Rb30 25 Or 26 & Fuel Economy

[xntrq]

I picked up my RB30 block from an R31 recently and I'm swinging in between either putting a 25 or 26 head on it. Given that it's a 3 litre block and the prices of fuel, it's come into a factor as it will be in my daily.

For those who have went down this path, could you please share some ideas on the fuel economy per full tank and what fuel? I'm looking at building two RB30 motors, one being NA and other being turbo.

RB25/30 Neo Head - NA

RB25/30 Neo Head - Turbo

RB26/30 Neo Head - NA

RB26/30 Neo Head - Turbo

Also some idea on the rwkw and ups and downs for 25 or 26 would be great

[KiwiRS4T]

Read the RB30 hybrid upgrade thread for KW

If you are building an RB30 to be economical I would say a Neo head would be best but the biggest determinant will be your right foot. I find I can get just as good economy (or just as bad) out of my RB30/25 as when I had the RB25DET if I don't boot it everywhere.

[Ben C34]

You would think neo head would be better due to vct.

[discoPumpkin]

yre gona be spending an awful lot lof money to be even concerned about fuel economy, it doesn't sound right

[xntrq]

yre gona be spending an awful lot lof money to be even concerned about fuel economy, it doesn't sound right

I've got the parts lying around so why not. Not going to go all the way to forged pistons and Nitto oil pump etc.

[luke gtr]

either.

I think the differences between the 2 will be negligible.

so, which ever works easier, which would be your factory head.

one thing to keep in mind, the cr.

get the right pistons at least to bump the cr up and make it driveable, or youre going to use more throttle to compensate, and in turn, more fuel.

[luke gtr]

oh, and the right tuner.

[34GeeTeeTee]

Increase cr with boost

[luke gtr]

still, then you would NEED boost for putting around.

you want cr AND boost.

[Ben C34]

neo head with rb30e pistons is around 9.5 to 1.

[discopotato03]

Correct me if I'm wrong but doesn't the Neo turbo head have chamber volumes about the same as the RB30 NA SOHC head ? And wouldn't that make the static CR about 9.5 to 1 . IMO having an adequate CR is where part throttle torque and economy is because it has a big say in the dynamic or throttled CR .

The GTRs six throttle inlet manifold was all about sharp throttle response because you could open the ports up to a big inlet tract . Trouble is that when you let lots of air in you have to hose the fuel in to maintain acceptable AFRs so the transients tend to be bad consumption wise .

Yes and the variable inlet cam timing makes for better low end torque and consumption - better overall compromise .

I think what you seek is a torquey engine that doesn't need a lot of throttle to get around in style , everything about a GTR is open it's lungs and go for ratshit fuel economy - it's not something Nissan gave any real consideration to . I can't think of any homologation specials from the 80s and 90s that had good fuel economy-especially turbo ones , things like RS500 Sierras Evos GTRs etc .

On paper a Neo turbo engine makes 206 Kw where I think a std R32 RB26 made 209 , the Neo would have been a simpler cheaper engine to make with one throttle and one turbo and in theory its power output wasn't far short . It's power delivery would be more user friendly for a road car and it should have got better normal use consumption .

If it were me I'd use turbo Neo heads on a fresh std RB30 NA or turbo because it's the best compromise for a road car . CR will be better and if the car was a single throttle one you get to use more of what it came with .

Freshening up a standard late RB30 NA - std pistons rods water pump - shouldn't be to exy though a turbo oil pump like maybe a 25T one is probably a good idea . IMO you only need the collar etc if you are going to rev to 7 and beyond or bounce off the limiter much .

Your call cheers A .

Edited August 4, 2013 by discopotato03

[34GeeTeeTee]

still, then you would NEED boost for putting around.

you want cr AND boost.

Dont put a turbo on that doesnt fit in your engine bay like some

[xntrq]

Thanks for the input guys.

Does anyone have a rough idea of the RWKW for a NA rb25/30 and approx K's on a full tank? Don't want to end up having to fork out $100+ each time i fill up. already doing $80 per tank and thats just 95

[discoPumpkin]

Well that doesn't make any sense because the rebuild cost for these 2 motors negates any possible fuel savings, u should be able to get atleast 350-500kms to a tank(street, not track) Any less and its the tuning that'a out of wack.

