Performance 6.5 Injectors

[Robyn]

YES AND NO

The addition of a free flowing exhaust (preferably cat free is possible)
A free flowing intake air filter and all other items such as injectors and such right up to snuff.

This will allow the best possible power with any given amount of fuel.
The power chips on the other hand allow far more fuel to be available and also modify the timing curve across the powerband.
The shift characteristics of the tranny are also modified too.

The additional fuel and subsequent turbo boost enhancements that the modified chip allows produces the extra power.
Using what is available is going to use more fuel.

A long distance cruise test with the truck on the cruise control at say 65 mph should show some improvements over stock.

The overall tendency though is, if the horse can run better the driver will let it do so and enjoy the ride.

The addition of a free flowing exhaust alone should help with MPG and engine life due to the reduction in thermal stress.
This would be confined to using the factory programing.
Once the chip is changed, all bets are off.

I personally did not swap the chip looking for MPG. The added power was a big issue.

With added power one should expect the real possibility of seeing some loss in fuel economy.
Afterall power is made from burning fuel, doing so efficiently is one thing but that only goes so far.
Power can be equated to BTU"S per hour produced and each pound of fuel only has so many BTU"S
How the engine uses this is the key to its overall efficiency.

Some of our engineer types can probably add some 40 line equations to this explanation but this is the best I can offer.

Efficiency will take MPG only so far then it will level off.

More fuel will take performance just so far then it will reach the limits of the engine design (Point at which it melts)

Just some thoughts.

[Bnave95]

A good vender who advertise at The Diesel Page is the way to go.
Here some history
GM DS4 pump @ 47,323 7-16-1998
New long Block @ 59,303 6-24 -1999
DSG Gear & Cooling Mods @ 77,900 5-17-2000
JK High Flow injectors @ 83,700 9-3-2000
Amsoil duel filtration @ 127,900 2-1-04
FSD @98K & 135,600 on cooler
SOL-D @ 135,600 #2 driver @ 136,115 and running same.
Pump and Injectors are running strong.
Truck mileage @ 161,326
Last week,2nd trans rebuild. First rebuild was at 65K
BTW it's good to see you all

[Hubert]

There was another post somewhere that made me rethink marine injectors and Hi-pop's and I thought I would share some thoughts....

It was posted that peak IP/line pressure and injection pulse line pressure was actually much higher than the "pop" pressure of the injectors.

So it dawned on me I have sized pressure cleaning nozzles before and pumps pump a flowrate then you select the nozzle size to build restriction and thus pressure. You have to match them up too big of nozzle and too little flow won't build pressure. Too small of nozzle increases pressure and can choke flow.

So I posted this

Thinking about it further... why the line pressure might exceed cracking pressure is maybe this...

It is kind of sorta like an airplane holding its brakes and reving the engine for a short runway take off. The opening pressure of the injector is also kind of like a mechanical switch so the injection pump won't pee diesel into the cylinder with the wrong time (early) and/or without adequate pressure to produce a good spray pattern.

If the injectors did not have a "pop" pressure the IP would more "slowly" (relatively) build pressure with rotation and pee fuel into the cylinder early then build pressure and spray the middle and last bit. And the combustion time would be all over the place.

In general (really always for positive displacement) pumps pump a flowrate and a nozzle makes the restriction and restriction makes the pressure. (With pumps there generally are relief valves/byapsses etc to control pressure but pumps don't necessarily pump a pressure its a combination of flow and restriction that makes pressure). Without a nozzle the IP would just pee fuel into the cylinder. With a smaller nozzle and more flowrate in a short burst puts higher line pressure and may strain the pump ie hi rpm hi fuel rates.

MAYBE? marine injectors actually may be easier on an IP during hi rpm than you might think even though they POP a little higher. They just open later to insure adequate pressure/flow to produce the desired spray pattern with the bigger orifice in the nozzle.

And this is what makes timing a bit hairy with hi pops/marine injectors with lower flow IP's. You have to match the pop pressure to the orifice size to get good spray then the fuel solenoid closed time has to be timed accordingly so the PCM gets what it expects.

