Small-Block Firing Orders
Q: I need the firing order for a 350 and a 305 Chevy engine along with the order on the distributor cap. I'm trying to get a friend's van on the road, and I'm sure the firing order is causing the problem.
A: We're talking about small-block Chevy engines, and they both have the same firing order. The 350 and 305 CIDs are basically twins with different bore and stroke values. The firing order is 1-8-4-3-6-5-7-2. This is how each cylinder is fired to keep the crankshaft turning smoothly and is also the order the ignition wires are attached at the distributor cap going in a clockwise direction. Where cylinder #1 wire is located can vary depending on model and year. However, a common location is at about 11 o'clock (standing behind the engine). If the distributor is installed correctly, the rotor will point to this spot when the engine is brought up to Top Dead Center on the compression stroke for cylinder #1. If you're unfamiliar with cylinder locations, they're 1-3-5-7 front to rear on the left bank and 2-4-6-8 front to rear on the right. Right and left are always determined while sitting in the driver's seat.
Chevy Exhaust Stopping
Q: I have a Duramax diesel and want to put an exhaust brake on it. I keep hearing people say it'll hurt my motor because of the back-pressure. Is this true?
A: Exhaust brakes are a common aftermarket add-on in mostly heavy-duty applications, but they're also available for General Motors' pickups with the Duramax 6600 V-8 diesel. There are drawbacks to a diesel engine while downshifting the transmission on a steep downgrade in order to provide engine braking. As opposed to a gas engine with a throttle plate that meters the amount of air entering the engine, the diesel has a wide-open intake that limits the production of backpressure needed to slow the truck and preserve its conventional brakes. The exhaust brake is a pivoting plate that blocks the exhaust side of the engine to increase backpressure on deceleration and therefore aid in engine braking. GM Powertrain Product Communications says the Isuzu-built Duramax was designed for use with an exhaust-brake assembly. However, GM doesn't produce one or recommend a particular exhaust-brake manufacturer. There shouldn't be a risk of engine damage unless resulting from the failure of the exhaust brake itself. Companies that produce exhaust-brake systems for the Duramax are Pacbrake Engine Brakes and BD Engine Brake Inc. Jacobs Vehicle Systems, a well-known manufacturer of exhaust brakes, doesn't produce one for the Duramax because its policy requires direct approval from the engine company. While speaking with a representative, we also learned something helpful for Ford PowerStroke diesel-engine owners. Ford has requested they do not produce an exhaust-brake system for the PowerStroke due to the possibility of damage to engines equipped with hydraulic valve lifters. The high backpressure condition tend to cause valve float that may result in valve-to-piston contact.