I lowered my fuel pressure from 50psi to 47psi, and the car felt about the same.....i went ahead and lower it to 44psi and i don't think it runs as strong a it used to, especially in the midrange. I guess it just doesn't work on my engine.
Rick

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'88 GTA 350 Full of Leprosy (rust)
Headers, catback, free mods, Xtreme energy cam, intake pieces and 2100 RPM TQ

13.39@102.50 MPH
1.90 Sec ----- Best 60FT
104.23 MPH -- Best Trap Speed
AIM HIGH!

 

every engine reacts differently, so there is only one way to find out if it is helping you or if it is hurting you, take it to the track and do some testing. were you having problems when it was set @ 50 psi?

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Brandon
"ScreaminDeamin 360"
350 60 over, TRW forged 9.83:1 pistons,Hooker Comp headers, crane cam 216/228 .484/.512, crane 1.6 RR's, ported plenum, home made ram air, 19 lb SVO injectors, crane AFPR, all going through 3 inch mandrel pipe and a flowmaster.
New project-89 IROC
http://users.argolink.net/bvana
http://ScreaminDeamin.cz28.com

 

Okay, am I missing something here. Raising the fuel pressure increases performance. 48 to 52 psi usually being the best. So why are you lowering the pressure?

 

raising fuel pressure doesn't always make more power and neither does lowering it.

If the engine is already too rich then raising pressure adds fuel and will hurt performance.
If it is too lean then it will add fuel increasing performance.

Atomization is improved with higher pressure so increasing it can help there but you should compensate with PROM calibration to get the A/F mixture right where best power is.

As Screemin' said, every different engine combo reacts differently.
Whether you get an improvement or not depends on if you're giving your engine combo what it needs.

You can't always feel an improvement "by the seat of your pants" either. Sometimes it will feel slower but actually be faster or the other way around, it may feel faster but have slowed down. The only way to really know besides dyno time is to go to the track and do comparison testing. Go by trap speed (MPH). the higher it is the better your power to weight ratio is. Be sure to let your engine cool to the same temp before each test pass.
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Tracy /AKA IROCKZ4me
'86 IROC-Z Camaro
"Cogito ergo zoom"

• 355 cid
• AFR heads
• Arizona Speed & Marine hydraulic roller cam w/ AFR hydra-rev kit
• modified SLP runners
• TRW forged pistons/ceramic coated
• fully balanced
• Edelbrock headers/ceramic coated
• SLP cat-back
• Paxton supercharger
• Nitrous Express nitrous oxide

My IROC-Z
EFI Performance Club on Yahoo
Club IROC-Z

[This message has been edited by IROCKZ4me (edited March 05, 2001).]

 

Actually, the car feels a bit better now. I think after the computer relearned the new settings (I disconnected the battery) it adjusted for the lower pressure. I'll be going to the track soon, I hope.
Rick

 

One of the best way to increase your performance after you've put some mods on your car is to go on a chassi dynamometer. A good mechanics with a dynamometer will help you to balance your A/F ratio, timing and other things like that. After i put my hedders, catback and air induction system, my mechanics help me to "dyno tune" my GTA. In just half an hour I've gain 13 rwhp.

I run my 350 GTA with the stock injector and standard fuel pressure. My A/F ratio is well balance and the engine perfom very well on all RPM range.

Just by curiosity, does any one have an idea of the RWHP a 350 TPI f-body with TH-700R4 tranny (modified with shift kit) and hedder, dynomax cat back and custom made air induction. My best result on a clayton 550hp chassi dynamometer is 271 RWHP. Does someone else have results like that with similar mods? I just want know if it's good.

Thanks

 

That seems like an outstanding RWHP to me! I had my FP at 48..but it wasnt pulling as hard in the uppers so I backed it back near stock..it took a while for the ECM to relearn that..but it feels good now. I am going to the Track tommarow night..I hope I gain at least 1 MPH..

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• Red '88 IROC 5 Speed 305 TPI w/3.08
• Dual Friction Centerforce Clutch
• Accel 300+ Racing Ignition
• Accel 300+ Pro Sleeve Plug Wires
• Accel U-Groove Plugs
• Flowmaster Force II 3 Chamber Cat Back Exhaust
• Hypertech Chip
• Hypertech Airfoil
• Removed, Then Re-installed (out of fear) MAF Screens
• Gutted Air Box
• Best E/T 14.686, 60' 2.205, 1/8th mile 9.461, 1/4 MPH 93.91
• Best 60' 2.17
• TPiS AFPR set to 44psi using Accel Fuel pressure gauge (Installed after run)

 

Your computer should automatically adjust the fuel pulse to get the optimum A/F Ratio based on the stored tables in the PROM. It is only if you go outside these parameters that you will have trouble. Raising and lowering the fuel pressure will change the spray pattern from the injectors and have a minor affect on A/F ratio because the computer is going to compensate for it based on the O2 sensor.

 

Your computer doesnt instantanously correct itself. The GM computer can take weeks to adjust. TPIS has verified that, read TPIS insider hints.

I always disconnect my battery after FP adjustments.

I ran 43#s for a week. Car pulled hard. Raised it to around 50#s and the car got dramatically slower. low/mid/and upper RPMs.

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91 Formula
305 TPI 5speed
1LE/G92/WS6

Paxton SN92 polished kit, SLP airfoil, ported/polished plenum, March pulleys, Crane AFPR(43psi),Crane Gold 1.6rrs,MSD coil,MSD6AL (5275rpm limit),Holley 9mm wires,Ac delco R43ts plugs,fastchip,Ford SVO 24# injectors,Bosch O2sensor,SLP 1 5/8" headers,SLP catback,shortened shifter,3:73s w/Auburn posi,170* t-stat,JET 195* fan switch, Macewen white face gauges, Autometer gauges, Zoom hi-performance clutch.