#Delco vacuum pump in big cam 350 how to

This helped the engine with ported vacuum advance at part throttle, but it still struggled at idle. We replaced the original vacuum can with an adjustable unit from Summit Racing. ThatвЂ™s when we discovered the vacuum advance can had failed. The engine ran great at WOT, but it never ran well at part throttle and generated barely 10 mpg on the freeway. We initially set this combo with 16 degrees of initial timing with 18 degrees of mechanical advance that put the total mechanical at 34 degrees at 2,800 rpm. We know this because the engine idled at 13 inches of manifold vacuum in Park but dropped to barely 8 inches of vacuum in gear, and it tended to surge and misfire at idle in gear. The tight torque converter in the TH-350 trans loaded the engine pretty heavily at idle.

small-block Chevy used a flat tappet hydraulic cam with 230 degrees at 0.050 duration, a JET Q-jet, and an aftermarket HEI distributor. Your particular engine will determine the actual amount of advance, so letвЂ™s look at a real world example. Performance engines with big cams often need more timing at low speed to improve idle quality. Since this also increases hydrocarbon emissions, during the вЂ™70s, the OEвЂ™s moved to ported vacuum advance that only added timing above idle. In the early days, the idea was to connect vacuum advance to a manifold vacuum source, which added more timing to improve idle quality. High vacuum indicates low load, while high load (WOT) produces nearly zero manifold vacuum. A great indicator of load is engine vacuum. Our attention is aimed at part throttle, low-load situations. The problem with mechanical advance: it is strictly rpm-generated and not affected by load. In order for our slow-moving fire to complete its low-density burn, we must create more time for that process by beginning the ignition sequence sooner - which is why we advance the timing. If the grass (air and fuel) on the prairie (the combustion space) is spaced far apart, it takes longer for that fire to burn a given distance (the combustion space). In an engine, the fire starts adjacent to the spark plug and burns across the top of the piston and combustion chamber. The combustion process has been described as like a prairie fire burning across a valley of dry grass. In order to create that situation, we must start the combustion process much earlier - before top dead center (BTDC). To create maximum force on the crankshaft, the accepted rule is to produce maximum cylinder pressure when the piston reaches 15 to 20 degrees after top dead center (ATDC). If combustion was instantaneous, there would be no need for advanced engine timing. When a spark plug fires, the result is more of a process, not the instantaneous explosion you learned in high school auto shop. This means the air is not very densely packed compared to what it would be if the engine were running at peak torque at wide-open throttle (WOT) where the cylinders might be filled to 100 percent VE or more. In terms of volumetric efficiency (VE), weвЂ™re talking about cylinders filled to perhaps 10 to 15 percent of capacity. This means the cylinders are only partially filled with air and fuel. Light throttle acceleration creates high manifold vacuum because the pistons are pulling against a highly restricted inlet. Our goal is to adjust the timing and mixture to produce maximum power and efficiency at part throttle. This is where a typical street engine spends as much as 99 percent of its time. This discussion will focus on naturally aspirated engines running at part throttle.

#Delco vacuum pump in big cam 350 how to

This story will dig into why this is and how to take full advantage of the benefits that simple vacuum canister offers.Д«efore we burrow deeply into the specifics, letвЂ™s first lay out a solid tech foundation for why vacuum advance is such a big deal. The truth is, all street engines can benefit from vacuum advance, and the more aggressive engines ironically need it the most. Unfortunately for those вЂњexpertsвЂќ who espouse such information, they have just not put a lot of thought into that mindset. Some version of that statement has been made hundreds if not thousands of times when bench racing sessions turns to engines and tuning. вЂњRace engines donвЂ™t use vacuum advance, so I donвЂ™t bother. How to Take Advantage of Vacuum Advance for the Street