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Old 07-28-2014, 11:24 PM   #178 (permalink)
Changfa diesel + Suzuki
changzuki's Avatar
Join Date: Jul 2012
Location: Northern, NY
Posts: 527

Centurion - '74 FIAT X1/9 Centurion Full Race DNA
Last 3: 143.5 mpg (US)
Thanks: 160
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For those of you who've followed this thread and/or responded - thank you!
Whether we agree or disagree in the end we all benefit one way or another from the shared information and this is why the ecomodders kick-azz when they show up to an invite!

My opinion is and always has been, you have to learn to crawl before you can walk so although information is free, at some point it should be twined with actual hands-on experience. Hopefully from that point a further learning ensues but only through persistence..

I read and either learn, or shore up my current knowledge through posts here on ecomodder but make no mistake; nothing on here is even remotely close to how hard I critique my own work - so don't worry about that - let'er fly!

A few pointed responses:

"Sendler wrote - And, isn't the injection pump still spraying fuel right out the tail pipe at the idle quantity times the rpm anyway? Better to just let it idle if you don't want to shut it off when coasting."

No. As I stated, fuel delivery is cut to the injector in a situation when the accelerator is allowed to remain weight free of my foot and the car's momentum is driving the rotation of the engine beyond that. I'll reference a video I uploaded just for you. It will demonstrate this principle - one I've watched in my house for years now. Stay tuned... Secondly, if you ever get the opportunity, get up close to an idling diesel and watch the things that are attached to the engine such as the dipstick, any bracketry, etc... The vibration at the diesel idle you're suggesting is phenomenal and can often lead to work hardening of those metals to the point of stress cracks and breakages. Diesels typically are idle friendly (smooth) up around 1250 or so. At the Green Grand Prix Centurion was vibrating from front to rear at idle - yes, the entire windshield was pulsing. Audibly this little engine could be heard above anything else there. I have no desire to idle this diesel when it's unnecessary to do so. (The soot blow-by into the oil pan at idle is another story but that's some other post..) A decompressor is as I mentioned a neat compromise and it works exceptionally well. The decompressor in the video is illustrated nicely at the end of the video showing many rotations of the engine after the fuel is manually turned off and the decompressor engaged - just like at the Green Grand Prix.

To BobS -

"Elhigh wrote - I imagine the injectors automatically cut out as long as the decomp lever is open, though, right?"

Not exactly. As long as the momentum of the car is driving the engine rpm beyond what the accelerator pedal is telling the governor, then fuel is automatically shutoff to the injectors by the governor. If the governor is held at this position manually and not allowed to recover as rpms drop from say pushing in the clutch, the engine will quit (it's starved for fuel). When I know fuel is cut to the injectors by the governor, then I take over and touch the horn button with my big toe and activate the decompressor. It's like having a huge tailwind come out of nowhere when you release engine compression. (Kubota D850 is well over 400 psi per cylinder. As a kind of comparison, it takes a bit of horsepower to run a one-lunger air compressor or auto airconditioner compressor for that matter.) This is a good question though because there are ways to automate the process as you've suggested - but in this case I'm part of the "automation".

"shorttimer wrote - ....After reading this thread, my only suggestion would be to see how much better the mileage would improve with a few more aerodynamic enhancements, because I believe you are close to the maximum efficiency of the power plant you are using in your current configuration. Please don't take this as a negative suggestion. I believe you've done an outstanding job."

shorttimer, Thank you for your kind words and I completely agree with you. The heart of a diesel lies in its fuel delivery system - it's a biggie. Also agreed, there's plenty of ways to improve Centurion and those aerodynamic items were intentionally left off the list. My reasoning for staying clear of those is two-fold. First I never wanted to drift too far from RQ Riley's original plans. At what point is it no longer the cover car from Feb 1982 Mechanix Illustrated? The other reason is the aerodynamic items such as those here on ecomodder are "givens", basically tried and true. My experience is when I spend time on the obvious, I either overlook or completely miss other important areas. So, this is kinda like working from the other end of the number line. This also leaves to the door totally open for some other ambitious soul to best Centurion - someday - but they will need to employ all the tricks of the trade and maybe even a few that aren't popular yet. The bar is high but certainly not out of reach. Thank you for your post!!!!

"sheepdog 44 wrote - You know people haven't learned from the past when the old becomes new again!"

So you've just described 9 Main Street in Colton! If I didn't agree wholeheartedly I wouldn't keep reviving some of this primitive technology and running with it just a little! Bravo!

--Ok, let me try to get to the next post to reference the governor video. This should help clear up some of the mystique of how these behave on working engine that you can see....


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BobS (07-31-2014)