Delphi bottom feed injectors

[pmkls1]

I just scored a complete holley TBI unit tonight from craigslist for $50 that uses the newer style Delphi bottom feed injectors. The unit is actually for a 4.3 S/T truck, but the only differences between it and one for my application (89 Firebird w/L31 vortec engine and original L03 TB and injectors) are the injector flow rates. The bores are 2" and the unit is rated at 670cfm just like all of their other TBI units save for the 2.8l model. I am relatively unfamiliar with the Delphi bottom feed injectors, but from what info I can find they may just be perfect for my application. I have posted in a few other threads that I have a walbro 255lph high volume AND high pressure fuel pump that overloads a factory fuel pressure regulator. I have been running with a base fuel pressure set at around 30psi, but suspect that I have been dealing with a lot of fueling issues due to running the O.E. TBI fuel injectors at that pressure. From what I can find, these Delphi injectors are intended for and are used in applications with higher fuel presures. The data I have found puts the max operating pressure at 70-100 psi depending on the part #'s and several O.E. applications have them running ~30psi. I am thinking that if this is true then the 4.3 injectors in the unit I got are perfect for my car because the flow rates at ~30psi should be closer to what my 350 needs than the 305 injectors I am using now. I just wanted to get a little confirmation on that info before I go throwing the Holley unit on my car. I noticed that the FPR on this unit has a little cap that is held in place by a little spot that is peened over and am assuming that after removing the cap the pressure can be adjusted similar to the O.E. units. It also appears that the diaphragm itself is identical to the factory units as well. If all of this is true, then I may just have happened upon an excellent piece for my car. If anyone has a little more info for me I would appreciate it as Holley ain't offering up much info on their website although they were kind enough to put up the latency info for these injectors.

[1project2many]

I missed this earlier.

As to the Multec bottom feed injector, it does get used at higher pressure. This style injector is used in many of the older four cylinder TBI cars with model 700 TB, on the big block medium duty truck TBI apps, and in PFI applications such as 92-98 LN2. All the injectors I have listed are good to at least 70 psi. I will attach the information I gleaned from Delphi's website years ago when searching for injectors to use in a turbocharged 94 2.2 Cavalier.

I wonder if the injector in that TB, sold as a replacement for a system running 13 psi max, is going to deliver too much fuel at twice the pressure. I realize that you're installing this on an L31 but the hp/liter figure isn't dramatically different from the S truck. Maybe a smaller injector would be more appropriate? Holley used to list the injectors under the category of replacement parts but I can't even find them by part number anymore. Here is a listing of the injectors they used to offer:

P/N 522-27 Injector, Fuel (45 PPH)
2-bbl TBI, P/N 502-3
4-bbl Pro-Jection, P/Ns 504-13, 504-23

P/N 522-36 Injector, Fuel (50 PPH)
2-bbl TBI, P/Ns 502-4, 502-7, 502-8

P/N 522-14 Injector, Fuel (57 PPH)
2-bbl TBI, P/N 502-5

P/N 522-26 Injector, Fuel (85 PPH)
2-bbl Pro-Jection (All)
2 x 2 Pro-Jection
4-bbl Pro-Jection (900 CFM)

P/N 522-74 Injector, Fuel (65 PPH)
4-bbl Pro-Jection (700 CFM)
2-bbl TBI, P/N 502-6

I'm guessing you have the 502-7 throttle body? A 50lb/hr injector @ 10.15 psi is 56 lbs/hr @ 13 psi and 85 lbs/hr @ 30 psi. Big. Can you get the 96 TBI injectors (52 lbs/hr @ 29 psi) or the Saturn TBI injector (52 lbs/hr @ 30.5 psi)? When I built my turbo engine I picked up four of the Saturn injectors for a total of $60 from a junkyard.


Holley's instructions for replacing the regulator do include pressure adjustment. http://www.holley.com/data/Products/...l/199R9804.pdf I can't guess what the range is but they expect the unit to be set around 12-13 psi.

As far as the TB goes I used to recommend avoiding them. The solution I favored was to get the replacement injector pod for the small injectors and install it on the OE TB. Once upon a time Holley used their own injectors and there were problems. I've also seen reports of bad bores and leaking shafts. Don't trust it until it's proven itself.

BTW, were you ever on diy-efi? There used to be a pmkls1@yahoo.com subscribed there.

