2002 V6 Petrol/LPG Economy

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Buckey woo

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Just wondering if anyone is running a simular set up.
Sprint gas LPG getting around 140km's from 30L and with fuel 260km's from a full tank. This is after new plugs/leads/battery/service and dyno tune.
I only ask because I was on car sales and a guy was claiming to get 400kms of a tankof the exact same model year etc. I asked what his set up was and he said air filter and something else but I am concerned he is either A: Full of it or B: Doing something I NEED to know?
Its a 2002 V6 petrol STR, with a roof top tent, roof tray, cooper atr 275/75R16, slight lift.
Anyways,
Still love it!!!
Also, its badged as a 3L (2960 CC) but everywhere I look on the net it says 3.3L. Do I have a special (underpowered) 4B?
 
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I don't know how large the tank in your car is, nor do I know how you're measuring it or whether or not you're taking the different tyre size into consideration. Yes, calculating fuel economy with any precision is a little complex!

The first thing you'd need to do is find one of those 5km odometer test things and pull over at the first sign, read your tripmeter value, then drive to the 5km sign and read it again. It should read very close to 5.0km and if it doesn't, the error is due to the tyre size. The tyres you're using are quite large and they will make the odometer under-read which will make you THINK your fuel economy is worse than it actually is.

That's where the good news ends. Larger tyres form a larger lever (distance between axle centre and road surface). That's harder to turn over, so the engine works harder to do it = uses more fuel. It's particularly noticeable in acceleration, so city traffic really eats into the fuel.

So, on to the calcs. 140km from 30L of fuel is 21.4LPHK (litres per hundred km). That's pretty high, even with a 5% error.

There are a number of things that affect fuel economy. I've already talked about tyre size. There's also cruising speed and acceleration rate (which is self-explanatory). In the D40 diesels we've found that cruising at about 2,000rpm (=95km/h on standard tyres) affords the best fuel economy because that is the exact point where the engine torque vs fuel input peaks. Beyond this point, the torque curve doesn't rise as fast so the extra fuel used is wasted. You'd have to find a dyno chart for your model engine to see where this point is for you - with petrol engines, it's usually higher.

The last thing is wind resistance. You're driving a brick with a tent strapped to its back - it doesn't have the sleek lines of a McLaren or a GT40, so it's going to use more fuel.

My apologies if you know all of this already - but some readers may not, and the info might be useful.

As for improving things: engine tune is important and air flow is vital, but you would expect that any half-competent mechanic would do a reasonable job with any engine, so if there aren't enough beans coming from your engine for the fuel being used, you'd have to start looking at mods.
 
the 3.3 v6 requires you to have shares in BP or shell, not much you can do apart from go back to 31's in a highway tread designed to minimise rolling resistance, also put your pressures up a bit more to help with that.
 
I'll say, I went back to 265s recently instead of putting 275s on new, I'm doing everything I can to improve the 3.3s economy. I've done the airbox mod and will hopefully soon finally get the Beaudesert exhaust system.
 
I've got a 3.3L V6 Nav and I get about 500ks out of the factory fuel tank. Not sure if that helps or not, though I think 260ks is ridiculously low for any car let alone a Navara. A Top Doorslammer would have better fuel economy than that.
 
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