What size injectors should I use?

[The Stickman]

Ok here is a question for you all with little to go on. I have a 350 Oldsmobile small block. It has a cam in it but have no idea of the specs. I bought the engine used. I will be using an Edelbrock Performer RPM high rise intake. I have a 4 barrle style TB. I will be going with a MegaSquirt for the computer. I need the injectors before I can send the intake off to be done as the guy needs them for the mock up. My room mate has a set of 19's but I think that will be way to small. Any ideas?

[GetMore]

Most likely those injectors are the same dimensions as the "larger" injectors you want. You should be able to send them out for the mock up.

[gkring]

roughly, double the injector size in pounds for horsepower per cylinder. That assumes 100% duty cycle, so do not cut it close. 19 pounders would be 19 X 2 X 8= 304 horsepower. Not even close. 30 or 40 pounders would be much more common. Pick any old injector off a 5.0 mustang or TPI camaro to mock everything up with. Your friends 19's are probably old mustang injectors and would make perfect mockup injectors.

[68Formula]

If it's a mild engine and you're not spinning it past 6k, it should be ok. If those are old Mustang injectors, the 19lbhr rating would be at only 39psi. If you want more flow you can run them up to 60psi (which is a typical pressure used today), and they can handle it. It will also help to improve atomization. Going from 39psi to 60psi would increase the flow to 24lb/hr.

BTW, what your vacuum readings at idle today? EFI systems usually don't like lumpy camshafts because of map fluctuation at idle. Typically a minimum of 112° lobe seperation is needed even with a mild camshaft (114° is better).

[BigBlockOlds]

I agree with the above. the stock injectors out of my bother's '02 Mustang fit just the same as the 42lb/hr injectors I finally bought later on. You shouldn't need the exact injectors your going to use to mock it up. Although you will want to stick with the same style injector body. For example, I don't think the injectors from an LS1 have the same dimensions as the Mustang injectors.

[Rhino]

Something to keep in mind is the pressure the injector was rated at. As an example... Ford typically uses 3 bar for their fuel pressure. The Gen III/ IV GM motors use 4 bar. You can use the SVO 30# (3 bar) injectors on an LS1. Effectively they flow the same as a 36# injector rated at 4 bar.

[68Formula]

Something to keep in mind is the pressure the injector was rated at. As an example... Ford typically uses 3 bar for their fuel pressure.

Until recently, they used 2.7bar over the past couple decades. The LS engines use 4bar as stated.

[MonzaRacer]

Megasquirt will adjust to anything lumpy wise nearly. VERY adjustable as you can set idle base where you want.

[86Cutlass383SR]

Some of the guys on ThirdGen.org are running cams on the street with 240* - 250* @ .050" lift on a 108 LSA on TPI based systems and GM ecm's. Granted you better know how to tune that beast but it *can* be done. The 220* cams on 114* LSA are for the guys who don't want to mess with tuning issues.

[RSX302]

Ok here is a question for you all with little to go on. I have a 350 Oldsmobile small block. It has a cam in it but have no idea of the specs. I bought the engine used. I will be using an Edelbrock Performer RPM high rise intake. I have a 4 barrle style TB. I will be going with a MegaSquirt for the computer. I need the injectors before I can send the intake off to be done as the guy needs them for the mock up. My room mate has a set of 19's but I think that will be way to small. Any ideas?

Injector sizing calc

INJ SIZE / BSFC X #CYL X % DUTY CYCLE = HP

.45 BSFC = Normaly Asp
.5-.6 BSFC = Supercharged/Turbo

19 / .45 X 8 X .9 = 304hp

Make sure you keep an eye on your Injector Duty Cycle. You don't want to run over 90%. Preferred around 80%.

[killer67]

I would use 42 lb