Question on Nimbus Fuel Consumption

[gidge348]

As some know I am modifying a Nimbus engine to go into a salt lake racer and now I am trying to work out the fuel tank size I will need.

The course I will be running on will have 3 miles in 3 miles timed and 3 miles to slow down on.

During the run I will probably have to start the engine and idle for about 1 minute before the start then accelerate through to mile 6 then shut it down and use the 3 miles to stop.

Best case scenario it will take 1 minute 50 seconds to do the 6 miles plus the 1 minute to start, that is about 3 minutes running, plus another minute to be safe so 4 minutes total running.

According to Wikipedia and other sources Nimbus fuel consumption is 270kg/hr.

So with a specific gravity of about 0.81 KG/L that is 333 L/Hr.

That is 16L for 3 minutes and 22L for 4 minutes, this really does not seem like much so it makes me think I have something wrong.

Firstly I guess the figure is for "Flight Idle consumption"?

Does any one have any other ideas on what the consumption would be?

Ian....

[racket]

Hi Ian

Mass flow 10 lbs/sec would equate to around a fuel flow of 10 lbs/min - 4.54 kg/min = 5.7 lpm ..............yep, your 16 litres for 3 minutes would be in the ball park :-)

Cheers
John

[gidge348]

Thanks John, much appreciated...again....

I guess it is not quite the fuel economy of my Daihatsu but I have heard of motor bikes that will use 25L in the same time. I was expecting 30 plus litres.

Ian...

[cursorkeys]

Dec 19, 2013 4:10:46 GMT -5 gidge348 said:

According to Wikipedia and other sources Nimbus fuel consumption is 270kg/hr.

...

Firstly I guess the figure is for "Flight Idle consumption"?

Does any one have any other ideas on what the consumption would be?

Ian....

Hey Ian,

The table I have shows:

5 Minute Power

710 SHP 270 kg/h (Mark 103/503 to 2590m) (Max Ambient +25°C at sea level)
685 SHP 265 kg/h (Mark 105/502 to 3410m) (Max Ambient +30°C at sea level)

One Hour Power

685 SHP 265 kg/h (All Marks to 3410m) (Max Ambient +25°C at sea level)

Maximum Continuous Power

600 SHP 243 kg/h (All Marks to 3600m) (Max Ambient +27°C at sea level)


Another table shows you should see '5 Minute Power' at 35000 RPM (Ng).

[ozbooster]

Ian i use about 4 litres / run getting to ~400hp at peak load on my bike on race gas and expect about 10 lit on methanol
a good 1/4 part of that is the return road, tow back uses much less fuel at $10-12/lit my pocket realy notices the difference

[gidge348]

Thanks Greg and Jon... Looks like I will run a 20L tank with a 2L surge tank and see how that goes or maybe 30L if I can find the space.

I am not sure where I got 25L for a bike run from.... ?

[turbochris]

These motors make some pressure inside and the fuel consumption reflects that. One of my typical dragstrip sortes is like 6-8 gallons of fuel (ernie hates that!) and I'm pumping most out the exhaust through spraybars! Run on diesel, no boost pump. These motors are sweethearts their ugly looks and weird output just put everyone off and they collect dust or worse get converted to thrust! Are you planing on exploring power settings over 700 hp? No experience when overclocked!

[gidge348]

Dec 24, 2013 15:22:11 GMT -5 turbochris said:

Are you planing on exploring power settings over 700 hp? No experience when overclocked!

I have seen quoted figures for everything from 690shp to 1050shp for the Nimbus. At the moment all I am going to do is run it standard but fit a water/methanol injection as recommended by John Wallis.

From what I have heard the gearbox was always the "Achilles heel" of these engines so if I go much over 700shp I will only do it in small steps.

I am looking forward to getting Jon's (CurserKey's) manual with all the mods listed to see what they were trying to fix and where the weak points lie.

One thing I noticed is that FPT input shaft is much chunkier and the bearings bigger than those shown in the manual, so I guess this was a mod to fix an earlier problem.

Cheers
Ian...