Crazy MPGs

[dripley]

11 minutes ago, dodgedieselnewbie said:

I would love to see my fuel gauge trickle down from full... but it won't go past the half mark on fill up.. lol  What do I need to fix that??

 

Any comment on whether 75-90 injectors would increase MPGs?

Sending unit could be bad or the float could be hung. Not sure how to check that with opening up the tank.

 

From what I was told the RV's are a more efficient injector over stock and so the difference. Not sure where the tipping point is on injectors before you start loosing mileage. Of course quality of the injector would make a difference too. Others here will know more than me.

 

Of course your right foot will make a lot difference too.

Edited April 14, 2016 by dripley

[TFaoro]

3 hours ago, Mopar1973Man said:

 

Not all... I've done my research here and some of the Mom and Pop places don't have filters or also using screens. Now most name brand places have standard and will keep to those standards typically. Even worse some are still using mechanical pumps with mechanical price boards. Those I don't even stop at...

So it's pretty much what I said... most of them have it. I never stop at the mom and pop stores anyway. Not enough turnover. 

1 hour ago, Dieselfuture said:

About 20-21 hwy with 8 hole and now same tune and driving stile 17-18hwy. Empty that is at 65-68mph

That's not just the injectors. I went from 125s to 300s and didn't loose that much mileage. 

23 minutes ago, dodgedieselnewbie said:

I would love to see my fuel gauge trickle down from full... but it won't go past the half mark on fill up.. lol  What do I need to fix that??

 

Any comment on whether 75-90 injectors would increase MPGs?

75-90 would help if you still have stockers. Most of it is in the right foot though. 

Edited April 14, 2016 by TFaoro

[dodgedieselnewbie]

12 hours ago, dodgedieselnewbie said:

I haven't done a highway trip in awhile. I am averaging 16.. stop and go around town. This is hauling around a small utility trailer most of the day.. weighing roughly 2000# loaded. I have a bedslide as well as a cap. I also carry a decent amount of tools and gear in back seat.  Does this seem reasonable?  

 

If I bump up injectors to say 75-90s .. can I see an increase?

 

I have 50s.. Believe me...  understand the right foot thing.. I can hold up traffic lol.. 17-18 around town too much to expect? If not... how do I get there? 

[TFaoro]

10 minutes ago, dodgedieselnewbie said:

 

I have 50s.. Believe me...  understand the right foot thing.. I can hold up traffic lol.. 17-18 around town too much to expect? If not... how do I get there? 

I don't think you'll gain anything. I  think you're asking too much of it. That's a lot of weight for around town to get good mileage 

[Mopar1973Man]

11 minutes ago, TFaoro said:

I  think you're asking too much of it. That's a lot of weight for around town to get good mileage 

 

For me that where I gain my most MPG is in town rolling slow. I get seriously high numbers like 30-35 MPG. The only difference is most of the small towns don't have traffic lights. So if you plan your travels right you can travel town with little to no stopping.

[Silverdodge]

I usually get 20 or so with my old and new cummins but this one's pretty damn smokey so I usually drive with my big tow

[leathermaneod]

Right before I sold my smarty I ran it for a week on catcher 5 with everything else default. I was doing 10 mile trips back and forth from work to home a few times a day. Most of the trip is rural highway running about 55-65, but there are some traffic lights near my house so some stop and go. I have 285/75's right now so I have to rev it out pretty good before I hit 5th, and sometimes stay in 4th depending if a slow poke is in front of me or not. Anyway with all that said I averaged 17.5. And that was with a little bit of fun with the catcher level 5. I also have BD 75hp injectors that came with my truck. I am thinking of downgrading(or upgrading depending on how you see it) to some rv275's though....

[abner99]

On April 13, 2016 at 8:59 PM, dodgedieselnewbie said:

I would love to see my fuel gauge trickle down from full... but it won't go past the half mark on fill up.. lol  What do I need to fix that??

 

Any comment on whether 75-90 injectors would increase MPGs?

 

Thats my question? That's my next thing. Everyone I know around here runs the rv275s and they get about 18 I'm stock injectors just have more air flow and I get right around 20 pounding down the road. Everything I've read and heard 75s get you at least 3 more. But sounds too good to me true. 

[Mopar1973Man]

it's the illusion of timing. So stock injectors flow only so fast. Now you open up the nozzle with a larger size now the flow rate is faster so you get you fuel in the cylinder faster giving the illusion of timing advancement. Problem as nozzle size increases the droplet size does too. So you require more cylinder heat and/or boost pressure to prevent smoke. Because as boost pressure goes up so does cylinder pressure... Higher cylinder pressure means more heat. 30 PSI is roughly 1,100 PSI at TDC in the cylinder. Just remember liquid fuel will NOT burn. All fuels have to be converted to vapor before it will burn hence the black smoke issue with large nozzles.

Edited June 1, 2016 by Mopar1973Man

[dripley]

I saw an increase of 1 to 1.5 mpg with the RV275's over stock. I also never got 20 mpg running the interstates but I also run 70 to 75 mph down the interstate. Now slow that down to secondary roads and I did hit 20mg a few times. 

[leathermaneod]

So with bigger nozzles delivering more fuel, why do guys normally report at least a slight increase in fuel mileage when going to bigger injectors over stock? Or do the gains end at about 50hp over stock? What I'm saying is, if I went from BD 75hp injectors to RV 275's, would I see an increase, decrease, or stay the same? Always assuming of course that I drive like I'm trying to get good fuel mileage.

