To Convert Or Not...

[pstanbis]

joel,

So do you have an RB30DE or DET ? And do you have to go to forged pistons if you put the 25DET head on?

[Cubes]

RB30DET.

Where the engine rebuilder is getting the pistons, they open up apparently this week, so its soon.

If you don't go forged pistons in the RB30E short motor and use the standard NA pistons you will have a 8-8.3:1 CR, which is good for turbo. Without forged pistons you will be stuck reliably at 250rwkw with a good tune. If you start heading towards 300rwkw the cast pistons wont handle the heat and break.

I used a R32 GTS RB25DE head (Like yours) had it rebuilt, ported/polished & inlet valves deshrouded. The cam specs for the head are 240dur 7.8mm lift on the inlet and 232dur 7.3mm lift on the exhaust. I'm going to use the 240dur 7.8mm exhaust cam from my RB20DET to help open up the top end a bit more. If it makes power to 6000-6500rpm then starts to drop off I'll leave the cams standard. If it drops off before 6000rpm then I'll throw a set of 256dur 9mm lift cams in it.

Do your figures. Work out how much its going to cost to get an RB25DET & RB20DET in the car with a working ecu (RB25DET = wiring mods, RB20DET will work easily with a T ECU), then work out what it will cost to give a RB30E short motor a freshen up (~1-1.2k) buy a head gasket, bolt on your RB25DE head, pop down to a jap importer & grab your self a cheap highflowed turbo, buy an second hand exhaust (~$700) then get your ecu remaped and have a solid easy 200rwkw with no lag and quick acceleration as you idle off from a set of lights.

It stresses me having to play with the clutch then waiting for the turbo in first to try and take off a little quicker than normal.

[pstanbis]

  Joel- said:

..Do your figures. Work out how much its going to cost to get an RB25DET & RB20DET in the car with a working ecu (RB25DET = wiring mods, RB20DET will work easily with a T ECU), then work out what it will cost to give a RB30E short motor a freshen up (~1-1.2k) buy a head gasket, bolt on your RB25DE head, pop down to a jap importer & grab your self a cheap highflowed turbo, buy an second hand exhaust (~$700) then get your ecu remaped and have a solid easy 200rwkw with no lag and quick acceleration as you idle off from a set of lights.

 

It stresses me having to play with the clutch then waiting for the turbo in first to try and take off a little quicker than normal.

I should proibably point out that i only have an RB20DE atm, meaning to go to RB30-type stuff, i would need another head (RB25DE) as well as block, turbo, ecu, wiring, Dump pipes, Intercooler etc, etc. as you've already suggested. some things i was wondering about though are the RB25DET you said would require a wiring change - aren't the sensors and stuff the same? it would definitely need another ECU to handle the increased airflow, different capacity etc, but shouldn't it just plug straight into the existing harness? As for the RB20DE, would that even make a worthwhile difference ? or would it be bettter to just hold off and go all out with the RB30 idea? <- this last ones open for comment, btw.

phil

[Ryno]

Joel,

You forgot to mention new injectors and fuel pump also, as the GTS Gear won't cope.

Trust me I added up the cost both ways for my conversion, and the RB25DET works out a lot cheaper, every time!

It's costing me:

$2100 for a 1995 RB25DET (64,000 km) engine, ecu, intercooler, wiring loom and fuel pump

$600 for a CES twin dump/front pipe (though you could get a cheaper single dump for $250)

$315 GReddy Turbo timer and Apexi pod filter

$800 labour to swap it all over

And after it's complete I can sell my RB25DE engine, ECU, and wiring - to recoupe some of the costs.

Sure a RB30DET would be nice, but when I added it all up (doing it properly and not dodgy) it was going to cost in the region of $8000 - (RB30 bottom end with forged pistons and balanced internals, turbo + manifold, dump/front pipe, intercooler + piping, blowoff valve, fuel pump, aftermarket computer to run the larger injectors). And with the RB30DET putting out so much torque, it would surely destroy my clutch and gearbox.

I am envious though Joel, if I could justify throwing the money at a RB30 conversion, I would have. But at the end of the day the RB25DET made far more sense.

Ryno

[Genesis®]

Ryno, you done your conversion already??

if you did, show us the dyno results and pics if any

glenn

[Ryno]

My car gets swapped over on the second week of Feb. The time won't be able to go fast enough!

[Genesis®]

keep me updated eh!

[Cubes]

It is a bit of a bummer if you don't have turbo to start off with.

I'd just bolt up the turbo bits to the NA with its decent compression ratio it should go well, better than a similiar modded T.

[pstanbis]

  Joel- said:

It is a bit of a bummer if you don't have turbo to start off with.

 

I'd just bolt up the turbo bits to the NA with its decent compression ratio it should go well, better than a similiar modded T.

I think go to pieces might be more accurate... the high compression ratio would put way to much strain on the internals, or so im told. I think there were some posts earlier on in this thread about the addition of a turbo to a N/A engine... ill have to check though...

[Ryno]

And even if you can get the engine to run without detonating, you're still going to need new injectors, fuel pump and computer

[pstanbis]

yesp, the list goes on....

[Cubes]

All comes down to how much power do you want to make. Be it now or later down the track.

Its a bit of a waste of money to buy a RB25DET if you are only going to rebuild it with stronger internals, different turbo,injectors, I think this is where the RB30DET begins to become better value for money.

It can also depends how much your willing to pay extra to have a freshly rebuilt engine.

Work out the $$, the pros & cons then make a decision.

I've always liked cubes.

Comparing the RB25 to the RB20, 500cc's makes a hell of a difference.

While your spooling i'll be short shifting down the road.