Why do bigger injectors run hotter while towing?

[PRout]

Simple question.

If you have Mach 1 injectors, towing heavy, pulling a grade at 55 mph, running say 1200 degrees EGT, why would Mach 4 injectors run hotter at the same speed, under the same circumstances? All conditions equal except different injectors.

This has been tossed around on these forums for awhile, but I'm still not understanding exactly why bigger sticks have a towing issue. Seems like timing would be more advanced, so I can see higher cylinder pressures, and if you have a fueling box, I can see the delayed fueling as sort of a retarted fueling situation, but forgetting the fueling box, why do bigger sticks have a towing issue? Is it because of less efficient atomization? Spray angle? Magnetics??

Please pass the advil, this thread is giving me a headache. .

 

[ScottLewis]

Strictly an uneducated guess but here goes:





More fuel = more heat.



Dan

 

[Cummins Thunder]

if running exactly the same speed, with exactly the same load, and the same amount of fuel being delivered from the pump, they shouldn't run any hotter...

 

[Froadin]

Efficiency.

Think about it this way, the mach 1's are like using water hose, and the mach 4s are more like a fire hose. The same amount of water will squirt out, where as the firehose will dribble/poor out. And atomization is the name of the game.



Just look at how many people like the difference between the mach 1. 5s vs the newer 1. 6s, more of a change in technique then anything else, but they run smoother.



And towing just magnifies any little difference there is. Any 'extra' unburnt fuel goes into heat FAST!

 

[jwilliams3]

if running exactly the same speed, with exactly the same load, and the same amount of fuel being delivered from the pump, they shouldn't run any hotter...

If that was true why would anyone ever buy a set of injectors?

We would just buy a hot rod fuel pump and be done.



Big injectors deliver more fuel per shot than a stock injector will.

Hence the heat.

You see all the fuel pulsed from the injector pump is not used much of it is returned...

 

[Froadin]

I think he is trying to say that for the same amount of power from each injector, which might be 1/2 throttle from the mach 1s and 1/4 throttle from the mach 4s.



He is saying if both injectors are injecting the EXACT SAME amount of fuel at the same time, why would the larger injectors still run hotter. Obviously if you push the skinny pedal all the way down, you will get a LOT more fuel from the mach 4s, but that isn't what he is asking (at least that's how I read his question).



And my answer was that the bigger injector isn't nearly as efficient as the smaller injectors are when you are only using a smaller amount of fuel.

 

[Forrest Nearing]

the difference is spray pattern and atomization...

 

[RMachida]

Isn't it just more unburned fuel leaving the combustion chamber and burning in the exhaust?

 

[PC12Driver]

Isn't it just more unburned fuel leaving the combustion chamber and burning in the exhaust?

I'll buy that. Bigger droplets taking longer to burn, still making heat as the gasses expand in the cylinder when the smaller droplets would have been done burning and already cooling off from expansion...



Maybe...



Or it could be that those with bigger sticks tend to use 'em?



With that being said, I didn't notice a temp change in towing when I went to my Mach 2s unless I was using the extra fuel. My egts didn't increase until I put on the bigger turbo.

 

[Boondocker]

My egts didn't increase until I put on the bigger turbo.

PC12Driver,

Are you saying that your towing EGTs got higher when you went from a (stock) to HTB2/12?



I'm under the impression that a slightly larger turbo will decrease EGT, at least under higher load such as towing. Unloaded cruising could run hotter because you're not fueling enough to pressurize a bigger compressor.



I'd like to have Mach 4 injectors for power without a pump wire tap, but figured I'd need a bigger turbo to maintain EGT. My current setup, with Mach 1. 6, Smarty on #3, and stock HX-35 requires that I drive by the EGT gauge when towing. I was hoping that a slight turbo upgrade, like a hybrid to keep my exhaust brake, would allow me to use more of the fuel I already have available by reducing EGT at load.



Neil



I'd like some of that Advil when it comes around

 

[PC12Driver]

PC12Driver,

Are you saying that your towing EGTs got higher when you went from a (stock) to HTB2/12?

Yep, that's what I'm saying. With heavy throttle the HTB2 will run cooler, but for normal cruising/rolling hills with a trailer, the stocker will move a bunch more air mid-throttle. The HTB2/12 is just barely waking up at cruise rpm/fueling while the HX35/12 was "on" and making good boost. If a hill sneaks up on me and I don't have my rpms up, my egt's will climb right past 1250 and boost will just sort of hang in the low 20s. If I hit the hill at the proper rpms (1900+) the HTB2 will light off and keep temps in check. The HX35/12 was already pulling hard by 1700rpm. Since my gearing and tire size puts me at about 1800-1900 rpm on the highway, that would put me right in the sweet spot of the '35 and just tickling the bottom end of the 'B2. For me, the HX35 was much easier to tow with.



