I had another thread about this but it died.

Anyway,my question is,when doing a COMPLETE exhaust is it totally necassary to up the fuel pressure?

Headers-High flow cat-catback.

I'm not really looking after the power of these parts but the sound.Will anything run out of whack with a complete exhaust and stock factory fuel pressure settings etc ?

 

i say, no, you'll be fine. i never messed with fuel pressure on my motor even with the big cam and headers and everything else that i did.

 

no, it will adjust as necessary.

 

IF ya really wanna spend that effort, just go get a new stock FP Reg. & install it. The internal rubber baffle can certainly decompose over long life usage. Our cars are close to 20 years old ya know.
Our little engines don't need/use that much "modification", just good "in garbage & out garbage" work.

 

My car was running lean on top end and needed the pressure bumped up. It was checked on a Diacom scanner.

I have stock 2.8 injectors. From what I have read, I still don't know if tese are 13lbs or 15lbs?

I have read that the 2.8 and 3.1 have the same injectors- I have also read that the 2.8 is 13lbs, the 3.1 is 15lbs and the 3.4 is 17lbs. Also the V8305 injectors are 19lbs (I have some of these sitting around for the new motor.

There are charts on this website that show HP increase on the TPI V8350's with a simple increase in fuel pressure and nothing else. Its on the tech article section and reads as follows:

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.

 

To me
Deans' last thread is so correct for a V8.
Yet, our little V6, using wrong sized injectors would be like "overjetting a carb" which decreases performance.
And increasing fuel pressure for our V6, I don't believe I've seen any claims for backing that up a HP gain, yet.
Doing so (increasing fuel pressure) in a V8 application, certainly does seem to increase power and performance.
The need for proper injector size is why GM decided to increase injector size for each 60* (3.1/3.4).
Dean, was the need for more fuel pressure before or after all your mods?

 

Karl, It was after, But I really don't have many engine "mods" so to speak.
*I have stock exhaust manifold and y-pipe (cat & catback is modified)
*I have 1.52 rollertip rockers
Polished intake runners down to the injectors ports. Nothing ported, just polished and now fiull of crap again thanks to the EGR.
*Gutted airbox with K&N's and a descreened MAF (it was loose already and slightly cocked sideways- I just removed it. Been removed now for years)
*Very hot ignition setup/system. Advance is 13*. Autolite plugs.
*Hypertech thermo prom w/ 180* thermostat drilled. Car sits mostly at 172* unless it is a hot day. My custom brass 4-core radiator I had made several years back has seen better days. New system on the drawing board- not going cheap this time.
That prom chip fails the ECM at full throttle and fully opens the injectors- thats where it was going lean at higher rpms
*Of course, I also have the very lightweight rotation drivetrain which helps me climb higher rpms than stock which is what is getting me into the lean condition.

Other than things like powerpully and a few custom goodies like the charging system, this motor is a stock crate engine with only 35,000 mile on it. Gordon drilled the stock FPR and installed a screw into it for adjustment. I have no gauge on it so I don't know what pressure I am getting.

I am really nervous what this thing is going to do when I put the headers on, especially if I also bolt the 62mm TB to it. Thats why I was asking in another thread awhile back about at what rate does a 13/15 lb injector equal say a 19lbs I have sitting around. EX: like does the stock ones I have at 50psi equal 19lb injectors at 35psi?

 

So I can leave it alone with headers/high flow cat/catback right?

 

If it were me, I'd leave it alone. You actually make more power when you run slightly lean, anyway. (Of course, too lean and you burn a piston!) But you'll be fine. If anything, send your injectors out to Rich Jensen at http://www.cruzinperformance.com to be cleaned - or, send him a junkyard set so you can drive your car while you wait to get them back.

 

Thanks for the replies dudes.

 

Dean,
I had/have seen (IN MAGAZINES) a FPR controlled by engine vacuum set up.
A clue?

 

My vaccum is perfect. Its only happening at top end under a load. It was going lean on WOT at about 4500 rpms. Not anymore since he altered that for me about a year ago. An I did pick up power on the top end. It was right after I installed the Carbonfiber driveshaft and I had more usable to end that it just felt flat all of a sudden. Best way I can decribe it is like how a 2stroke dirt bike will suddenly pickup power when it gets into the powerband, well this droped off kindof like that, just not as extreme. The main problem why I had him check it was the car would get hot quick when I started to get up in the rpms alot when driving hard. Thats why he hooked the Diacom to it and we went for a drive to see what everthing was doing.

 

Vacuum varying the pressure level necessary for the Fuel Pressure Regulator