I've about got my forged lt1 finished. It's a 383 with heavily ported stock castings w/new seats, 2.02/1.6 valves, a 292 xfi cam & 12.5-1 static comp. ratio. I don't want to cut any corners on this motor. I want a quality set of fuel injectors. I figure 30-36 pound injectors will be sufficient. I am considering purchasing matched injectors. Is this necessary & would i notice a difference over a standard set? I will be constantly altering the tune with lt1 edit. I was thinking maybe f.a.s.t., r.c. or racetronix brands. Any comments and/or part numbers would be very helpful. Thanks - NICK

 

If you plan on increasing the hp you should go with 42's in my opinion. Bigger than you need allows room to grow and will not hurt your performance. How many horses are you putting out right now?

 

36's are OK up to ~500 flywheel HP. 30's won't cut it on that engine. If you expect to make more than 500HP, step up to the 42's. Buying a flow matched set makes good sense.

 

I think you're going to need 42's. Check out www.rceng.com for a great calculator or injector sizing.

 

The RC Engineering, and most other calculators tend to be on the "conservative" side. The suggested BSFC (0.050 #/HR/HP) and duty cycle (80%) are chosen to avoid problems with any possible setup. A well-tuned normally aspirated "performance" engine should be able to achieve a much more efficient BSFC. And, not all injectors exhibit the same deterioration of performance as duty cycle exceeds 80%.

Yes, use the online calculators to get in the ball park. But don't hold them as absolute requirements. I've tended to lean toward the less conservative side. If you assume a BSFC of 0.476 and an 85% DC, you come up with a simplification of the formula (at least for 8-cyl engines) of Injector size = flywheel HP X 0.07

 

Fred,

I'll agree w/ you that they are conservative. However, I did a break in on my 383 on the engine dyno and w/ the VE & BSFC that was calculated my builder told me 42lbm/hr injectors. I had already calculated it via rceng.com and came up w/ the same result. Now, I never completed the project so I don't know how well the car ran w/ 42s. I know you've gone through more extensive builds and been around many more radical machines, but that's my experience.

Later,


Steve.

 

I was under the impression that a larger set of injectors are harder to tune for a descent idle, that is why i was leaning toward the small side. Is this true? If not, i would consider some 42's. Injuneer, what brand & size would you choose if you were in my position? I have no idea how much it will put down at the flywheel, I hope at least 500, but I dont want to over estimate like quite a few people I see & talk to. Thanks.

 

The problem with too large an injector is whether the combination of injector size, injector type and PCM drivers can be turned down to the small pulse widths required for idle. Numerous people have reported that they have had no problem with idle, with the 42#/HR injectors on the stock PCM. I never ran 42's on a stock PCM, so I have to rely on what others have said.

I would go with the 42's. Look at the brands sold by Racetronix to start. Whatever brand you buy, make sure they are from the manufacturer, not some relabeled stuff like the Accels. Go with Bosch, Lucas, Delphi, Siemans.... FAST is supposed to have some interesting new injectors, but I haven't heard too much about them, or who makes them.

 

Ebay has Lucas 42's for $300. I have looked a lot and that is the best price unless you go with Accel and they have a bad reputation on this site. One auction is make and offer so you could get them for less.

 

Flowmatched injectors are definitely not a bad idea as long as you don't mind spending the extra $40 , well worth it in my opinion . This way at least you know for sure what you are getting , I have seen some injectors flow so much off , that I can't even use them to make a matched set because I will probably need to flow another 500 injectors to find 7 more alike , another option that people like to use is standard new injectors in "Flowtested" sets where applications have rich/lean cylinders and they would like to have the ability to place slightly rich/lean injectors there for more accurate afr's in each cylinder .

Mike