How much boost do you have your HX35 set for? I wouldn't think that egts would be a problem with your HP level and that turbo.

 

[Cooker]

For me, the HX35 was much easier to tow with.

FWIW - I tried a couple S300 variants and I also found the HX35 was easier to tow with.

 

[PRout]

Now i really have a headache, time for some codine. .

 

[PC12Driver]

Now i really have a headache, time for some codine. .

Yeah, sizing everything up everything on these engines to do what you want is a 3-d problem, not 2-d as is popular belief around here. There's much more to it than a) bigger injectors need bigger turbos to keep them cool and b) bigger turbos need bigger injectors to drive them. There's that whole powerband and drivability thing that often gets overlooked. Bigger turbos take from the bottom to add to the top. What you'll find is Cummins has selected turbos that match our little 359ci engine for its intended purpose and rpm range quite well. Like they have the inside scoop or something...

 

[Diesel Freak]

Yeah, sizing everything up everything on these engines to do what you want is a 3-d problem, not 2-d as is popular belief around here. There's much more to it than a) bigger injectors need bigger turbos to keep them cool and b) bigger turbos need bigger injectors to drive them. There's that whole powerband and drivability thing that often gets overlooked. Bigger turbos take from the bottom to add to the top. What you'll find is Cummins has selected turbos that match our little 359ci engine for its intended purpose and rpm range quite well. Like they have the inside scoop or something...

EXACTLY!!!!!!!!!!!!!!!

 

[Boondocker]

How much boost do you have your HX35 set for? I wouldn't think that egts would be a problem with your HP level and that turbo.

I just have an old Edge boost elbow, so no idea what max boost is. I've hit 35 psi and am not comfortable with that, knowing that it's useless anyway. When pulling hard, 20-25 psi is the max sustainable range. I'm pretty conservative about EGT, being in the 1200* range makes me paranoid. I'm talking about maintaining throttle control to keep the EGT where I want it. The idea of Wide Open Throttle, especially when towing, is out of the question. That tells me I have more fueling available then I can safely burn.



Does all this mean that Mach 4s are out of the question too?

Or can I get bigger injectors, stock turbo, and manage it will my driving style?

Or can I get bigger injectors, hybrid turbo, and manage it will my driving style?



There's probably no answer, but I'll keep mulling it over because there are some parts of my brain that don't hurt yet



Neil

 

[PC12Driver]

35 psi is right on the edge of useless boost with your stock turbo. Keep it in the low 30's and you're golden. You can actually see the pyro needle speed up once you pass 35. Drill out the wastegate so all six dump and you'll get better control of your boost.



M4s out of the question with a stock turbo? Not at all. You'll still benefit from quicker acceleration. You just can't keep your foot in it as long and towing would be hairier. I think Hohn ran this way for a while - look up some of his posts.



And for your next two questions the answer would be yes. But the catch being that the larger the injectors or bigger the turbo, the more managing of your driving style you'll have to do. With just an EZ I could leave it in sixth with the cruise on and pull any grade below 8,000' without slowing down or hitting 1200* (with a 10k camper in tow). Now, 200hp later, I have to downshift more often to keep the turbo pumped up and blowing boost so I don't torch the engine.



It's all just a matter of deciding how much you're willing to give up to get big hp numbers.



And don't forget about cams. You can keep the stock turbo and not give up its bottom end performance, but still run about 100-200* cooler on top for about the price of a turbo.

 

[GiesJ]

And don't forget about cams. You can keep the stock turbo and not give up its bottom end performance, but still run about 100-200* cooler on top for about the price of a turbo.

I think there is a lot of wisdom in this paragraph.

Jason

 

[NoSeeUm]

Great topic and some very interesting discussion. To tell the truth I still can't quite get my mind around all of it.



I think I'll just push the "I believe" button.



Jim

 

[NoSeeUm]

...



And don't forget about cams. You can keep the stock turbo and not give up its bottom end performance, but still run about 100-200* cooler on top for about the price of a turbo.

Perfect advice, proven true in my case.



I just wished that I was smart enough to figure out the "improved intercooler" formula and if upgrading to a better one would be good dollar per degree F decision.



Jim