I'm trying to plan what I'm getting this summer to speed this LB9 up. Someone told me once that headers, catback, and an AFPR is almost a guaranteed 50HP, is this true? I know an AFPR is a rough tuning instrument, but I don't plan on learning to burn my own proms. I'm still a little confused as to how to use an AFPR also. Do I need some kind of computer monitor to use it properly? Will it hurt mileage that much? Right now these are my planed mods, they're going on an '87 Z28 LB9 (305 TPI) w/700R4:

SLP Single Inlet Cold Air Induction(stupid MAF, no dual for me)
Hooker Headers #2055
Hooker Catback
AFPR(can anyone recomend a good one?) and fuel pressure gauge

 

Well it's not a guaranteed 50HP so don't get your hopes up too high. The only real tuning tool for it that you'll need is a fuel pressure gauge...either a removable one or a in-line fuel rail one from Accel.

You can make your own AFPR for cheap. But I personally went with the unit from Holley...nice looking billet aluminum piece and very very easy to adjust.

 

Does it hurt mileage that much? Or does it all depend on how high you set it?

 

I only put mine on this winter so I haven't got to play around with it alot. But logically yes it should affect your mileage depending on how high you set it.

 

Someone jump in here and correct me if I'm wrong, but an AFPR isn't going to do anything to change the MPG. Higher fuel pressure is primarily going to improve the fuel atomization, you might get a little extra fuel thru the injector, but its not going to be noticable from fill up to fill up... To flow a significant amount of fuel (enough to notice in your wallet or on your odometer) you'd need to swap injectors or increase the pulse width/duty cycle of the injectors.

 

i think im gonna agree with drew on this one more or less because i bumped my fuel pressure up from 35-45 psi and really saw no loss in MPG.

 

I agree with Drew, I bolted on a TPiS AFPR and really haven't seen any change in gas milage, even with my headers i didn't notice a large change

 

I can't help but think that the AFPR, properly set, would improve mileage. It might not be noticable, but if you're changing from a squirt type pattern that a low fuel pressure would cause to a spray atomized type pattern that a higher pressure (within reason) would give, it would seem you would get better mileage, a minute amount of added horsepower AND less emissions to boot.

 

If you're cruising and the car is operating in closed loop properly then it will have no effect on the MPG because the computer uses the O2 sensor to control the enrichment. Basically the computer will cut the pulse width down to compensate for the higher pressure. It is also somewhat true for larger injectors. I went to the 24 lbs with no other changes and picked up a couple of MPG, I'm assuming that it came from better atomization and the fact that the injectors are no longer dribbling into the intake. Later

 

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.

This is from the FAQ section of this site.

 

As stated above the ECM reduces the pulse width of a larger
injector so actual fuel flow will remain the same. That is unless
the injector is so large that the Block Learn table in the ECM
bottoms out then it will throw a code 45 for being too rich.

The benifit comes from better atomization of the fuel as also
stated above. Actually a smaller injector with a higher pressure
set so the Block Learn figure is at 128 (the center of the table)
will atomize the fuel into smaller particles which will burn more
completely and thus produce more power with the same amount
of fuel.

The ideal injector would be one that could turn a liquid into pure
vapor. That would ensure ALL of the fuel in the cylinder
had the best possible chance of burning.

 

I talked to a guy who owns a Corvette shop here and he said
they use 305 injectors and up the pressure to get a better spray
pattern.

 

Hey

I am planning on getting a AFPR for my 1985 IROC Z Camaro witha 305 TPI LB9. The good thing about AFPR is that u can adjust them to any setting. When u are driving on the street from day to day u can set it to the stock setting, Then when u go to the track on friday night u can set it to 50 PSI to get the maxium performance. I dont think that setting it to 50 PSI for 4 hours a week is goin to do anything to then engine or milage. To me the only thing that AFPRs are good for is better ETs at the track. Im not sure if they do anything for day to day driving. Im I was wrong anywhere people tell me so I know what Im talking about.... thanks

http://camaroz28.cardomain.com/id/56424

 

I think that FAQ is pretty much BS.

 

There are other reasons besides racing to use the AFPR. A totally stock 305 MAY benefit if it has low fuel pressure. GM says anything down to 28 PSI is "within specs".

So taking a low fuel pressure and bumping it up to the "targeted stock setting" could improve overall performance.

In regards to MPG or fuel delivery amounts. It's not so much a matter of how much fuel is delivered as it is how it is delivered and how it is consumed.

 

i have mine set at 48 PSI all the time (vac hose disconnected), and have no loss in MPG. Hey, IROCKER, you have the Holley AFPR unit right? in the picture in Jegs, it looks like it comes with the rubber gasket as well. Is this true?

 

As has already been stated, as long as the car is operating in closed loop, the AFPR won't hurt mileage at all. I was getting 26 mpg in my 305 w/ 50psi on 22lb injectors in mixed highway driving.

The important thing to rememeber is that no one setting is right for everyone. The beauty of an AFPR is that you can adjust / tune it under controlled conditions like at the track, or in some back to back g-tech runs. SOTP is garbage. You might think it's faster from the changed exhaust note of running it too rich.

And yes, a lot of the FAQ is garbage. It's legacy though, and nobody really has the time to edit out the junk. That table of gains was probably copied from the TPIS book or something 6 years ago, lol.

 

Hey

Is it true that a AFPR will give u HP and lower ur ETs at the track

http://camaroz28.cardomain.com/id/56424

 

Actually after reading what Mike said I retract my original answer. The better atomization thus leading to better efficiency would make more sense. The efficiency of the spray pattern would probably make up for the small amount of extra fuel being pump through.

tpivette89: It comes with a replacement diaphram. Very easy to install and use.