TBIThrottle Body Injection discussion and questions. L03/CFI tech and other performance enhancements.
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Alright, First of all good stuff from you guys so Maybe I could get some direct help. I've got a 1992 Firebird with a 350 H.O. Crate motor from GMPP. Basically 350 4 bolt main with Iron Vortec heads. GM Performance Parts350 HO Overview Complete Breakdown There. Anyways, LOVE the TBI setup, have had the stock 305 or 350 TBI ported out to a bigger CFM rating than stock. It's got 350 Injectors brand new and the Fuel pressure is around 11.5 or so. I do have a gauge I just havent checked it recently. Had some major problems after doing the swap obviously but finally got the Dough for chip burning and tuning equipment. Been reading through the Come in for a free tune and I'm going static at 3500 RPM. What would be the desired fuel pressure to get these injectors from going static so low? It would rarely see the north side of 5000 because of it's low Redline but 5200 rpm would be a safe shift point for murdering this motor. Is it possible to up the fuel pressure to a desireable level with stock equipment like Fuel pump, regulator and injectors and O-rings? Would it be better to check a junkyard for a 454 TBI unit and get those injectors too? How much pressure can the stock pump and stock regulator handle? Kind of stuck on heavy cash because of the tuning equipment but i'm heading in the right way. In advance before I go
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Last edited by smartman__007; 10-30-2006 at 10:18 PM.
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Fast355 has run the stock injectors at over 30 psi, so they deffinately are not the restriction. The stock pump on the other hand won't make much more than 12 psi on stock 305 injectors. It' wouldn't be a bad idea to get a set of bigger injectors, I'm running about 18 psi on a set of 70 lb/hr injectors on a very mild 350.
Thanks for the reply. Sorry about that pm beggin you for help with burnin proms. TBI just got me down, but after playing with 3/4 throttle and below the power potential is INSANE. Tell me if i'm doing math right, your injector setup is currently supplying 105 LB/HR of fuel? So getting the delivery of fuel on my setup a tad higher or within the vicinity would suffice? I'll need to replace the stock pump to up the psi to around 22 which is 111 LB/HR according to my math with 61 lb/hr injectors.(Stock Replacement 350) Just to make sure i'm not trying to feed a dead horse here. Thank you Once again BMmonteSS You da man along with Shifty and RBob with TBI.
Last edited by smartman__007; 11-01-2006 at 10:21 AM.
Quote: Been reading through the Come in for a free tune and I'm going static at 3500 RPM. What would be the desired fuel pressure to get these injectors from going static so low?
3500 rpms(350 injectors) at load could very well be static. would not surprise me in the least. that is where mine were this summer. static that is. you need the gauge and up the fuel pressure till you get results on DC. be prepared for a major retune as a result of high FP. stock pump has to go. i have had a GM tpi pump now for 3 years and works well maintaining fuel flow at WOT.
Sounds good Ronny... Best bet would be to get a good fuel pump and crank the pressure up. Yeah I kind of figured a major retune would be in order but i would rather have good WOT than perfect idle right now... Idle can be fixed.. WOT is a pain with stock equipment. What pressure do you run your 350 injectors at with TPI pump? Basically what is the limits of the TPI pump?
i have 80 lbs at 24 lbs today. 12.7/1 WOT as commanded in tune. the problem with WOT is it almost requires a WB02 or you are guessing. plug reads will work but that is a PITA. GM TPI has ability to provide more than enough fuel. why do you need a Holley 670?
Cant remember where i said something bout a holley 670... Thanks once again everyone. Cant beat a good old FBODY forum like this... according to my math I would need to see 22 psi out of the FPR to get the fueling high enough for WOT...I'm going to check stock PSI limits this weekend and see what i can do to increase it to 22 without swapping pumps right away. Please correct me if i'm wrong but whats the rating difference between the TBI and TPI fuel pumps? LPH or GPH??
Thanks again... I actualy got bored in school and searched extensively and found these specs
Fuel Pumps
The OEM fuel pump for TPI/LT1 is an "in tank" fuel pump with an operating rating of 50 PSI and 24 GPH. This pump is recommended for all vehicles with in-tank pump mountings. We also offer a chassis mounted fuelpump which has an operating rating of 60 PSI and 30 GPH. This pump is also an AC DELCO unit. It is important to note that Throttle Body Injection systems operate at 12 PSI. Almost all carbureted systems operate at low pressure utilizing a mechanical pump. An electric pump is definitely required as referenced above for all Port Injection systems. A return line is required to the fuel tank. A 3/8 or 5/16inch supply line is required. 3/8 is recommended. 5/16 inch is recommended for the return line. The fuel tank must be vented so as not to buildup pressure. Recommended location for the fuel pump is close to the fuel tank.
The stock tbi fuel pump typically has a stall pressure of 15-16psi, meaning, you cannot adjust the pressure higher than this because the pump will no longer push fuel at any higher psi. We've seen a few stock pumps push 18-20psi but this is not the norm.
I just put in a Walbro 190 pump it worked out great. Personally if I were changing pumps I would go with a walbro 190 or 255 just because you are only going to want to do that job once, believe me. Do it the best possible the first time, that's why I wouldn't drop the tank to install a GM pump.
Also, the problem with the stock pump, it may be reading 15psi at idle when you're looking at the gauge but it isn't pushing the volume that your motor needs. So the pressure would be dropping under load when you can't see the gauge.
In advance before I go 
