Which RB??

[Guest RBxxSilvia...]

Howdi...

I've read a few threads about RB20DET's vs RB25DET's but nothing has cemented in my mind which one is better...

I guess it comes down to money, availability & purpose...

So I am looking to fit one into an S13 Silvia... looking for around 250-300kw at rear wheels. It's going to be a frequently driven street vehicle and also see some 1/4 mile useage. Looking to get a low 11sec pass...

So if both engine were staring u in the face which one would u choose to fit into the Silvia?

As mentioned above, it's mostly going to see the street more than the track... so streetability must be considered. Also, not keen on touching pistons or rods... want to keep these stock...

So whats the advantages/disadvantages of both engines??

[T0nyGTSt]

The RB25 seems more adaptable to aftermarket ECU's.

True?

T.

[Guest RBxxSilvia...]

I believe both engines can adapt to many ECU's

It will be fitted with a fully programmable ECU anyhow...

What I really am looking to find out is what engine is going to make the power I'm after and make it reliably.. ie.. don't want to have to run huge boost or rev it to 10,000rpm to get there

[meggala]

go the rb 25 with out a doubt thats the one for tha task you want

no question no doubt I own an rb 20 and 250 rwkw is possible but not as easily as the rb 25

cheers

[Guest nt_80]

So Meggala your saying it's easier to get power out of the RB25DET?

I know it's possible out of the RB20DET but will it be under more strain than the RB25DET?

[meggala]

yep for those pwoer goal fefinatly there have bene a few cases where the transplant has been doen and the people wanted to go over the 250 rwkw and they went rb 25

[red17]

Personally i wouldnt do either of those conversions. The RB motors are vastly heavier than their SR counterparts (SR is all alloy). Sure you might find the RB easier to get gains when modifying, but you make the car weigh more and ruin the Silvias great handling balance entirely in the process.

For the power figure your looking for i'd stick with modifying an SR (however im not sure if 250rwkw can be done on that motor without changing pistons and rods). Ask a good tuning shop.

If you plan on doing the conversion then be sure to whack some nice brakes on. Stock S13 Silvia's have horrible brakes.

Red17

[Sydneykid]

Hi RBxxSilvia..., auto or manual?

If your going auto, then an RB20 will do the job just fine. Set the stall up for 3,500 rpm, run a 4.9 diff, some rear drag slicks and it'll do 11's with around 220 to 225 rwkw. That's easily in reach of a RB20.

Hi red17, I agree on the SR20, but since it's a drag car handling is irrelevant, in fact extra weight in the nose helps.

Hi T0nyGTSt, since RB25DET's have VVT (RB20's don't) we find them harder to tune on aftermarket ECU's. Power FC's excepted of course.

So I would go RB20, much cheaper and easier to buy. Use the lower price to buy more bits.

Hope that helps.

[red17]

Originally posted by RBxxSilvia...

It's going to be a frequently driven street vehicle

If it was going to be a drag car then id say go for it. This quote clearly implies that it ISNT. So handling is most certainly RELEVANT.

Red17

[Guest RBxxSilvia...]

The weight factor doesn't bother me.

There is not much difference in weight between the RB20 or RB25

After speaking to the ppl that have done either conversion they have no complaints about the weight or the handling. It seems to be only the ppl that HAVEN'T done the conversion having a winge.

[S13 Silvia]

After speaking to the ppl that have done either conversion they have no complaints about the weight or the handling.

That's me

[Guest mmdb]

question for meggala: how fast do you think a s13 with an rb25det stock can run? Maybe running boost of 10-13 psi?

[meggala]

possibly into the 12's

with traction

low 13's for sure

[mr180]

The SR is capable of going over 250rwkw on stock internals. It's been done before and has proven to be fairly reliable as well as long as it's treated ok. Same goes for the RB20 and RB25.

I think the problem with the SR and RB20 is that it will have more lag compared to the RB25, and if you're looking at 250-300rwkw on low boost, lag will be an issue so the RB25 is definately the lesser of two evils in that case. You will have a wider power band with the RB25 and thats what you want on the street.

I know there are a few guys here with over 250rwkw on the RB25 like whatsisname, merli, bigpsi, and others so maybe you should try to get their opinion. Don't know of any using the RB20 though.

Whatever you decide it will still be a sweet ride. If you are going to do a conversion I would go the RB25. You shouldn't have any worries with the gearbox as well. I almost bought a R33 half-cut myself and was planning on doing the RB25 conversion. I'll see how the SR goes first with about 240rwkw(I hope)

I don't think the weight of an RB is a big issue either. Never heard any complaints about that from the conversions i've seen. Check out this link from SXOC. Some pommy dude put an RB25 in a sil80. Check out the weight figures.

http://www.sxoc.com/vbb/showthread.php?s=&...highlight=close

Right, these were the corner weights prior to the conversion:

LF = 333 RF = 328

LR = 315 RR = 334

Front Total = 661.5 (50.4%)

Reat Total = 649 (49.5%)

Total weight = 1310kg

After the conversion:

LF = 365.5 RF = 358.00

LR = 314.5 RR = 326.00

Front Total = 723.5 (53.0%)

Rear Total = 640 (46.9%)

Total weight = 1363.5kg