More power from my stock 350

[chiro22]

Howdy all,

picked up a 1973 Cheyenne and it needs a bit of work. It has a crate 350 and it looks like there's a leak in the head gasket. We did a leak test and the engine itself is solid.

I figure if I'm already opening the engine, wanted to see what some recommendations are for relatively simple ways of creating more HP.

Would I be able to tell a big difference with a head/cam change or should I do a cam/intake/carb change?

If I go with a head/cam change or cam/intake/carb, what parts should I pick up?

I did just put a shiny new high performance edelbrock carb.

I'd like to not spend a fortune, bc this is a hunting/fishing truck. Just looking to take it to the next level with dependable gear.

[rich weyand]

Comp Cams 12-300-4, 12-235-2, or 12-230-2 cam.
http://67-72chevytrucks.com/vboard/s...4&postcount=11

If you want torque, you don't need new heads, and torque is what you drive.

Put a dual-plane manifold under the carb. 2701 under an Edelbrock, 2101 under a Qjet.

Hooker 2452 (2WD) or 2453 (4WD) headers with an H-pipe and duals all the way back.

AR23/VC1853 vacuum advance can on a stock HEI distributor.

Good 8mm wires, like Taylor 74206.

ACDelco RT45S or Autolite 24 plugs at .045" gap.

Vacuum advance on manifold vacuum (drivers side of the Edelbrock) not ported vacuum (passenger side of the Edelbrock).

Time it properly. http://67-72chevytrucks.com/vboard/s...gnition+timing

Tune the Edelbrock properly. Put in the 8" step-up springs, and adjust the mixture in the power circuit (it will be too rich) and cruise circuit (on the 1406 it will be too lean). I can help with this if you go this route. Also, pull it apart and adjust the floats -- they will be wrong right out of the box.

[slotard]

How big of a difference you have depends a lot on what you have now. If your setup is already pretty good, you can't get as much on a low budget vs if you have something decent.

[MikeB]

Originally Posted by slotard

How big of a difference you have depends a lot on what you have now. .

Exactly!

What do you know about your current engine? There are a wide variety of crate engines. Is it a new GM engine, or an aftermarket rebuild from someone like BluePrint? Can you contact the previous owner to get the specifics?

How much cranking pressure (with the plugs removed)?

What kind of intake and exhaust manifolds? If stock exhaust manifolds, is there a heat riser valve? Does it work?

Dual exhausts? What pipe OD?

Ignition timing at idle with vacuum advance hose plugged?
Does the mechanical and vacuum advance work?

The things above are what you need to know before you run out and buy performance parts.

You'd be surprised at what you can gain with proper timing and free flowing exhaust. Many years ago I had a 69 C10 with a stock, high mileage 307. Adding a small 450 cfm 4bbl, dual exhausts (only 2"), and setting up a performance ignition timing curve made a HUGE seat-of-the pants difference, and increased fuel mileage by at least 20%.

[chiro22]

Originally Posted by MikeB

Exactly!

What do you know about your current engine? There are a wide variety of crate engines. Is it a new GM engine, or an aftermarket rebuild from someone like BluePrint? Can you contact the previous owner to get the specifics?

How much cranking pressure (with the plugs removed)?

What kind of intake and exhaust manifolds? If stock exhaust manifolds, is there a heat riser valve? Does it work?

Dual exhausts? What pipe OD?

Ignition timing at idle with vacuum advance hose plugged?
Does the mechanical and vacuum advance work?

The things above are what you need to know before you run out and buy performance parts.

You'd be surprised at what you can gain with proper timing and free flowing exhaust. Many years ago I had a 69 C10 with a stock, high mileage 307. Adding a small 450 cfm 4bbl, dual exhausts (only 2"), and setting up a performance ignition timing curve made a HUGE seat-of-the pants difference, and increased fuel mileage by at least 20%.

Let me get some info together and get back to you.

[68c10owner]

Getting more power can be as simple as a tune up or could be changing parts. Obviously you want to make sure the tune is good. Then if you want more power you will have to dive into the engine. If you dont have headers and dual exhaust that is one of the first things you should do. A performer intake would show some better performance over a stock intake but probably not a real noticable difference.

If you are pulling the heads for head gaskets you could swap to a better head. Vortecs are cheap and make more power than any other oem head. This does require a new intake, valve covers and rocker arms but you will see a increase in compression, still low enough for our junk CA gas, and a increase in power.

You can also add a camshaft but dont go too crazy. I have actually been considering this camshaft,

http://www.summitracing.com/parts/lun-90350lk/overview/

Should be a direct "bolt in" meaning stock rockers, pushrods and springs. Would work well with either your stock heads or the vortecs.

[chiro22]

This is the carb that's on the crate chevy 350 engine...Edelbrock 1406 Performer 600 CFM Square Bore 4-Barrel Air Valve Secondary Electric Choke Carburetor.

Anything I should do to the carb right out of the box?

[chiro22]

Really appreciate all of the info. I'm having a buddy of mine who is a mechanic and knows way more about older trucks than I do take a look at it. He "speaks the language" is there a simple list of things I can show him to check, tune and upgrade?

[rich weyand]

On the Edelbrock:

Crack it open and adjust the floats. They'll be wrong. Use #1499 gasket to put it back together.

Oh, while you have it apart, put in .092 primary jets (#1425).

Once back together, put 065/052 rods in it (#1460) and change out the step-up springs for 8" springs (from kit #1464).

Move the accelerator pump actuator to the shortest of the three positions (most actuation) on the lever.