[Mopar1973Man]

MPG is about quality of spray. A injector with a finer spray pattern, matched pop and flow rate will produce better MPG's. Most vendors just grab 6 injectors off the shelf and toss then in a box to ship. Like mine I had Eric at Vulcan Performance do the pop test and flow match of all 6 within 3% of them all.

[leathermaneod]

1 minute ago, Mopar1973Man said:

MPG is about quality of spray. A injector with a finer spray pattern, matched pop and flow rate will produce better MPG's. Most vendors just grab 6 injectors off the shelf and toss then in a box to ship. Like mine I had Eric at Vulcan Performance do the pop test and flow match of all 6 within 3% of them all.

Is that more important than size then?

[Mopar1973Man]

Again... Quality of spray. The finer the mist the easier it is to convert to vapor to go BANG! So quality of the nozzle, quality of the pop test and flow matching. So a poor quality nozzle like Edge Jammers popped and flow match will still be crappy for MPG because the spray is poor anyways. It just a dirty nozzle.

 

This one reason I always kind of chuckle about the cold air intake. Because colder the air long to convert and loss of timing for ignition. Take notice to the IAT temp and the high marker. No fooler used.

 

 

The low numbers are towing my RV.

 

Edited June 1, 2016 by Mopar1973Man

[Mopar1973Man]

More on compression and heat.

https://en.wikipedia.org/wiki/Fire_piston

 

Quote

Rapid compression of a gas increases its pressure and its temperature at the same time. If this compression is done too slowly the heat will dissipate to the surroundings as the gas returns to equilibrium with them. If the compression is done quickly enough then there is no time for equilibrium to be achieved and the absolute temperature of the gas can suddenly become several times that of its surroundings, increasing the original room temperature of the gas to a temperature hot enough to set tinder alight. The air in the cylinder acts both as a source of heat and an oxidizer for the tinder fuel.

The same principle is used in the diesel engine to ignite the fuel in the cylinder rather than the spark plug used in the gasoline engine. It is closer, however, to the hot bulb engine, an early antecedent to the diesel, since the fuel (tinder) is compressed with the gas, while in a diesel it is injected when the gas is already compressed and at the high temperature.

Fire pistons have a compression ratio of about 25 to 1. This compares with about 20:1 for a modern diesel engine and 7:1 - 11.5:1 for a gasoline engine. The piston of the fire piston is made deliberately narrow so that the force on the piston is not so great as to make it impossible for unaided human strength to compress the air in the cylinder to its fullest extent. To achieve the compression ratio, the final compressed volume of the tinder and air must be small relative to that of the length of the piston tube. These two factors together mean that only a tiny amount of tinder can be lit by a fire piston, but this is sufficient to light other tinder, and then to light a larger fire.

Easily combustible materials such as char cloth or amadou work well as tinder in the fire piston. The tinders that work best in the fire piston combust at a very low temperature. Cotton fibres for example combust at 455°F (235°C) and will light in fire pistons.

 

The key part here is...

 

Quote

Rapid compression of a gas increases its pressure and its temperature at the same time. If this compression is done too slowly the heat will dissipate to the surroundings as the gas returns to equilibrium with them. (Like the coolant jacket especially if the coolant is already cold or low temp thermostat is used)

 

So now consider cold start and colder winter time weather conditions. Efficiency is reduce not to mention the high cetane fuels that aid in the ignition quality but have reduced BTU amount per gallon. So coolant and IAT temperatures play a key role in ignition quality and MPG numbers. Then again back to injectors if you have a good fine mist then iginition is easy but if you had large 100HP or larger then the quality falls. When I say warm I don't mean crazy hot just added warmth to promote good ignition quality. Being that the 98.5 to 02 ISB Cummins is the lowest compression ratio of all the series we need all the help we can get for ignition quality.

 

So now look back at the fire piston and consider your fuel (tender) and compression. Then it all starts to click together a bit easier.

Edited June 1, 2016 by Mopar1973Man

[TFaoro]

I think the two biggest factors are quality of spray and your right foot.

I'm still getting better mpgs with my 300's than I did with the stockers. I did lose about 1mpg from the 125's though.

Edited June 1, 2016 by TFaoro

[Royal Squire]

Couldn't some of the mpg gain when changing from stock injectors be attributed to the stockers being worn out?

[notlimah]

So basically, injector quality of spray falls off over 100hp injectors? Is that just because you can only contain quality to a lower amount of fuel being flowed? Or, 100hp+ injectors are just putting out too much fuel to be able to maintain a higher quality of fuel spray? Almost a quantity vs quality thing

[Mopar1973Man]

Droplet size.

 

For example nice hot day say 100+ outside. Now take a standard garden hose at 60-70 PSI and spray nozzle and create a fine mist upwards in the air. That mist will most likely evaporate before hitting the ground. Now take a 2 1/2 fire hose at 60-70 PSI and nozzle attempt the same thing you'll end up with water on the ground and evaporation will be poor because the droplet size is too big.

 

TFaoro on the other hand is using boost pressure to created the added heat to burn the fuel by twin turbos. More boost pressure means more cylinder heat to convert the larger droplets. Just remember just cranking the engine around will produce 400-450 PSI of compression more boost means high cylinder pressures, which in turn means bigger nozzle injectors can be used because the heat is present to burn the fuel.

Edited June 1, 2016 by Mopar1973Man

[TFaoro]

I did run 125's on a single that has lower boost at cruising speed than an hx35. The highest I got was 23.xx

It's crazy the amount of factors that go into it, but I definitely would not be going over 100's with a stock turbo unless you're at a very low elevation. I could peg a 1600* pyro with 90hp injectors and an edge comp.