[Robyn]

The marine injectors are fine when used with an IP that is set up to use them.

Our trucks have an IP that can deliver a set amount of fuel and do so at a specific rate of flow.

The injectors are speced out to pop at a given pressure. The specs have a minimum and a maximum.

I have found that the best way to go is to have the injectors set up to near the top of the specs and to be sure that they are all equal in pop pressure.

Having them scattered all over the map is just poor tech.

The cyl to cyl ballance can and will be effected somewhat by a radical difference in pop pressures across the 8 different injectors.

The quest for more power and performance from the 6.2/6.5 engines has led so many folks to jump on many different band wagons in search of Eldorado

The truth is that properly set injectors along with an IP that is set to deliver the amount of fuel that the engine can burn efficiently is the best that one can hope for.

Air supply (Turbo and aftercooler) and its efficiency.
An exhaust system that will allow all the spent gasses to flow out easily.
Cyl head flow work (port matching etc)

The magic pill, screw in horse power is not in the cards, at least not by using Marine injectors.

Marine injectors coupled with an IP set up for marine use (Larger displacement) will do wonders but must be used as a package to reap the benefits.

The truck cooling systems can't handle that amount of heat rejection.

In speaking with a well known local IP shop, I have discussed this subject in detail, the larger marine injectors will do little to make more power with the use of the standard automotive IP.

My personal thoughts are very much to the point, this stuff is being siezed upon by profiteers, and sold to the unwary/unknowing public as a quick way to make King Kong out of the little 6.2/6.5

I have seen adds like "40+ HP injectors" just scew these little babies in and feel the difference.

Now here is what will happen in many cases.

Joe down the street has a 1995 Burb that has 190K on the clock and gets the hots for more power.

Over the last many years the injectors in his truck have slowly lost pop pressure and the nozzles have worn away to the point that they are fuctioning poorly.

Hard cold starts is quite apparent along with poor mileage and less that optimal power due to a poor spray pattern and a low pop pressure.

Now screw in the new "marine injectors" the pressure is back up where it should be along with the spray pattern being where it should be.

Joes truck now starts right up and really runs great. Power is where it should be (or closer) and the mileage is back too.

Here is the 40+ hp gain. No real gain at all, just repairing what had go away over the 190K miles.

Very likely, using good factory spec injectors on a sound engine would have yielded exactly the same results.

I like having my injectors set even and to near the top of the POP spec

Cold starts are far quicker and cleaner in cold weather. The engine runs smoother overall and will get better economy (if driven to do that)

Just some thoughts.

Robyn

[Konrad.INc]

Hello

I have had couple of questions burning in the back of my mind about fuel injectors for some time now. You might have to excuse me, being an engineering major I have to have all the gritty details on things. I have been looking at new fuel injectors for my 1984 6.2L J code for awhile now. I am trying to get as good of fuel economy as possible out of this motor while leaving it N/A and I am wondering about these "high pop" injectors. What would the pressure difference be between a regular and high pop injector? How do marine injectors differ from automotive injectors? What kind of specifications are injectors usually rebuilt/built to? Does anyone flow match injectors to make everything as smooth and efficient as possible? I am assuming that high pop injectors are what I'm looking for, who sells these? Lastly, just kind of an off question, how often should injectors be rebuilt or replaced. I have never replaced injectors on my 190000 mile truck but it does smoke on startup and is a little bit of a pain to start in the winter.

Any knowledge helps
Thanks

[More Power]

Theoretically, a higher POP can increase the atomization efficiency and possibly power/fuel economy. Only if a vendor posts what pressure his injectors pop at, it's only an adjective that means (or should mean) some pressure higher than specification for a particular application.

There is a downside to higher pop pressures if your fuel injection pump is worn or when the injection pump and fuel are hot. Due to manufacturing tolerances within the injection pump's pumping plungers, a hot thin fuel and a worn fuel injection pump might produce hot starting problems or low power problems when the engine is hot - with a higher injector pop pressure.

Matching pop pressures within a set of eight is a good idea, but unless you have a shop do it for you, you'll get a set of standard spec injectors with spec pop pressures (which pop somewhere within a range of acceptable pressures). It's a tedious process to match injectors because shims are used to vary spring rate within the injector. Flow rates should be fairly consistent between injectors because flow is determined by the injector orifice and the injection pump's pumping volume. Spray patterns are usually not an issue with new or rebuilt injectors, but the patterns do degrade over time - as does pop pressure.

Marine injectors sometimes have a different orifice diameter and/or pop pressure. I've written about this in an article now available in the subscriber section.

The pump & injector manufacturers recommend replacement on the order of 75K miles. Our recommendation is to track fuel economy, startability and general performance. If you notice a decline, it may be time to consider replacing the injectors once other causes are ruled out.

Jim

[Robyn]

In reference to the "POP" pressure and how these injectors work.

The injectors in the 6.2/6.5 engines have a sping loaded valve that the fuel pressure must overcome in order to get past.

The fuel pressure builds up to "POP" in a scant few miliseconds. Once the POP is reached the valve lifts off its seat and the fuel passes through the nozzle ports and into the engine.

As the fuel delivery reaches the end of its cycle (Pump plungers have exhausted the fuel in them) the pressure starts to drop off and the valve in the injector slams shut.

These injectors when working properly will make a noticeable clicking sound as they close.

6.5 TD engines will in many cases have a noticeable "clicking sound" coming from the heat shield on the turbo. This noise can be moderated by placing a gloved hand on the heat shield. The noise is the closing of the injectors and is telegraphed through the manifold and turbo.

Now all this said.

The marine injectors have larger nozzle openings and can pass more fuel in a given injection cycle.
There is really no advantage to installing a set of Marine injectors in your "C" engine as the IP can only deliver X amount of fuel.

IMHO, most gains seen by folks installing these Marine or HP injectors are likely seeing improvement due to the fact that their injectors were crap anyway,and the new injectors simply got the "POP" and spray patterns back to a more normal level.

The IP is what controls the amount of fuel being delivered.

As Jim mentioned if the IP is tired and loose, the higher pressure injectors can cause hot start and other issues.

I tend to believe that 100K miles is sort of a magic place as far as useful life span.

I have seen injectors and IP's go way beyond these numbers but the performance, mileage and cold start ability fall off dramatically.

I have run 6.5's way past 200K but cold starts were like a mosquito fogger on a cool morning.

The actual line pressures during normal running will rise to the "POP" then maintain the given pressure across the injection event, then as the fuel is depleted and the pressure drops off and the flow can no longer hold the valve off it seat the injector abrubtly closes.

Hope this helps understanding how these injectors work.


Robyn

[Konrad.INc]

To start with, I actually have a J code engine. However I do understand that the volume of fuel delivered per cycle is largely dependent on the injection pump instead of the injectors. I replaced my injection pump last november when it started acting up and I could not get the truck to go more than 35mph without huge clouds of gray/whiteish smoke comming out of the exhaust. Currently I do look like a "mosquito fogger" every time I crank up and the engine is cold. I have been talking with one of the advertisers on this site about injectors and he says that the high pop injectors run 150bar and the regular injectors pop around 130-135bar. If the injection pump is fairly new would it be safe to postulate that the injectors will wear in/out with the injection pump? EG when the injection pump has say 50K miles the injectors will have worn out a little bit and the pump still should be able to operate them properly? On another note, does anyone suggest one brand of components over another (bosch, Sandyne or delphi)?

Thanks again

[Robyn]

Your pump should be fine with a fresh set of squirts.

I really dont see that there is going to be any real advantage to the higher pressure injectors.

Stock injectors will do all that the engine is capable of with the stock IP.


Robyn

[AllThumbs]

Thanks to all for this wonderful discourse on injectors and how they work. I think my up coming project will deal with the mosquito fogger (only at start up).