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Neo Cam Specs Vs R33 Rb25, Do Neos Hold Power Longer?

Rolls

By Rolls,
in Engines & Forced Induction

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Rolls Grand Master

Rolls

Posted
Posted

Just found this really interesting link.

http://www.tomei-p.c...haft-specs.html

Looks like the neo rb25 has even more lift than the rb26s on the exhaust cam, curious to see if this follows through on dyno sheets with neo rb25dets, do they seem to hold top end power better than r33 rb25s?

neo in 8.4 ex 8.7

rb26 in 8.6 ex 8.28

though the 26 ex has more duration and different LCA

Reason I ask is rb26s seem to hold power to 8k and beyond, where as 25s always seem to fall over by 7k.

GTSBoy Grand Master

GTSBoy

Posted
Posted

Hard to know. It's not just the cam profiles that are different. The Neo combustion chamber is flatter, so the valve heads are closer to horizontal, which makes it harder to make the ports flow nicely. So for all we know the bigger cams might have been to compensate for some lost flow.

Rolls Grand Master

Rolls

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Posted

Hard to know. It's not just the cam profiles that are different. The Neo combustion chamber is flatter, so the valve heads are closer to horizontal, which makes it harder to make the ports flow nicely. So for all we know the bigger cams might have been to compensate for some lost flow.

Yeah I realise a lot is different, apparently the neo head is very similar to the 26 head which is why I am wondering what is the main differences that lets the 26 keep making power to 8k.

Eg if you get a turbo config on a 26 that comes on at 4k it will keep pulling till 8k, if you have the same turbo config on a 25 it has usually started dying in the ass by 7k.

R31Nismoid Grand Master

R31Nismoid

Posted
Posted

Eg if you get a turbo config on a 26 that comes on at 4k it will keep pulling till 8k, if you have the same turbo config on a 25 it has usually started dying in the ass by 7k.

Doubt that very much given my GT3040/RB25 setup pulled to 8,000rpm on a stock RB25 head/cams with a rebuilt bottom end.

The only time to see them die off around 7000rpm is because of the turbo selection.

A GT3076/.82 for instance, does not fall over @ 7000rpm.

Problem people have with a 25 head is valve float due to age/condition etc when going over 7000-74000rpm.

GTSBoy Grand Master

GTSBoy

Posted
Posted

Yeah I realise a lot is different, apparently the neo head is very similar to the 26 head which is why I am wondering what is the main differences that lets the 26 keep making power to 8k.

Yeah, the Neo head is not "very similar" to the 25 head. The 26 chamber is probably more like the older 25 chamber. The thing that is similar is really just the solid lifters.

iseekool Veteran

iseekool

Posted
Posted

Yeah I realise a lot is different, apparently the neo head is very similar to the 26 head which is why I am wondering what is the main differences that lets the 26 keep making power to 8k.

Eg if you get a turbo config on a 26 that comes on at 4k it will keep pulling till 8k, if you have the same turbo config on a 25 it has usually started dying in the ass by 7k.

Would capacity, compression ratio or bore/stroke ratio come into play, even though the capacity difference is very small.

GTSBoy Grand Master

GTSBoy

Posted
Posted

Hard to know. It's not just the cam profiles that are different. The Neo combustion chamber is flatter, so the valve heads are closer to horizontal, which makes it harder to make the ports flow nicely. So for all we know the bigger cams might have been to compensate for some lost flow.

I might retract part of what I said about the valve heads being "flatter"......I must have licked a cane toad. As far as I know the included angle between the valves is the same on the Neo head as on the other RB heads, so therefore the valve faces must be at the same angle to the inlet and exhaust port gasket faces - give or take. So that shouldn't make the ports particularly harder to make flow.

The Neo inlet manifold almost looks like the Nissan engineers sacrificed some of the "optimisation" of shape that yuo see in the earlier manifolds. They are more square and simple. I don't know if they just did it to gain some room for the extra TC butterfly, or if they did it because they worked out how to make it flow without the obvious "optimisation" visible in the older ones, or if they had some other reason. Nevertheless, there is some potential for the Neo inlet to be different to the others. Having gone to the effort of typing all that, and as has been posted above - the 26 has a very different inlet again, one which you would expect to be superior in just about every way that really matters.

Legionnaire Collaborator

Legionnaire

Posted
Posted

Needs to be analyzed vs. valve head diameters (particularly exhaust), lobe separation angle, and some other parameters.

Also solid lifters in Neo head have to have some clearance betw. lobe and tappet, so subtract that from cam lift figure.

RRob Community Regular

RRob

Posted
Posted

Does anyone know of any difference's between ER34 and other neo(c35 laurel) cams?

Did a long motor swap and lost 70HP on the same boost. Not a huge deal as i'm hoping poncams will wake it up.

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