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Cheap injector upgrade

Guest KILLER-T

By Guest KILLER-T,
in Engines & Forced Induction

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Sydneykid Grand Master

Sydneykid

Posted
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Hi guys, we have found no difference in the flow of the R34 RB25DET injectors to the R33 RB25DET injectors, they both appear to be 370 cc's. We get around 250 rwkw (400 bhp) on the standard injectors in both before they run out of flow, that's using a GTR fuel pump though.

We use Series V RX7 Turbo injectors in RB20DET's as they are 550 cc's and top feed, high impedance so they work with the standard ECU (or Power FC) without any hassles.

I know that the R33 RB25DET's injectors are side feed, high impedance but I have not yet had to pull a set out of an R34 RB25DET, so can't help there.

RS500 Experienced

RS500

Posted
Posted

INASNT,

given that they flow 370cc/min each at 100% duty cycle, i calculate that they should be good for a total maximum of approx. 440hp or 330kw (flywheel) which would give you your 250rwkw.

Although, of course, i'm not too sure if the OE fuel pump can keep up with the fuel flow needed for this power, but yes, a hi-rise fuel press. reg. would definitely help.

rev210 Grand Master

rev210

Posted
Posted

The fuel pump pumps less volume of fuel the more the pressure is raised. So to squeeze every last drop from the std injectors then you need a very big pump to be sure of decent fuel supply. A bosch 044 would be the go and then you can get quite alot out of the std injectors.

Sydneykid Grand Master

Sydneykid

Posted
Posted

Hi INASNT. you asked "how did u manage to get 250rwkw out of the stock r33 injectors?"

We have done this more than 5 times in R33's and twice in R34's, so it is certainly not a one-off, lucky break. We generally use R33 GTR fuel pumps and Tomei fuel pressure regulators. The exceptions were that one of the R34's had a Tomei fuel pump and no adjustable fuel pressure regulator and one of the R33's had a Bosch 044.

All of them had Power FC's and were tuned for air fuel ratios between 11.5 and 12 to 1. They had a variety of other mods including hi flowed, HKS & Garrett upgrade turbos, camshaft pulleys, camshafts, exhaust manifolds, exhausts (generally with split pulse dump pipes) etc.

When we put an R33 standard fuel injector to the flow test (after ultrasonic bath cleaning) we find that they have flow rates ranging from 380 to 395 cc's. The 370 cc rating has always seemed to be a bit conservative. When we over pressure them (using a higher flow and pressure pump and adjustable fuel pressure regulator) we find an extra 10% flow is typical and sustainable ie; 420 cc's is very common.

The real world experience is backed up by the mathematics, if you take say 6,500 rpm, at 2,476 cc's, over 6 cylinders, with an a/f ratio of 12 to 1 and boost of 1.3 bar, you end up with 313 cc's of fuel being required every minute. If you allow 80% duty cycle ie; leaving 20% for acceleration, start and cold run enrichment, that = 391 cc's which is within the scope of a standard 370 cc injector to provide.

Hope that helps.

PS; that's why we never do the "GTR injector in GTST" mod, the extra capacity with 440 cc's is simply not worth the effort (or cost) when we can easily get 420 cc's out of the standard injectors.

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