What is the best diesel engine choice for a boat. In a way, that is sort of like asking what woman you should marry, since the question is posed without any parameters. Explaining Boost. Boost is the amount of air pressure created by the supercharger. Supercharger boost is largely misunderstood, even by some experienced performance enthusiasts. Supercharger boost, however, is not totally constant. If your engine is not as free- breathing as it could be (because it has a stock or low performance cam, small valves, restricted ports, etc.) you will typically see the boost readings go up in the higher rpm ranges. This is because the boost the blower is making cannot fully get into the cylinders due to these restrictions, and the boost pressure starts building up in the manifold, which is typically where the boost readings are taken, therefore, artificially high readings will be observed. Interestingly, this means a supercharged engine can make more power with lower reading on the boost gauge. There are a few basics to remember. Assuming a constant speed ratio between the engine and the blower, a larger blower will make more boost than a smaller one on the same size engine. As engine size goes up, boost goes down if the blower speed and blower size remain constant. Conversely, as engine size goes down, boost goes up. On a given size blower and a given size engine, boost can be increased by running the blower faster in relation to the engine's speed (overdriving) or it can be decreased by running it slower (underdriving). However, there is no reason you can't run a larger blower on a small engine, such as a 6- 7. Conversely, it is not practical to run a small blower on a big engine, because you would have to turn the blower so fast to make a reasonable amount of boost that the blower would become very inefficient, particularly at higher engine speeds. Sun Machinery Corp. Box 482, Oceanside, NY 11572 I believe there are some posts elsewhere in this Forum that is related to this topic. You may be inclined to search for them. The Cummins 5.9 liter is the same diesel. 3 SIZING METHODS AND SPECIFICATIONS SAMPLE SPECIFICATION: The engine starting battery supplied shall be nickel cadmium, alkaline electrolyte system, designed for extra. Special Bulletin! 09/08/09 Is the Oil Pressure in your Turbo Engine TOO LOW?? Engines that are turbo charged absorb a hefty percentage of the oil to lubricate the turbo.When Roots blowers are turned at very high speeds, they actually can heat up the inlet air to such an extent that the air expands substantially. This overheated expanded air loses so much density that even though your boost gauge says the blower is making boost, in reality you aren't putting any more air into the engine than an unblown engine would get. A slow turning blower, especially a larger one like a 6- 7. This leakage reduces low speed boost pressure, with a resultant decrease in the amount of additional power produced. This is why it is important to have a blower that is sized in relationship to the engine displacement. In this instance, if the blower pulleys were selected to make decent boost at low engine speed, you would end up with excessive boost at higher engine speeds. Additionally, keep in mind that the larger the blower, the more potential for low speed boost . In actuality, the blower normally only goes into boost when the throttle is opened substantially or when the vehicle is under load, such as going up a steep hill or pulling a trailer. In order to make boost, the blower must get air, and during most driving you will only have the throttle open a slight amount. Interestingly enough, even when not making boost, the spinning rotors improve the volumetric efficiency of the engine to the point where you can maintain high cruising speeds at lesser throttle openings, and in normal driving around town, you will notice that the vehicle is much livelier even when not making boost. This phenomenon can improve gas mileage under certain circumstances, although typically on an overall basis fuel economy will decrease about 3%. This isn't much of a factor. If your car was getting 2. These boost levels are based on 3. The 1. 0- 7. 1 through 1. These levels are based on a 5. See our additional drive ratio charts at the end of this section. If your engine is smaller than this, your boost will be higher. If your engine is larger, your boost will be lower. Depending upon how well your engine breathes, the amount of observed boost on a gauge can vary substantially. If you install a Weiand blower and your observed boost comes up on the low end of our estimated range, it means you have a really good breathing engine. Another factor that can contribute to low boost is a restricted air inlet or too small of a carburetor. Remember that at full throttle your engine is going to need about 5. Are your air cleaner and carburetor capable of letting in 5. If not, you won't make the boost that the blower is capable of. As a basic rule of thumb, the 5 to 8 pound boost range that is provided by the standard pulleys supplied in Weiand's supercharger kits is suitable for compression ratios in the 8 to 9: 1 range when used with 9. If your compression ratio is higher than this, you will have to run less boost. If it is lower than this, you can run more boost. The key to any supercharger installation is that detonation must be controlled. Detonation in