411rwhp from stock internals

[Sydneykid]

Hi MiniMe, there are a number of ways to look at "engine efficiency". One is that a petrol engine is around 65% efficient in using the energy stored in the fuel it uses. This of course allows for the power consumed in driving the ancillaries (water pump, oil pump, A/C, power steer, alternator etc) and the losses through the drive train. The other 35% goes mostly in heat into the water and oil etc.

The lower numbers (35 to 50%) only compare the calorific value of the fuel versus the power at the wheels. That's why the numbers are lower.

The basis of all these calculations are based on Newton's theory energy can be neither gained not lost, it is merely converted into other forms of energy". Einstein of course disproved this with E=MC2, but for the course of this post I will assume no atomic reactions going on in my Skyline.

What we were talking about in the previous post was the efficient use of airflow ie; how much air is available versus how much the engine ingests. Numbers like 85% for a pushrod Windsor V8, 92% for a modern twin cam 4 valve, 97% for a Formula 1 engine etc.

Simplistically, that means a 2.5 litre engine at 1 bar only uses 4.6 litres (not 5 litres) of air every 2 revolutions of the crankshaft based on the 92% efficiency rule of thumb. Since we know that RB's produce best power around 12.5 to 1 air/fuel ratios, calculating the fuel required is easy.

Hope that answered your question

[GTS-t VSPEC]

There are only 2 tuners in Perth accredited to use the Dyno Dynamics shootout logo at the moment, 1 of them is SST, and go's to show that Dyno Dynamics are satified with the accuracy of the dyno.

[Cubes]

Simplistically, that means a 2.5 litre engine at 1 bar only uses 4.6 litres of air every 2 revolutions of the crankshaft

1 bar?

Is there a forumula to work out the amount of air a 2ltr for example is using at 7000rpm with 92% Effiency on say 10psi.

[2rismo]

Einstein of course disproved this with E=MC2

which has in turn, been disproved, Capt. Accuracy!

ROFL... i'm just causing trouble now.... This is an interesting discussion especially for us cheapskates!!

Keep it going.

Oh and GTST_VSPEC, run the thing will ya? please? give the cheapskates some hope!!

Adrian

[rob77]

I'll be running mine soon.

[GTS-t VSPEC]

Adrian, Trust me I'd love to run it down the strip, but on stock internals I'm not sure if it would cope. My suggestion is not to be in too much of a hurry to change injectors until it's really necessary:D

[fatz]

i might bring the coroller around to the dyno c if i can get 411hp out of it

on stock internals

lol

might have to get them to change the scale me thinks

[Steve]

Originally posted by Sydneykid

Simplistically, that means a 2.5 litre engine at 1 bar only uses 4.6 litres (not 5 litres) of air every 2 revolutions of the crankshaft based on the 92% efficiency rule of thumb.  Since we know that RB's produce best power around 12.5 to 1 air/fuel ratios, calculating the fuel required is easy.

Hope that answered your question

Joel, atmospheric pressure is 1 bar, boost of 10lbs is 0.68bar, added together is your multiple factor for the capacity (or absolute pressure - which is quite often the way turbo compressor maps are represented), so 2L engine times 1.68 is 3.36L of air (per 2 revolutions). With a 92% efficiency, multiply by 0.92 = 3.01L (3.091) of air for every 2 revolutions of the crankshaft.

divide 3500 (for 7000rpm) by 60 seconds = 58.3 (induction strokes per second) times 3.01 litres of air = 175.48 litres of air per second at 7000rpm.

A/F ratio of 12.5/1, so 12.5litres of air for every cc of fuel, the engine would require 14cc of fuel (175.48/12.5) per second, or 50 litres of fuel in one hour (0.014L x 3600seconds).

Also an RB25 at 7000rpm and 1 bar boost would consume 268.3 litres of air per second, so 21.5cc per second or 77.4litres per hour.

I hope those figures arent too far out - perhaps Sydneykid would like to check them for me:D

the only problem is that basic calculations like this dont take into account the density of the air due to temperature and the size/efficiency of the turbo.

there must be a method of calculating the amount of fuel required per hp and engine produces, which would be more accurate.

