This is assuming that driving is non agressive, and shifting is done before VTEC would engage. I am wondering how the swirl effect of the VTEC on the smallest cam(one valve in the intakeonly opens a hair creating the swirl=more lowend torque) , as well as the roller rockers , effect the efficiency(MPG) of the engine. better or worse.

Also, is there a compression difference between VTEC and non engines? What would be required to bumpup the compression a point or two. How would this effect efficiency? Would the higher comp let you make more use of the fuel at lower rpms(before vtec) I doubt it would at higher revs.

Flow, By creating a better flowing engine, it seems like it would run more efficient due to less drag of pulling air and pushing exaust. Is this always true? It seems that as a person straps beter flowing parts to an engine,efficiency drops, but this could be due to driving habits.
some say that the less air you allow into an engine, the less fuel the engine will use because the fuel is metered depending on how much air is comeing in. Myth or fact?

On the other hand, if the amount of fuel is set, making you run rich, more flow will put the ratio where it should be, creating more power out of the same amount of fuel, thus increasing efficiency so long as the car is driven lightly.

An example would be whether a stock exaust manifold would yield better mpg than a set of headers. and if headers, 4-2-1, or 4-1?

correct me if I am wrong, but isnt the super efficient Honda engine called the CCV or something? WHat makes it different to give much better milage(most definitely along with less power)

I apreciate all feed back, I feel that understanding these concepts better will help not only with efficiency, but with creating power in a smart manner, so there is no waste where there is potential power/efficiency.

cheers
sohc

 

I assume you are attempting to ask about the D16Y5.

Bump compression up by purchasing a D16Y8 headgasket.

VTEC-E turns on from 2700-3200 depending on pedal pressure so, to save gas milage you really have to drive light and try to drive that light.....it's a PITA IMO.

 

What is the diff between that head gasket and the stock one?? BTW I am dealing with a F series engine, incase they dont even make one for it.

cheers
sohc

 

Whoa, that's a lot of topic to try and tackle all at once.

First, let's confine what you are talking about to engine efficiency and not vehicle efficiency (mpg). Many things other than the motor affect mpg ratings, and the EPA numbers are hopeless in trying to find small differences anyway. Engine efficiency is known as BSFC, or Brake Specific Fuel Consumption. Most people use the lbs/bhp per hr formula, which is a way of stating fuel consumption in pounds to horsepower output per hour, and generally rolls around between .35-.55 near power peak on production motors. BSFC is stated at specific RPM points and throttle openings, so things get a lot more complicated to actually quantify here too because that kind of data isn't easy to come by. At any rate, I'll post back later with points in regard to what you actually brought up, but I wanted to get that straight before the responses went into too much detail using mile per gallon ratings.

 

The swirl effect is done to further homogenize the mixture, which can only help BSFC numbers (smaller ratios equal higher efficiency BTW). The more homogenous the mixture, the more closely it can be pushed to it's autognition point without causing detonation or pre-ignition. In fact most any mixture motion is a good thing, though what methods really work best in maximizing mixture homogeny are still being discovered (it's damn hard to see what really goes on in the combustion chamber).

Static compression is the primary way by which the average person can increase engine efficiency. Again this centers around auto-ignition point and flame front speed, but a simple statement can be made concerning compression: more is always better, up to a point. That point being the instant when additional compression causes either detonation or pre-ignition with properly optimized ignition timing. Static CR is actually closely tied to cam profiles and overall engine airflow (VE, or Volumetric Efficiency), which is all summed up through the concept of dynamic compression. I won't go into any detail on that here, but suffice it to say that optimal static compression ratio depends on just about everything having to do with the specific engine in question; from airflow ability to fuel delivery, to the ignition system, combustion chamber dynamics, etc. To put it simply, if you've done your homework and know that the engine in question can use more compression, it will increase efficiency at all RPM points by generating more heat (and thus pressure) from any given mixture that's being combusted.

Airflow does not in and of itself create either efficiency or a lack thereof. It's how you are able to use that air (or more correctly the oxygen present) to make power that defines the efficiency. For instance, turbos and superchargers are great at increasing airflow ability, but their effect on engine efficiency is debatable. Generally they increase BSFC numbers, but in specific applications where more power is needed to move a large vehicle, this can still result in a net improvement in mpg ratings. Again this discussion tends to get complicated and very application specific in a hurry. Small increases in airflow ability though, such as bolt-ons on a typical production motor, make virtually no difference one way or another to engine efficiency. There's just not enough change being made to the overall package to really affect it.

When talking about a/f ratios, what works best for maximum power output or efficiency are generally two very different things. Most of the research going into production engines these days focuses on lean burn technology for part throttle cruising and light load acceleration, where engineers are getting into very lean ratios (25:1 and higher) aided by technologies like direction gasoline injection. At WOT though, when maximum power is what's needed, the a/f ratio goes down to normal levels and the BSFC goes up pretty fast. Leaning out the motor can be great for overall efficiency at light loads, but it's useless if the engine has to work it's *** off all the time just to move the car because it can't make enough power to easily do so.

The ol' CVCC motors? Those used a stratified charge to both make an easily ignitable mixture (lean mixtures get hard to ignite reliably) with a rich pocket of a/f at the spark generation point, while the majority of the combustion chamber was filled with a much leaner mix. The charge was startified by using a pre-chamber of sorts that was filled with more fuel vs. it's volume than the larger, main combustion chamber, and a small common area connected the two chambers. The spark plug was placed in the pre-chamber which ignited the rich mixture easily, which in turn ignited the leaner mixture by flame front travel from the pre-chamber to main chamber. All this allowed the Hondas to meet emmissions requirements without the aid of a catalytic convertor (as well as generating respectable BSFC's), but the government smote that technological aid when it mandated that ALL US cars must have a convertor, regardless of whether or not they actually needed them.

Hope that all helps, peace.


[Modified by texan, 6:54 PM 12/2/2002]

 

Wow, very helpful dude! thanks!

cheers
sohc