superspirit

Well income tax is on the way, going to finish my S10 LT1 blazer project. I have a stock bottom end with fresh crank, bearings and rings, pocket ported stock heads, LT4 hotcam kit, stock throttle body reworked to 52mm, the thinner iron head gaskets, a T 56, and 4.10 gears in a narrowed 8.8, I have 1.5 inch primary D port headers, going into a 2.5 exhaust system with X pipe and magnaflow's. My question is with the above combination in mind, What size injectors should I run. I have been thinking about 30 lb/hr but have come upon a decent deal on some 34 lb/hr injectors, would they be too big? also a possibility of a small shot of nitrous down the road. And yes I know the hotcam springs are not ideal, I will be upgrading those soon. so injector size opinions please.

SS RRR

iTrader: (2)

Stock 24lb injectors can support up to 420hp, if not more. Stock 24lb injectors will work just fine.

355z28

iTrader: (8)

Honestly a stock injector will be fine on that setup. If you change I would go to a 30lb/hr.

I ran stock injectors on a 355 with a hotcam kit and the factory injectors were more then enough. The car went 12.2@112 and the duty cycles were still good.

Mystery Bird

iTrader: (7)

Stock are fine for your level.

SwampWS6

iTrader: (7)

Stock should be fine but I would go 30 just to give yourself a little growing room. Your build specs could change now or sometime in the near future.

93BlackT/A

If you run an injector that is too big lets just say the above member runs a 36lb or 42lb because he may build bigger latter. Is there any side effect to running larger then needed?

SS RRR

iTrader: (2)

There is chatter about running too large of an injector and fuel not atomizing correctly. There really is no need to run a larger injector for that reason. When one is ready to step up, just get them then. If you buy used, then I can understand, but if that is the case then the injectors should be tested to make sure the spray patterns are correct.

Mystery Bird

iTrader: (7)

FWIW I ran 30's in my 381 down to 11.2 @ 118 MPH. The duty cycle would hit high 90's around 6400 RPM's. I switched to 36's and did not go any faster what-so-ever but the duty cycle dropped to high 70's. I have always run the smallest injector I can get away with.

SwampWS6

iTrader: (7)

That is why I only said 30#s. 30+ would be too much for your current setup and essentially would be overkill at that point. Lots of guys including myself ran 30#s with a 383.

Dont get me wrong Im not telling you just to go buy a set just cuz. If you were planning on a large bump in compression or displacement then go for it. But like Mystery bird was saying, on your current setup you wont see a performance increase just because you have larger injectors.

Alex94TAGT

I don't much care to delve into this discussion, but I'll toss out my thoughts since nobody ever dares question the advice of forum regulars.

No, there isn't, aside from cost. I run 65# low-z injectors with an Acceleronics Versafueler, and I know of many LT1 guys who run larger. If this was a problem, we wouldn't do it.

Excessively huge injectors, particularly the older high-impedance variety, can cause tuning difficulties at idle due to physical control limitations involving their minimum pulse-width -- but that's nothing you're going to run into on your application.

Nevertheless, this won't stop the resident "pretend-engineers" here from recommending that you drive a small injector static / near the ragged edge of failure (≤100% DC), thus sacrificing the stability of the control system for a measly +5hp gain (something no electrical engineer would recommend in a million years). Such a recommendation, without also recommending a wideband installed on the vehicle, is unconscionable. Reported duty cycles, by themselves, are not reliable -- and even if an injector doesn't fail outright, it may not be consistently delivering its rated fuel volume over time.

Such individuals will also claim that injector vendors recommend sizing injectors to maintain ≤85% DC only because they have a vested interest in selling you injectors. I'd argue a different point: injector venders could be held liable and sued for damages, unlike some folks on an internet forum handing out potentially bad advice. My guess is these same folks wouldn't pull out their wallets if someone like me were to follow their advice and burn a hole through a piston -- odds are, they'd shamelessly shift blame onto me for following their careless advice instead.

You can bump up the fuel pressure to effectively increase the injector flowrate, which also helps with "atomization" of the fuel, which I'd venture is where any horsepower benefit lies, but you should keep the pressures within reason. I can post some youtube videos of injectors failing at excessively high duty cycles / fuel pressures (>60psi). Newer injector designs are supposedly superior and have mostly eliminated these concerns, though I've not messed with them myself and can't comment further.

93BlackT/A

Well after those video's what brand of injector is the one to buy? Which is the best???

355z28

iTrader: (8)

FWIW Darren (Gump) that runs SS has some of the fastest stock appearing lt1s, They actually step down to 19lb/hr injectors in one of the cars he built because he gained more with a proper sized injector. If anyone remembers the high school race car he helped build the information is in that thread.

96capricemgr

iTrader: (1)

If you read the info from the few guys with fast cars saying stay smallish on the injectors they say the gain in down low, the cars launch harder. Duty cycle is pretty much meaningless. Now granted few folks are individual cylinder tuning LT1s but for most of us if the bank to bank wideband reading is good and the injectors were a matched set it is good enough.

May well be a little different on boost but this poster is talking about a very mild NA setup.

Shownomercy

iTrader: (1)

I wish I went with larger injectors, my rail pressure now means I run out of fuel pump before injector.

96# high Z injectors cost more than my car is worth though. I haz a sad.

Mystery Bird

iTrader: (7)

If I were you I would invest in a wide band, watch your AFR's and compare duty cycles to see if you need larger injectors at your level. I'll bet you don't. The stock injectors if there in good shape do fine job.

Ed Wright

iTrader: (1)

Which one of you guys are pretending to be an engineer? LOL
No engineer here.

I hope the new keyboard expert's versafueler doesn't take a dump like they sometimes do, and leave him walking. smh

An awful lot of the top Stock & Super Stock racers run high duty cycles with zero issues other than running faster. Not like you spend several seconds there. I do know if you hold a Lucus injector wide open too long the windings fail sooner than Bosch. Longer than you will ever see in the car unless you are running a flying mile someplace.

Most people that work with this stuff also know the reported duty cycles seen on scan tools with factory ECUs (GM at least) are inflated. Measure them with a good fast DSO and you find large differences in the scanner and actual measurements. Not many pros go by the scan tools for this.

93M6Formula

I'm glad i read this thread. I probably don't need anymore injector than 24lbs on my 355 i'm building.

superspirit

Thanks to all who have replied, I believe the stock 24 lb/hr's will work fine, so going to leave those alone. now to find a mail order tuner as there are no LT1 tuners within 500 miles of here, I have done several searches on here and the general consensus seems to be madtuner, and his price isnt bad either. but would really like more input than I have been able to find. I have downloaded tunerpro rt, but dont have an aldl cable yet so havent been able to play and learn anything yet, I have never done anything more than reflashing a PCM with update from gm through their service programming system,so I have absolutely NO tuning experience.

ahritchie

iTrader: (1)

I'm just gonna through this out there...how come GM engineers saw it fit to put 28# injectors on the 330HP LT4 over 24# 300HP LT1 injectors? Discuss.

I found this on the Grand sport registry:

The engine's higher rpm also exceeded the LT1's fuel injector's ability to keep up, so the LT4 got larger fuel injectors rated at 3.5 grams per second (28lbs/hr), replacing the 3.0 gram (24lbs/hr) injectors of the LT1. The larger injectors were designed to keep pace with the better breathing, higher revving engine.

93M6Formula

But at what fuel pressure? Injector lbs/hr is also dependant on fuel pressure.