DISCLAIMER: I really am not sure if these figures are 100% kosher (ie method of calculation), so flame away all you mech eng types etc

[Ustasa]

An internal combustion engine dispenses with most of the energy in the fuel through the exhaust (30-40%) or the cooling system (30-40%). The rest (30% at best) goes into the combustion process to drive the crank. Mind you the combustion process is irreversible in nature (the products cant be recombined to form the constituents) and also governed by the laws of thermodynamics. Add in the fact that you also have the drive train losses to contend with and the petrol IC engine starts to look pretty shit indeed.

[Guest INASNT]

Originally posted by GTS-t VSPEC

Adrian, Trust me I'd love to run it down the strip, but on stock internals I'm not sure if it would cope. My suggestion is not to be in too much of a hurry to change injectors until it's really necessary:D

Just run it atleast once with some nittos, the engine wont be that fragile that it will break after one run

[Emre]

My suggestion is not to be in too much of a hurry to change injectors until it's really necessary

As clear as you suggestion is, i think you fail to recognise the risks associated with it. As it was mentioned earlier a fuel reg is a band aid solution for a need of more fuel, in most cases marginally more fuel. Running the pressures that you are running on standart fuel lines would not be advisable to anyone.

Just run it atleast once with some nittos, the engine wont be that fragile that it will break after one run

That's the thing; the engine does not need to be fragile to fail at those conditions. Unless you are prepeared for the worst, the outcome will leave mental scars for a while.

On a different note, i am detecting a bit of a dig and sarcasm towards SydneyKid. Is there a reason behind this ? Am i missing anything ?

[GTS-t VSPEC]

We love Sydneykid, he's a fgreat guy and knows heaps of stuff, doesn't mean we can't pull the piss out of him occasionally:D

Emre, Rob77 is running 344rwhp with no fuel reg and standard injectors (70% duty cycle), so my suggestion is why would you change them if it's not necessary.

[BU5TER]

I'm a touch lost here (whats new though haha) so what your saying is you've now got all this power but you are to scared to run the car down the 1/4 because of the stock internals

If thats right whats the use in having the power then? hahaha you can't use it?

[Steve]

Because he can:)

[Steve]

PS: I dont think there are too many people that dont have alot of respect for Sydneykid, or dont value his input.

[BU5TER]

Originally posted by Steve

Because he can:)

:bahaha: Thats a good one, Its a damn shame we wont see any times to back up that power then, In my book it sort of defeats the purpose of having power if you can't use it or show it down the 1/4, but I guess its ok if you just want to be a DYNO QUEEN

[Sydneykid]

Ohh shucks guys, you only really know that you are appreciated when someone bothers to take the piss out you.

[BU5TER]

or gets there nickers in a knot for 3 months over something not that bad then has to vent hehehe sorry about that Sydneykid

[Steve]

Originally posted by Buster

.....I guess its ok if you just want to be a DYNO QUEEN

ROFL

[Sydneykid]

Hi Steve you should have finished the calcs.............

21.5 cc per second at 14.7 psi = 24.9 cc's at 17 psi

+ 20 % enrichment (acceleration, cold run, start etc) = 29.9 cc's

6 cylinders = 6 injectors

60 seconds in a minute

299 cc per minute for each injector

Looks OK for a 370 cc injector?

Except that is at sea level, at 0 degrees C and 0% humidity. Not gunna happen on a roller dyno in Australia. That is unless someone has their dyno in an environmentally controlled room (ala F1).

So let’s deduct some;

Humidity, say 25% (it's not raining)

16 degrees C (not too hot, not too cold) that's 10% (5% for every 8 degrees)

Let’s say the dyno is at sea level, so no adjustment required.

299 + 25% + 10% = 411 cc's

Oooops we ran out of injector capacity.

None of these calcs are perfect, but I have used them often for working out approximately the right size injector, I then add 30% or so to be sure. So 411 + 30% = 534 cc's. For this engine at that power, a set of 550 cc injectors would be my starting point.

You can do this a number of ways, a good rule of thumb used by many in the automotive business is 1.7 bhp per cc of injector capacity. Thus 1.7 * 6 * 370 = 377 bhp.

So, I'm still perplexed..........