Compressor Cover a/r

madmikeismad

madmikeismad

So mad
Joined
Dec 19, 2009
Messages
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At what point does it matter? How does it actually effect anything? I can't find anything good on it.
 
Hopefully Weston will chime in. He has some back to back comparisons on an engine dyno that were rather interesting.
 
CurtisEmery said:
Hopefully Weston will chime in. He has some back to back comparisons on an engine dyno that were rather interesting.
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That would be awesome. I'm just not capable of imagining how different a/r would effect anything. Except maybe a tighter a/r slowing down spool and making the charger work harder. Velocity? But that goes out the window as soon as the air reaches the 3" (for us) tubing.
 
It does have an effect on total airflow. Smaller a/r can and will choke the compressor if driven hard enough. It becomes more critical in the larger comp wheel offerings for a given frame size. Example: S400 with an 80mm or larger wheel tend to like the JD race cover or the even larger cat cover. Its application specific,what works on one engine combo may not necessarily yield the same results on another.
 
CurtisEmery said:
It does have an effect on total airflow. Smaller a/r can and will choke the compressor if driven hard enough. It becomes more critical in the larger comp wheel offerings for a given frame size. Example: S400 with an 80mm or larger wheel tend to like the JD race cover or the even larger cat cover. Its application specific,what works on one engine combo may not necessarily yield the same results on another.
Click to expand...

I get that, but when would you ever need a smaller a/r? Why not just always run bigger? Unless of course you're using smaller tubing.
 
The smaller a/r would be more likely to work better on a s400 with a 67-72mm wheel. Like I said earlier its not an easy question to answer. The airflow requirements of the engine really dictate which cover will be ideal. A good example is a stardard cover s480 t6 1.32a/r on a 5.9 cummins will make say 60psi for arguments sake. The same charger on a gasser of similar displacement would probably be choked around twenty psi. Obviously the gasser as much higher ve than the diesel allowing it to make similar power at .much lower pressure. This where gains in compressor a/r can be realized. Im not going to tell you it will equate to x amount of hp,because there is know way to know other than trying. I suspect some the gains in the larger covers also comes from better mwe design as well. The larger inlet and smoother entry probably aids in air flow once the charger is reaching is max flow capabilities.
 
madmikeismad said:
That would be awesome. I'm just not capable of imagining how different a/r would effect anything. Except maybe a tighter a/r slowing down spool and making the charger work harder. Velocity? But that goes out the window as soon as the air reaches the 3" (for us) tubing.
Click to expand...
Bringing this back. I forgot to touch on your tubing size comment. In most applications I have seen other than some of the larger frame/comp wheel combos, the compressor outlet is smaller than the three inch charge pipes you speak. I have found that the cylinder head and how well it flows is usually the restriction in the system. Changing a/r may make a small difference in overall performance but nothing drastic.
 
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