Internal Mods For More Torque From A Rb25

[The Bogan]

Ive got all my bolt on,s done(i think ) now I'm going to have the internals done, what should i do to to maximise my torque down low.

Or have i got this wrong and just need to up the boost and tune it when she is rebuilt, I'm getting pistons , rods, bearings, head rebuilt and adjustable cam gear on the exhaust side, What else should i look at.

Ive got, TO4 High mount, Greddy inlet Plenum, 800cc injectors, FMIC, Link ECU, Greddy Profect B Spec 2, Bosch 044 fuel pump.

I don't want a Rb30 bottom end and will be using the 25 crank.

Ive searched around but couldnt find much on making torque only kw.(or are they hand in hand)

Thanks for your help.

[NYTSKY]

Upgraded cams and adjustable cam gear will help a little.

A good quality exhaust manifold and gate setup will help the turbo spool a bit earlier resulting in a bit more torque down low.

[The Bogan]

I thought aftermarket cams would hurt the torque down low, im thinking of what a lumpy cam did to my old LJ 202, it took a while to get going but top end power was good.

[SATO GTS]

Swallow your pride and get a 30 bottom end if you want torque.

After rebuilding a 25 with hks cams, piston's, rod's, balancing, porting, O/S valves and the usuall there is nothing better then a 25 or 26 head on a 30 bottom end if torque is what you after. I sort of thinking that I should've built a 30 bottom end up instead.

Don't get me wrong, mine is nice to drive but the extra capacity from the 30 does not do a built 25 justice.

mmm sweet torque.

[The Bogan]

Sorry mate but i want my 25, I just wanted to know how to get more from it.

[SATO GTS]

Well you could go stroked with a 26 crank and 26 rods and custom piston's to give you some extra stroke and do the usuall touch up to get it spinning smooth.

[R32 Driver]

just rebuild it

smash in more boost and retune......

cant get more torque without increasing the capacity

[kwikr33]

just get oversized everything.....throttle..exhaust....manifold...etc

[_Ryan_]

was all ready to say HKS or Tomei 2.8 kit, but then you said you want to keep the 25crank

Interested to follow this thread anyway.

Good luck.

[and3_3]

Well a smaller turbo would help, but i doubt less top end power is what you want.

A good tune with that exhaust cam gear will make it alot more torquey though so see if thats enough for you.

[rob82]

Swallow your pride and get a 30 bottom end if you want torque.

After rebuilding a 25 with hks cams, piston's, rod's, balancing, porting, O/S valves and the usuall there is nothing better then a 25 or 26 head on a 30 bottom end if torque is what you after. I sort of thinking that I should've built a 30 bottom end up instead.

Don't get me wrong, mine is nice to drive but the extra capacity from the 30 does not do a built 25 justice.

mmm sweet torque.

I tend to agree - I had a an RB26 in an R32 RWD making about 240rwkw and in going to an rb30/26dett with the 2860r the difference in torque is massive. I think you will find the torque comes from the larger rod/stroke ratio than the cubes. I often found that with the 26 you were constantly serching for the right gear to use but with the 30 you just leave it in whatever gear and put your foot down.

The only real way of increasing torque is to increase compression ratio - I wouldn't do this with std cams tho. You may be able to get custom pistons with a bit more dome to get the comp up to 9.5:1 - make sure you deshroud the valves and clean up any sharp bits in the chamber tho.

Failing that I would get a smaller turbo charger.

[MBS206]

I'd have to say the only way you'll achieve this, is dump in the RB30 bottom end.

It absolutely SHITS all over the RB25 and RB26 in terms of Torque, and can be revved out just as hard when built.

OR, you can bump up your CR.

But the bumped CR will NEVER get you any where near the torque of a streeted, basically nothing done RB30...

[PM-R33]

+1 for bumping up the compression ratio since your allready rebuilding it. Only real way to get better power down low without changing that turbo setup (or going bigger displacement). Some poncams (or something with small duration but a bigger increase in lift) will help down low a bit.

Edited January 11, 2009 by PM-R33

[discopotato03]

Properly port the head , fit slightly over sized exhaust valves and bump the compression ratio up to 9.2 - 9.3 .

What are we calling a T04 ?

A .

[Al]

Four options (In my preferential order)

1/ RB30 bottom end- I've done it and absolutely loving it

2/ Stroker Kit

3/ Fit a supercharger- Expensive and need to ditch a/c

4/ Increase the compression ratio- Not really advisable on a street car, with a big turbo, as 9:1 is already considered high. If you intend yo run race fuel then no problems.

[leg46y]

Can i ask whats the reason you want to keep the 25bottom?

[r33_racer]

a good crank scraper/head oil drainage to bypass rotating assembly? Free power there, why doesnt anyone think outside the usual stuff?

[R31Nismoid]

just get oversized everything.....throttle..exhaust....manifold...etc

And how does that work? Oversized means it takes longer to fill, increasing lag

I tend to agree - I had a an RB26 in an R32 RWD making about 240rwkw and in going to an rb30/26dett with the 2860r the difference in torque is massive. I think you will find the torque comes from the larger rod/stroke ratio than the cubes. I often found that with the 26 you were constantly serching for the right gear to use but with the 30 you just leave it in whatever gear and put your foot down.

Interesting - having had a RB25 (GT30) and now the RB26 (GT-SS), i dont find myself ever looking/searching for the right gear with the RB26.

Being its a good 700-800rpm more responsive as opposed to the RB25... i dont really need to go digging for a gear unless im really wanting to move.

I cruise around in 5th even @ 60km/h and have no issues as boost come on nice and early (3300rpm) and being my car @ 100km/h sits around 3k, im never left wanting

Just my view of it

[The Bogan]

Im on a buget of $10,000 for motor, gear box reco and enginnering the whole car and im not after huge power, Just more than ive got now, The 25 will give me a easy 300+ which ill be happy with as this is also my daily hack.

Im going to go oversize pistons, clean + balance the rotating assembely, head work + valve springs + oil mods + std cams, exh gear and then run it at about 20 psi and see where i get.

Getting Quotes now. $$$$$$$$$$$$$$$$$$$$

And for all you 30 fans im getting that quoted to.

[dangerman4]

ive got a fully built 25 for sale with all the goodies making 350 rwkws if your interested

$8k including ETM highmount, 3582r-iw all lines etc.

you can then sell all your stuff and it will only cost you a few grand to update to 350 kws

http://www.skylinesaustralia.com/forums/fi...t-p4359570.html