i read that you can gain some serious HP just from rasing the fuel pressure by just a couple of pounds, is this true ?

 

no

not serious

AFPR allows for tuning, most properly done with an engine scanner and monitoring BLM's

If you put in a bigger cam, or heads, or something thats going to suck more air you'll need more fuel to stay away from running lean, then you can justify it. But dont think more fuel = more power.

Better tuning = more power.

good luck

 

Here is a copy of the text from the tech articles info

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.

 

50 hp!!!! Forget headers! Im going to put 6 AFPR ON MY CAR!!

pfft

 

Tpi Roc is correct - adding more fuel does not help UNLESS you need more fuel.

That table you refer to originally came from TPIS but it doesn't disclose what the "fuel requirements" of the engine were before they adjusted the fuel pressure. Not to be a bad guy, but the primary purpose of that table was to sell AFPRs. And, most guys that get into eprom burning on basically stock engines have found the stock eprom calibration is already overly rich. The last thing you need for more performance is more fuel.

Yes, higher pressure promotes better atomization which helps combustion. But if you are already rich at 40 psi, increasing the fuel pressure to 46 psi is just going to make you overly rich and slow you down.

Us guys that burn our own eproms take advantage of the higher fuel pressure and then adjust the eprom to ensure our mixture is at 128/128. This way you pick the fuel pressure YOU WANT and then tune the engine to ensure it has the proper mixture.

But, in all honesty, the performance difference from when I ran 40 psi to 46 psi was not that noticeable EVEN when I had the proper mixture. I got far more performance from controlling the spark advance curve.

 

I don't believe the numbers I see here I find them exaggerated. But raising fuel pressure creating better atomisation will make more power. It's not going to be richer since the computer will adjust the total fuel delivery, but better atomise. Why not 100# then, simply because the computer would need to be reprogrammed and the ole system was built for low pressure operation so piping would need to be improved as well etc. We see after market builders selling tricked injectors (racing) with similar capacity but improved performance.

Talk to Pro Stock mechanics, they spend hundreds of hours into their carburettors alone in part to increase atomisation.

This industrial world is dealing with this ever since the barrel of oil went from 2-3$/barrel to 15-20-30- and 35$ a barrel not mentioning environmental pressure.

Not saying 50# is the perfect setting, I personally raised mine to 50# and realised some improvement and I don't think 20% more fuel pressure will jeoperdise the integrity of the system.

Same amount of fuel, same amount of air can and will make more power if better atomised.

 

What's the difference for day-to-day street driving and the track in this case? Is it just a matter of fuel economy or does driveability change with more fuel pressure? Thanks

 

That is ONLY true in part-throttle, and ONLY if you are not excessivly rich already. You CAN (if your engine is already overly rich) trigger a SES O2 rich code - even at part-throttle. The O2 sensor can only correct so much.

And, for WOT, the O2 sensor doe NO correction. And that is what people are primarily trying to do - increase WOT performance.

Increasing fuel pressure DOES increase fuel, make no mistakes about it. There is a mathematical formual to predict the equivalent size of injector at various fuel pressures @ WOT.

As for part throttle, increased fuel pressure will often give a SOTP feeling due to the "pump shot" effect of the higher fuel pressure. Again, this can ALL be done in the eprom and, in fact, should be done in conjunction with modifying the eprom to get optimal performance. Adding more fuel (which increased fuel pressure does), does nothing if you are already running rich.

I also don't recommend exceeding 48 psi (even when you can modify the eprom). Higher fuel pressure is hard on your fuel pump and you risk burning out your fuel pump prematurely. A few people have already found that out - the hard way.