whats the point..that will be the green eyed monster and subaru snobbines showing its face...this is a superb achievment for any car as most imprezas cant achieve this and those that do normally blow up..i wish i had the cash and ***** to mod a car up to these speeds

 

overboost

Why are you trying to switch to 1000 cc injectors if you are only planning on 500 + HP??? Do you have an adjustable fuel pressure regulator at all? 550 cc injectors are more than enough for that kind of power providing there's enough pressure in the fuel rail. Fuel pump upgrades is a good idea, especially if you do try to up fuel pressure in the rail. It seems like alot of money for a solution that usually can be solved for just £100.

 

500+ BHP on 550cc injectors? Are you sure? I'd say they need to be bigger than that...

 

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"500+ BHP on 550cc injectors? Are you sure? I'd say they need to be bigger than that..."
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Yes, I'm sure. Plenty of 500 BHP + cars use 550 CC. (Modern F-Bodies & BPU Supras). Some MK3 Supras use stock 440 cc and they are pushing 400 + at the wheels. The 550 cc rating is attained from 42 PSi fuel pressure. Stock fuel pressure regulators only go so far, especially when turbos simply add pressure inside the intake & throttle body. So you need even more fuel pressure to supply enough fuel.

Bigger injectors work, and they can give you more fuel without raising pressure. But the cost to supply extra fuel through that option is much more expensive.

 

550ccs on a Supra at 400BHP is fine, as the Supe has six cylinders, at the last count, Sunny's fiesta only had 4 - or do you know something I don't?

 

Number of cylinders don't really matter. 550 cc injectors with 30 Psi *above* manifold pressure is enough for 500+ HP. This is why you need an adjustable fuel pressure regulator to up the fuel pressure - especially on turbocharged cars. Usually stock fuel pumps just are not up to the job of supplying enough fuel on high pressure rails, so that's something to take into consideration also.

 

Hmm, no. of cylinders does matter, as 6 x 550cc injectors obviously supply 50% more fuel than 4 x 550cc injectors at the same pressure ratio and duty cycle. I'd say you'd need at least 2 and probably 3 times the fuel pump capacity of the original pump minimum! Most cars in my experience uses a 1:1 FPR as standard to maintain baseline fuel pressure across the injectors on boost. aftermarket FPRs can have a higher ratio to increase the fuel pressure more than the boost pressure, but I still don't think 550cc injectors are good for much over 400BHP...

 

I managed an 'indicated' 350-360 hp with 440's at 98.7% and stock pressure. Extending the logic (but ignoring volumetric efficiency ) suggests 550's are good for ~440 hp.

I havn't done the maths myself, but apparently adding 1 bar to fuel pressure of 3 bar will give around 15% extra flow.

I reckon I could maybe just squeeze 500 hp out of 550's. But 850's would be a better/safer bet!

Richard

 

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"Hmm, no. of cylinders does matter, as 6 x 550cc injectors obviously supply 50% more fuel than 4 x 550cc injectors at the same pressure ratio and duty cycle. I'd say you'd need at least 2 and probably 3 times the fuel pump capacity of the original pump minimum! Most cars in my experience uses a 1:1 FPR as standard to maintain baseline fuel pressure across the injectors on boost. aftermarket FPRs can have a higher ratio to increase the fuel pressure more than the boost pressure, but I still don't think 550cc injectors are good for much over 400BHP..."
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Yeah, you're right about the cylinder number. But then 1000 cc injectors (which what overboost proposed) is a bit of overkill for 500HP, even in a 4 cyl engine.

 

Hello Cosworth427,

I am currently using 750cc injectors and injector duty is exceeding where my tuner wants it to be. Different engines require different quantities of fuel to produce horse power.

You say "550 cc injectors are more than enough for that kind of power providing there's enough pressure in the fuel rail"

- Have you put a zetec turbo engine on the dyno to back this statement up?

You say "Bigger injectors work, and they can give you more fuel without raising pressure. But the cost to supply extra fuel through that option is much more expensive."

- Yes but higher fuel pressure puts the pump under more stress. Everything in my car has been designed for reliability aswell as power. Therefore if the extra cost means extra reliability then that’s the reason why I take such routes.

Also you say "Yeah, you're right about the cylinder number. But then 1000 cc injectors (which what overboost proposed) is a bit of overkill for 500HP, even in a 4 cyl engine."

- If injector duty is getting out of what my tuner thinks is out of our safety margin using 750cc injectors then I don't see how 1000cc's are a bit of an overkill?

Also note that in addition to bigger turbo and larger injectors other elements in the fuel system will be changed to accommodate.

Thanks - Sunny.

 

"I am currently using 750cc injectors and injector duty is exceeding where my tuner wants it to be."

You're confusing injector duty cycle with rated capacity. 550 cc, 750 cc, 440 cc, or whatever are rated at 43.5 PSi @ 80% duty cycle. I don't know why your injectors are having problems with duty. Being that you don't want them reaching 100% duty to get the power you are getting. Do you have any idea of the fuel pressure in the fuel rail at the latest? And what about the flow rate of your fuel pump(s)?

"Different engines require different quantities of fuel to produce horse power."


Wrong. Your fiesta wouldn't/shouldn't need any more fuel than a Supra, Scooby or Camaro to get say, 500 horsepower - unless there is something seriously wrong with your fuel supply or just running too rich.


"- Have you put a zetec turbo engine on the dyno to back this statement up?"

Have YOU put up a dyno to say it cannot be done with smaller injectors than say 1000 cc? And yes, I was mistaken with the assumption that 550 cc injectors were enough, when I didnt take into account that you only have a maximum of 4 injectors vs my experience with 6 .

"- If injector duty is getting out of what my tuner thinks is out of our safety margin using 750cc injectors then I don't see how 1000cc's are a bit of an overkill?"

Perhaps you're right though. Your boost levels will be seriously high, and I have no idea how powerful the fuel pumps you are using if you had to increase fuel pressure at the rail. With my car, and several others, aftermarket fuel pumps give us excellent flow rates at higher pressures, and at a fraction of the price of larger injectors. Upgrading fuel supply via larger injectors for me have always been the more expensive option.

Anyway, good luck with the upgrades.