Urba Centurion Update - (Kubota diesel, 100+ MPG in mixed driving - Fall 2012 on)

[redneck]

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400 miles on a 1/4 tank of fuel...

Awesome...

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[Xist]

Originally Posted by redneck

400 miles on a 1/4 tank of fuel...

Awesome...

This has to be off of the ten-gallon tank (160 MPG). Changzuki, do you only use the two-gallon tank for competitions? Thanks!

[changzuki]

Originally Posted by Xist

This has to be off of the ten-gallon tank (160 MPG). Changzuki, do you only use the two-gallon tank for competitions? Thanks!

Xist - you are correct - 400 miles on the quarter mark is drawing from the ten gallon stock Spitfire tank. The two-gallon was used exclusively for the Green Grand Prix. I should've included that info

~CrazyJerry

[Xist]

Why did they design a car that would go over a thousand miles on a tank? I would have thought that, if nothing else, a ten-gallon tank would be unnecessarily heavy, but I do not think that I appreciate how small gas tanks actually are. I found an aluminum five-gallon one on eBay that is 12"x12"x8.5" and 8.25 pounds. Their ten-gallon one weighs 12.5 pounds.

Why are you wasting 4.25 pound?!

[changzuki]

Originally Posted by Xist

Why did they design a car that would go over a thousand miles on a tank? I would have thought that, if nothing else, a ten-gallon tank would be unnecessarily heavy, but I do not think that I appreciate how small gas tanks actually are. I found an aluminum five-gallon one on eBay that is 12"x12"x8.5" and 8.25 pounds. Their ten-gallon one weighs 12.5 pounds.

Why are you wasting 4.25 pound?!

Xist,
Along with the tank weight that you've mentioned, there are other heavy items too - among them the latest transmission w/overdrive unit. Many (not all) decisions to lighten this car up are scrapped mainly because I don't want to drift too far from the original set of plans RQ Riley created for Centurion. The other long-term goal is the Tri-Magnum sitting in the next bay patiently waiting to finally be finished. Trying to save my pennies for that, and, am about a year behind that target.. Your point is well taken though!
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~CrazyJerry

[Xist]

What decisions to lighten the car have you scrapped?

[changzuki]

Originally Posted by Xist

What decisions to lighten the car have you scrapped?

Xist,
Here is a list of those items:

Scrapped plans for items that could've been eliminated/changed to lighten Centurion:

- Heater core and cabinet / hoses / fan and motor / switch and wiring / associated ducting
- Fresh air system / fan and motor / switch and wiring / associated ducting
- Front and rear bulb housings / lenses / buckets
- Heavy lexan on side and rear windows
- Rear window hatch framework
- Full-length exhaust
- Rear wing
- In-car camera system
- 10 gallon Spitfire fuel tank
- Kubota brass/copper radiator
- Lead acid battery
- Interior wood trim
- Windsheild rear view mirror
- Spitfire 1500 4-speed and overdrive unit
- Rear drums

~CrazyJerry

[changzuki]

Just a quick clarification on the earlier shot:
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Whatever this tank yields for mpg is not a result of :
- the decompressor (not using at this time)
- an alternator cut (not using at this time)
- pulse-n-glide
- eoc (engine off coast)
- clutch in or neutral coasting
- idling in top gear (all local speed limits are being matched)
- a lightweight 2 gallon tank (using the stock 10 gal Spitfire)
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Onward - ho!
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~CrazyJerry

[changzuki]

- Down on power
- Intermittent pronounced vibration
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Nothing obvious is really jumping out to explain this.
Although this recent transmission w/overdrive unit is heavier, and when turning it by-hand at the input shaft it does require more effort that the old straight 4-speed, but hardly seems possible for the performance loss...
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Even cold, the engine starts excellently without hesitation and goes right into a perfect idle, minimal to no exhaust smoke. The crankcase vent blowby is also minimal, nothing worth noting.
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At one point with hood open and the engine idling, I did notice a drop in rpms and a pronounced shake of the engine (actually the entire car). After a few seconds the engine magically recovered and all was "normal".
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I've NEVER had any great success with the many automotive "canned miracles" that will restore lost compression, clean fuel systems, and jump your mpg up by "X" amount. But the price is do-able and the marketing on the label is the answer to all my problems so..... $20 later, I am $20 poorer and nothing else has changed.
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The fuel filter is a sizable spin-on can and should go a very long time before needing replacement, but after all the "stuff" I ran through the system, figured it was probably better to go ahead and replace that too. It had trapped particles but gravity flow of fuel through it was not impeded.
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The Kubota documentation does not encourage the use of the decompressor as I have used it. A compression (imbalance) test suggests there is no problem though...
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At this point the fuel system is suspect and after many failed attempts to replicate the rpm drop / engine shake, the winds of change were about to blow in. With the engine idling and a 3/4 open end wrench at the ready, the shaking resumed! Cracking the injector line on cylinder number one only made a marginal difference and more importantly, there was evidence of air in the escaping fuel! Cracking injector lines number two and three would nearly make the engine stall so they were carrying their loads just fine. Once the air was bled from line number one, the idle was once again perfect.
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Over the course of the next few runs the wrench was along for the ride and ready to leap out and crack line number one. Each and every time the results were the same - air in the fuel from the #1 injector.
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It was time for a closer look!
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~CrazyJerry

[sendler]

Air? or possibly compression coming backwards through the injector. Rotate the injectors to see if the misfire moves.