HP - 396cu = 325,350,375 what changes?

[marriest]

What is changed to effect HP on the 396 Cu engine?  Cam, Carb, Lifters?
Just curious or is it something else?

[boomer632]

Compression ratio, cams, lifters to name a few. I think the L78 375 got the hottest cam with solid lifters, 4 bolt mains, rectangular port heads and Holley 4346. Lesser HP got smaller cam, oval ports heads, different compression rations and Rochester QJ carb.

[william]

The '69 L35 325hp and L34 350hp engines are similar and shared block [2 bolt mains], head and intake castings. Both used oval port heads. The L34 had a higher performance hydraulic camshaft, different carb and distributor calibration. I believe it also had a forged steel crankshaft. Neither really a high-performance engine.

The L78 shared block and head architecture with the L34 & L35 but that's about it. Block, head and intake castings are different. Heads had rectangular ports, bigger valves. Block had 4-bolt mains. Intake manifold was aluminum and used a Holley 780 carb. High performance mechanical lifter camshaft. I believe it used different connecting rods.

[Sauron327]

My friend has an L78 and just rebuilt the motor. Rectangular ports don't turn on until the pedal is mashed and higher RPM's. That is not the way he drives so he went with oval.

[169INDY]

https://www.motortrend.com/how-to/chevrolet-lied-stone-stock-1969-l78-396-big-block-makes-50-hp-more-than-factory-rating?galleryimageid=71cc4068-9cda-461c-9c18-94d2679c4859

[marriest]

WOW! Great information!
What was the reasoning for building 3 different engines with the same block?
Just to have options or were the other reasons?

[crossboss]

FWIW, and as mentioned, the 'Oval Port' heads will be the better street engine bar none. Think LS5 VS LS6 454's.

[169INDY]

^^ TBD^^ I am testing a L78 transplant for my L35 after 30 years.

I can tell you my first impressions on the STREET is the 396/375 is Pulling like gangbusters. & I am still in the first few miles.

[MO]

WOW! Great information!
What was the reasoning for building 3 different engines with the same block?
Just to have options or were the other reasons?

Could have been insurance driven. Could also have been that they were available across the brand which made easy options for higher profit. Could have been that their dad wouldn't let them have an L78, so they got the L34/35 and upgraded when he wasn't looking.

[bcmiller]

My friend has an L78 and just rebuilt the motor. Rectangular ports don't turn on until the pedal is mashed and higher RPM's. That is not the way he drives so he went with oval.

Generally true. Oval ports will perform better below 5k RPM. Take some 049 or 781 oval ports, add larger valve and a port job - then then will be equal to or better than rectangle port heads above 5k.

[crossboss]

^^ TBD^^ I am testing a L78 transplant for my L35 after 30 years.

I can tell you my first impressions on the STREET is the 396/375 is Pulling like gangbusters. & I am still in the first few miles.

Maybe correct. However, it will take time (RPM) for those big ports to work. The oval port car will be ahead of you off the line and through most of the race. Torque moves the car. Think Buick/Olds/Pontiac 455 VS 426 Hemi/Boss 429s. Believe me, I know all about big port engines...

[DuWayne Ladner]

Yes sir 169Indy, I as well am about to find out how a freshened L78 CE code punched out to .60 over, hyd roller, 3.73 gears is about to pull and sound and perform, this coming week hopefully. Freshly restored 9’ SS 396 L78, rec Sept 22’, but dropped a cyl in less than 30 miles driven. Been in engine resto last 7 months, and about to be rolling again. Now ya keep in mind, haven’t shared my full history, maybe touched on it on quite a few MARO groups on FB, but I have not driven my Camaro since about 1986. So yes 169INDY, I am stoked and once again I want to feel, hear, and slap me some 4- gears of my M-21. Ya know thunder under the butt and that, oh my, power pull, again. Thanks ya, God Bless.

[67nut]

Along with the rectangular heads, the solid lifter cam isn't as street friendly as a hydraulic one. But up the RPM's................... and look out! There's something to be said though about the sound of a solid lifter cam that gives me goose bumps.






Steve
The difference between a hobby and insanity is about .001"

[PHAT69AMX]

Could be sanctioning body rules for what is legal for use in a given class of racing, such as NHRA Super Stock.  For a given carb, intake, etc to be legal it must be available on a minimum of 50 cars as factory built from what I understand, at least is was 50 units minimum in 1969.  Then any car could use those pieces and parts and still be legal.  Say a '69 ZL1, a person could build a "clone" and it would still be legal in NHRA Class using all the parts factory installed and sold on the (50) copo cars, even though it was not an actual ZL1.  That might be why the less-street-friendly L78 396 option.

[Kelley W King]

I have both a rectangle port L78 camaro and an oval port 396 as well. The valve size is more important than the port shape. If you put the large valves in an oval port it might pass a rectangle port on the street but not in stock condition. No bench racing here, real life experience. The L78 cam does need at least 355 or 373 gears to get going just like the Z28.