Anyone know if the new 79's from Racetronix are the same in design as the Siemens or like the stock injector internally? Reason i'm wondering is because i'd like to know if there at risk of locking up at high fuel pressure like the stock units. I run a dry NOS N2O kit with my setup and cant risk a lock up. I'm currently running the Siemens 60's. I compared the 2 on racetronix site but couldn't really tell one way or the other. I'm guessing there the safe version of injector. Thanks.

Ken R.

 

Hey Roguedriver, a little off topic, but do you work at Yearwood?

Just wonderin'

Eric

 

Don't work at Yearwood. Place is pretty darn nice though now that they remodled. They actually carry a lot of stuff now too. How's your car running on the MAF? I read your looking to go SD but curious how your MAF tune turned out and how the turbo setup is running.

Ken R.

 

The Racetronix site indicates they are a "disc" style injector, possibly similar to the Lucas design. Why not just ask the folks at Racetronix?

Stock Rochester injectors are "ball and seat".

Both of those injector types are generally not happy with very high pressure. The "pintle" style seems to work best with high pressures. But again, those are very "general" comments. Racetronix should be able to give you a specific answer. With the NOS dry kit, fuel pressure is typically raised to 85-90psi. Is that what you are running? Wouldn't seem you would have to go that high, if you are already running a 79 #/HR injector.

 

I'm running the 60's right now at 14psi on a boost referenced regulator. Just finished my fuel line upgrade (moved the fuel press sender to the feed side and all is well now by the way) as well. Going to see how it runs on the dyno first and spray it as well (5176 kit). My pressure runs high, but never seen it in the 90 range, even on the 150hp setup. Curious to see where it runs now and where my duty cycle is at. 79's are just a though in case i'm pushing the duty cycle too much.

Ken R.

 

On the 5176 kit, the blue pressure regulator supplies enough nitrous to the fuel pressure regulator to push the pressure to 85-90psi, depending on the jet in the "tee" for the vacuum line. If the jet is large enough, or you have no jet in the fitting, allowing the nitrous to bypass into the intake manifold via the vacuum line, you aren't going to see high pressures. Thats the way to "tune" the 5176 kit, but its so crude, I wouldn't rely on it for a setup like yours. Its fine for a stockish engine, where you just run it a bit rich and play it safe.

 

Suggestions other wise? Wet kit, or homemade dry kit? I've still been pretty successful on tuning it and can get it pretty rich on the nitrous, but i am down to i believe like a 34 jet in the tee where as i ran a 59 before the charger, then down to a 44 or 47 when i put the smaller S Trim on. When i put the T Trim on, i went down to the 34 and was seeing A/F's around the 11.5:1 range. Cant remember what my fuel pressure was at that point, but if i remember right, it was around the 75ish range on 14psi. That was with the stock fuel lines and the Aeromotive LT1 regulator and the 60# injectors. Wasn't too worried about the duty cycle before, but am curious to figure it out now. Doesn't upping the fuel pressure also up the duty cycle of the injectors or am i incorrect in saying that? I know i'm safe now from an A/F perspective. I actually had to pull fuel back out of my tune after upgrading the lines in the area where i was trying to add it to compensate before the upgrade. Just looking to make the setup a little safer from a fuel perspective. Thanks for the input also.

Ken R.

 

No. Increasing the pressure increases the injector's flow rating. Since the PCM knows the flow rate has increased, it calculates shorter pulse widths. Since duty cycle is defined as injector pulse width divided by the time it takes for the crank to make two revolutions, shortening the pulse width reduced the duty cycle. You want the DC as low as you can get it, and preferably under 80%.

I run at 58psi, producing a 78 #/HR rating on the Bosch injectors, and duty cycle is at or below 70% with a dry 300-shot (800 total at the flywheel).

 

Thanks for the info Fred. Think i'll calculate the DC next time i scan it and see where i'm at.

Ken R.

 

Multiply pulse width (in mSec) X RPM, then divide by 120,000

 

I'm seeing about 83% max. PW is 16 left and right at 6200rpm. That sound right? I did (16 x 6200)/120,000 = .826

Ken R.