I'm building a LT-1 motor that has a few mods and cannot figure out what size injectors to use. I was hoping that someone could help me to figure out which pounds to go with. Engine specs are: 383 stroker, flat top pistons (just two relief cuts), stock valves in the heads, ported, polished, and matched heads to the manifold, 58MM TB, no EGR. More detail if one needs'm
I was thinking around the 28 or 30 pound injectors???

 

Read this: http://www.rceng.com/technical.htm
Enjoy! :)

 

Well I guess I'm a tard because it said two differant injectors. For 450 hp it said use 26# and for 500 hp use 31#. Motor should be around 500 HP according to Desk Top Dyno 2000. I don't think I mention the cam is a .510/.510. I guessing 28lbs, I'm thinking 30 would be too much.
Anyone else that can help with the subject??

 

You need to know what fuel pressure you will be running. Most LT series systems run at 44 PSI, then figure out how hard you want to work the injector (Duty Cycle) I always use 75% as 80% is considered maxed out & the Inj's can lock and burn beyond 80% Then just plug the numbers into the blocks on the chart & it will figure it for you, be realistic on how much horsepower you will be making, 500 seems a little high, who knows though? 450 would seem realistic to me. A stock Z06 makes 405 HP & uses 28.8 LB an hour injectors @ 58.4 fuel pressure so use that as a guideline. I run the Z06 Injs (28.8) on my Vette at 58.4 PSI and I have seen the duty cycle go all the way to 88% under full load on my Datamaster scan, so I need to upgrade to 30's on my car & it only makes 415-420 HP :seeya


[Modified by superlund, 11:22 PM 11/30/2002]

 

Uh, the cam is really small to be making that much power. Is this a nitrous application?? Stock p/p heads or aftermarket? I will GUESS and say get a set of LS6 injectors.

 

Just some food for thought

I make 365 rear wheel horsepower out of my 350. My data logs show a 100% injector duty cycle at 6000 RPM's, meaning that they are being worked like crazy just to keep up. Injector duty cycle is never supposed to exceed about 80% The motor makes really good power but I just thought that was a terrible load on the injectors. This is on a set of SVO 24# injectors.

I borrowed a set of SVO 36# injectors and programmed myself a new chip. The only change I made to the chip was the injector constant. The car ran very well with the 36's and the injector duty cycle was cut down to like 69% at 6000 rpm's. To me this is a whole lot more acceptable than 100% Now I just changed the injector constant and it ran great. If I had the time to tune it out properly you'd never even know it had 36# injectors in it.

Now I'm only making 365 hp at the wheels, which is about 420 at the flywheel depending on the correction factor you use. If you're going with larger displacement and plan on making close to 500 hp then I would go with 30's or even 36's. You can probably get away with a smaller injector but if you can keep around that optimal 80% duty cycle then you can rest assured that your injectors aren't being over worked. Within reason you can always get less fuel out of a larger injector easier than you can get more fuel out of a small one.

 

Just a little personal experience coming at you.

I've locked up injectors by commanding a high duty cycle. Over 120% duty cycle on a 1/4 mi pass. If I remember right it was closer to 150%.

Locking injectors with a duty cycle just above 80 % is going to take a LONG wide open pull to even come close to locking them up. I'd be thinking 10's of minutes.

I use 36 lber's on my 383 at stock '90 fuel pressure. 379.8 rwhp @ 5600, SAE RWHP corrected. Between 78% to 80% duty cycle depending on conditions. Warmer less, cooler more. The higher RPM's you turn the smaller the time the injector has to open, the higher the duty cycle to deliver the same volume of fuel. Duty cycle is the percentage of time the injector is open out of the available time.

I hate seeing these posts with the words never in them. We're in a gray area here. You can run smaller rated injectors at higher fuel pressures and they'll work perfectly. The ratings are at a certain fuel pressure and when you increase the fuel pressure above the rating point you increase the amount of fuel delivered. You make them bigger.

You "can" also make the spray pattern better by doing that. Notice the "CAN" , it's not always a given. You can also reach a point where the injector is not able to open against the fuel pressure against it. Fuel volume from the pump also decreases as the pressure goes up.

Something between a 28 and a 36 lb injector will do what you need.

I also think your hp expectations are on the optimistic side. Hopefully I'm wrong. Dyno numbers are the only truth.

 

Spray pattern is the exact reason I run the Z06 injectors at 58.4 PSI, I upgraded to a Walbro GSS340 pump W/hot wire kit & use an Aeromotive regulator to set the pressure at 58.4, I had been considering going to the Ford Motorsport 30's and dropping the pressure back to about 46 PSI, to try & lower my duty cycle. Glad you posted your experience with Inj locking, I may just stay put with the Inj's I have until I get into the 90+% range.

 

I don't guess that aeromotive FP regulator clears the fuel rail covers does it? It looks like a real nice piece but I really didn't want to have to hack on my covers any.

 

Nathan, you must slot the beauty cover on the D/S to clear the vacuum/Adj screw on the Aeromotive, I slotted my cover then decided later to take them off anyway as I'm always tinkering with something underneath them anyhow. I prefer a no frill's look anyway. Just sold the covers on Ebay last weekend. You can see in the pic's how the slot looked. Still got a fair price out of em with the slot. :D http://cgi.ebay.com/ebaymotors/ws/eB...872355112&rd=1

 

Maybe this might help some of you. Total specs of the enigne. 383 stroker motor stiff bottom end (forged crank, pistons), flat top pistions with two relif cuts per valve. Cam is a .510/.510 gross lift. Heads are stock and have been ported and polished with rollor rockers. Stock manifold Ported and polished and has been matched to the heads. TB 58MM, 28 LBS injectors. According to DD2000 looking at 500 to 449 HP at 55 to 6000 RPM.
So really we are looking at 430 maybe 440HP. Is this what I can really expect from motor alone?? Also on the N2o question, 300 shot is installed.



[Modified by DarkRose94, 4:53 PM 12/2/2002]

 

I have the Holly FP regulator and it fits perfectly under the covers. Looks good too.

 

Cool... :cheers:

 

For the sake of discussion, pairing the right injector with the right application is worth the investment in time researching the issue.

The 80% duty cycle planning factor (as stated above) is widely used and generally accepted in most applications. It is possible to "oversize" injectors. This can lead to poor performance at low RPM/low power settings. When injector "ON" time is too short, the injector opens and closes more quickly and you can have larger variances in fuel flow. Maybe too much, maybe too little. Short "bursts" (small injector "ON" times) are harder to maintain consistent flow. I'm GUESSING emissions could suffer, some driveability problems, etc. I suspect the closer you are to the WOT-80% rule, you are less likely to experience any lower end problems. If your're setting up a race car, not really important, daily driver, maybe.

Again, good research will usually pay off. Hope you achieve the desired level of performance.

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