Max HP with 85 lb/hr. TBI Injectors? [Archive]

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Savage Sierra

07-23-2007, 12:16 PM

Anyone know how much hp a 52mm x 2~ 85 lb/hr. injectors in a TBI can support. I'm building a 383 TBI motor with re-worked 193 heads and the engine has dyno-ed at 356 hp and 447 trq at the flywheel. Brain at TBI chips says that 85# injectors will support 375 plus hp, Holley's tech people say 300 hp and other people say 325, wtf? :dunno:

Has anyone in here made more than 350 hp with a TBI and if so what size injectors did you use and at what fuel pressure and duty cycle?

91chevZ71

07-23-2007, 02:22 PM

max supported HP depends on fuel pressure

13 psi= 321 HP max (85pph)
16.5 psi= 362 HP Max
22 psi= 418 HP max
I would run them at 22 psi, giving you some headroom on duty cycle

yes, there are limits on pressure but you're not even close. Fast's Van has small injectors at +++ psi (like 30 or something),

Savage Sierra

07-23-2007, 03:41 PM

Actually the injectors are rated @ 65 lb/hr. at 11.5 psi and 85 lb/hr. @ 21 psi and this is within the 80% D/C. Do you know the math for the 85# @ 21 psi?

91chevZ71

07-23-2007, 07:45 PM

I have an excel spreadsheet that does it for me, but since I don't know jack I can't get it to display the formula.

85 @ 21 psi = 411 HP

Savage Sierra

07-23-2007, 09:56 PM

I have an excel spreadsheet that does it for me, but since I don't know jack I can't get it to display the formula.

85 @ 21 psi = 411 HP

So I can make up to 411 hp with my current set up and a better fuel pump? Why does everyone list so many different numbers, isn't there just one chart?

pfk

07-23-2007, 10:09 PM

So I can make up to 411 hp with my current set up and a better fuel pump? Why does everyone list so many different numbers, isn't there just one chart?

Here's a thread with a great explanation of the calculations

injector calculations (http://www.fullsizechevy.com/forums/general-discussion/performance/200226-tutorial-you-getting-enough-fuel-support-your-performance-upgrades.html)

91chevZ71

07-24-2007, 07:53 AM

pfk, you found it. awesome. I've been looking for that thread for like 2 weeks

THanks!!
Mike

Savage Sierra

07-24-2007, 11:25 AM

Thanks for the help, Great links, My math is weak but I got the just of what was said. Bottom line I can pump up the power with the 383 and be good with a better fuel pump. Walbro? What do you guys suggest for a fuel pump?

91chevZ71

07-24-2007, 11:41 AM

MStefak

08-12-2007, 11:34 AM

Or you can use the stock Vortec pump used in the 96-98 trucks 90PSI capabiliies (I confirmed 85 PSI on mine) and like 40 gallons an hr i think. Its cheaper then the walbro

oldred95

08-12-2007, 04:53 PM

It will be able to support more then your 383 will be able to produce.

Tbi-MAX

08-12-2007, 08:25 PM

i got a walbro 255 in my fuel pump to feed my 383... actually just turned the psi on the regulator up... my fuel injectors are noisey as hell now with the hood open.. but with it closed, sounds like the truck is supercharged... lol

HaulnA$$

08-13-2007, 02:59 PM

I think the concensus is that Walbro 190/255 pumps are the way to go. (Apeusa.com)

Well, I plan to go with a walbro 190 when this one gets serious about quitting. A 190 might be ok, but you could opt for the 255 to error on safety's side. I was thinking about a 255, but I have heard that you can't run the 255 with the GM TBI because the physical size of the return side of the injector pod is simply to small. I have also heard that you can (go figure). who knows.

Check out apeusa.com and call the guy, good dude
MikeAt TBI fuel pressures, the Walbro 190 will support in excess of 600 HP. A 255 would be severe overkill and will actually shorten the pumps life since 95% of the fuel bieng pumped is just going in a big circle from to the tank to the regulator then back to the tank making the pump work harder for nothing. JMHO