25-12-2012, 11:25 PM
It does help, but I'm not sure how much by.
You have to remember at a cruise condition at say 45mph the gross power losses might only be about 25bhp.
So your engine needs to make only 25bhp. If the 3rd pump deactivation can save you a 'small' 0.5bhp even, then that is a whopping 2%, which in fuel economy terms is quite significant for a simple switch... not sure what the exact figure are, but clearly they were worthwhile for the investment in having it.
I've tested with it on/off in the past and noticed no absolute changes in accelerative performance. However, along with de-EGR, I do believe there may be some element of 'lag' when it changes state from off to on... like the throttle is a bit more docile at lower speeds and then flooring it vs with it unplugged. I'd have to do more testing to be sure.
I was doing that testing about 6-7yrs ago now so can't remember for sure on the qualitative stuff, but in quantitative terms it generally seemed best to leave it plugged in on the grounds that there was no clear benefit to de-activating it... unlike with EGR which is easily noticeable and logically beneficial to remove for 'performance' purposes.
Dave
You have to remember at a cruise condition at say 45mph the gross power losses might only be about 25bhp.
So your engine needs to make only 25bhp. If the 3rd pump deactivation can save you a 'small' 0.5bhp even, then that is a whopping 2%, which in fuel economy terms is quite significant for a simple switch... not sure what the exact figure are, but clearly they were worthwhile for the investment in having it.
I've tested with it on/off in the past and noticed no absolute changes in accelerative performance. However, along with de-EGR, I do believe there may be some element of 'lag' when it changes state from off to on... like the throttle is a bit more docile at lower speeds and then flooring it vs with it unplugged. I'd have to do more testing to be sure.
I was doing that testing about 6-7yrs ago now so can't remember for sure on the qualitative stuff, but in quantitative terms it generally seemed best to leave it plugged in on the grounds that there was no clear benefit to de-activating it... unlike with EGR which is easily noticeable and logically beneficial to remove for 'performance' purposes.
Dave