Fuel And Air For 700hp?

[c-west norway]

I have a rb26 engine and are going to tune it to around 700 flywheel hp.

On the fueling side I have twin valbro 255l fuel pumps in tank,700cc sard injectors, nism fpr, stock fuelline and stock fuelrail.

Will this setup be capable of flowing fuel to 700hp?

Right now I am running a hybrid intercooler (300x600x80mm)

With 3"pipes.

Do i need to go for a larger one? (300x600x100mm maybe?)

regards,

helge

[Warpspeed]

Yes it will be o/k, but the injectors will be operating right at their limit. Check that the fuel supply and return lines can actually flow sufficient fuel so that the fuel rail pressure remains under the full control of the pressure regulator at both idle and flat out.

No real way of estimating intercooler efficiency or induction temperatures. So very much depends on ambient temperature, and how the car is driven.

[Tommyk]

Those injectors will be too small for 700hp i reckon. I'm pumping around the 550hp mark and my 700's are at about 91-92% (according to the pfc). From my understanding you will have to uprate these to larger units, eg 800's should be good for that setup.

Stock lines do not like upped fuel pressure So if you uprate the pressure on the fpr, something may burst

Anyway good luck and let us know how you go

[c-west norway]

Those injectors will be too small for 700hp i reckon. I'm pumping around the 550hp mark and my 700's are at about 91-92% (according to the pfc). From my understanding you will have to uprate these to larger units, eg 800's should be good for that setup.

Stock lines do not like upped fuel pressure So if you uprate the pressure on the fpr, something may burst

Anyway good luck and let us know how you go

<{POST_SNAPBACK}>

Thanks for your help guys!!!

I think I will try the current setup to see if it works.

Will keep you updated....

all the parts for the engine has now arrived, and I will take to my builder the next weekend.

specs:

je pistons 1mm oversize

eagle rods

arp head studs

n1 oil pump

tomei 1,2mm gasket kit

tomei baffle kit

tomei cams

pfc

pfc boost kit

300zx afm

garret gt35/40r

hopefully this will get me to a safe and reliable 650-700hp

[Sydneykid]

As usual the numbers tell the story;

In a 6 cylinder 700 cc's injectors = 700 bhp

That's with around 20% left for acceleration enrichment

Having flow tested several brands of injectors they always flow a bit more than their rating. Around 3% seems to be normal.

The injector duration usually maximises at rpm where the acceleration enrichment shouldn't need to exceed 10%.

So you should have around 13% overhead on the 700 cc injectors at 700 bhp. That's enough for another 90 bhp or so.

Confirmed by the real world;

I have seen an engine (on the engine dyno) make 750 bhp with 6 X 700 cc injectors.

700 cc's X 6 = 4.2 litres per minute = 252 litres per hour

So one 255 litre per hour fuel pump would cover them.

But I am not a fan of Walbro pumps, an old post of mine explains why;

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Using the standard wiring (ie; 11.5 volts at the pump) the R32GTR fuel pumps are OK for ~265 rwkw. If you use a relay and dedicated wiring (ie; 13.8 volts at the pump) they are OK for ~300 rwkw. The Z32 fuel pump is pretty similar to the R32GTR one. The R33GTR fuel pump actually flows slightly more. I have not tested an R34GTR fuel pump, or seen a proper test of one. Following is the best test of Nissan pumps I have seen;

The following is a good example of what happens to a fuel pump's flow when the voltage changes;

Fuel pumps are rated at flow versus pressure, that's why I laugh when is see stuff like "500 bhp fuel pump". Bosch fule pumps are rated at 73.6 psi, Assuming 36 psi fuel pressure (above boost) the Bosch pumps will flow their rated capacity up to 2.5 bar boost.

As you can see from the above at 13.5 volts the Walbro GSS341 flows 260 l/h (its rating) at zero boost (ie; ~36 psi fuel pressure). But at 2 bar this drops to 220 l/h.

A comparsion in size;

Flow at pressure is all about consistent torque, and a fuel pump needs torque from its electric motor. As usual if you want more torque you need a bigger motor.

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Hope that was of some help

cheers

Edited February 5, 2006 by Sydneykid

[Tommyk]

Hey Gary,

Perhaps you can answer some more of my questions which may (or may not?) be relevant to this post.

Based upon the apexi hand controller, I get the following results from airflow and fuel. I have seen fuel peak at 92% injector duty cycle on 700cc injectors. My airflow seems to peak at around 4.05v on nismo afm's, which is approximately 1600kg/h off the nismo airflow chart. Can I use either or both of these results to represent something, eg power ? I sort of feel that at 92% duty cycle on my engine and turbo setup is a bit high? What are your thoughts?

Cheers

[Sydneykid]

Hey Gary,

Perhaps you can answer some more of my questions which may (or may not?) be relevant to this post.

Based upon the apexi hand controller, I get the following results from airflow and fuel. I have seen fuel peak at 92% injector duty cycle on 700cc injectors. My airflow seems to peak at around 4.05v on nismo afm's, which is approximately 1600kg/h off the nismo airflow chart. Can I use either or both of these results to represent something, eg power ? I sort of feel that at 92% duty cycle on my engine and turbo setup is a bit high? What are your thoughts?

Cheers

<{POST_SNAPBACK}>

Hi Tommy, fluid flow dynamics, not my best subject, lets see if I remember enough;

The problem that I have with using the Apexi peak reading is it includes acceleration enrichment (if any was needed during the capturing of the max reading). For example it may well have been 80% + 12% = 92%. In that example the real power producing, as distinct from accelerating, injector duty cycle may well be 80%.

The numbers;

Fuel

700 cc per minute X 6 = 4.2 litres per minute

4.2 litres per minute x 80% = 3.3 litres per minute

3.3 litres per minute X 60 = 198 litres per hour

198 litres per hour X 0.7 (specific gravity of fuel) = 138 kgs per hour

Air

1600 kgs per hour

A/F ratio

1600 / 138 = 11.6 to 1

Power

700 X 80% = 560 cc’s = 560 bhp

560 bhp / 1.34 = 418 kw

418 kw – 80 kw losses = 337 rwkw

Usually these sorts of rough calculations need an engine efficiency correction to 90%. So 337 rwkw @ 90 % = 304 rwkw. I can’t remember, is that somewhere around your dyno readings?

Cheers

[Tommyk]

Dyno figures were around the 300awkw mark.

Cheers Gary

I will be at wsid this wednesday to confirm these power figures anyhow