tDR Posted January 1, 2008 Share Posted January 1, 2008 I reckon they're most fuel efficient just shy of a ton and off boost Quote Link to comment Share on other sites More sharing options...
MrRalphMan Posted January 1, 2008 Share Posted January 1, 2008 I reckon they're most fuel efficient just shy of a ton and off boost Well that would be nice... Quote Link to comment Share on other sites More sharing options...
RedM Posted January 1, 2008 Author Share Posted January 1, 2008 I reckon they're most fuel efficient just shy of a ton and off boost That would make sense based on my driving the other night. This was on the Autobahn, just for the record. Quote Link to comment Share on other sites More sharing options...
ufop Posted January 1, 2008 Share Posted January 1, 2008 so many things to take in to account though how well the car is setup and performing, wind, gradient, tyers, traffic lol I was always told that trying to drive as smoothly as possible is one of the best ways to get good mpg.... I wonder what the boy racers in saxos get when they are either always on the gas or brakes around macdonalds car parks? lol driving on cruise control on cars I have had in the past is good too but always depends how busy the roads/motorways are. Still doesnt answer the original question though :-0 sorry Quote Link to comment Share on other sites More sharing options...
carl0s Posted January 1, 2008 Share Posted January 1, 2008 I tend to go for throttle position rather than an actual speed. I will drive to 60-ish mph, then drive the journey with very light throttle, boost gauge showing -1psi or thereabouts, and let the car speed up / slow down as it naturally does. This means 80 - 100 on slight downhill gradients or smooth road with little resistance, and 55 - 60 on uphill. Economy seems to improve a bit like that. Also, I found the journey from Manchester to Leeds uses less fuel than the journey from Leeds back to Manchester. I decided it must be due to uphill/downhill and air density or something. You weren't doing Manchester -> Leeds were you RedM? Quote Link to comment Share on other sites More sharing options...
Thorin Posted January 1, 2008 Share Posted January 1, 2008 Also, I found the journey from Manchester to Leeds uses less fuel than the journey from Leeds back to Manchester. I decided it must be due to uphill/downhill and air density or something. That's just the car naturally resisting being driven back to the wrong side of the Pennines. Quote Link to comment Share on other sites More sharing options...
RedM Posted January 1, 2008 Author Share Posted January 1, 2008 You weren't doing Manchester -> Leeds were you RedM? Does the 250 miles each way not answer that? Quote Link to comment Share on other sites More sharing options...
carl0s Posted January 1, 2008 Share Posted January 1, 2008 That's just the car naturally resisting being driven back to the wrong side of the Pennines. Does the 250 miles each way not answer that? Ah, I wasn't paying attention there Quote Link to comment Share on other sites More sharing options...
Digsy Posted January 2, 2008 Share Posted January 2, 2008 The both 2JZ engines are most fuel efficient at abut 2000 to 2500 RPM (2000 for the GTE and 2500 for the GE). You can see this from the official performance charts, which include a curve for BSFC (brake specific fuel consumption) in g/PS.hr (grams of fuel used per PS per hour). The lowest point is about 200 grams @ 2000 for the GTE and just under 200grams @ 2500 for the GE, so in theory if you drove around this engine speed you would get best fuel economy on a run. The thing is, though, that these curves will be at full load (WOT), and even cruising at these low speeds in a high gear you won't be anywhere near that. The curve changes shape as load reduces. In order to answer the question fully you would need a full speed/load BSFC map. Engines tend to be optimised for full-load performance, which means that basic geometry like the compresion ratio is set for full-load. In theory you could run much more efficiently at low loads if you could increase the geometric compression ratio. However, without a complex variable compresson ratio system (which no-one has managed to put into production yet) you can't do it. A quick Google turned up a lovely map which clearly shows that the optimum region is at full load, low engine speed: Clicky The relevant slides are in the middle of the presentation. So in summary, a "miss daisy" drive (low engine speed, low load) quite probably would be less fuel efficient than a more spirited drive, as long as you remained off boost a lot of the time (low engine speed, full load). Quote Link to comment Share on other sites More sharing options...
carl0s Posted January 2, 2008 Share Posted January 2, 2008 You are a bright chap. I love having you around Quote Link to comment Share on other sites More sharing options...
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