cheap performance mods?

[sweatmachine]

I have a bone stock '78 heavy half, 350 w/ 4 barrel, and just before I got it my uncle installed a new stock spec cam.

It has stock (or at least really quiet) exhaust, no cat, and stock air cleaner.

1. How much hp could I expect to gain from opening up the exhaust and air filter, and rejetting the carb to match?

2. Exhaust: I can weld, and have all the equipment. I was thinking of welding up my own system. What muffler should I go with? Loud is ok.

3. I've messed with a lot of motorcycle carbs, but never a carb on a car/truck. What adjustments/jetting should I expect to need?

Thanks guys!

[dammitmitchell]

depends on the carb you have dude

these guys her will fill you in pretty well but for your carb adjustments youcan grab the PDF files free off the internet for that

[streetstar]

Dual exhaust, and free breathing carb setups often add hp's, but do little for the torque curve, this can make your truck run awesome at 100 mph, but soft on the bottom end---

so it can help to maximize the whole package -- (rear end ratios, stall speed, etc. )
Duals can take away from your seatofthe-pants experience if thats all you do to it.

An "rv" type cam or off-road oriented camshaft is usually geared towards maximizing torque and would be a good bet for a truck that still retains its stock converter and rear gear ratios. Probably around $200 and a fun weekend to do that swap ---

Next most effective would be to swap the heads for a set of the newer "vortec units -- preferably with a smaller combustion chamber to tighten up the compression
that'll run the better part of a g-note after you buy the heads, intake and all necessary gaskets (maybe 750 if you shop around)

Your Q-jet carb , if its in decent tune -- will be the best bet for torque and will support quite a few hp's too -- no real need to change it

And make sure the fuel and ignition system is in top-notch order first -- it would be crazy to spend a ton of money on a motor when all it needed was a fresh fuel filter ---

[xtreme80]

Carb jetting can make a huge difference. What kinda carb is it?

What I usually do with mine, is to lean it out with jets one size at a time, till it starts stumbling. You'll feel a low end difference it once it starts to need more fuel. the motor will "hesitate" in a sense.. Once I get to that point I use the metering rods to richen it slightly until I'm just to the point where it runs good, but any more lean and it would stumble.

This may not be the true professional way to do it, but it's always worked great for me. My buddy has a 5.3 GMC Sierra, and changing jets is literally the difference between pulling on him from a stop light and not. This method works for me.

As for exhaust, I have mine run with no mufflers. It's loud and sounds pretty good, especially at WOT. My next exhaust (soon) is going to be a set of shorty headers with high flow cats and single chamber mufflers. Pretty much race mufflers. Should be about as loud as it is now, with a more smooth sound.

[sweatmachine]

I'm not dead-set on duals, I just wanted some more sound and flow. Would I be better off with a high flow single muffler, or no muffler at all?

I'll have to figure out what carb it has, I think it's the stock 4bbl.

[streetstar]

Originally Posted by sweatmachine

I'm not dead-set on duals, I just wanted some more sound and flow. Would I be better off with a high flow single muffler, or no muffler at all?

I'll have to figure out what carb it has, I think it's the stock 4bbl.

A single 40 or 50 series Flowmaster with 3" tubing to the y-pipe and outlet would flow very well for an otherwise stock setup

But if you have thoughts of doing more to the engine and trans someday, i'd probably run duals with 2.25" tubing and some long tube headers (ceramic coated ones last the longest)
that way you don't have to re-do it in a year or so