First Goal: 550hp LS1 Getting 30mpg

[brucepick]

In my last post here I wrote "limit it's revolutions". I might have better said, "reduce its revolutions".

A good amount of energy / fuel is needed just to turn the engine. That's why we go to taller gearing, and also kill it and coast so we can eliminate as many engine revolutions as possible. You'd be surprised at how much energy is used just to make it turn.

Mine needs approx .155 gal/hour at 670 rpm idle, and that's with the alternator disabled and replaced with a deep cycle battery. (With alternator charging, it's more like 17 gph.) Interestingly, at 2000 rpm which is just about exactly 3x idle, it needs about .47 gph. In other words, no change in fuel qty per revolution even at 3x the speed, it's just about linear, so far as I can tell.

Doing some more math, I found that at 2000 rpm at about 50 mph and 50 mpg (yes, my car does that, sorry), the engine is using roughly HALF its fuel just to keep the engine turning! The other half of the fuel is available to move the car forward!

So, you can reduce your total engine revolutions by gearing it taller, or by coasting with engine off (or idling is also good), or even a "rubber overdrive" aka bigger diameter tires. Bigger tires = more rotating mass, there are penalties for that so taller gearing is better. The less you turn the engine, the higher your overall mpg will be.

[ksa8907]

It sounds like you have some money to throw around. Personally, i like power and would never sacrifice it. Do you think there is any ground to make up on with aerodynamics?

[bazman]

Originally Posted by ksa8907

It sounds like you have some money to throw around. Personally, i like power and would never sacrifice it. Do you think there is any ground to make up on with aerodynamics?

lol, well I'm trying to keep costs within perspective, it's not a Zo6 or Viper but I want it to be a great example of power and efficiency and learn while I do it so I don't have to make mistakes on something more expensive later.

As for aero - I'm sure there is something to be gained by an underside tray. I may look into that, certainly for the front anyway. My fabricator will cry if I cover his work of art under the rest of the car

Outside the car still looks stock, right down to factory wheels. I'll post up a pic or 2.

[bazman]

Here she is:

[ksa8907]

Stock wheels you say? Are those chrome or aluminum? Some forged aluminum wheels would save you weight and more importantly rotating mass.

The car looks pretty aero, what about exhaust placement to reduce the low pressure zone at the rear? Notice that so many new cars have a slightly "upswept" exhaust?

[bazman]

Stock wheels are alloy. Lighter wheels would help but I will wait till the car is no longer a daily driver - or if I need that last tenth mpg to reach my goal. For now I enjoy it being stock to look at.

Rear exhaust design is limited by the fact there is a turbocharger sitting right at the back where the rear muffler would normally be :-D

[02ws6]

Looks as if the magic is gonna be in the tune..

This is datalogging on board tuning.. Thought you might be interested in the results.. This guy also did some ghetto aero mods but nothing too crazy..


I did some FE testing 64.8mpg - D-series.org

[mcrews]

that is a sweet ride.

[bazman]

Well I thought I'd put a scangauge 2 on after hearing all the wonderful things they can do. It gives good info on intake temps (great to see them come down when the water/meth injects), water temps, ignition timing in real time etc... the one thing it does not do is give accurate fuel consumption read outs - it's miles out despite recalibrating it 3 times. It is a complete and utter fail at fuel consumption lol. Not sure why. I have no MAF and run a MAFless tune but would not think that'd change the computer read out. It also does not adjust fuel consumption for more throttle - the fuel use it displays is purely based on speed.

ON that basis by 160kph I am getting around 320mpg! Yeee Haa

[some_other_dave]

Contact Linear Logic, the manufacturers. The instantaneous MPG in my SGII changes drastically with throttle position changes. It is possible that there is something going on with the OBD2 protocol in your vehicle that the SG isn't dealing with very well. They have, from what I have read, been very responsive to their users.

-soD