Quote:
Originally Posted by Wiegraf
On 2 identical motors.. one n/a , one turbocharged.
Cruising at or closer to 0 inHg
Vs
as much vacuum as possible....
which is better for MPG?
I know cruising closer to 0 inHg is counter to what is efficient.
My thinking is while cruising at
(Example incoming)
2 60mph at 2000 rpm in N/A car at 16inHg (or whatever a vx cruises at)
Or
60mph at 2000 rpm in Turbo Car at 0 inHg/PSI ( give or take 1 or 2 in either direction psi or inHg)
The turbo car has more loss in Mechanical Efficiency (ME) from driving turbine wheel (albeit small) and Thermal Efficiency (TE) but it is also using free wasted energy (in the form of Hot exhaust gases) to spool turbine to Force more air into a cylinder thus increasing Volumetric Efficiency (VE). Also at closer to 0 inHg/PSI there is less pumping losses associated....
This is alll just early-morning-drive-to-work thinking....anyone want to chime in.
Also to add.. this was originally posted on my Facebook and the loss and thermal efficiency was a problem because I was referring to normal car and heat soak. However in the interest of this form a lot of people use a warm air intake so I'm wondering if the thermal efficiency will actually be a benefit as far as this conversation
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To make this work you have to lean out the engine and increase the IAT temps drastically.
Example a 1.5L at
2000RPM
16.29 hg
70 IAT
14.7 A/F
BSFC .50
will make round 14.5HP
If we drop it to 0"HG it will now make 32.2 HP with the same BSFC. Actually the BSFC will get better but for now we will keep it the same. 32 HP is to much for light load cruising and the car will accelerate. So we need to lower the amount of air. So lets start with a much higher IAT at a 14.7 A/F ratio.
150*F = 27.9 HP
200*F = 25.8 HP
250*F = 24.0 HP
300*F = 22.4 HP
As you can see we need to also lean out the A/F ratio to get back to 14.5
150*F = 27.9 HP plus 29:1 A/F = 14.2 HP
200*F = 25.8 HP plus 26:1 A/F = 14.6 HP
250*F = 24.0 HP plus 24:1 A/F = 14.7 HP
300*F = 22.4 HP plus 23:1 A/F = 14.3 HP
Now this is just a example but it shows you need to lower the amount of
air lbs/min to make it work.