volumetric eff. of engine

volumetric eff. of engine

1986cj7

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southeast missouri
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1986 cj7 258, t-176 4-speed, d-300, moser one piece axle in back in amc 20,G2 4.10 gears front and back, detroit truetac front and back,G2 4340 chromoly front axles in a d-30, 4" rough country lift, 33" tires
Was just looking at a thread and it had a carb cal. for cfm for an engine. Now it asks for the volumetric efficiency of engine? Just was is this and what does it do, or tell me?:eek: Any answers will be great! Thank in advance!:)
 
efficiency with which the engine can move the charge into and out of the cylinders. More specifically, volumetric efficiency is a ratio (or percentage) of what quantity of fuel and air actually enters the cylinder during induction to the actual capacity of the cylinder under static conditions. Therefore, those engines that can create higher induction manifold pressures - above ambient - will have efficiencies greater than 100%. Volumetric efficiencies can be improved in a number of ways, but most notably the size of the valve openings compared to the volume of the cylinder and streamlining the ports. Engines with higher volumetric efficiency will generally be able to run at higher speeds (commonly measured in RPM) and produce more overall power due to less parasitic power loss moving air in and out of the engine.
 
our stock 258s will at best have 70% IMO a pure drag car NA will be closer to 90, turbo cars are over 100 to the 110 range if the tune is marginal
 
our stock 258s will at best have 70% IMO a pure drag car NA will be closer to 90, turbo cars are over 100 to the 110 range if the tune is marginal
So how would I go about messureing this do I need to messure the intake ports and intake valves and the clinder size and do some math or how is this done? Just wondering and would be nice to know!!!! And thanks for the info!!:chug:
 
So how would I go about messureing this do I need to messure the intake ports and intake valves and the clinder size and do some math or how is this done? Just wondering and would be nice to know!!!! And thanks for the info!!:chug:
There are some very complex formulas and equipment needed to measure true VE. The 70% quoted is just an average of what you should expect for a non-race / non turbo or supercharged engine.

Lets say you have an engine that can actually flow 100 cc's per cyl. and it's an I6. You measure the actual amount of out flow while running and it's 420 cc's. Your VE is 70% (420/(100 x 6)) = .7

Volumetric Efficiency:* Calculating your cars volumetric efficiency

Volumetric Efficiency 101

Volumetric efficiency - Wikipedia, the free encyclopedia
 
Thanks stroked10 and CJ Looks like I got some reading to do! Thanks!!!!!!!!!!!!!
 
Was just looking at a thread and it had a carb cal. for cfm for an engine. Now it asks for the volumetric efficiency of engine? Just was is this and what does it do, or tell me?:eek: Any answers will be great! Thank in advance!:)


Hi again,

Just put true tracs ft/rear on my CJ7 yesterday.... So from your info to the left our set ups are very similar. I think we both have 258s also.

The 258 is like a tractor motor.... lots of torque at low rpms, long life, relatively simple. When we look at carbs the idea is to "size" the carb to the engine and use... CFM of the engine is used to size the carb throat/opening so we have the correct velocity of air that will have a change in pressure and take the fuel with it... Too slow and the fuel can droplet out of mixture and too fast you run out of top end "feed" for the motor. Usually the 258 is 300 cfm. Usually a smaller carb is better than a bigger one if you have the choice.... and on a non high performance tractor style motor even more so...

Doing the little things will increase satisfaction and how the engine runs..

I Changed my 78 intake to a 1981 alumium intake.... better intake better flow.... I also saw a 1984 intake at the same time.... The casting quality outside/inside was far better on the 1984. Smoother casting on the inside will increase air flow, thus be a better preformer.... Never seen this posted on line.... but very true for our CJs. I wanted the 84 but it was not mine so I use the 81. On the other hand the rough casting would be better at idle and lower rpms and would smooth out the fuel delivery..... at least that is the conversation I had with a sharp guy 5 yrs or so ago....

Many carbs have adapter plates.... Matching the plates and gaskets for a smooth mateing surface is a very good idea. Better air flows...

Same can be said for the intake and exhaust and gaskets.... Make the openings match each other and you will have a much better runner.. From my experience Jeeps need this work.... and will not be very close to matching. There are some good write ups on "gasket matching" and manifold porting would be a few steps further. Most of us can handle gasket matching and would be a good thing...

