Cam upgrade for a bone stock 350ci SB
 

What is a safe and reliable cam shaft upgrade for a bone stock 350ci SB? I’m talkin brand new with flat tapets and piece rear main seal. How much horsepower can I expect to gain for a couple hundred bux?

While I’m in there I may as well add hydraulic lifters. Any ideas for those?

What year engine and what is it in? What is the intended use of the vehicle (highway, towing, in town, etc)? Manual or automatic trans? Rear gear ratio/tire size please. I'll try to give you a really good answer if you give me the info.

Upgrade
 

The engine will be new next year 2020 and have a SM465 manual transmission with an NP205 transfer case. It is running 35” Mickey thompson Baja claws with a 2.73 ring and pinion. I am using it for general off-roading and am looking to gain some “hard to reach” horsepower while the engine is out of the truck.

I am sending back an engine engine I purchased last year for defects I can no longer live with under the warranty and it is bone stock. The reason I am telling you this is because the normal reaction for someone to have after hearing about installing engine upgrades on an engine someone else has yet to purchase is, “ why don’t you buy it that way instead of adding it later?” Sometimes it can be cheaper sometimes it isn’t.

Thanks for the suggestions.

1984 Chevrolet Blazer

Please let me know which engine you are planning to buy so I can know what heads and pistons and compression ratio you are dealing with. Makes a difference in cam selection and other stuff.

Do you mean 3.73:1 gears with the 35" tires?

2.73 gear ratio at the rear differential. 35” tires and the compression ratio is 8.5:1. The current cam is .383”/.401 & 112 degrees lobe separation. 4” bore 3.480” stroke. 76cc cast iron head chambers.

these numbers will not change if I get another motor or not.

A little off the topic of a cam suggestions, but 2.73's with 35's has to SUCK! I have 33s with 3.73s in my K5 and it's ok with a stock 350; a bit sluggish off the line, but rolls down the road decent enough. It is just my hunting truck anyway, but I certainly wouldn't want to run it with 35s and 3.73s.

Anyway as far as the topic at hand is concerned, my suggestion is and always has been to talk with a cam suppliers (yes plural, call/email as many as you can think of Comp Cams, Lunati, etc) for cam recommendations to fit your particular application. They are literally experts where we are simply end users. There are a TON of options they can play with to make the most of the other parts that are on the engine (intake, carb, heads, exhaust to name a few).

I doubt any aftermarket cam is going to increase low-end torque enough to make any difference with those gears. In fact, they'll probably make it worse.

Do yourself a favor and change the gears. The thing will probably feel like a rocket with 4.11s after driving it with 2.73s. 4.56s would be even better if you had an overdrive transmission, but they're a little too low for freeway cruising with 35s and an SM465.

Wow an admin and senior member ganging up on the new guy. Must have done something right!

Ganging up on you? What are you talking about?

I think Toma A and Swartllk are just surprised by your choices - I was too. With a manual trans that calculates out to 1835 RPM @ 70 mph. In the ballpark of typical overdrive RPMs. Horsepower is a function of both torque and RPM (RPM you will not have), so horsepower increase is not what to look for. It's a torque increase (at whatever RPM you will be operating at) that you want.

You can increase the sharpness of the torque curve (higher peak but narrower power band) by reducing the LSA (lift and duration being equal). This should not be confused with increasing the horsepower by moving the same torque curve to a higher RPM - which is often done by keeping LSA the same and increasing duration. First camshaft will have more torque/power at a given moderate RPM, but power will fall off quicker at high RPM. Seems that you need your power all down low.

That said, David Vizard (the engineer and engine builder/racer - the one who writes books) claims a formula for optimal LSA in a carbureted small block Chevy without power adders like turbo, supercharger, or nitrous - it is dependent on engine size. For a 350 he claims a 108 LSA cam is always optimal. (400 takes a 105 LSA, 383 takes a 106 LSA and 327 takes a 109 LSA) Then he selects intake/exhaust overlap in degrees, which in turn specifies the duration of the camshaft. Note that LSA affects overlap, and thus the duration requirement. So a 240@0.050 cam is way different for a 108LSA than it is for a 112LSA. The 108LSA cam of same duration has 8 degrees more overlap (which is a world of difference to your engine). Also, a tight LSA camshaft raises effective compression ratio (dynamic compression) because the intake valve will close sooner (for same duration) and with 8.5:1 static CR you need all the help you can get to maintain as much of that as possible. One thing that can be done without really adversely affecting performance at any point is to open the valve further using higher ratio rockers. Vizard always seems to recommend taking advantage of that. You can get his book on Google Play and read it if you want to know more.

Vizard has a cam selection chart in his book How to Build Max-Performance Chevy Small Blocks on a Budget. They are all custom spec Lunati camshafts that can be ordered. DV248-08HFL or DV256-08HFL with 1.6 rockers seems to be what you need. How much increase I don't know, but I would suspect you to be able to feel it - especially at lower RPMs. Don't try to compare duration numbers here to your 112 LCA camshaft (apples and oranges).

Anything that will increase volumetric efficiency (get more air into/out of the engine while those valves are open) will help without affecting driveability. This is where headers and intakes help. But the real power increase these days comes with incorporation of good heart shaped chamber aluminum heads from companies like Profiler or AFR.



https://cimg1.ibsrv.net/gimg/blazerf...3ae53b15fb.png