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

[EnricoPalazzo]

Cool Thread guys,

Btw i downloaded Dyno 2000 desktop, man i have no idea how to use it Need the book hehe

[Warpspeed]

Hello GTS200X,

The RB30 has both longer rods and a taller block height. I cannot remember the exact rod ratios of all these engines, but I do have that information here somewhere. All the RB engines end up in the 1.6 to 1.7 range, so there is no vast difference in this respect.

Steve, higher compression ratio does in fact lift the torque and power curves throughout the range by a small but fairly constant amount. At lower engine RPM it does this by raising the compression pressure (obviously). But what is not so obvious is that it also helps the volumetric efficiency at the high RPM end as well.

What happens at TDC around the valve overlap period is that some exhaust gas is always trapped in the combustion chamber at whatever the exhaust back pressure happens to be. The larger the combustion space, the higher the volume of trapped exhaust gas.

After the exhaust valve closes, and you are on the induction stroke, fresh charge is drawn into the cylinder. But the trapped exhaust expands, and takes up room that could otherwise be filled with fresh charge. It also adds heat to the fresh charge as well, expanding it. This works against the fine job your intercooler has just done.

If you can get away with a higher compression ratio, the combustion chamber will be smaller, and the piston can pump out the exhaust and pump in the fresh charge more efficiently. In other words at TDC where there is more piston crown, trapped exhaust cannot remain.

This is all particularly true with a turbo engine because compression ratios are lower, and exhaust back pressure higher than with a highly tuned n/a engine.

Enrico, yes you definitely need the book to understand the selection menus available. Even then it can be a bit tricky to use.

[BOOSTD]

how about the Toyota Chaser 2.5ltr 206kw and 376nm peak torque @ 2400rpm

[Cubes]

Thats comparable to the R34 206kw RB25...

That max torque figure is damn low..

[BOOSTD]

great city bus I'm thinkin

[51jay]

hmmmm......RB25DET 475N.M at 2700, max about 840N.M at 5100, 625 at 7000, 235rwhp at 6800

[Cubes]

hu?

[51jay]

[EVOIV]

Actually, everyone knows that the 206kW figure of the GTR RB26 engines are not true. I have read that it's more like 220kW.

[Cubes]

They make around 175rwkw on average. A 225 LS1 Manual V8 Commodore makes 164 stock so I'd say the RB26DETT is closer to 230-240kw at the flywheel.

[Spoolup]

Where do I get a copy of this Dyno 2000 software ?

[Cubes]

Do a search on the www... Google. You will find their site there.

I can't remember off the top of my head.

[Warpspeed]

Hello again Brad.

Go to any speed shop or car place, they will have a catalogue for "Mr Gasket Co" the US based hot bits distributor.

In that catalogue will be software products developed by Motion Software. There will be Dyno 2000, and I think there is a later Dyno 2002 version as well, but not absolutely sure.

My copy of Dyno 2000 cost $160 twelve months ago.

There is a website somewhere where you can download a demo program. Well worth a look.

On the supplied CD, there is a huge operating manual that you can print out. It discusses engine theory, and how the simulations work, it is an excellent read quite apart from the software itself.

[Spoolup]

Thanks very much guys...Im deciding whether to go RB30DET or RB26 crank in RB25....I think this may help.

Cheers

[Warpspeed]

It will certainly be an eye opener. Personally I am going the RB26 crank in the RB25 block route. If you remember, you supplied me with the RB26 crank and rods to do it a while back !

But really it all comes down to airflow determining final power, not engine capacity.

The difference in the shape of the torque and power curves that a 14mm stroke difference will make, will absolutely astound you.

[Cubes]

I actually don't know if it simulates 100% warpspeed, as i've been researching and a RB30DET with the same setup as a RB25DET does make more top end power and more power over the complete rev range.

It also peaks power around the same also.

Its still just over 6k, like the RB25.

[Spoolup]

lol..i wondered how you knew my name....do you want some hks rods for that crank ?

yes, thats the decider....its torque that makes a streeter pleasent to drive, but how much torque is overkill ( not that there is such a thing ) and how much is not, especially when deciding which way to go ( and like you, I also have a 26 crank and 25 block) ...Ill be getting the software asap

[Cubes]

http://www.skylinesaustralia.com/forums/at...=&postid=433625

As you can see Raists60 RB30 still makes slightly more top end slightly earlier but look at the mid range power.

For the street it will make a much quicker car.

Apparently the only change was the RB30 bottom end. No more boost etc..

Here is his post in the RB30 conversion thread.

http://www.skylinesaustralia.com/forums/sh...3625#post433625

[Warpspeed]

My philosophy is to keep the basic engine breathing (volumetric efficiency) as good as possible over as wide an RPM range as possible, and then use supercharger boost to lift the whole torque and power curve to what is required.

So if you begin with an RB30DE that has a lot of natural low end off boost torque, but poor top end breathing, a big turbo is going to fix the lack of top end and make a very nice package.

On the other hand a normally aspirated six throttle body RB26 is going to lack torque, but breathe very easily to well above 8,000 RPM. A decent positive displacement supercharger is going to lift the torque right up, and you will end up with a far more flexible engine with more low end, and a far extended top end. And it will not be short of power or torque either.

The other possibilities are an RB26 turbo, which even stock, is going to lack torque below 4000RPM, and when powered up will be even less flexible. It becomes a narrow power band racing engine.

A supercharged RB30DE would be the exact opposite. Bags of low end torque, and completely dead at the top end. It would make the ultimate truck engine.

So I think a turbo RB30, or a supercharged RB26 would be the go for the ideal street engine.

[Warpspeed]

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.