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csavaglio · 08-31-2014

Bear with me...I'm working mid shift and this is reaching back about 10+ years to when I used to drag race a lot.

As I recall, this was one of those little (and possibly negligible) tricks guys used to use at the track.

Basically, when you go WOT, the vacuum signal drops way off, increasing the fuel pressure by the regulator. The idea of pulling the line is that you have 0" of vacuum at the regulator and it gives full pressure all the time.

There were some different schools of thought. One was that the higher pressure created a better spray pattern and better atomization of the fuel from the injector. The computer would back off the pulse widths to compensate for the slightly higher fuel output. Because of the better atomization, you create more power.

Another thought was that more fuel equals more power. Higher pressure equals more fuel. So higher pressure equals more power. The reality is that fuel injected cars with a proper tune, injectors, etc are rarely fuel starved (usually the opposite...that's why Mark Haibeck and the others lean out the cars a bit). The computer's trying to keep everything at a pre-tuned equilibrium, so, using the real-time 02 sensor values and the learned block values, it will tune out the extra fuel (as much as its limits allow, of course).

Another thought is that you're adding enough fuel to override what the computer can tune (it can only back off the injector pulses so much) and you end up with a rich idle and part throttle.

Personally and real world, I saw exactly no difference at the track on my time slips with several back to back runs with and without the line hooked up.

A popular bolt on was the adjustable regulator, where you could tune the pressure you wanted but keep the vacuum line so you got the variable pressure. Again, the idea was that higher pressure gave better atomization. Realistically, I don't think I saw any difference here either.

I have no idea what kind of regulator the LT-5 uses, compared to the L98/LT1/LT4. I doubt there's any real gain. I never saw anything. I used to like comparing stuff at the track....paper vs k&n filter, throttle body airfoil/without, street/race tires, and even, when I was running my 383, stock/52mm/58mm throttle bodies.

Even if there's a few hp, it's nothing you'll feel and wouldn't see anything on a timeslip, so why bother.

Chris

08-31-2014	#5
csavaglio Join Date: Oct 2013 Location: Colorado Springs, CO Posts: 160	Re: Fuel Pressure Reg. ? Bear with me...I'm working mid shift and this is reaching back about 10+ years to when I used to drag race a lot. As I recall, this was one of those little (and possibly negligible) tricks guys used to use at the track. Basically, when you go WOT, the vacuum signal drops way off, increasing the fuel pressure by the regulator. The idea of pulling the line is that you have 0" of vacuum at the regulator and it gives full pressure all the time. There were some different schools of thought. One was that the higher pressure created a better spray pattern and better atomization of the fuel from the injector. The computer would back off the pulse widths to compensate for the slightly higher fuel output. Because of the better atomization, you create more power. Another thought was that more fuel equals more power. Higher pressure equals more fuel. So higher pressure equals more power. The reality is that fuel injected cars with a proper tune, injectors, etc are rarely fuel starved (usually the opposite...that's why Mark Haibeck and the others lean out the cars a bit). The computer's trying to keep everything at a pre-tuned equilibrium, so, using the real-time 02 sensor values and the learned block values, it will tune out the extra fuel (as much as its limits allow, of course). Another thought is that you're adding enough fuel to override what the computer can tune (it can only back off the injector pulses so much) and you end up with a rich idle and part throttle. Personally and real world, I saw exactly no difference at the track on my time slips with several back to back runs with and without the line hooked up. A popular bolt on was the adjustable regulator, where you could tune the pressure you wanted but keep the vacuum line so you got the variable pressure. Again, the idea was that higher pressure gave better atomization. Realistically, I don't think I saw any difference here either. I have no idea what kind of regulator the LT-5 uses, compared to the L98/LT1/LT4. I doubt there's any real gain. I never saw anything. I used to like comparing stuff at the track....paper vs k&n filter, throttle body airfoil/without, street/race tires, and even, when I was running my 383, stock/52mm/58mm throttle bodies. Even if there's a few hp, it's nothing you'll feel and wouldn't see anything on a timeslip, so why bother. Chris Last edited by csavaglio; 08-31-2014 at 04:12 AM.