Internal Mods For More Torque From A Rb25

[R31Nismoid]

I think the OP is looking for something free like more boost!

other than that, there is no simple way other than increasing capacity and so on, everything else that will 'increase' it will be minor and barely tangible for a street car

[bubba]

Generally longer intake runners= more TQ, so your better of with the standard intake manifold rather than the greddy. You'd want to increase stroke as much as you can and also possibly the smallest turbo that can reach your desired power levels..

+1

Why bother then?There's only so much torque you can get a from a short stroke 2.5ltr i6 without major changes. It doesn't sound like you want to do anything reasonable to increase TQ.

+1

I think the OP is looking for something free like more boost!

other than that, there is no simple way other than increasing capacity and so on, everything else that will 'increase' it will be minor and barely tangible for a street car

+1

Low down torque monster is pretty much the definition of my engine in it's current setup.. RB25/30 with RB25 turbo, lets see your 20/25/26 pull up a hill at 2000rpm in 5th gear lol

[R31Nismoid]

Mine does pull up in 5th @ 2000rpm ... :erm:

I go up a very steep hill near me and hold 80km/h, i could accel but that would put me over the speed limit and cops frequent that area

I actually tested it last night, i have solid boost on before 3000rpm loaded up in 5th from 2000rpm

And thats GT-SS

[bubba]

Mine does pull up in 5th @ 2000rpm ... :erm:

I actually tested it last night, i have solid boost on before 3000rpm loaded up in 5th from 2000rpm

And thats GT-SS

Nice, does it pull hard? or pulls enough to not have to downshift?

[R31Nismoid]

it'll hold no problem on mid throttle, and accell if i want it too.

If i lax off though it will fall to the point where ill need to go into 4th, but steady throttle no worries.

Admittadly it doesnt go rocketship momentum, (a 3ltr would simply do better no question) but once i hit around 95-100km/h (if i start from say 80) on a good hill... its on full boost by 95-100, which is i think 13psi at present/250rwkw and then from there the speedo does spin up fast

But thats the joy of responsive turbos on smaller capacity, so you can have similar (and i stress, similar, it wont ever be the same) goodness of a 3ltr if you cap you power to 350rwkw or less

[PSI Parts]

Having not much experience with RB30s, I did hear that they are probably not the best engine to rev out compared to a RB25. Anyone care to elaborate on this?

[R31Nismoid]

you dont need to rev them out

[aDrew_C]

They'll still rev fine to 7k... they're similar to a 2j in that regard.. both are held back by harmonics at this point and making them rev harder is big $$

Anyway, RB30 ftw. They're not just for big power, I know a lot of big power people with 26's making over 800hp, not fun cars to drive. 30 bottom end is practical torque. It doesn't cost stuff all more than building a 25, if you actually want more torque and don't strongly consider it you're obviously not facing reality and have some sort of dirty image whenever someone says RB30 stuck in your head.

[rob82]

As has been said - keep the standard intake manifold, increase the compression up to 9.5 - 10:1 (definately de-burr the cahmbers) , keep the camshaft duartion smallish (260 ish) but use agressive lobes with fast ramps - may need custom grinds (I would talk to Tighe cams and ask what grind were in Lukes car - they will know) and use good quality valve springs in order to keep valve float at high rpm under control.

The larger the duration of the valve event the lower the dynamic compression. IMO every camshaft install should be acompanied by an increase in static compression in both aspirated and turbo applications.

Remember that you have a large turbo thats is only going to start breathing around 4500rpm so peak cylinder pressures are going to be around 5500 - 6000rpm which is quite high meaning you have mechanical advance to compensate for the high compression.

Not sure if its available for RB25's but have you thought about HKS Vario cam or whatever its called, may give you more inlet advance than factory cam phasing. Good way to dial in more inlet advance/overlap down low and pull it out so as to not sacrificing top end power.

