Well not sure it's in the right section but here goes.
We all talk about tuning for power and in the end that just comes down to how much fuel and air we can get into the cylinders. There is some power to be won back from the pumping losses of the engine by fitting hard pipe kits, porting, bigger throttle bodies, better exhaust systems etc.
So the tuning for the car can give both better power and economy. I like many of us here love my vr4 legnum but the fuel consumption is awful there is just no other way of putting it. If i don't move my foot and cruise on the motorway all day with the wind behind me then i can almost manage 24mpg. If i press the loud pedal i can virtually see the fuel gauge dropping. I can empty the tank in little over 60 miles when gunning it!!! that's scary. It also doesn't help that the fuel gauge is the most non linear gauge ever not even slightly corrected for the shape of the tank! It site above full for 50 miles the top quarter dissapears in 10 miles and the bottom past zero seems to last ages before the fuel light is on so until you actually fill up you have virtually no idea how much fuel you have or how much further you can go.
So we understand that power needs fuel, there is no argument about that but why does cruising need so much damn fuel when we are only using the same power as a 1.1 metro not even at full throttle (well almost!!). If we could save fuel when cruising then we could have more ready when we want to use that power.
The basic design of the engine is good. Cross flow, very efficient low loss top end due to the roller followers, modern combustion chamber design etc.
Ok we lose some efficiency due to the lower compression ratio. But somewhere i saw some testing that showed that the legnum runs a rich afr almost all the time something like 11:1 in real testing with any sort of boost. Is this true?
Surely cruising at 80mph the turbos are not boosting the engine simply using exhaust waste energy to overcome the pumping losses and give only slightly over atmospheric pressure, but not a vacuum. Therefore that should easily make up for the loss from the compression ratio and then some. So the engine should be more efficient than the normal v6 surely?
Yes when pressing on the boost will consume fuel but just cruising the engine shouldn't eat it.
It should be feasible to get 30-35 mpg out of a vr4 with simple engine management changes surely. My 2.5 v6 alfa will do that and it hasn't even got a roller follower top end. Granted it is more aerodynamic and the cam profiles wont be made for vr4 levels of power but it's no slouch and we have had it dynoed at just over 200bhp.
has anyone tried to increase the mpg as well as power by bringing the net efficiency up as a whole.
has anyone had success remapping the car for uk fuel where they can run leaner then countries with low grade fuel? I was under the impression that jap fuel was some of the best but is this true?
Any ideas for achieving the end result practically and reasonably. Ie no HHo generators, no complete race car aerodynamics.
Lets just see if we can match similarly powered Bavarian mpg.
Discuss for fun lol