Quote:
Originally Posted by RustyLugNut
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And, I can attest with great conviction and authority, that modern fuel systems are about as efficient as they can be with only percentages to be gained in improvements - not integer factors or orders of magnitude. This is why members of this forum start with the low hanging fruits of driving techniques, mass and aerodynamics. A modder can double his fuel economy easily and consistently.
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I will start with your discussion of the "Lie". The need for the 14.7:1 fuel ratio you discuss in your blog. You show by your simple math that the vehicle in question is running an air to fuel ratio of about 36:1. However, you omitted one important aspect - what is the manifold vacuum at that speed and load? 20 mpg @ 60 mph at full throttle is what you have calculated if you do not have the manifold air pressure accounted for. This makes your math useless and your conclusions utterly false...
Again, welcome to the forum and for your willingness to put your ideas up for scrutiny.
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Thank you all for your welcomes, I do feel welcomed and I appreciate the level of respect, honesty and integrity that I feel from you all.
I appreciate you trying to 'educate' me on my 'obvious' wrong thinking but I ask that you bear with me as I address your points.
My thinking started out just like yours. I AM a certified automobile technician. I got all the 'normal' training, experience, etc. However, I had experiences that took me on a different track and I'm thinking (as an ecomodder) you really need to know what I learned.
My customers didn't care why they got higher mileage (most got at least 25% higher mileage and I was able to double mileage of about 20% of them), they only cared that it worked. I've built my business with a 100% satisfaction guarantee from day one. So you are unlikely to 'convince' me that I'm wrong, since I can help you prove (for yourself) that I'm right.
To address your specific question above, concerning the engine vacuum. I'm thinking that you did not read the comments at the bottom of my blog, where I addressed that very issue. I'll address it again here.
As a mechanic I was taught about volumetric efficiency. Since there seems to be a general misunderstanding about it, you can review it here
WikiPeadia and/or in your mechanics texts. The key point here is that the
engine intake vacuum has only a little effect on volumetric efficiency!
Yes, the engine has to work to maintain a vacuum, and that work can consume up to 30% of the engine's power (again review my blog). But that work is
separate from volumetric efficiency. My mechanics instructor explained it this way, 'vacuum is stretched air'. When you move air faster (in an enclosed space) its absolute pressure drops.
So the engine is sucking 'against' the restriction of the throttle plate and that is creating the vacuum... But the air is STILL getting into the cylinder, it's just having to move faster to do it! So, in the end, as the piston has finished sucking on the intake stroke and has started on the compression stroke, the engine has at least a 70% air charge in the cylinder. This is what is known as volumetric efficiency... the more air charge in the cylinder, the higher the volumetric efficiency.
You can do a little experiment with a syringe to see the effect. As you pull back on the syringe, it sucks in air; there is a vacuum but air still gets in anyway, it just moves faster as the vacuum rises. If you suddenly plug the end of the syringe as you pull it, you'll find that the plunger will go back to that point when you release it. Air was sucked in as long as air could move. The throttle plate allows air past, and as you accelerate (and go under load), it allows more. So your volumetric efficiency stays up.
You should be able to find out the actual volumetric efficiency curves for your engine from your OEM. But as my mechanics textbook told me, 70% is on the low end of average (some engines do much better).
If you review my blog again (I'm suspecting from the comments I see that many of you will need to read it several times as I clear up points), you'll see I DID include the volumetric efficiency into my calculation,
so quite literally considered (took into account) the effect of the engine's intake vacuum. And again, if your engine's volumetric efficiency is higher that the 70% I used as a given, then you'll notice an even 'leaner' ACTUAL air:fuel ratio than the 36:1 I calculated.
Do the math,
it's simple for most of you fellas because you have scan gauges. I've showed you mine (my math) now show me yours.
Prove me wrong with your own vehicle (show me your math).
This is a simple calculation,
doable by anyone who is open minded enough to try it. Most people (especially mechanics) are afraid to try, because if I'm right, their whole world is shaken.