CumminsBeast
New member
- Joined
- Dec 20, 2008
- Messages
- 93
During some tuning experiments the other day, I noticed a couple things about EGTs and injection duration. I started out thinking I couldn't heat up too much with my setup because of my small sticks (25hp) and stock CP3, but I was proven wrong when I turned up my Smarty. I thought I had enough turbo to handle any cooling issues (64/71/14), but found that I can hit 1400 degrees with Smarty only on SW7. This sparked some thought...
So we all know it takes fuel volume to make horsepower. The two ways to pump fuel volume into the cylinder during one stroke of the piston is 1)pressure 2) duration, and 3) flow rate (bigger sticks). For the purposes of this discussion, lets assume you have an adequate injector pump, and have the capability to tune in the max rail pressure a normal common rail injector can stand without exploding (~27,000 psi, safely...I know, this can be argued). Now, we're left with two ways to get fuel into the cylinder; duration and flow rate.
Bigger is always better, so the bigger the injector, your guaranteed a higher flow rate to achieve the volume needed for a specific horsepower goal (lets also assume we have adequate airflow for the desired horsepower). This means the duration can be short (smaller amount of "programming"), and alot of volume is injected in a very short time. If you have a smaller injector though, you'll need to turn up the duration to get the same volume during one stroke. However, there is a limit to the length of time you can spray fuel, and the longer the fuel spray lasts, the less opportunity you have for the fuel to get burned. By using less duration with the bigger sticks, you'll leave more time for the fuel that was injected at the beggining of the stroke to be burned.
I was convinced before that my small sticks would yield lower egts; now I'm thinking bigger sticks will get me lower egts....at least in my case. I know there are certain scenarios where that will become false. I think the duration is killing me basically, and I think this is the trouble alot of people get into and I thought I would try and explain this a bit here.
These are my thoughts from a mechanical engineer's perspective. Anyone who has experienced either excessive EGTs with seemingly not much fueling mods and a big turbo, or anyone who's EGTs went down with bigger sticks and less programming, please comment here. I would like to hear some other experiences/perspectives on the issue. Or maybe just some objections to my explanation above.:rockwoot:
So we all know it takes fuel volume to make horsepower. The two ways to pump fuel volume into the cylinder during one stroke of the piston is 1)pressure 2) duration, and 3) flow rate (bigger sticks). For the purposes of this discussion, lets assume you have an adequate injector pump, and have the capability to tune in the max rail pressure a normal common rail injector can stand without exploding (~27,000 psi, safely...I know, this can be argued). Now, we're left with two ways to get fuel into the cylinder; duration and flow rate.
Bigger is always better, so the bigger the injector, your guaranteed a higher flow rate to achieve the volume needed for a specific horsepower goal (lets also assume we have adequate airflow for the desired horsepower). This means the duration can be short (smaller amount of "programming"), and alot of volume is injected in a very short time. If you have a smaller injector though, you'll need to turn up the duration to get the same volume during one stroke. However, there is a limit to the length of time you can spray fuel, and the longer the fuel spray lasts, the less opportunity you have for the fuel to get burned. By using less duration with the bigger sticks, you'll leave more time for the fuel that was injected at the beggining of the stroke to be burned.
I was convinced before that my small sticks would yield lower egts; now I'm thinking bigger sticks will get me lower egts....at least in my case. I know there are certain scenarios where that will become false. I think the duration is killing me basically, and I think this is the trouble alot of people get into and I thought I would try and explain this a bit here.
These are my thoughts from a mechanical engineer's perspective. Anyone who has experienced either excessive EGTs with seemingly not much fueling mods and a big turbo, or anyone who's EGTs went down with bigger sticks and less programming, please comment here. I would like to hear some other experiences/perspectives on the issue. Or maybe just some objections to my explanation above.:rockwoot:
