I was just wondering if you guys think my car needs this mod? I'm going to buy a Holley unless there is a better one? Mods are in my signature.

 

I have heard it helps, that is in the near future for me. here is some info from one of the tech articles on this page.



Q: What fuel pressure setting will give me the best performance?

A: The stock setting is 42 PSI. Much track testing has showed that any type of increase will greatly benefit both horse power and torque. Here's some dyno testing on a stock 350 motor which substantiates those claims:

42 PSI (stock) 46 PSI 50 PSI
RPM Torq HP Torq/diff HP/diff Torq/diff HP/diff
------------------------------------------------------------------------
2250 237.7 101.8 254.9/17.2 109.2/ 7.4 275.0/37.3 117.8/16.0
2500 241.7 115.1 262.1/20.4 124.8/ 9.7 283.3/41.6 134.9/19.8
2750 241.5 126.5 275.2/33.7 144.1/17.6 297.0/55.5 155.5/29.0
3000 237.1 135.4 278.2/41.1 158.9/23.5 305.5/68.4 174.5/39.1
3250 233.8 144.7 278.9/45.1 172.6/27.9 311.3/77.5 192.6/47.9
3500 241.0 160.6 278.2/37.2 185.4/24.8 309.5/68.5 206.3/45.7
3750 246.6 176.1 283.4/36.8 202.4/26.8 303.3/56.7 216.6/40.5
4000 250.4 190.7 278.3/27.9 212.0/21.3 298.0/47.6 227.0/36.3
4250 251.6 203.6 272.5/20.9 220.5/16.9 289.1/37.5 233.9/30.3
4500 253.5 217.2 257.3/ 4.2 220.5/ 3.3 277.0/23.5 237.3/20.1
4750 245.0 221.6 242.1/-2.9 219.0/-2.6 266.4/21.4 240.9/19.3
5000 227.6 216.7 225.0/-1.4 214.2/-2.5 237.8/10.2 226.4/ 9.7

It shows that by increasing the fuel pressure to 50 PSI, results in maximum torque increase of 58 ft-lbs (along with a much flatter torque curve) and a maximum horse power increase of 19 HP over stock. 46 PSI also provides a noticable increase which should work well for day-to-day street driving. An adjustable fuel pressure regulator (see Chap 5.2) is required to increase the fuel pressure.

 

Increasing fuel pressure only increase TQ (and power) IF your engine needs more fuel. On a basically stock engine, the stock GM eprom is already overly rich (as many people have found out when they start to burn their own eproms). Increasing fuel pressure will actually slow your car down because now you are excessively rich.

YES, increased fuel pressure will help with atomization with gas, but if you are already too rich (and most basically stock engines are), it will not increase power. You really need to re-tune the calibration for the higher fuel pressure to get the full benefits, or you will just be too rich.

 

If the AFPR boosts the fuel pressure and you start to run too rich a properly tuned engine should detect that and "close" the injectors sooner. This is the whole idea behind an AFPR. You still get the higher pressure for better atomization and the injector shuts off sooner so you don't run rich. Same amount of gas forced through the injector at a higher velocity (for better performance). Always a bonus.


P.S. Someone correct me if I'm wrong....

 

86z28tpi - that is always what I have heard also, the injectors should have a shorter pulse time if you have higher fuel pressure. I know I'm running leaner in closed loop just from adding a K&N I'm not running dangerously lean, but a AFPR wouldn't hurt me. so if you've done hardly anything to your car I would recomend it(I don't have one yet but I'm getting one in the next couple weeks) I've heard it really helps

 

The computer will compensate for higher fuel pressure, but, only in closed loop. In open loop (WOT, or cold engine) the ecm uses the tables only. So, in open loop, higher fuel pressure will richen the mixture. (and yes, GM did make the engines run rich in open loop.....)

Prom tuning is the best way to take advantage of adjustable fuel pressure.

 

As ploegi said, in WOT you are in Open Loop. Actually you are in PE (Power Enrichment Mode) which is a special mode of Closed Loop that DOES NOT use the O2 sensor for any fuel corrections....so you run off tables. But it behaves like Open Loop and hence mose people refer to it as Open Loop. But PE is the correct technical term.

In part-throttle, where you are in true Closed Loop, yes the O2 sensor DOES correct the fuel and will shorten the pulse width of the injectors to maintain 14.7:1. But the ECM can only compensate so far. With your fuel pressure too high, running a 160 T-stat and a relocated MAT, you could cause an overrich situation that the ECM cannot correct for and trigger an SES O2 Rich Error.

One point that people haven't mentioned when they "crank up" the fuel pressure on a basically stock engine is the throttle response seems "crisper". This can in fact be true. This is because the higher fuel pressure is like increasing the "pump shot". But you really want to do this more in the eprom as you can control the amount of the "pump shot" for various TPS/MAP values. By just raising fuel pressure, you will increase this "pump shot" effect throughout the TPS/MAP range with MORE happening at the higher TPS/MAP values. This can result in too much of a "pump shot" and make your engine bog.

That is why I recommend the best way is to set your fuel pressure to what you want (46-48 psi is my prefered settings as going higher can shorten your fuel pump's life and lower doesn't get as much of a benefit from the better atomization). Then you tweak the eprom to ensure that the proper amount of fuel throughout the engine's operating range and in all situations. Fuel pressure by itself can help in some areas but hurt in others. It's kind of like just advancing the distributor by itself - helps in some areas but hurts in others.

 

BTW, it was this VERY situation that caused me to look deeply into eprom burning. With my relocated MAT on my SD car, when the air temperatures dipped under 20*F, I actually triggered an SES O2 Rich error. Switching to a 180* t-stat helped, but when the temperature got colder, it too triggered an SES O2 Rich Error. I then reconnected my stock MAT sensor in the cold weather (which fixed the problem) and then got into eprom burning. Then I modified my eprom's Fuel Tables (and MAT Compensation Tables) and now I run damn near 128/128 perfect in all operating conditions, in all weather temperatures with a relocated MAT.

I also decided to stay with the 180* t-stat. I am now able to tune for even more consistent performance with the warmer t-stat and I don't have to freeze my butt off during winter.