Edited January 16, 2009 by rob82

[TriniGT]

Also getting a Twinscroll Exhaust Manifold and Turbo setup will help with spooling as well, if you are trying to get everything out of the setup, needless to say a good tune.

[Tangles]

just had my head flowed etc, tomei cams and metal head gasket

feels really really nice on road, totally different to how it was pre-xmas

the engine has taken over from the turbo so to speak, she's real nice! but the turbo is plainly not up to the task

good for what it is, but its gt2835 hunting time

[toffy]

NO2

[Roy]

Umm, why more costs? is this what the guy you want to build your engine said?

Are you not putting a decent oil pump and a new water pump in there anyway?

The only difference in machining costs would be getting a spot for the tensioner drilled/tapped and maybe oil/water fittings if a non turbo block.

Why are the pistons cheaper? was he going to do you a standard non-turbo build?

30's aren't for big numbers, they're for people who want lots of torque/drivability. They do help if you do want big numbers though as you can spin up bigger turbos.

I dont dismiss how some people are to do ti for roughly the same money...many can not. There is extra machining costs for the RB30. (Cam belt etc). There is a crank collar mod you have to do. There is work you have to do on the VICS when using the RB25DET head. There is changes to his existing dump pipe from his highmount setup. Odds on will have to change his turbo to cooler pipe as well as the filter to turbo pipe. Oh and the coller to throttle body pipe.

So, he also then needs to play around with Power Steering belts and pulleys. He also has to consider whether there will be issues with strut braces. He then also has the issue of engine number change which invites the local authorities to inspect his high mount setup etc = headaches

IOt is clearly more expensive to build...i would say 8 out of 10 RB30 builds cost way more then the original budget!

So, to the OP...extra torque to the RB25. Your only real options would be looking at the effeciency of a range of things. Original inlet manifold, solid lifter conversion with better cams say 250/9.3mm or so. Clean up the head, a good split pulse manifold and associated turbo. Look at the tune and look at the tune again.

It wont actually add to the torque of the engine....but will improve the feel of driving...things like wheel size and weight (as light as possible) Ditch the clutch fan and go electric. Make sure you have a good flywheel....

As others have said their is not any dramatic way to improve torque....about the only way i can think of is make sure the engine spins the turbo onto boost and let the turbo make the power. Indycar and many forced induction race engines size the turbos to make torque gains and build the engines to make boost as early as possible...not make hp. So basically let the boost make the hp, turbo to get the torque. When looking at this you have to consider that many classes of turbo race cars are forced to run FIA restrictors so that changes the thinking in engine building and tuning.

So all of the above is small things that can be tweaked to improve the big picture. The only real way to get a dramatic gain is go down in turbo frame size. Others have said go RB30...you dont like that option. You can downsize the turbo which doesnt seem to be what you want as then you are not able to utilise your bolt ons. But fact is with a built engine you can easily jam another 6-8psi into the engine which means you can justify a smaller tubo running 22psi rather then a bigger turbo running 15-16psi

[bubba]

I dont dismiss how some people are to do ti for roughly the same money...many can not. There is extra machining costs for the RB30. (Cam belt etc). There is a crank collar mod you have to do. There is work you have to do on the VICS when using the RB25DET head. There is changes to his existing dump pipe from his highmount setup. Odds on will have to change his turbo to cooler pipe as well as the filter to turbo pipe. Oh and the coller to throttle body pipe.

So, he also then needs to play around with Power Steering belts and pulleys. He also has to consider whether there will be issues with strut braces. He then also has the issue of engine number change which invites the local authorities to inspect his high mount setup etc = headaches

IOt is clearly more expensive to build...i would say 8 out of 10 RB30 builds cost way more then the original budget!

You could say that about almost any engine build..

As for extra machining costs for a 30, what you have mentioned is only a few hundred dollars worth.. tapping/drilling tensioner locations isn't a big deal. Longnose mod on crank can be done without a collar for about $100 if you machinist knows what he's doing.