If u want a fuel saving, get a Prius

Edited August 5, 2013 by discoPumpkin

[legzy86]

Not a 26/30 but I was getting around the 500km give or take out of 60L of 98 in my 32 GTR with around 300kw. And that wasnt being overly light on the throttle either.

[luke gtr]

Thanks for the input guys.

Does anyone have a rough idea of the RWKW for a NA rb25/30 and approx K's on a full tank? Don't want to end up having to fork out $100+ each time i fill up. already doing $80 per tank and thats just 95

you are going to keep forking out the same for filking up

it comes down to how OFTEN you now fill up.

as previous post, my run in tune, I got 500ks to tbe 70l tank doing the putty rd and back.

around town, about 350.

[xntrq]

you are going to keep forking out the same for filking up

it comes down to how OFTEN you now fill up.

as previous post, my run in tune, I got 500ks to tbe 70l tank doing the putty rd and back.

around town, about 350.

Yeah thats where I was getting at. I'd like to maintain my 480KM/80L or colse to it.

[luke gtr]

city or hwy?

[discopotato03]

I don't think you'll get that in the burbs with the 26 inlet system , I'm not sure if you'd see much advantage of that if mostly driving around at smallish throttle openings . On the open road at fairly consistent engine loads and throttle openings it may not make much difference .

I tend to think that since Nissan made the last revision of the RB cylinder heads in R34s the changes they made would have been to do with running leaner mixtures and not detonating on the sameish available pump fuels . At that ultra low emission vehicle (ULEV) point many manufacturers had to revise heads so that their engines could perform acceptably using lean mixtures . They had to have better cooling around exhaust valve seats and ports and having less chamber surface area (more compact chambers) means less area to absorb combustion heat . What I think they were trying to do was remove more of the heat via the exhaust gasses than the engines cooling systems - also helps keep heat in cat converters .

I don't remember there being any changes in the R34 RB26 chambers and ports though someone here would know . GTRs were not really designed with economy in mind (IMO) and as long as Nissan got them past the emissions standards they probably didn't care that much about economy . Having all round reasonable performance and better consumption would have been the realm of the GT and GTt and the latter was a step up from the R33 GTS25T .

I think it's safe to assume that had Nissan produced an R34 GTt with an RB30 it would have used the Neo turbo 25 head and inlet system and only minor rejigging . It would have had more part throttle torque everywhere and probably longer diff gears to take advantage of the extra soft pedalling torque . I think if you want the best of both performance and economy you should consider the last revisions of what the factory did because they were after these same things , but limited themselves to 2.5L .

A .

Edited August 5, 2013 by discopotato03

[xntrq]

city or hwy?

city/suburbs. I get on average 420 when the fuel light comes on but can stretch it to 480.

I don't think you'll get that in the burbs with the 26 inlet system , I'm not sure if you'd see much advantage of that if mostly driving around at smallish throttle openings . On the open road at fairly consistent engine loads and throttle openings it may not make much difference .

I tend to think that since Nissan made the last revision of the RB cylinder heads in R34s the changes they made would have been to do with running leaner mixtures and not detonating on the sameish available pump fuels . At that ultra low emission vehicle (ULEV) point many manufacturers had to revise heads so that their engines could perform acceptably using lean mixtures . They had to have better cooling around exhaust valve seats and ports and having less chamber surface area (more compact chambers) means less area to absorb combustion heat . What I think they were trying to do was remove more of the heat via the exhaust gasses than the engines cooling systems - also helps keep heat in cat converters .

I don't remember there being any changes in the R34 RB26 chambers and ports though someone here would know . GTRs were not really designed with economy in mind (IMO) and as long as Nissan got them past the emissions standards they probably didn't care that much about economy . Having all round reasonable performance and better consumption would have been the realm of the GT and GTt and the latter was a step up from the R33 GTS25T .

I think it's safe to assume that had Nissan produced an R34 GTt with an RB30 it would have used the Neo turbo 25 head and inlet system and only minor rejigging . It would have had more part throttle torque everywhere and probably longer diff gears to take advantage of the extra soft pedalling torque . I think if you want the best of both performance and economy you should consider the last revisions of what the factory did because they were after these same things , but limited themselves to 2.5L .

A .

so you're saying a 25det neo head would be more economical?