RB20DET KW's Per Litre is Better than RB25DET? Why?

[Cubes]

It is quite amazing the fat mid range but.

On the dyno loaded up he said the RB30 came on to full boost around 2300rpm however generally on the road it hits full boost at 3000rpm.

Its interesting how the power curve goes flat up the top end.

I'm not sure if that is a good thing or not. Maybe it is as when you click the next gear it will be making basically peak power already 240kw where as on the RB25 it has to build up to that powerlevel from say 200rwkw.

Matthoon also posted his RB30 dyno reading of 320rwkw on 14psi. That is using the RB26DET head or was it just the cams?!?! and doesn't go flat up top.

[Warpspeed]

A flat power curve means the torque is decreasing as revs go up, I would rather see a flatter torque curve with the power rising to a peak.

[180sx_dogg]

haha ive done the complete oppersite...

ive done the rb20det conversion in the 180sx.....i love it and wouldnt look back.

[Messiah]

hope this helps

500 horsepower is equivalent to roughly 1.3 billion joules per hour.

1 liters of fuel contains 35 million joules, so a 500-hp engine has to be able to burn just over 37L of gas per hour.

However, car engines are only about one-quarter efficient -- three quarters of the gasoline's energy escapes as heat rather than as power to the wheels. So the engine actually has to be able to burn at least 148L per hour, or 2.4L per minute.

Petrol requires about 14.7 kilograms of air to burn 1 kilogram of gas. Air weighs 1.222 kilograms per cubic meter at sea level. A Litre of gasoline weighs 1.34 kilograms. So the engine has to be able to process 1.34*2.4*14.7 kilograms of air per minute, or roughly 38 cubic meters of air per minute. That's 38,000 liters of air per minute.

If a straight 6 engine is turning at 6,000 rpm, it can inhale a total of 18,000 cylinders' full of air per minute. If it needs to inhale 38,000 liters of air per minute, it works out to roughly 2 liters per cylinder-full. That's a 12-liter engine.

But an engine that size wouldnt be able to turn at 6000 rpm maybe (ok it could but not easily) maybe closer to 4000. soooooo

4000*6/2 is 12000 cylinders per minute. we still require 38000 litres of air for 500hpso

38000/12000 = 3.2 ltrs a cylinder * 6. we now need a 19.2 ltr engine.

but wait theres more...

ok so how do we get 500hp from 2.5/6 litres. the turbo, double the airflow and you can effectively double your fuel.

ok i think thats enough maths forme today... you can add up the rest

What does this prove... its proves that power is more complex than simple litreage.

RPM is relative to cylinder size, air flow to rpm, air flow to fuel consumption.

[Revhead]

And thankyou www.howstuffworks.com

[Messiah]

And thankyou www.howstuffworks.com

yeah.. was a good page.... i should have mentioned that i pulled it and modified the numbers for a skyline... my bad

[raist60]

Hey man just thought id mention at the time of those runs it was a GT30 dash 11 (475hp) turbo, the 25 had no trouble spinning it up. It also was running a .82 a/r housing with a fairly tight nozzle and small turbine wheel. It was a pretty responsive turbo on the 25, on the 30 it was psychotic. I have since upgraded as it was cutting my top end pretty badly.

Joel.

After looking at those two power curves, have to agree the RB30 is going to be heaps stronger at the same maximum boost.

But I suspect though that the same rated boost level was only reached at the very top end with the RB25 combination.

Fitting the RB30 allowed the turbo(s) to come on boost far sooner and create that massive mid range torque.

I would like to bet that some slightly smaller exhaust turbines/housings on the RB25 combination would also have come on boost sooner as well and given a similar if not identical result.

Still, it has ended up a mighty impressive engine though, no matter how he finally did it.

[Revhead]

Hehe no dramas mate, I just recognised it from a few days ago

[Cubes]

What did u end up going Raist?

So I assume power no longer flattens out up top like it used to?