Turbo6

I have a solid roller 383 almost completed with all the nice parts including competition ported AFR 220's, callies, oliver, etc. I'm having some difficulty in determining the injector sizing for the motor. The estimated power should be around 500rwhp and it is set up for a large hit of nitrous (wet), 4-bolt block main studs, ARP headstuds, etc.

In deciding on injectors I'm getting conflicting views. Some are saying that 36# injectors would be sufficient. I'm thinking I need 42# injectors to keep the duty cycle lower. I believe Racetronix recommends a duty cycle no higher than around 80% if possible. Any thoughts or experiences from guys that have built naturally aspirated setups like this before? I have a fully ported/worked over LT4 intake I am using currently with the buildup but will likely convert to a nice single plane setup w/ EFI in the near future. Any thoughts/opinions?

got_hp?

the fuel system is such an important aspect of the engine, why skimp on injectors that are just barely adequate?

according to the calculators ive seen, 42lb injectors at 85% duty cycle will support in the neighborhood of 600 crank hp or 500 rwhp.

if you plan to make more than that in the future, might as well step up now and get 50lb'ers so you wont have to upgrade later.

FASTFATBOY

You need 42's or 50's, a 340 gss pump and some sort of pump voltage booster just for the engine. Depending on how much spray you use, I personally would sump my tank and have a dedicated low pressure system for my nitrous, and have a regular ol carb type system on it.

BTW it takes more than 600 flywheel hp to make 500 at the tire.


David

got_hp?

that would depend on transmission, tires, gearing.

600 - 15% drivetrain loss is 510 isnt it?

FASTFATBOY

People use that 15-20% rule like head flow numbers, it is not gospel. There are a huge number of factors that most people do not think about on the dyno.

Rear gear ratio

Tire and wheel combo

pinion angle

Type of rear end, 12 bolt/9 inch

Torque converter

Type of transmission, glide, turbo 350/400, 4L60


Besides it is pretty hard to make 600 or better at the flywheel with the stock intake, only a handfull have.


David

kmook

Check out http://www.rceng.com/technical.htm and input your data get get the correct injector size you need.

And as got_hp said Why skimp? Give yourself a buffer and go with the bigger injectors.

Also this should be discussed in a engine tech forum, transfering.

Injuneer

Just as a reference point, drive train loss with my Street Twin, T56, 3" chrome moly DS, 3.73 Strange 12-bolt and street tires was 12.3% with 635HP at the flywheel and 557rwHP. That's based on running the engine on an engine dyno with full intake and exhaust, then putting the engine in the car and doing a chassis pull. With a TH400, very loose convertor and slicks, the rwHP dropped to 507rwHP, showing a 20.2% loss.

Injector size is critical - why risk going undersize? There is no downside to going "large".... as long as the injectors will respond to the low pulse width required for idle. You can "black box" the stock PCM to handle low impedance injectors, for faster response times and lower pulse width limits. Consider the Lucas or Delphi/Lucas disc type injectors for faster response times.

My calc says you need more than 42's, or you need to run the fuel system at close to 50psi with 42's.

Just as a point of reference, my engine only makes 500flywheelHP running NA, but has a 300-HP dry nitrous system, and I'm running the equivalent of a 74# injector (64# at 58psi). Duty cycle, with the thirsty 0.52 BSFC required with nitrous is still only 70%.

Racetronix

Please consider these injectors here:
http://www.racetronix.com/3172FM.html

They are hi-z so you do not require ECM / PCM driver modifications.

FASTFATBOY

You made 507/557 WITH a 300 horse shot of hose Something not added up there
Or did I read it wrong?


David

Turbo6

Concerning the location of this thread. I didn't put it in LT1 tech as the only LT1 part on it is the block.....that and the fact that I didn't want 18y.o. kids with a catback regurgitating information that they read or heard somewhere. I was hoping to get the opinion of those smarter than me and figured that this engine was "advanced" enough to warrant being in this forum considering I'll be making more power than most...

Anyway, I digress.

To Racetronix,
You recommend the 57# injectors. To me that seems like way more injector than I would need. They would only be running around 50 or 60% duty cycle, right? I wanted to stay as small as possible so that driveability and tuning would be easier. In the past I raced turbo buicks and I'm basing my thoughts on my experience with them where you made sure you had enough fuel, but if you could do the job w/ 72# injectors, you wouldn't run 96#'ers because as they got larger, they weren't as precise and a little more tricky to tune. Any thoughts?

Racetronix

57's are very manageable. Buick owners use them in small 231CID motors w/o problems on old school ECMs. We sell 1000's per year to V8 owners.
Remember time to inject narrows as RPM increases. You must factor in max motor RPM, FWHP, BSFC etc.
50's would probably be better but many people have trouble tuning them on LT1 and LS1 factory PCM's so we recommend the Siemens over the Delphi 50's.

Turbo6

Thanks for the quick reply.

I agree w/ you on the MSD 50's. I ran them in my buick for a while and didn't like them at all. Went through ton of chips working with Joe Lubrant at Precision turbo and couldn't ever get things just right.

So, in your experience, the 57# injectors have a very nice flow curve and are more tuneable than the 50's, even at low RPM's for driving around on the street?

Racetronix

Siemens are great. I use 57's in my car and it runs smoother than it did with the factory injectors. You will find Siemens Deka 1 injectors in more performance applications than any other high performance injector. Don't forget Bendix designed the injector for G.M. Buick Motorsports years ago before Siemens bought them out.

Injuneer

You mixed apples and oranges.

My system sprays 300HP in 2 stages. I gave him the drivetrain losses for a single 125HP stage case that happened to match the levels of HP he was talking about. Point I was trying to make is that at the losses in a T56 are not all that great at 500-600HP.... only 12.3%, but losses could range to 20+ percent for a loose automatic. Just trying to help him understand what flywheel levels he needed to make to put down 500rwHP, since he didn't tell us what tranny he was running it through, and people were suggesting a variety of numbers.

My other numbers:

With the T56 I was only spraying 275.... 765flywheelHP/673rwHP 12.1% loss.

With the TH400, spraying 300..... 803 flywheelHP/632rwHP 21.3% loss.

Racetronix

[QUOTE=Injuneer]...but losses could range to 20+ percent for a loose automatic...QUOTE]

Ahh yes but what about the TQ #'s?