souping up a 305

I have an 87 el camino with a 305 and overdrive tranny.

I want to "desmog" it to let it breathe better.  Am looking to add manifold, carburetor, headers and dual pipes, as well as stronger ignition components.

Anything to look for when taking out all the smog devices from the engine?  What about retuning, etc?  

This is going to head in a different direction than perhaps what you're thinking but of course we just can't tell you to do things that aren't legal. But you can intreperet the data and decide for yourself which way to go.

Well to start with de-smogging is illegal, so you need to make sure you’re living someplace that doesn't inspect and that means even in a place that doesn't require regular checks as sometimes the officer that pulls you over wants to look under the hood. Then the problems really start.

87 is somewhere in the GM carb to injection transition years, but with an OD 700R4 gear box I'd expect that this engine has at least TBI on it.

The smog stuff you want to remove really doesn't detract from power and certainly doesn't limit breathing contrary to popular belief. The EGR only functions at low speed and doesn't do anything negative to WOT. AIR pumps only inject air to burn unburnt fuel in the exhaust. PCV crankcase systems only return blow-by gases to the intake. If your engine is pulling oil thru the PCV, you've got other problems mainly the engine is worn out and needs to be rebuilt or replaced. GM factory catalytic converters do plug up the exhaust system and as they age it only gets worse as the converter goops up with carbon. But generic honeycomb converters can be had at the parts store up to 3 inch pipes that both clean the exhaust and let the engine breath for less than a hundred bucks.

The real issues to improve power are cam timing, advance curve, and cylinder head design. These things are weak from that period as a result of the manufacturers trying to meet federal gas mileage standards and emissions at the same time. Without the precision of fuel injection, these standards are opposed to each other in terms of technical solutions. With fuel injection mixtures can be held at ideal nearly all the time, especially with getting rid of mixing fuel at a central point like a carb or TBI and trying to distribute a wet mixture thru a manifold. When you arrive at TPI with dry air manifolds and port injection, the problem of keeping precise mixture ratios for each cylinder goes away and with it emissions go down and power goes up. TBI is more precise in metering what the engine needs than a carburetor, but has the same manifold distribution problems where the overall mixture has to be rich enough to keep the leanest running cylinder, usually 4 and 7, as close to nominal as possible. So everybody else being 1,3,5,2,6,8 are running richer and some a lot richer than 4 and 7.

Assuming you have a TBI 305, the best fix with out getting too far into the injection is first a set of modern heads. Edlebrock Performers are a bolt on and alone will boost output by 40 horses. Vortecs are popular and work well but are a PIA when it comes to intake manifolds. You can opt for the newer Vortecs that GM just released and these take older intakes, but they so expensive you might as well look to the after market where for your money you get better designs. Your 305 probably is a roller cam block, GM uses pretty mild cams. A TBI system can handle a cam up to about 210 degrees of duration with say about .45 to .48 inch lift. TBI really likes a lot of LSA (Lobe Separation Angle) something with 112 degrees or more will work fine. Aluminum heads transfer heat faster than cast iron, combined with improved combustion chamber shape, compression ratios can be increased up around 10 to 1. The 305's smaller bore might push this to 10.5 or even 11 without problems. These modern heads all have Ricardo Fast Burn chambers so less total timing advance is needed, but you can bring the timing rate in faster. If your motor is computer controlled this is a new chip. The TBI can be bored out to 2 inches at 670 CFM see TurboCity, but the stock bore is good enough for a 305 turning a max 5500 to 6000 revs.

Exhaust will be best with long tube headers, if you need AIR, headers can be had with the necessary attachments. Duals are nice but not necessary, a street engine actually does a bit better with a large single exhaust, the more frequent cylinder pulsing helps keep atmospheric pressure from pushing up the pipe and keeps exhaust gas velocity up which helps cylinder scavenging. But with headers, single gets to be a problem as these usually end with 3 inch collectors fairly well back and finding space for a Y pipe of suitable size say 2 and 1/2 inches gets to be a problem. So duals are simpler to install. If you stay with cats, come off the collector with a 2 and 1/2 inch reducer to a 2 and 1/2 inlet cat. Drop the cat’s outlet to 2 and 1/4. At the collector or somewhere just ahead of the cats put in a crossover pipe and install the O2 sensor there. From the cats back run a 2 and 1/4 pipe to the mufflers. Hang the mufflers in back by the gas tank. Weight behind the rear axle helps traction and handling on the El Camino. Drop the muffler outlet to 2 inches and bring out just below the bumper. The reason for 2 inch pipes out is that the exhaust gas temp has been falling thus the gases contract, so to keep velocity up in the pipes they get progressively smaller as you get further back. Dumping exhaust behind the rear of the vehicle finds a natural low pressure area that gets bigger the faster you go. So this always applies some suction on the exhaust side of the engine helping to clear the cylinders of burnt byproducts. Dumping exhaust out the side is an iffy proposition unless you've got a wind tunnel. There is a lot of turbulence along the side and from underneath the vehicle, you could end up dumping exhaust into a high pressure area along the side or create a turbulent flow with the pipe that rams atmosphere into the pipe causing back pressure. Dumping out back just about 100% guarantees that won’t happen.

If you still want a carb just do the same stuff less cat converters and O2 sensor and of course the injection. You'll need to get the fuel pressure down to 6psi with a regulator and change the ignition to something the GM computer doesn't control. A computerized curve rather than mechanical is a lot better, these can be had from MSD.

This engine should put out around 300 to 330 hp with no problem. The Problem will be the old bottom end and the old transmission neither of which will like the added power for long. So you should plan on doing both while it's apart. Same goes for cooling, a new radiator, heater core, hoses, water pump is a lot less expensive than a toasted freshly rebuilt engine. For a bottom end overhaul the only special thing you'll need is KB "D" dish pistons, if you need a dish to control compression ratio. The "D" dish rather than a circular dish provides much better combustion and anti-detonation characteristics by really jamming the fresh mixture over to the spark plug side of the chamber, this is a really BIG help to the engine.

Bogie  

If I remember right, the only Chevys with F.I. in 87 were the Corvettes and the Camaros. Your Elky should have a late model computer QJet on it. I think Edelbrock has an aftermakret replacement for this carb that's better than the factory piece, but I'm not sure.

As for improving the motor, heads will be one of the best improvements. If you check with Comp Cams, they have specially designed 305 cams to help improve power.