mortec.com, not quite enough informaiton to figure the complete assembly...

Audie

High tin blocks are out there but I do not know where they were spec'd

There were no screw-in studs on anything before 1970 so they were not a requirement for the 69 L-46 in the original configuration. Might have been used in '70 and up though as they are included with L-82 for sure. it just makes sense that they would be included during L-46 production for '70 and up. Not a big deal as they are easy to add.

The factory 64cc heads such as the "186" that have the big valves (from the factory) will definately have the chamber unshrouding where the small valve versions of the same head casting will not. The later smog open chamber heads do not have unshrouded chambers.

I ain't gonna BS you about the rest cuz I dun-no. ;)

-Mark.

L46-350cid\350hp Specifications (still in draft)
 

RPO L46 = 350cid\350hp (Hi Per V8)

Brake horsepower: * 350 hp (261 kW) @ 5600 RPM (See note 1)

Torque: * 380 lb-ft @ 3800 RPM

Bottom end: + Good for 6500K RPM

Block: ** 4-bolt main, +++ #3970010 (+ possibly high Nickel/Tin content
Iron 010/020 numbers under timing cover and other locations)

Camshaft: * Hydraulic Flat Tappet (See note 2)

Valve lifters: * Flat Tappet - Hydraulic

Compression ratio: * 11.0:1

Heads: ** 2.02\1.6 Valves (See note 3)

Crankshaft: ** Forged steel (See note 4)

Rods: ** Hardened "pink" rods (See note 5)

Pistons: ** TRW domed, forged, and pressed pins (See note 6)

Oil pan: + Windage tray

Harmonic Balancer: +++ 8” non-finned, 6 ¼” Hub, 8” diameter, 1 ¾” thick

Intake Manifold: * Cast Iron Spread bore (See note 7)

Carburetor: * Quadrajet, 4-bbl (See note 8)

Exhaust: ** 2" Exhaust pipe with Walker mufflers

Exhaust Manifolds: ** RH - #3932465
++ ** LH - #3846559

Tachometer: * 6000-RPM Redline

Air Filter: ** Open element air filter (Early), Dual Snorkel (Late)

Water Pump: ** #3782608



Ignition: + Distributor w\points & HP curve
** #1111491
** #1111493
** #1112021

Alternator: ** #1100900

Transmission: ** Main case #3925661, Extension Housing #3857584, Side
#3952648 (Right side of maincase, just in front of extension
housing)

Rear End: **** CAM=3.36:1
**** CAT=3.08:1

Radiator: **+ Copper with plastic fan shroud and no overflow tank.

Console Data Plate: * 350cid, 350hp, 380 lb-ft Torque (L46)

Valve Covers: ** Aluminum, 7-finned, with twist on cap and each side vents

Notes:

1. + A 1966 L79 (327/350hp) with a fresh stock rebuild run on a chassis dyno, and his best was 238 hp at the rear wheels.

2. * Part Number 3896962, Hydraulic, 69-81 L-46 and L-82 Corvette cam, moderate torque, excellent power, casting #3896964. The casting symbol is a vertical diamond.

* Duration at lash point: (I:312\E:312)
* Duration at .050” Tappet Lift: (I:222\E:222)
* Maximum Lift with 1.5:1 Rocker Ratio: (I:.450”\E:460”)
* Valve Lash: Zero\Zero
* Lobe Centerlines: 114

3. Heads – ** 300hp engines did not get screw in studs or guide plates, 350 hp did.

** Casting #3927186, 63.305cc combustion chamber. 2.02 Heads got screw in studs, and guide plates. Casting #3991492 may appear on this part after 4/5/71. Casting #3947041 head was possibly used interchangeable with this head through 1969 and 1970 production. Small camel humps casting symbol.

** Casting #3927187, 63.305cc combustion chamber. Casting #3927186 may appear on this part until 10/9/70. After this date #3991492 may appear. Casting #3947041 head was possibly used interchangeable with this head through 1969 and 1970 production. All #3927187 heads have 2.02\1.60 valves. Casting symbol is small camel humps.

** Casting #3947041, 63.995 or 63.305 combustion chamber. 1970 had 2.02/1.60 valves, used as interchange on some models with #3927186 and 3927187 heads. Casting symbol is a slanted triangle.

+ The 69 L46's had pressed in rocker studs while the 1970 and later L46's and LT1's got the better screw in variety. 1970 did not get push rod guide plates. Uses steel shim head gasket.

+ Heads have machined combustion chamber relief (un-shrouded) for flow and 2.02/1.6 valves, pressed in rocker studs.

+ There were no screw-in studs on anything before 1970 so they were not a requirement for the 69 L-46 in the original configuration. Might have been used in '70 and up though as they are included with L-82 for sure. It just makes sense that they would be included during L-46 production for '70 and up. Not a big deal as they are easy to add.

+ The factory 64cc heads such as the "186" that have the big valves (from the factory) will definitely have the chamber un-shrouding where the small valve versions of the same head casting will not. The later smog open chamber heads do not have un-shrouded chambers.

4. ***** Large journal (2.10"\2.450"), stroke 3.484, casting number 3941182 or **3941188.

5. ** Rods are forged, shot-peened, magnafluxed, and heat treated to 500 degrees for ten or more hours Introduced in 1970 as a pressed-pin design with large rod diameter journal and high-rpm rod bolts used in the 302cid.

