|
I have read posts from a few people who think having the throttle open on deceleration would reduce engine drag. I think it might actually increase engine drag. Let me explain my thinking.
When you have 20 inches of manifold vacuum you are only allowing about 1/3 of atmospheric pressure into the cylinders. Lets say 5 PSI instead of 14.7 PSI.
You compress that 5 PSI to 1/10 of that volume for a total of 50 PSI pressure on the piston surface per square inch of surface area.
Now if you keep the throttle at WOT then you are compressing 14.7 PSI atmospheric to 10 times that amount or 147 PSI of pressure per square inch.
Compared to 50 PSI that's significantly more energy required to compress the air. Now it is understood that that same pressure will help to push the piston down after TDC, but with the engine already pulling the piston down I would tend to believe it would take more work to move 3 times the amount air through the engine.
Another reason I think this is true is when you check the compression of any engine, you have to open the throttle to get a better reading. When you do this the cranking speed slows down slightly, which also indicates it takes more work to push the air through the engine with the throttle wide open.
Not meant to be any argument but the slower cranking during a compression test, with the throttle open, is fairly good evidence.
regards
Mech
|