Thirim

I'm finding conflicting calculators online when selecting what size injector I need.

LT1, 383
CC503
1.6:1 RR
1-5/8 (or perhaps 1-3/4) headers, likely shorties
supposedly LE ported intake
58mm TB
Trickflow GenX185 assembled heads

My guesstimates are in the 480HP mark .. I'm using 450 and 500 as my calculation numbers.
Using 43.5psi, .50 lbs/hr/hp max 80% duty
I get anything from 35lbs/hr to 42lbs/hr (rounding up) for inj size.

First time messing with injectors so I'm not sure how the fuel pressure and duty cycle play in. I mean I know what it is and why it's a factor but how much can you bump up the pressure and how close to the 80% do you want to be (or over) ??
stock fuel lines with addition of braided pressure to 6an thread on rail. High flow pump in tank and adj FP reg.

Thanks

Thirim

Also like to add, I know it's easy to say go bigger, but I'm concerned about the control. Having the injector stay open too long is just as bad as having it open too quickly. I don't have a good grip on the safe limits on either side I guess.

..Megasquirt PCM btw

Injuneer

Rule of thumb (mine) - NA engine, multiply flywheel HP by 0.070 to get the minimum recommended injector size. e.g. - 500HP X 0.070 = 35 #/HR. That represents a more realistic 0.476 #/HR/HP brake specific fuel consumption, and an 85% duty cycle.

As you mentioned, going too large may present problems. But the factory PCM can satisfactorily produce the required short pulse widths required for idle, with 42 #/HR injectors. Not sure how well the Megasquirt copes.

Injector flow rating is a function of pressure. Flow increases with the square root of the ratio ( Pnew / Prated ). If you run Ford, SVO, etc. injectors, they are usually flow rated at 2.7 bar (39.15psi). When they are operated at the LT1's stock 3 bar (43.5psi) they flow 5.4% more than rated.

Thirim

Good info!

Since 500HP is likely the higher end of this build and likely a little too high, I'd be fine with 36# inj. But 42# wouldn't hurt.

..Now to find some injectors lol

Injuneer

I would agree that you aren't looking at 500HP at the flywheel. It's a fairly mild build. 36's should be fine.

Just curious... what in your build requires the Megasquirt controller?

Thirim

I had the Megasquirt from when my friend bought and installed one a few years ago. I wasn't sure if the 383 could be tuned with a stock ECM.. I know without building and installing a Megasquirt into my current stock LT1 I wouldn't have had a clue and there is no one around here to lean on for ECM tuning.
I learned/am learning a lot.
.. I also kinda sealed the deal when I ditched the voltage side of the Opti in lieu of LS2 coils ...forgot to add that to the list of goodies .. Megasquirt 3x runs them directly, no need for LTCC or Efi Connections's kit. Although I did buy their sweet brackets for the coils, and their OE replacement coils. The Opti gives the Low/Hi Res signals to the Megasquirt for timing

Injuneer

The stock PCM will have no problems with the mods you have listed. You can get a basic mail-order tune that will get you to the 90% point. Then use tuning software to optimize it.

Whether you could justify the cost of the LTCC in lieu of the Megasquirt is unknown. But Bob Bailey's stuff is very good. I'm all for the 8 LS1 coils using an aftermarket ECU, and run a MoTeC M48Pro and their 8-channel IEX driver to accomplish that, using only the Opti cam position signals. But this is for a setup running a two stage 300-shot of nitrous, a dry system w/ 78#/HR low impedance injectors running at 4 bar (58psi). The ECU can move through individual tuning for each mode of operation from normally aspirated through two stages of nitrous. I used a different approach for the coil mounting:

https://www.camaroz28.com/forums/mem...coils-6225.jpg

https://www.camaroz28.com/forums/mem...-bank-6226.jpg

Based on my past experience, I would strongly recommend you stay away from 1-5/8" shorties. I had a set of 1-5/8" JBA's, and they choked a basically stock LT1 with minor bolt-ons. Good bottom end, but no top end. And, based on engine dyno testing, the guys that built my engine were able to show me that at 496 flywheel HP, I did not need a 58mm throttle body. A 52mm would have sufficed.

I'd mention the software you would need, but you haven't provided the specifics of your vehicle - year in particular. And we don't know "where "around here" is.

https://www.camaroz28.com/forums/lt1...nature-879835/

Thirim

I like the alternate mounting of the coils! .. I'm in the learning mode with the aftermarket ECM, the Megasquirt was laying around for a couple years so it was already paid for lol.
I think it will do everything you'd be asking it to do as well. It's very flexible.
I did read that a 58mm TB was not needed, but it was used and a deal that I gobbled up before I realized that. I'm not out anything if I need to step down.
As for a signature, I guess I never got around to it.. I'll get at it lol.. But it's a 1989 TA, currently mostly stock LT1 minus smog, T56
.. and I'm in Nova Scotia, Canada.. not many speed shops around, the ones that are mostly specialize in carb'd motors. I'm aiming for a very streetable car. Never been to the track but that's not saying I won't ever be there

Injuneer

No problem with the 58mm TB.... I still run mine. The guys in the shop still laugh when they see it. A buddy of mine had a 58mm too, but his 383ci LT1 (30th Anniversary convertible) was making 1,125HP with 20+ # of boost.

I'm impressed with what I read about the Megasquirt..... seems very capable. The MoTeC I have was not cheap, but I got it for about 1/2 original price from a guy whose car was totalled. It's a neat package, very compact, and extremely flexible, with built-in data logging.



I have it tucked behind the stock PCM, out of sight. I kept the stock PCM for the speedometer and for the idle air controls. The MoTeC could not handle the LT1's "stepper motor" IAC, only pulse width modulated. I also tried to keep all the emissions systems functional, at least for a while.

Thirim

certainly a more professional package.
The MS3x will do the Speedo and the IAC .. you have a selection of outputs and within reason you can have them do whatever you want. Some are higher current, some lower.. The harness has the most popular ones labeled. So I didn't have to add wires to the harness, I use N2O output 1&2 for my fans.
If you're knacky at the electrical stuff (you must be if you're into this stuff lol) then I'd invest in a MS3x the next time you're forced to buy an ECM. You can save about $200 also if you want to try to build the thing from parts (that's what I did, it's basically paint by number)

97WS6SCharged

I ran the older MS3.0 in my 355 S10. Was a bit of a pain to get it up and running but once you figure it out it's really nice for tuning. Real time modifications are awesome.

Also, FWIW, going a little larger on the injectors won't hurt as long as you use a good quality set. I'm running 96 lb/hr injectors in my 408 and you would never know it unless you saw the scanner at wot where they hit about 35% DC.