6. + Part numbers are stamped into the top. Standard piston is 3942541, the +.001 was GM #3942542, and the +.030 was GM #3942543.

7. ** Large raised letter S on underside, and oil splash shield, casting #3965577

8. ** 1969, Model 4MV, 7029207, ST
** 1970, Model 4MV, 7040207, ST non-CA
** 1970, Model 4MV, 7040507, ST-CA

* Source = GMC
** Source = Corvettes by the numbers
*** Source = Corvette Black Book
**** Source = 1970 Corvette Registry
***** Source = Mortec.com

+ Quote from Corvette Forum member
++ Source = NastyZ28.com
+++ Source = Chevrolet Small-block V8 Guide
++++ Unverified

ttt

That sucks that they never made the 460hp LS6 in the vette.

I'm calling :bs (no offence) :D

Well I have a 1970 300HP car. I tried to find all this out two years ago. Without spending big bucks I modded it as close to the L46 350HP motor as I could. I changed the following:
1. 2.02/1.92 valves in head, deshrouded valves/port and polish, screw in studs.
2. L46/L82 cam
3. Bigger exhasut. Stock exhaust is 2*1/4, the L46s came with 2&1/2 but it left the engine at 2&1/4 and then about 3 inches later goes to 2&1/2 with a welded flange.
4. Carb jetting.
5. LARS modded distributor for HP curve
6. Finned valve covers

To my knowledge my only shortcoming is the crank/rods/pistons in my engine. Hence my redline is 5300ish. My engine tops out in the 4000s. I probably need to look at flows to examine if my exhaust/intake is choking my engine.

I managed 228RWHP / 290 RWTQ after my rebuild. This is pretty close to the 327 below. I should be closer to 250-260RWHP and 320RWTQ with my engine being a 366 now.

From above:
Notes:

1. + A 1966 L79 (327/350hp) with a fresh stock rebuild run on a chassis dyno, and his best was 238 hp at the rear wheels.

Hate to disappoint you, but my '70 L46 definitely has hydraulic lifters, as I've seen them. Also, all of my reference material for my car clearly says they're supposed to be hydraulic. Like the other poster said, only the LT-1 motor had solid lifters.

300 hp stock crappy cam cast intake and 10.5 cr with a q jet 194 valves

350 hp 450/460 lift with 11 to 1 cr same cast intake and q- jet with fuelie heads and 194 valves.

the 202s were on the lt1 a bit later


both hydrailic


amazing the power even the base engine had back then but that is pre emmission and the drop in compression cost 40 hp then the heads even the heads were bounty full

anyone knows you could have just put a cam, intake , holley and headers in and you had 400 horses a little work on the heads and the bigger valves and you were over 450 with stock flat pistons

Now thats my 69. I was mistaken about the lifters before. It is one sweet ride. Also this car is equipped with power everything.

Must be a little mixed up here??
LS-6s were in Chevelles rated at 450hp & in vettes rated slightly more conservative.

What IS a shame is that they never actually got the LS-7 in a production vehicle, rated at 465hp, real world # indictaed they ran about 550 & more with the simple addition of headers! I know, my bud had a 69 with a installed stock LS-7 with headers:) Little hard of drivetrain parts thou!

Sorry for the hyjack :nono:

No they never made the ls6 for the corvette in 1970!! Your thinking 1971 where they made the ls6 rated at 425.

6 engines were offered on the 1969.

350/300hp...

L46 - 350/350...

L36 - 427/390.....

L68 - 427/400....

L71/L89 - 427/435...

and........the final motor option.........

L88/ZL1 - 427/560hp.........

ZL1 was an aluminum engine, and only two were sold.

the NCRS spec book says the 350/300 uses a 6" x 1 1/4" harmonic balancer. cant find that info anywhere else. comes up 8" in every parts book i search. would anyone know the oem number? i have a 69L 12-02-69 build on motor, 3970010 block

and i believe that option cost more then the car did

Cylinderheads, cam sh, intake manifold, headers, carburetors, exhaust. Car flies now
 

I had same situation and upgraded Cylinderheads, cam shaft, intake manifold, headers, carburetors and exhaust. Car flies now.
https://cimg3.ibsrv.net/gimg/www.cor...9088271d1f.jpg
https://cimg5.ibsrv.net/gimg/www.cor...c86a3b88f8.jpg

This thread is 14 years old. Let it die.

Actually, Lars does have a badge and has a citation book. He just doesn't have a pen right now.

I found all this stuff useful and helpful even though I didn't have a Corvette 14 years ago. My Corvette now is a completely new car and sounds amazing. I felt like sharing that in case it's useful to anybody else. I guess I deserve a ticket if he finds his pen.

FWIW
Pertinent to original question: Base 350's cam specs weren't shown
so here 280*/288*, .390"/.410" (same specs as L48 cam)

https://www.gmheritagecenter.com/doc...t-Corvette.pdf

New guys probably got the automatic old related threads showing & doesn't know how to turn it off; don't scewer 'em for that

Thx Chimera! Shouldn't skewer anybody for anything like this anyway. Corvette owners aren't crabby from everything I can tell. Have a great day fellas

Consider starting a new thread rather than continuing a conversation from years and years ago like it’s still active.

You can add a link to an ancient post if you want to reference information there. :thumbs: