• 454 big-block TBI (from a '93 pickup) on my 400 small block. About 380 horses/440 ft-lbs. Will go up to about 430 hp/530 ft-lbs. if I upgrade the heads.
• Injectors: 65# @ 12 psi. Flow-matched.
• Adjustable external Mallory fuel pressure regulator, presently at 22 psi. Not using vacuum modulation (I don't want that variable in my tuning.)

Problem-- I need more fuel at WOT, and I'm pretty sure it's because the injectors/pressure combo isn't up to the need.

I'd like to avoid buying a set of larger injectors. But if I must, I will.

But first, what is the maximum fuel pressure that can be run on TBI injectors, before they either leak or lock?

I replaced the factory original 305 injectors (45# units) when they started leaking. I was running them at 25 psi at the time, but they were about 15 years old, and I think they were ready to die, anyway.

 

I have run 36-38 PSI with 46,55, 61, and 68# injectors without trouble. The problem you will run into is lack of resolution as the pressure gets higher, especially around idle. I bet your cam pulls good vacuum because of the 400 CID, so a VAFPR might be a good place to start. I would set up an external regulator that is Vacuum referenced, 30 PSI under load and low 20s at idle.

Here is a nice complete install on a TBI truck.

http://fullsizechevy.com/forums/showthread.php?t=117719

Another on a S10 Blazer

http://home.alltel.net/mcfly/fuellines.htm

Yet another S10

http://members.shaw.ca/betterthanyou/regulator.htm

Here is a write-up, IIRC it might even be yours though.

http://www.diy-efi.org/pipermail/gme...ly/000580.html

Dominic Sorresso's setup on his Crossfire Corvette is perhaps the most sanitary looking installation that I have seen.

 

My Mallory adjustable regulator can be vacuum modulated. 1 psi for every 2 inches of vacuum. All I have to do is connect a vacuum hose.

I had the vacuum on with the old 305, but I had such tuning headaches I haven't done it with the 400 yet. But then, the 305 was a bit over-cammed for the gearing.

Yeah, the 400 idles with up around 20 inches. I guess I should give it a try. VE table, here I come!
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That looks just like mine, except my regulator sits at the left front of the manifold, behind the alternator. The one in your first link IS just like mine. Seems that's the way to mount a TBI external regulator. And the one on DIY-EFI is mine!

 

I thought that it was yours. Have you looked into the EBL?

Here is how I setup mine.





I have plans to setup mine just like the first on that I posted soon. I will be writing a patch for the $0D code to reference the VAFPRs resultant fuel pressure and therefore injector flow rating into the code. The $0D code has alot of extra room in it once the EGR, Catalyst Overheat, Transmission Abuse, etc is removed.

 

Yeah, I've drooled over the EBL. But I've balked at the price. I know it's not much, but I've got so many other things to pay for right now, I'm holding off.

 

I know how it goes and it is expensive when you are comparing it to a stock ECM with a Flash chip adapter soldered in that you already have. I just could not stand the 160 Baud rate any longer. So in my opinon it was worth every penny that I paid.

Just a FYI, I setup my MAF TBI setup for under $250.00 including the Moates G1 adapter and 2 27C512 flash chips.

https://www.thirdgen.org/forums/tbi/...i-zz4-cam.html

 

This build is so well-behaved, I may not have to touch the VE table, or not much. Maybe just the PE AFR table. Only one way to find out.

You think the 65# injectors are sufficient for 430 hp if I just up the pressure at WOT? I'm only turning 5300 RPM max, no matter what the power output. My early calculations said 65# would be plenty, but some of the on-line calculators I've tried indicate that I may need the 90-pounders. But again, there's that resolution at idle issue. Ultra-high pressure or big flow rate, you get the same problem.

I've also dreamed of an aftermarket multi-port system, like DFI. But then, there's that money thing again.

 

I am thinking of dropping a single plane converted to MPFI onto my engine in the future as well (Have a 4-bolt main roller cam 350 that is about to become a 397 (4.040 x 3.875) with Dart Iron Eagles (180cc) on it. The later model TBI PCM can be easily modified to run PFI and even ran a PFI style motor from the factory, CPI 4.3, so the ECM code is already in it to run PFI. It just needs the Peak and Hold drivers modified to eliminate the Hold feature.

I know for a fact that 68 lb/hr injectors at 32 psi were enough to properly fuel my 423 FWHP 312 with room to spare.

 

Well, I hooked up the vacuum to the VAFPR. I set the pressure at 30 psi, then connected the vacuum hose. Idle fuel pressure dropped to 18 psi. I left it there, for now. If the regulator fits the specs, that means it's pulling about 24 inches vacuum at 600 rpm idle. Not bad at all.

If I need higher pressure, I'll have to buy a new gauge (mine only reads to 30).

On the drive to work today, no check engine light. And that flat spot was improved, too. By the way, the flat spot isn't there at all when in open loop. OH! And the WOT was definitely helped.

So, I'll do some recording on the BLM's and see if the main table needs any adjustments. Then I'll get out the stopwatch and adjust the PE/RPM table, and see if the pressure/injector combination is sufficient.

Thanks for all your input.

 

You should be ok at 30psi. You said those are flow matched 65#'s at 12psi, so at 30psi and 85% duty cycle and a .45 BSFC in a 400 cube block, is enough to support 388hp. So, if you get it up higher than that you'll need bigger injectors or more pressure.

 

"Dominic Sorresso's setup on his Crossfire Corvette is perhaps the most sanitary looking installation that I have seen."

Fast,

Thank you for the compliment. RBob gave me the "inspiration".

 

Thought I'd post a final follow-up....

30 psi at WOT, 18 psi at idle, seems to be a great combination. I made the mixture a bit richer in the PE vs. RPM table, and it's running merrily up to red line without noticeable power drop-off.

And I found the fix to the flat spot from 1600-2000 RPM, due to a lean condition in that range. Apparently, the values in the #2 Fuel table do something more than just get added to the #1 values. I could raise the VE settings in the #1 table, to ridiculous levels, with no affect. BLM's in the range 1600-2000 rpm and 30-50 MAP would run in the 160's.

But when I put the #1 table back to original, and added 8 to the #2 table in that RPM range, BLM's dropped to 130 and the flat spot disappeared.

Thanks, everybody!

 

Double check the XDF or ECU file definition for VE #1. Many of the definition files have the two axis reversed. With this the user ends up changing the wrong area of the VE table.

RBob.