Hey Everyone...Let's say a complete set of injectors pop @ 1800 psi...and another set pops @ 1500 psi...

So, that being the case...which set would introduce more fuel? Or would the volume of fuel be the same?

Which set would produce more power if the volume was equal? Or would the power be the same?

Reason I ask is...I have 2 identical sets of bb injectors that do this because of the way I have them shimmed. I am thinking the 1500 psi set should be matched with an older 124k pump I have in reserve if my newer pump ever goes out.

Thanks

 

one would think that the pop pressure has nothing with the power delivery, as much as it does with the duration of open time it gets and the delivery of the fuel would decifer how much power you will get per one cylinder. persay if your 1500 set is open for the length of the time that your cam opens your intake valve then you should get a great fuel to air mixture and be reciving a good amount of power. where as if your 1800 set opens for about .2 and your intake valve opens for .410 like racins cam does then you should be making better power out of that one cylinder because you would be getting a way better air/fuel mixture. then again it all depends on your spray patterns also. as long as you have good spray patterns then you should be good either way. as we have all figured out " the magic of the motor is in the timing events."

 

Most of the difference would be in timing. There is a guy who owns unique diesel that swears his rig makes more power with injectors that pop at 900psi. But I would think what he is feeling is slightly better turbo on his Hx50 cus at that pop pressure, the fuel probably is hardly atomized at that pressure and that extra fuel would help spool the turbo a slight bit. At the same time, he is leaving some power on the table from the fuel not burning due to atomization and the timing you have to take out. I think higher pop pressure is the way to go and if someone wants more fuel from the injector, the best way from what I understand, is to get more lift from the piston in the injector.

 

I believe your guy at unique diesel. An idi with or without turbo doesn't need a perfect atomization spray because of the pre-cups...Now if you use lower pop pressures you must re-time for those pressures and I think you will find that your IP will last a lot longer with no loss of power.

 

There is no set time for Pop-pressure to do its magic... Its all relative to how much fuel is being pumped from the IP... Lower pop pressure is going to result in a very long (relatively of course) injection event, where as a higher pop is going to result in just the opposite, and the amount of fuel is going to determine the total amount of time the injector is open from pop to close... The goal is to have a combustion event that starts with the optimal injection advance (not too advanced and not too retarded) and having the fuel being completely burnt before the exhaust valve opens... Obviously we cant get this perfect for all RPM's, but we can get close...

A N/A engine can live with a lot less pop pressure, because it simply doesnt push that much fuel... Its duration from open to close will not be very much, so to tune that to the optimum cylinder pressures, its needs a low pop-pressure to be efficient. However, and engine with a 180cc pump, and efficient turbo setup, is going to need a higher pop-pressure because of the sheer volume that the pump is pushing through the injector... Its duration from open to close is much longer than a pump that puts out 65cc's... Now if you put 1800psi injectors in the engine that has the 180cc pump, chances are you injection event is going to be too long for the amount of fuel your pushing vs. cylinder pressure... Youll be junking a lot of fuel (read: power) out of the exhaust... A little can actually help spool the turbo, but it doesnt take much to over do that benefit...

Pop pressure has very little to do with atomization... And atomization is severly overrated in these engines... As soon as that stream hits the hot wall of the Pre-cup, its atomized as much as its going to get until it exits the pre-cup... Injector Duration is everything... It all has to do with timing... not pump timing, but timing in relation to crank angle and cylinder pressure...

And just for reference... I see no evidence that increased pop pressures result in worn pumps... The only possible parts something like that could wear out is the rollers and cam ring... And we are not approaching the pressures that would cause that... The biggest weak link we have in the pump is the shaft and cam pin... if you arent breaking those, you arent putting the stress on the pump to wear it out...

 

What is the highest pop pressure that you have experimented with?

 

Highest I have run is the current 2500psi... But the highest I have pop-tested is 3500... I have tested a single set of injectors from 1500-3500psi to see the difference in spray pattern...

 

and there just wasn't much change?

how would you describe the spray pattern? hollow cone, cone, stream, ect...

 

From what i understand to high of a pop and to low of a pop pressure is bad. It sounds hard to get the right match for an engine. I guess this is why everyone replaces injector pumps and iinjector at the same time

 

Not at all...

I expected more atomization at higher pops, and all I got was a stiffer handle on the pop-tester. The stream is a middle ground between a stream and cone... Basically just your typical injection pattern...

The biggest shocker came when I shaped a few different pintles to see how they would change the pattern... One pintle I completely cut the tip off of... Further than DPS injectors, right up to the seat... It actually atomized better than stock injectors (For what thats worth)... I also sharpened a tip on one, and it didnt perform any different than stock... finally, I increased the stroke on one while leaving the tip completely unchanged, and it performed exactly like stock (like it should)... The only question is whether or not the extra stroke is necessary, so far my standard rebuilds are cutting it great... I will know when I get my dyno time and can test my different injectors out... The extra stroke should theoretically cut the injection duration down but that hinges on whether or not the pintle is being "lifted" far enough to make a difference... I think an increased lift with a low pop could do big things for power with a large pump... But this is theory until I can test it out with a measuring device...
Im still of the opinion that injectors do very little as far as an IDI is concerned, they are more of a tuning aspect than anything...

 

Based on what? Lol

Whats high? and whats low?

Im lovin' my 2500 pops... but I have a ton of fuel...

Injector pop pressure is hugely determinant on total fuel... Its all in the injection event, bottom line... Lots of dynamics at play

 

Try decking the block and shortening the rods to match what was shaved off so the stroke is less than stock say to 3.5" and see what happens...This is theoritacal of course...get some shorter pushrods...etc...in other words make it like a 402 gasser block and see if the IP can keep up. You would lose a little low end torque, but hey with a type 4 cam who knows what would happen then...Wish we could do that and other mods on a computer program to find out...LOL

 

Justin actually has his own can grind that is more suited to a turbo application. Don't get me wrong though. The Typ4 cam is a good cam even on a turboed engine but it was originally made for a na engine.

Also your idea sounds kinda cool but might cost a bit to do. Would there be much benefit to destroking a diesel though? Cus rpm is pretty limited in a diesel and I dunno what the benefits would be due to that.

 

Increasing pop pressure retards timing and decreasing pop pressure advances timing. You are better off running stock pressures unless you can time the IP dynamically to match your pop pressure. I still believe a good spray pattern helps with cleaner combustion, even in the IDI. If your injectors shoot a stream, that is not good. There should be a spray pattern; it doesn't have to be perfect but reasonable will do.

I run stock injectors with slightly advanced timing. Only a few degrees. It helps clean up smoke by burning the fuel a little longer and I am not complaining about power, either. I do have a turbo, which changes intake cylinder volume, so I feel the need to compensate for the denser air.

If you want to increase fuel flow, you can adjust the fuel screw on the IP. There are plenty of threads on how to do that.

 

The spray pattern its a somewhat debated topic. I have actually read somewhere that when the Recardo cup was designed, that the design was more efficient when the injectors tended to be more stream like rather than an ultra fine mist. That is not to say that you want a stream but as Racin has said, the precup does most of the atomization. So consequently atomization is not as important from the injector in an idi as it is in a direct injected engine...