Make sure the vacuum advance is on manifold vacuum (drivers side of the 1406).

Change the vacuum can (see above).

Time it properly (see above).

You do have a thermal gasket under the Edelbrock, right? They don't like to be overheated.

You should also use the original thermac air cleaner. No carb likes to be cold. Though in Cali you might be able to get away without it.

[chiro22]

Originally Posted by rich weyand

On the Edelbrock:

Crack it open and adjust the floats. They'll be wrong. Use #1499 gasket to put it back together.

Oh, while you have it apart, put in .092 primary jets (#1425).

Once back together, put 065/052 rods in it (#1460) and change out the step-up springs for 8" springs (from kit #1464).

Move the accelerator pump actuator to the shortest of the three positions (most actuation) on the lever.

Make sure the vacuum advance is on manifold vacuum (drivers side of the 1406).

Change the vacuum can (see above).

Time it properly (see above).

You do have a thermal gasket under the Edelbrock, right? They don't like to be overheated.

You should also use the original thermac air cleaner. No carb likes to be cold. Though in Cali you might be able to get away without it.

Really appreciate this...are the numbers you included #1425, #1460, etc. from a certain catalog or are those edelbrock part numbers?

[rich weyand]

Edelbrock part numbers.

[rich weyand]

Oh, and put a stock HEI distributor on it if it doesn't have one already. Not some "high performance" POS. A stock one.

[slotard]

What jets etc would you suggest starting with in a 650 Edelbrock on a truck 350? Guy I bought it from claims maybe 275hp and that feels about right. It had a 750 on it because it's what he had around... Performer intake, Comp High Energy 252H cam, roller tip rockers, a little porting on the heads (but nothing special), cast manifolds, 2.25" exhaust

[rich weyand]

The setup above seems to work pretty well on a wide variety of low-compression 350 SBCs.

[MikeB]

Originally Posted by rich weyand

oh, and put a stock hei distributor on it if it doesn't have one already. Not some "high performance" pos. A stock one.

LOL! No truer words were ever spoken. I laugh my a$$ off reading claims about cheap, so called, Chinese "HEI" distributors that generate nothing close to high energy.

Hey, I can generate high voltage by sliding across a seat, but without decent current behind the spark, you got nothing.

I got a killer deal at Amazon last year on a new GM HEI. However, some would say I'll be held back by not having a zillion volt coil.

[MikeB]

Originally Posted by slotard

What jets etc would you suggest starting with in a 650 Edelbrock on a truck 350?

If it's a used carb, I'd determine which jets, rods, and springs it currently has. And then go from there using the excellent user manual. Altitude, engine vacuum, coolant temp, and exhaust efficiency will affect your final settings.

Also, are you sure it's a 650? That would be their Thunder AVS series. The 1406 that you mentioned earlier has a totally different jetting chart.

[slotard]

Oops, you're right. 1406 so 600.

And I'm glad that the guy I bought the truck from put a GM HEI setup on it, and included a spare in one of the utility compartments.

[rich weyand]

OK, now which vacuum can is on it. If he added the HEI to a crate engine, he might have already used the right can. Look down between the vacuum advance can and the distributor cap. You can see the "arm" of the vac advance can where it goes from the can into the distributor. It will have numbers/letters stamped on it. Report back on what it says and I can tell you whether you should change the can or not.

This is the location of the numbers:

[MikeB]

Hey Rich, what numbers should I be looking for on my GM HEI vacuum can? I do know it had 20 degrees (!) vacuum advance, so I limited it to ~10 using a stop plate that I made. Is that where you are headed?

Thanks.

[midnight rambler]

following this

[rich weyand]

The two characteristics of a vacuum advance canister that matter are 1) total advance and 2) vacuum required for total advance.

The vacuum advance cans on emissions-era distributors are usually too much total advance. The cans used on aftermarket distributors usually come in too early (with too little vacuum) for the SBCs in our trucks, which run higher vacuum than "high-performance" engines.

The AR23/VC1853 is right for non-emissions low-compression SBCs, with 7.5 camshaft degrees (15 crankshaft degrees) at 12" of vacuum. Most cans have more advance than that, and kick in at a lower vacuum level.

[MikeB]

Thanks Rich. I need to get out my MityVac to determine how much vacuum it takes to start advancing. Got my total advance (initial + mechanical) dialed in, as well as the 10 degrees vacuum, but never gave much thought to when vacuum starts kicking in. Probably should get the Crane kit with adjustable canister and adjustable stop plate to really dial it in.

[rich weyand]

Those fully adjustable widgets are a PITA. Just get the AR23, IMO, which is already adjusted to what you need.

[special-K]

I'd never mess with a brand new carb to bolt on a stock motor. I'd get it running as is. It will surely run somewhere near right and establish a baseline. Most likely it will be fine as is. Also, if you are going to change the cam and maybe the heads, might as well wait and tune the carb to whatever changes you make

[rich weyand]

You need to tune a carb to the application. That's not "mess with a brand new carb". The installation instructions are pretty specific about the need to tune the carb once installed.

The Edelbrock is tuned to a different base application than 350 SBC in a truck. Stock out of the box on a squarebody, it'll run richer than a cob in the power circuit, the accelerator pump shot will be weak, the power circuit will come in way late, and it will be lean to the point of mis-fire on the cruise circuit.

That tune above has worked for me on a variety of cams in an SBC 350 with low-compression heads, and checks out on the numbers with a wide-band NGK A/FR meter.