a blown engine is more destructive than in an unblown engine, and damage to piston ring lands (or worse) will occur if you continue to drive a blown engine that is detonating. This requires purchasing additional optional pulleys. Remember that rarely are any two modified engines similar in how they react to boost and compression ratio combinations, so don't expect to copy what someone else may have done and achieve a successful installation. Unfortunately, as in many aspects of dealing with modified engines, trial and error is about the only way to achieve your ideal combination. In most instances, this will provide you with enough information to provide a workable and safe combination that will provide substantial performance improvements. For those of you who would like to achieve the ultimate in performance from your particular setup, the data provided in our charts will give you an excellent starting point on which you may build to reach your goals. If you have a high compression ratio, such 9. Table 1 provides this information. Then read across to the right under the boost you want to run and the number in the box will be your . Experience has shown that if you attempt to run more than about a 1. To some degree, this can be controlled with boost retard devices, but we do not recommend that you set up your engine and supercharger to provide more than a 1. Please note that all engines differ in their tolerance to detonation. You can build what appear to be two identical engines and one will detonate and the other one won't, so the numbers given in this chart are not absolute hard and fast figures. However, if you follow this chart, you will be close enough that if you do experience some detonation, you should have no trouble controlling it with one of the aftermarket boost retard ignition systems (such as the such as the Holley Ignition P/N 8. This gives you an effective compression ratio of 1. If you are building your engine from scratch, it is a good idea to try to build it with a relatively low compression ratio, such as 7. It is fairly easy to change the boost to get the best combination of performance and power, but it is extremely difficult to change the compression ratio, especially if you want to lower it. Additionally, you will make more total power with a low compression, high boost engine than you will with a high compression, low boost engine. Note that for most street applications with 9. The 6- 7. 1 and 8- 7. GMC diesel engines. Table 2 shows the amount of air per blower revolution the Weiand blowers pump. How you plan to drive your vehicle is important because you can set up your blower to be more efficient at high engine speeds or more efficient at low engine speeds, or you can arrange for the best compromise for the full engine rpm range. A smaller blower can be driven at a higher speed, which will produce a substantial amount of boost, particularly at lower engine speeds. However, this high blower speed will be less effective at higher engine speeds due to the overheating of the inlet air as discussed earlier. This combination will not produce the low end power that the faster turning small blower will, but will significantly outperform the small blower at high engine speeds. However, if you never drive your vehicle in the higher speed ranges, you may be giving up impressive improvements in the lower speed ranges. You may choose to do this anyway because you want the look of the larger blower and are willing to give up some bottom end performance. The 6- 7. 1 is best for mid to high rpm ranges. The 8- 7. 1 is for all- out competition style engines that will see high rpm usage. The Pro- Street 1. These recommendations are based on setting up all three blowers at a similar boost output. The Pro- Street 2. The smaller superchargers use new (not remanufactured) CAD/CAM designed two lobe rotors. These rotors were designed to hold their tolerances 3. Two lobe rotors feature thick walls and a solid shaft, which prevent flexing at higher boost levels. The supercharger case is smaller because the two lobe rotor design takes up less area in the case. This allows for a more compact package for easier underhood installation in many applications. The helix style rotor was developed by General Motors for larger GMC superchargers. They are more efficient than a two lobe rotor because they use less horsepower to supply a greater volume of cooler air charge to the cylinders. Helix rotors also resist flex under extremely high boost situations. These superchargers use larger cases, allowing for a greater volume of air displacement per rotor revolution. This design has even more . These blowers were developed for Alcohol Dragster and Funny Car racing and are extremely expensive, making them impractical for anything but professional racing. The increase in performance is not justified by the increase in cost for street applications. With one of Weiand's superchargers, here are some of the improvements you can expect. Improved starting. A properly set up blown engine typically will fire instantly, usually before the engine has even made one revolution. This is because the blower immediately is pushing the inlet charge right into the cylinder, rather than waiting for the engine vacuum to draw the charge into the cylinder. Substantial increases in bottom- end performance.
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