How would this go?

[floody]

I'm considering a few engine options for my r31, with the idea being for street driving, with supersprints/trackdays as well.

I am thinking, RB25DE, with good extractors, exhaust, mild cams (step one or something),a bit of headwork, and maybe GT-R six throttle intake/injectors, good cold air setup, Haltech computer. Also would like to balance the bottom end and raise the rev limiter a bit, run a real light flywheel too. what sort of power do you reckon I could be going for? I want over 210hp at the engine.

cheers,

floody

[Nismodified]

your after 210hp at the engine ?

well, the RB25de already makes a nice 190-195hp at the engine mate

after all that work, my conservative(!) guesstimate for power output would be at least 280hp at the engine.

[floody]

Holy shit! well If I could achieve 100hp/litre I'd be stoked,but you reckon 280hp is achievable? mad! Of course I'd also like to run the thing on pump gas so the standard compression would have to stay, and I want it to be pretty streetable (only got one car )so I might aim a little lower than 280hp.....I didn't realise they made that kind of power stock, so I'm conservatively thinking, maybe a goal from about 230-250hp would be relistic, if its still going to be street driven.Anyway, cool, thanks for the input Nismodified.

Anybody know what kind of RPM the rb25de bottom end (stock crank, rods,balancer, pistons) can handle on a regular basis. I'm not going to scream its head off on the street.

Are the GT-R throttles/plenum a good idea? I was mainly thinking that, second hand, they would have to be cheaper than say EFI Hardware's dcoe style ones, and a custom manifold. Of course I don't even know if the bolt patterns match up?

cheers,

floody

[nismoman18]

i occasionally take mine to its limit at 7500, going to 6-6500 is enough though, theres hardly any power after 6000 so no realy need unless u just want to hear the engine scream. GTR plenum would make u lose alot of kilometres per tank, but is sumthing i would love to do too

[Nismodified]

ive had the idea about the throttle bodies as well, but it is a rather expensive route i would imagine.

it certainly would make the airflow to each cylinder even and mite sharpen up repsonse, though it all depends on how good the current plenum is of cause.

i would also love to have 6 trumpets sticking out of the side of the engine !!!!

i dont know about the strength of the bottom end, im not even sure if they are the same parts as the turbo, ive already started a thread but not havnt got too much replies, i dont think many people are after that level power and money spend from an NA engine.

like nismoman18 said, there not too much point reving too hard, peak power is at 6400, and it drops down sharply after 7000rpm.

this can call change with new camshafts of cause =D

[floody]

I would like to have 6 trumpets poking out, but really a nice plenum/intake tube such as the gt-r setup is a better option-I want the car to still be relatively quiet*, and not to suck in small birds, kittens etc. Now I figure if the breathing side is opened up with the six throttles/exhaust/cams, and I go to town on having the crank machined (knife edged, balanced, and maybe lightened, as well as nitrided) then it should rev somewhat harder than 6400 when asked, right? A big factor is whether the GT-R plenum and throttles would be a plus or minus performance wise-I'm willing to assume they would flow better than the long runner/single throttle setup, but I'm not sure. And, as I asked, does anyone even know if they fit?

*IN terms of quiet, it would be getting a 2.5 inch exhaust, with a good cat, and some kind of NA-cannon style exhaust (tanabe style) with a nice, restrictive baffle fitted for the street

cheers,

floody

[floody]

How exactly does the RB25DE and RB26DETT inlet manifold stud pattern differ?Could I get a diagram with measurements of thse anywhere?

is it just one or two studs that could be relocated, or is it more involved than that?

I just think the RB26 throttles and plenum would be useful in a NA performance application, they might be expensive, but its gotta be cheaper than a DCOE manifold and 3 dcoe TB's.

cheers,

floody

[floody]

Triple DCOE manifold for a rb25de? anyone?

cheers,

floody

[slip]

If you are going to build the bottom end, why not make an RB30DE with cams/headwork/high comp pistons/computer?

[slip]

GTR does not bolt onto gtst head. I have seen an adaptor that was custom made to bolt an rb26 plenum to an rb25 head. Twas nice. Might be cheaper to just buy an aftermarket rb25 plenum, but you wouldnt get the individual throttle bodies probably.

[floody]

Yeah, problem with plenums is that its not the gt-r plenum I'm interested in, so much as the six throttle setup. The only reason I like the GT-r plenum is because its a nice simple design, and suited to having a very direct air feed from a filter mounted in place of the battery.

I guess it would be a fair suggestion to just do an rb30de, but then again, it seems a rb25 bottom end would be more free revving. I can't really decide, but given the fact the rb25de bottom end could probably be left pretty well untouched (the machining I was considering seems pretty crap for $:results ), with the main concern being breathing and cams, The rb25de would be cheaper by far (e.g not having to rebuild the bottom end).

So basically, the dilemma is go the rb25 and get more RPM, or go the rb30 and get more torque. I think either would work just as well, and the problem with the rb30 is I'd basically have to buy an rb25 anyway so it gets a bit more expensive. I'm leaing towards an RB25, just on price and the relative newness of its internals.

cheers,

floody

[Ryno]

Have you tried looking for aftermarket cams for the RB25DE?... I'm interested in swaping mine over, (in an effort to get more horsepower) but had no luck finding any. Fill me in, if you know something I don't,

Cheers

[slip]

floody, the rb30e has no top end power, the head...the head. Strap a high flowing head on, and you have it all. Revvy does not mean fast! My 20,000rpm roadbike was slow.

[slip]

Rb20det's are revvy, but they are sooooo gutless.

[Nismodified]

Originally posted by Ryno

Have you tried looking for aftermarket cams for the RB25DE?... I'm interested in swaping mine over, (in an effort to get more horsepower) but had no luck finding any. Fill me in, if you know something I don't,  

Cheers

have u asked around to get ur camshaft reground?

a mild grind would give decent results, but i cannot say from experience, only what i have researched.

you cannot do more then a mild grind on with the rb25de, because you have to start to modify the head.

[Warpspeed]

Sounds like an interesting project.

If you start on the basis that the stock RB25DE already makes pretty good specific power, you need to really think very carefully about what you want to change.

Do you just want more top end power, or more midrange grunt from it ? For an everyday road-car 20% more midrange torque and no more extra power might liven up the on road performance quite a bit.

But if you just want to drag race it, more top end power is going to be a lot better. But it will be slower in traffic, and frustrating sometimes to drive.

For a road-car I would fit an RB30 bottom end, with some mild head porting,and some mild aftermarket cams. And strip out as much weight as you can as well.

The RB26 six throttle body setup is going to lose you a lot of midrange torque because of the short runner length. With large cams it will really start to haul over 6,000 RPM though, but be slower down low.

[floody]

The main purpose would be circuit sprinting, trackdays, and as my daily driver. Trafiic doesn't stress me too much-I'm in Hobart

The latest option thats cropped up is an ECCS rb20 head, as I can get a whole blown up rb20det for $200. I understand there are some oil and coolant passage issues? obviously the rb25 top end would be better, but this is very cheap. Can it be mated to the rb30 block?

The tommy kaira M30 (HR31) ran the rb20 head/rb30 export block setup, right?

cheers,

floody

[Warpspeed]

No, the RB20 has smaller cylinder bore, and water passages will not line up with other larger RB motors.

RB25, RB26, and RB30 all have the same bore size, and blocks and heads all interchange. There is a slight problem with mixing VVT heads with non VVT blocks, but it can be overcome fairly easily.

Best combination is RB30 block with RB26 head, or early non VVT RB25 head. Later RB25 VVT head can be made to fit though.

RB20 head only fits RB20 block, no other combinations possible.