Cruising VS boost ?

[erhayes]

For those of you who have real-time data acquisition systems in your CX7s. Do you have a plots showing STEADY STATE CRUSING SPEED vs boost pressure? I find lots of WOT data but, not crusing data. Thanks Ed

 

[wwest]

I can't say for sure about the CX-7, but my brief experience with the RDX was that it is very difficult to stay "off-boost", even while "cruising" on a level roadbed at a constant speed under cruise control.

In order to accommodate boost once it "arrives" the engine is pretty severely de-rated , FE, Fuel Efficiency severely compromised, for non-boost driving. The DFI aspect of the CX-7 engine would normally allow for a 12:1 "native" compression ratio.

It would undoubtedly be best if a type of Atkinson/Miller cycle were used. Delayed intake valve closing off-boost might allow a "native" compression ratio of 14 or 15 to one and then progressively increase the valve closing delay as boost rises. 13:1 Atkinson Cycle mode effective cylinder compression ratio for idle for cruising. Then switch into, gradually into, the the Miller Cycle mode, current, ~10:1 compression ratio under full boost.

Actually the wastegate bypass could be eliminated "on-boost" via management of the intake valve delay timing. Allow Full, FULL BOOST, but "leaking" a portion of the cylinder air mass back into the intake manifold to prevent engine damage.

 

[erhayes]

Interesting comments wwest: i would have preferred a larger higher efficiency turbo that had max torque peak at ~ 3,500 rpm. I usually drive below 2500 and need the turbo for merging and highway passing. I really care less about the 0 to 30 time. I am most interested in the 40 to 80 acceleration. I think the 2.3L is basically too small for the 3700 to 3900 pound care so that turbo was sized for quick spool-up. JMTs Ed

 

[Cue]

I've never logged this, but I've always watched it as I do tons of long driving. At 70mph cruise on relatively flat highway, your pressure will be anywhere from 3 vac to 4 boost.

 

[erhayes]

Thanks Cue: I hope you will pass some more values on steady cruise speeds vs pressure. Thanks, really interested in 65,70, 75 mph ranges on level road using the cruise controll.