How to choose the right air blower for your application

13 May.,2024

 

How to choose the right air blower for your application

There are multiple compression technologies that are used for generating low pressure air. The three main technologies that are popular today are lobe, screw and centrifugal; and within the centrifugal technology there is multistage, high speed turbo or integrally geared centrifugal blowers. So, this takes us to five types of blower technologies that are used extensively within the low pressure market.

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Each technology has its own space like lobe typically is the best when it comes to pressure below 0.3 barg and flow less than 500 m3/hr, while screw works better at higher pressure and flow between 500-5,000 m3/hr and then centrifugal technology takes over for larger volumes.

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However, the decision on a compression technology is steered by energy efficiency which is also linked to the specific application of low pressure air.

Roots Blower Sizing - Page 3

Another area, is carb sizing. If you are going to be running a supercharger, ESPECIALLY one that is a bit small for the application, you do not want to under carb the setup. When it comes to these old roots blowers, you need to throw the idea that "my engine only needs 950cfm, so a 950cfm carb will work fine" out the window. You really need to size the carb or carbs, with the consideration that it is no longer gonna be on top of a N/A setup. Things work a little differently on a roots.

Short of running the engine on the dyno and switching carbs, or running it on the lake, and switching carbs, you may never realize you are undercarbed. What happens when you are undercarbed, and lets say you are trying to make 6lbs of boost, but only seeing say 4lbs on the gauge. Naturally you simply install a smaller pulley, to spin the blower harder, to get to 6lbs. When, quite possibly, you just didnt have enough carb, or a restrictive flame arrestor, etc. So by installing a smaller pulley, you just introduced more heat than necessary into the charge.

True story here. I went on a fun run a couple months ago. My engines are 468ci, with 420 B&M blowers, and twin 850 holleys. While on the run, I had noticed my starboard engine was down on boost about 1lb. Never had that happen before. Normally they are both at 6lbs, but the starboard was maxing out at 5lbs. I started to think my blower was wearing, or belt was slipping, or something was going on. Back at the dock i started looking things over. What I noticed, was when I had the carbs apart for a jet change a few days prior to the run, I had pinched the secondary linkage by binding the accelerator pump arm. I put the throttles to wot, and went back and looked down the throats of the carbs. Yup, sure enough, the secondary on only 1 carb, wasnt opening all the way. Mind you, I still had one 850 carb fully opening, and the primary of the other one fully opening. Theoretically, I had 1275 cfm of air available. But, it obviously wasnt enough. Now, if I used that little carb cfm calculator, it would have told me that my engine would be just fine with 1275cfm of carb. The real world told me different. Fixed the linkage problem, went back out, and got my 1lb of boost back. How much is 1psi of boost worth on a setup like mine? About 25hp.

Would it be safe to say, that on my engines, going from 1 big ole 1350 single dominator, to a pair of twin 850's, would have netted a 25hp gain on the dyno? quite possibly. Its not uncommon to see guys running big massive throttle bodies, or some big twin 1050-1350 dominator carbs, on top of a psi style blower. Its not that the engine really needs 2300-2500 CFM of carb/throttle body, but its the blower that likes it. Basically, you want just enough carb, where the blower doesnt have to work harder than it needs to , to get the desired boost level.

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