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why would the idle fuel be highest? The relative pressure at the injector nozzel should be constant, i.e. if you have 3bar of fuel pressure in the rail and then boost the intlet pressure to 1bar this pressure closes the regulator to increse the pressure to 4 bar in the rail - thus 4 bar pushing fuel out and 1bar pushing fuel back into the injectors relates to 3bar actual. At idle = no boost therefore the rail pressure sould be the base amount 2.5bar or what ever it is. Could be worong havent really looked at the 20vt set up. But otherwise what you say is right about pre-compressor pressure - I wonder how hot this air is going to the regulator though?

Rich

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Vacuum feed dear Rich Instead of the fuel pressure being 2.6bar (or how ever much vacuum feed is given to the FPR) on idle it now will be 3bar due to the loss of vacuum feed. Hence why the EVOcars chip asks you to set your fuel pressure at idle of 3bar with the vacuum feed disconnected

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Begbie, you mean run the 3 bar FPR I guess by the quote above?

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I was refering to the way the EVOcars chip is setup for the integrales i.e. they have an adjustable FPR and so do i

David, i dont see how the vacuum feed to the dump valve can be blowing air, unless your using a supercharger and forgotten to tell us all I dont think its possible, because the engine generates a vacuum on idle and this is how the dump valve works, uses vacuum to pull it open after coming off boost

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Those with large FMIC will have defo have more pressure drop.

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Furthermore, when air is cooled, the pressure drops, no matter what so literally, it's impossible to have an ultra high efficiency intercooler with less than stock pressure drop. So, can a larger intercooler that cools better give a lesser pressure drop? Impossible

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Its not as simple as that David.

Pressure drop is proportional to air velocity, v2/2g as described by Bernoulli.

The less restrictive the intercooler is, the less pressure drop there is. There obviously is an effect of lowered air pressure from cooling but it will be outweighed by kinematic losses from air movement.

In short pressure drop is dependent on the diameter, frictional characteristic and length of the pipework from turbo to inlet manifold including the internal routes through the intercooler, regardless of whether the intercooler itself is small or large.

If you have a large intercooler with large diameter air routes it will create far less of pressure drop than a small intercooler with small diameter restrictive routes.

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If you have a large intercooler with large diameter air routes it will create far less of pressure drop than a small intercooler with small diameter restrictive routes.

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sorry for jumping in, but surely cosmo the situation you describe is a non-too efficient one. Large diametre air routes mean less air to alloy contact area to dissipate heat, right?
So I suppose it's a matter of finding the fine balance between tubing characteristics, fins, shapes, etc that don't restrict airflow too much, but let the air cool down enough.
I was rather surprised reading one very elaborate web page someone posted here on intercooling that the suggested size for an intercooler is _TOO_SMALL_ for what ppl seem to be sticking in front of their radiators
[If I remember correctly, it was suggesting about quarter size of the ProAlloy for a 300+BHP machine, of course I may have fcuked up my maths, these sqin always confuse me...]

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Another note on the over fuelling issue. I've test the injector flow on the ASNU flow bench, guess what, at 3 bar and 80% duty cycle, it converts to a flow rate of 340cc/min, and at near 100% duty cycle, it's already way over 440cc/min....so that's why many of us can run such high BHP with the stock injectors. Most injectors are rated at 80% duty cycle + whatever working pressure.

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Just did a search on Google and this thread came up I am intrigued to see that you have flow tested the standard injectors and found them to be capable of 440cc at 100% duty! While nobody would want to run them that high it does explain why we are able to achieve such high output especially given that most of us are maxxing out the injectors. If you combine this with a higher fuel rail pressure then this will of course enable even greater flow. Would it be fair to say that at 90% duty and with a 3.8bar regulator you would be able to flow in the region of 400-420cc? Perhaps you could answer this David as you have tested them?

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Another note on the over fuelling issue. I've test the injector flow on the ASNU flow bench, guess what, at 3 bar and 80% duty cycle, it converts to a flow rate of 340cc/min, and at near 100% duty cycle, it's already way over 440cc/min....so that's why many of us can run such high BHP with the stock injectors. Most injectors are rated at 80% duty cycle + whatever working pressure.

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Just did a search on Google and this thread came up I am intrigued to see that you have flow tested the standard injectors and found them to be capable of 440cc at 100% duty! While nobody would want to run them that high it does explain why we are able to achieve such high output especially given that most of us are maxxing out the injectors. If you combine this with a higher fuel rail pressure then this will of course enable even greater flow. Would it be fair to say that at 90% duty and with a 3.8bar regulator you would be able to flow in the region of 400-420cc? Perhaps you could answer this David as you have tested them?

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Hi Flea,

I've flow tested them on the ASNU flow bench. It's intriguing to find out that most injectors flow a lot less than what is being perceived. However, in the case of our injectors, they're more I've tested the duty cycle from my 20VT by tapping into the ecu's injector using a DMM(digital multimeter), the duty cycle at WOT is around 99%(though theoretically impossible). I've also flow tested the OE injectors at 4 bars of fuel pressure and guess what? The flow increased by 10%!!! However, there is a downside to this, as the pressure goes beyond the recommended level, the flow of the injectors became less uniform (when compared with the rest under 3 bars, off by 2~3%), so I can say that as you increase the pressure beyond the recommended value, the linearity of the injector flow goes out of line a bit, so there's always the possibility that you've increased the flow by upping the pressure, however, you might have created a scenario where all the injectors are working less coherently, so you overall AFR (one O2 sensor reading the average of all 5 banks) could be in the 11~12, however, there could be 1 or 2 cylinders running really lean!!

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And remember flea, that we have rising rate regulators, so that at 1.5 bar boost pressure, the injector is also running with a fuel rail pressure of 4.5 bar not 3 bar, so this may account for even more!


Maybe Nigel, might want to give it a go with 20vt injectors after all?

Joe

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Hi Doc,

You're right in saying the the relative pressure difference is maintained between the injectors end and the plenum, however, even though the injectors are being regulated to work at 4.5 bar when the boost is 1.5 bar, there is the cancelling effect of the 1.5 bar in the plenum working against the injector, hence the constant pressure difference of 3 bar, so the flow of the injectors can not be said to be that produced at 4.5 bar, instead, it's still 3 bar. As it will be very difficult to test the flow of the injectors with these parameters (4.5 bar fuel pressure working against 1.5 bar of plenum pressure) I can only assume that the flow of the injector is not affected by plenum pressure as it is maintained to work with a constant pressure difference.

Only when you upgrade to a 3.5 manifold referenced fuel pressure regulator, will you get a truly higher working pressure