which injectors to choose!

Ally Dawood

Member +
What are the best injectors to get for a TD05-16G turbokit,Many have told me 550cc but infact their out of stock where i wanted to buy them ,But i can get sard 650cc injectors..is it ok or is it too much..or maybe i stick with 440cc
 

Texx

Super Moderator
Sard 650cc injectors will be more suitable than trying to push 440cc injectors to their limit, if an injector fails there's a good chance it'll result in piston damage. As a quick guestimate, you'd have to run 440cc injectors @ 90% duty with a base fuel pressure of around 4bar to get enough fuel into the engine to produce 300HP. Under these conditions even a simple low battery voltage issue would be enough to cause a lean AFR and likely break a piston or two.

You'll probably need a standalone ECU to control 650cc injectors successfully, a piggyback ECU (such as the Emanage Ultimate) probably won't be able to trim off enough fuel from the stock ECU injector duty cycle to keep the AFR in check during off boost light engine loads. This would likely result in poor warm start issues, poor fuel consumption and if severe enough premature piston ring and cylinder bore wear.
 

Texx

Super Moderator
440cc injectors would be at their limit at around 250-260hp when maintaining a reasonable duty cycle, the only way to push for more horsepower would be to increase the base fuel pressure. An increase in fuel pressure would then bring the fuel pump into question due to the fact that as fuel pressure increases actual fuel flow tends to decrease, this raises it's own concerns so the obvious answer is to use larger injectors that will flow more fuel at the injector's rated pressure.

For 300hp, 550cc injectors would be the minimum you'd want to install, with a base fuel pressure of 3bar and aiming for a maximum duty cycle of 80% they would be good for approx 320hp. 650cc injectors running the same base pressure and maximum duty cycle would be good for around 380hp, so clearly 650cc injectors would be the better choice as long as you are using an ECU that can control them.

Fuel pressure vs fuel flow from the fuel pump is very very important, thinking you can just crank the fuel pressure up via the fuel pressure regulator to get more fuel into the engine is not as straight forward as it sounds. First of all you need to understand that a fuel injector is designed to run at a specific fuel pressure (the most common is either 2.5bar or 3bar), too high or too low a fuel pressure would have an affect on the nozzle's ability to atomise the fuel. This is why base fuel pressure should be set with the FPR vacuum hose disconnected, the 2.5bar or 3bar injector operating pressure must be set in relation to atmospheric pressure. The FPR will increase fuel pressure at a 1:1 ratio in relation to inlet manifold pressure. If the FPR did not increase fuel pressure in relation to manifold pressure it could result in zero fuel flowing from the injector into the manifold. If for example you set base fuel pressure to 3bar without using a rising rate fuel pressure regulator, and then ran 3bar of boost, the fuel pressure would equal the manifold pressure and so there would be no pressure difference to cause the fuel to flow from the injector. If for example you decided to run 4bar base fuel pressure but this time using a RRFPR, and again ran 3bar of boost, at peak boost fuel pressure would be at 7bar and by this point the fuel pump would be struggling so hard to maintain that pressure it would be flowing very little fuel.

So in summary, always aim to run injectors with a 3bar base fuel pressure (or whatever pressure they are designed to run at) and a maximum duty of 80%, if the injectors your using cannot supply enough fuel for the power you want to achieve then you should be upgrading them and not cranking the fuel pressure up or trying to run them at a higher duty cycle. If you push the fuel pressure too hard your fuel pump will likely fail, if you run too high a duty cycle then either the injectors will burn out or the engine could potentially run lean under certain circumstances. In either case your engine will suffer and piston damage is highly likely.
 
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