I am currently starting to restore my 71 Vette with the 350/270HP motor in it. I’ll be pulling the motor this week to send it off to be machined so I can rebuild it. Seeing as it is being rebuilt, I would like to try and squeeze a few more HP out of this smog era 350. I have a 66 L79 Vette and I love the sound and power that comes out of it. That being said when looking for a cam for my 71 I came upon the comp 12-671-4 which is a modern grind based around and made to sound like the old L79 cam from the 60s. The specs are 229/236 duration @.050 and .468/.462 lift. Now my question is, knowing the car only makes 8.5:1 compression compared to an L79s 10.5-11:1, will this cam be too much? The car it’d go in has a 3.08 final drive and is a four speed car with A/C no PS or PB, but I do know these cars rely heavily on the vacuum system for critical functions like headlights and wipers and such. Also important to note is I plan to use stock diameter valve springs and do not plan to do any additional machining or work to the motor besides the cam/lifter/spring swap. Thanks for the help.

 

The car will be a total dog with that cam! On a stock motor I would do headers (good ones), carburetor jetting, and distributor recurving and call it a day. With 8.5 compression and 3.08 gears, the stock cam is your best bet.

 

If you are rebuilding it, you will be boring it and need new pistons.
Increase the compression to 9.5 or 10:1
Please do not leave it at 8.5 CR

You'll thank yourself.
Those low CR engines only lasted a few years while GM learned to deal with emissions.

You can put that back to 330-350 HP easily with more CR and that cam.

But you may still want to go with a milder cam if you stick with the 308 gears. I'd cut 7-10 degrees off.

 

Are you going to change the pistons and increase the compression? New heads? A bunch more machine work? All that adds up, and you'll still have a 50 year old engine.

Seriously consider just storing that engine in the corner of your garage for the next owner to throw away, and run a crate engine of some flavor instead.

 

Why???
I rebuilt my original engine for half the cost of a crate engine including the cost of new heads.
Are they giving away engines somewhere??

 

Same. Full rebuild with all forged internals. Still cheaper than what blueprint wants for a comparable hp motor.

 

Raise the compression to 10.5 to 1 and it will love that cam........
Use the Elgin Z/28 spring/lock/retainer kit......but do yourself a favor and have the heads machined for viton positive valve seals.......
I built a budget 350 earlier this year for a guy and it was a 1982 L83 350 short block, low mile freshened and honed....single long valve relief TRW forged piston (stock L83 slugs) and a pair of old 1968 327/300 heads 64cc chamber, 186 casting......used the .015 steel shim head gasket.....piston .016 in the hole for 10.48 to 1......used an Elgin 234/234 .480/.480 108LSA cam.....Vintage 1968 Weiand WQCV intake with a modified 600 Single feed Holley.......in a 1956 Chevy with a 4 speed, haven't had that much fun in years LOL......it revs super quick, ultra responsive, and the cam sounds sick as hell......nice little engine, not a Rocket but will surprise the hell out of you, especially for a "backyard ball hone build"...my guess is about 360hp.......keep the compression up and you will be happy.....change out your pistons!
Your gear sucks....but you can change it later.....it would go like 3.42.....not too much....3.73 reduces highway capability......

Jebby

 

I have a similarly spec’d crate motor (8:1, smog heads, L82 cam) in my ‘71, and with 3:08 rear, it is indeed a dog off the line.

 

Go with flat top pistons and get the compression up to at least 10:1 and that cam will work. At 8.5:1 it’s going to be soggy and no fun.

I’m running 11.3:1 and a 230/236 cam on pump gas.

 

rebuild the engine correctly, go with 10:1 pistons, aluminum heads (AFR if you can afford them), and if you can afford a roller cam go with that as well plus the headers. Anything less is a waste of your time and money. 400 hp is a really fun motor.

 

If you don't have money for pistons or heads have the machine shop square and deck the block .020 , mill the heads .010, steel shim head gasket and Comp Magnum 268 cam

 

Another vote for 10.5:1 CR. You will like it a lot more and get more smiles per mile with it.

 

Compression and airflow are they key to making any engine perform better. You don't have to go crazy but at least 9.0-1 and maybe 9.5-1 with iron heads will help that cam on todays pump gas. Any head porting will be a HUGE plus. Aftermarket heads will be a night and day difference for power.
For keeping the stock heads "stock" and your 3.08 gear I would look for something in the 214-218 degree range at .050.

 

Compression is often overlooked being deemed to "difficult" to deal with or some other reason. I build a copy of an L-88 engine using the 427 from my 1968 C3 and I love the way that 427 revs and the torque it makes is incredible. I will use as much compression as I can reasonably get away with in my hot Rod engines..

Airflow is Critical so anything to increase the flow will yield more power. The "cooler" the air is that gets compressed and burned in the engine the less detonation you will experience and more power can be made.

With a 3.36 rear and a 4 speed it is possible to put my Corvette in fourth gear at 20-25 mph and go from there with no shaking or lugging. Even with a 3.36 rear axle I have traction issues so I ended up spinning my tires for 1/8th (half track) and then they slowly "catch". My GTech Pro calculates that the car should drop into the 10's if I didn't have traction issues. I have been fortunate that my 427 with a 3.36 was able to beat several Corvettes with powerful engines and 4.11 rears.

Compression is a great way to go, especially if you have access to high octane gas. I was in Arkansas and they had both 100 and 110 octane at a Gas Station... Wow, I wish. When the SNOW injection system is running the gasoline is equivalent of 116 Octane and that stops any pinging. I keep some extra windshield washer fluid for any trips and to save money using the injection equipment. It would be possible to use 87 or 89 Octane using the Snow injection system. The Water/Methanol injection sure makes higher compression more do-able. The Water helps cool down the combustion chamber and the Methanol makes Power which makes it a "win-win".

Happy Thanksgiving Day to all out there!

 

Agree with 214 to 218 duration with stock c. r. The old Isky 264 mega cam with 214 214 @ 050 and 450 lift 108 lsa should work okay with your stock set up. Ran one in a stock low c r 350 in a 76 Camaro. Similar to the old Comp 268 HE cam. At least the engine will sound better than the stock cam!