There was also enough slack in my piping that I didn't have to modify to suit the extra 38mm deck height. I only had to modify the piping for clearances reasons as the bonnet didn't shut! Depending on setup, the only pipe that I can see almost definitely needing modded is the dump pipe, but really, that's not a huge deal.

If you're doing a full forged rebuild of an engine, then the cost of going 30 is negligible when compared to the rest of the rebuild costs. And 3L torque is a no brainer

P.S. Ash, nice once, I've got taller gears though so when I'm talking 2000rpm.. I talking 60kph ish. Likewise if I let it slack off a bit I have to downshift.. 1500rpm up a hill just doesn't quite do it hehe. I do love putting along at under 1000rpm in the morning while the car warms up though

[jase-r34]

^^^ Now that's an answer ^^^ lol

[Roy]

You could say that about almost any engine build..

As for extra machining costs for a 30, what you have mentioned is only a few hundred dollars worth.. tapping/drilling tensioner locations isn't a big deal. Longnose mod on crank can be done without a collar for about $100 if you machinist knows what he's doing.

3 simple questions then...

1. What has your RB30 conversion cost to date?

2. How much power do you currently make

3. Are you a DIY'er and sounds like you did much of it yourself, what % did you do?

[Tangles]

depends on the budget

I wanted more torque, got it, happy with the outcome.

headwork, tune, other stuff 2k

tomei poncams, 8.8mm tomei springs, head gasket(s)

heaps of head gear when aussie $ was 97c-exchange to U$A - $2400

all up was $4500 and got some more parts not yet fitted, still sorting to do - cat is restrictive

a little more tune time will yield good results

on road it feels so copletley different, I thought like a 3Litre would TBH. so so so smooth

power all around, an awesome onroad car.

think of a 280kw engine potential package, sitting on a kai-gt2530 journal turbo (slide) holding it back to 220kw

gt3071r-iw is next, after sorting the cat and more tuning

Im in love with my Stag engine is perfect tbh, starting saving $ as of now for the gt30 fix (cat fix is free )

[bubba]

3 simple questions then...

1. What has your RB30 conversion cost to date?

2. How much power do you currently make

3. Are you a DIY'er and sounds like you did much of it yourself, what % did you do?

1. Are we talking purely engine here?

To date (current setup) about 3.5k for a forged RB25/30, stock rods, serviced R32 RB25DE head, N1 oil pump, 550cc injectors, z32 afm then about $600 for the remap.

Another 3.5k in parts are about to go on to make 400rwhp (GT35R, TiAl 44mm gate, exh mani, custom plenum, gtr cooler/bovs/piping, oil cooler), budgeting 1k for buying bits of pipe, getting the ENZED guy out etc etc and looks like 1.2k on the High Energy sump heh

^^ This is phase 2, phase 1 was getting the basic 30 (with all the RB20 ancillaries bolted on) in the car, running and registered. **Phase 3 may involve 3.4L crank

2. 245rwhp @ 4600rpm (same power as my RB20 made but not at 6500rpm ) Rb25 turbo that chokes the motor up at 5800rpm

3. Pretty much all of it with help assembling the internals (I more watched and learned for that part )

Edit: the amount of torque and response in a little 32 with suspension and fun things such as button clutch and 2-way makes for a very entertaining ride!

Edited January 17, 2009 by bubba

[dangerman4]

we should probally ask a more accurate question of the topic starter.

how much torque do u currently have, and how much do you want.

tangels auto stagea above has a bit over 300nm out of a 25.

my built auto 25 has over 500nm, mine comes on sooner and holds for longer.

so how much do you want?

[PM-R33]

Out of curiousty, when you say you want more torque, do you want to make the car drive off of boost better or want to make the car faster or what exactly for?

Because honestly without increasing displacement, nothing you can really do in your setup is going to do a noticible increase without changing parts.

Edited January 17, 2009 by PM-R33