Ignition.... every stock jeep...... every one..... if still running the stock igniton can be helped with grounds and Teamrush.... I am talking a 20% boost in rpm range (1000), more pep, better starts, better fuel mileage. Jeeps have a few weak links that can be fixed easily.... Not to mention poor grounds is the primary failure of the DuraSpark Modual the stock ignition. My duraspark is 34 years old and still works, its my plug/play back up to the MSD.

I think it is great to look at the tech stuff and grow your base... just do not forget the simple stuff too.
 
Thanks for the info I've seen smoothing out the ports of the intake man. for better flow. This is something I'm thinking about doing. The most important thing in doing this is to take a little at a time off. So I'll have to do some research on this also. You also say that a rough casting is for low rpms and better idle. I happened to look down the intake mainfold when rebuilding the carb and mine has a row of little pins sticking up on the bottom of the manifold about the size of a soda can. I figured this to cause turbulance in the air/fuel mixture as it is suck into the motor. I just never heard of volumetric eff. of engine before and was couisious. And I will look into the grounding because i've been redoing lights in dash and they all come off one ground and if it was to go bad they all would quit working, so yes this is something good to look at. Thanks!!!!!!
 
Glad to help.....

Gasket match ..... use the gaskets to mark head..... stain or blue the intake, header, head and use the gasket hole to scribe the opening with a awl or similar. Then open the holes to match the gasket... This way when the air flow it has a smooth path, when the air hits the side of wall of the header on way out, or the head on the way in from intake it will curl the air and cause lots of turbulance...

great info on grounds for CJs

Jeep Aux Grounds by JeepHammer
http://www.jeepforum.com/forum/f8/been-reading-good-book-jeephammer-833631/

Making Battery Cables by JeepHammer
http://www.jeepforum.com/forum/f8/making-battery-starter-cables-correctly-691172/

Aux Grounds
http://www.jeepforum.com/forum/f8/cj-5-wont-idle-614545/

Punch List for CJ problems and good results
http://www.jeepforum.com/forum/f8/cj-5-wont-idle-614545/

Ignition Test Steps by JeepHammer
http://www.jeepforum.com/forum/f8/here-we-go-again-not-getting-spark-918041/
 
Thanks for the info I've seen smoothing out the ports of the intake man. for better flow. This is something I'm thinking about doing. The most important thing in doing this is to take a little at a time off. So I'll have to do some research on this also. You also say that a rough casting is for low rpms and better idle. I happened to look down the intake mainfold when rebuilding the carb and mine has a row of little pins sticking up on the bottom of the manifold about the size of a soda can. I figured this to cause turbulance in the air/fuel mixture as it is suck into the motor. I just never heard of volumetric eff. of engine before and was couisious. And I will look into the grounding because i've been redoing lights in dash and they all come off one ground and if it was to go bad they all would quit working, so yes this is something good to look at. Thanks!!!!!!


Ooops...

Forgot the under the carb there are rows of pins....

The 80s Jeep Water Jacket Aluminum Intake has a few thing going on and is a improvement to the heavy cast iron intake/exhaust of the 70s.

The 80s Jeep Water Jacket Intake uses the coolant heat to warm the intake and air/fuel mixture. A lot of V8 intakes use the engine heat to keep the intake at a uniform and consistent temp.... Consistemt Temps will keep the fuel from condensing for froming droplets and leaving the air flow. The 258 needs some heat to keep the Air/fuel uniform in mix and to keep it from condensing in the intake...

Heat for Intake for 80s Jeeps
1 Warming coolant heats the jacketed intake and works very well for the intake that hangs off the side of engine.

2. The PINS is a "Porcupine Heater"..... this supplies heat first until the coolant warms up the intake.. This works off 12V, and the Key can turn this on via a relay... Use the relay to turn this heater on/off or the Switching control... Uses ground from the intake, and switches 12+ with a relay. There is also a coolant switch on the intake manifold... Once this reaches 160f Coolant Temp the Normaly Closed switch not opens up.... Use this switch to control the ground leg to the relay.... if the relay opens the porcupine heater turns off.

The 258 runs better if all these heaters are hooked up.....
Coolant Heating on Jacketed Intake
Procupine Heater, first one to heat up, Key on Switch. After 1-2 min can put palm on bottom of heater and should feel warm to touch. The fuel evaporated in the intake... evaporation is a cooling process. So it this feels warm, the disk on bottom of intake is working, great.

There is also a electric choke in many situations.
 

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