[pmkls1]

Yeah, that's me on diy-efi. I haven't posted on there since finding this site just because it is hard to keep up with more than 1 thread at a time and the list goes silent a lot. The throttle body I got is the 502-7 and from the info I found the injectors are rated at 50lbs @ 12psi and 72lbs @ 21 psi. There is no information on the FPR as they do the same thing as GM and set the pressure at the factory. The pod is functionally the same as the GM ones, but the layout is a little different. The FPR housing is inverted compared to the GM units which actually makes service possible without removing the pod. Since the housing is inverted the "bottom" is facing up and all that appears to be covering where the adjustment screw should be is a little steel cap that is secured by a section of the edge being peened over. The housing itself is different in shape, but the 4 bolts securing it and the diaphragm appear to be the exact same pattern as GM along with pics of the replacement diaphragm. The billet housing I have on my stock TB has a spring that will easily adjust to pressures in the range I am running and I can use it if needed when setting the pressure .IF all of this is true, then I have a better chance of getting my fueling issues sorted out. The existing injectors in the Holley unit pretty closely match the stock L03 injectors I have now as far as flow rates and are too big at higher pressures. BUT, the Delphi injectors are designed to work at higher pressures so they should perform in a more uniform and consistent manner. I haven't attempted to change the pressure on my existing setup since I installed the billet housing ~3 years ago and should be able to get the pressure lower than 30psi which should help my situation a little. I am thinking that I can probably get the pressure down to ~21 psi. That was the minimum pressure I could get the setup to run ~3 years and 70k miles ago on the L03. Given the very slight increase in fuel demand of the L31 and the mileage and age on the pump, I am thinking that it is a reasonable goal. Regardless, I was relatively unaware of these style injectors and their flexibility with fuel pressures. Even if I had to pick up some smaller injectors I would still have a fuel system that all of the components are actually compatible.

As far as the throttle body itself, it APPEARS to be of fairly decent quality and I cannot visually see any flaws such as poor machining or cracks and the shaft seems tight as I inspected it pretty close.. But, I will keep your advice in mind. I am actually holding off on installing it for now because I had a few things in mind that I wanted to do all at once. I have another set of lifters that I am "rebuilding" to replace the ones in the engine because I have a few spongy ones that I believe may be causing intermittent idle issues. While I have the intake off, there is a little blending that needs to be done with the adapter in order to run a throttle body with 2" bores. The bores in the adapter are for a 2" throttle body, but the casting is a little rough in the transition area. I figured that I will do all of that at once since I will have everything apart.

I think that along with a decent set of headers the larger throttle body would really suit the L31 pretty well. I really wanted to go with a port injection setup and will do so eventually, but if I could get the TBI setup working well and making good power then I can focus on other areas of the car. I have the beginnings of a 400+hp L31 based engine in the basement that I haven't bothered to begin working on as it's useless without a fuel/induction system to go on it. I could easily slap a carb on it and have even considered doing that with the car now, but I REALLY wanted to stick with EFI for several reasons. Well, gotta run for now. Thanks for the info, I thought that I had found the correct info but I really wanted some confirmation before messing with something new on an already complicated setup.

[1project2many]

There is no information on the FPR as they do the same thing as GM and set the pressure at the factory.

Interesting. The instructions I linked to are also linked from the 502-7 product page and they clearly spell out a pressure adjustment procedure.

I have the beginnings of a 400+hp L31 based engine in the basement that I haven't bothered to begin working on as it's useless without a fuel/induction system to go on it. I could easily slap a carb on it and have even considered doing that with the car now, but I REALLY wanted to stick with EFI for several reasons.

You can still convert a carby manifold or watch for a SBC marine intake. The tunnel ram style marine intake is good for 500-600hp stock. Worked great on an hot cammed engine I built.

[pmkls1]

Interesting. The instructions I linked to are also linked from the 502-7 product page and they clearly spell out a pressure adjustment procedure.

Oops, I didn't look at the link you put up, but I couldn't find that info previously. I'll have to take a look at that link and see then. All that I could find was just instructions on checking the feed pressure and also checking that the pressure in the return line didn't exceed 4psi.

You can still convert a carby manifold or watch for a SBC marine intake. The tunnel ram style marine intake is good for 500-600hp stock. Worked great on an hot cammed engine I built.

I may run the TBI setup & carb intake that I have now if I get things sorted out and am pleased with the results. The HP figures that a 2" bore TBI unit can support vary depending on where you read. I would think that it can probably support over 300hp, but 400+hp is unlikely. I would still consider using it as a temporary means of getting the engine in the car and broken in though. I have only come across a marine intake once so far and for the price they wanted I could get a HSR or an Edelbrock Pro Flo XT. Money is the limiting issue with an intake setup for me. And it seems that unless I come across a good deal on a used intake just about any option I can find will still be in the same price range. From what I can figure, the cost for a manifold, TB, injectors, fuel rail & regulator would be ~$800 new. The amount of fab work to convert a carb intake to multi-port or to use an LT1/4 manifold would still be pricey as I don't have the equipment to properly do it myself. And lastly, a 4bbl TBI setup is also still pretty pricey too. If I ever get caught up on some of my other projects and start feeling a little ambitious I may fab up a custom sheet metal intake. I have access to a MIG welder and my MIG skills are decent and improving so a steel intake is possible. TIG welding is a different story, though. I don't know anyone with a TIG and have never used one so learning on a $200+ intake doesn't sound like a good idea to me. Anyhow, I'm rambling on now. Thanks again for the info and advice. When I do get the Holley unit installed I'll post an update on how things work out. Oh yeah, I almost forgot to mention that in addition to being subscribed to diy-efi I am also a member on TGO and have been for years although I don't believe that I have ever posted there.