Jump to content
SAU Community

Recommended Posts

How do these motors compare? The neo has a very similar head, rods, pistons etc but 100c less displacement, however the neo has VCT as well.

For a street car would the VCT not be more beneficial than the extra displacement? Or are there other items the RB26 features which makes it a better engine.

Link to comment
https://www.sau.com.au/forums/topic/367529-neo-rb25-vs-r34-rb26/
Share on other sites

  • Replies 64
  • Created
  • Last Reply

Top Posters In This Topic

I don't even think it's 100cc, more like ~65-70

Either way not noticeable, for the street - VCT. Hence you see a few NEO/26's getting around now.

25 NEO heads on built 26 bottom ends. Its to get the VCT, kinda like poor mans V-CAM. Much cheaper but less options which for the cost isn't too bad.

Depends overall what you want of course, if you are talking stock motors I'd get a NEO for a conversion personally if budget is a consideration. You'll get a pretty good setup and only have to change on turbo - bolt on etc.

RB26 with variable cam timing :) RRR

Sounds like that is basically what the neo is lol, 50cc of capacity is nothing.

edit: The earlier rb26s had 8.5:1 compression, do the R34 rb26s also have 8:5 ? cause the neo has 9:1

edit2: apparently they do, imo that makes the neo quite a bit better than the 26

Edited by Rolls

Im loving my neo more than myself, all in all a great motor no doubt, its only mildly modded though, but then again i still want a RB26!! Dont know why, i guess every RB25 owner does... Dont think theres much differences in them

neo's are fantastic engines... the only thing they dont have over an RB26 is the high RPM limit and ITB's. I bought some RB26 ITB's and plenumn set up for mine but the thing is the factory long runners is what gives it so much midrange torque. putting short runners on there will move that torque further up in the power band. So i'll be looking at adapting the 26 set up and then making a custom plenumn with longer runners.

See I never got why rb26s get a higher rpm limit, in Bathurst they limited them to 7k not 9k which certainly says something to me. Also this might be wrong but I see a lot more blown up rb26s than I do rb25s, could this be due to the higher rpm limit? What allows them to safely rev higher, is it really any safer than revving say a 25 that high?

See I never got why rb26s get a higher rpm limit, in Bathurst they limited them to 7k not 9k which certainly says something to me. Also this might be wrong but I see a lot more blown up rb26s than I do rb25s, could this be due to the higher rpm limit? What allows them to safely rev higher, is it really any safer than revving say a 25 that high?

Solid Lifters in the RB26 over the earlier RBs, but NEO's have solids too.

Cant see why the 26s rev higher...Longer stroke, same journal sizes mean the 26 will be "maginally" harder on bearings over the 25

I don't know how true it is but I heard.......... lol...... The earlier 25's, the VCT was more for off boost driving and worked up to 3000rpm and in the 34 NEO 25 the VCT works over the whole rev range... Can anyone else confirm that as I would like to know myself if that is correct or not.

I've heard internally the VCT works different on a NEO, but externally it is the same (an on off solenoid), I have no idea what the internal difference is though. But yeah, surely there is no reason why the rb26 gets a higher rev limit, surely this is why they blow up so often with people setting redlines at 9k? If someone said they were revving their 20 or 25 to 9k everyone would think they are loopy.

edit: apparently the rev limit is 8200rpm on the 26, it is 7200 I am fairly sure on the 25.

Edited by Rolls

What does vct stand for- variable something timing? And if thats something good then how come the 26 which is the ultimate nissan engine (we will keave out the vr38dett for now) dosent have that? Also how will a vg30dett from a 90s 300zx compare to the 25 neo and 26- ive heard they r stronger and with a bit more punch due to the 3000cc but we all know zeds r a b$$tch to work on, maybe thats the reason the 300zx hasnt taken the import scene like the skyline

the vg30det is a massive motor which doesn't really fit in anyone's engine bay and is a pig to work on, also most of them have overheating issues in the 300zx due to inadequate cooling so they have earned a bad reputation.

VCT stands for variable cam timing, I really have no idea why they don't put it in the 26, I can't imagine it really adds much to fail and it adds midrange to the car which is always useful.

But yeah with the VCT and higher comp, if you had the same turbo surely the neo 25 would make a bit more power than the 26?

Edited by Rolls

But yeah with the VCT and higher comp, if you had the same turbo surely the neo 25 would make a bit more power than the 26?

Its not that simple, having the same turbo means you should get the same result in terms of power on each (if all other factors are the same) however the VCT has the potential to give more area under the curve by altering the cam before the turbo gets into its efficiency.

If you are flowing the same air (same turbo and equivalent boost levels) shouldn't the higher compression give you more torque hence power? Higher compression ratio = higher percentage of energy extracted.

Edited by Rolls

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now



  • Similar Content

  • Latest Posts

    • I'm looking for some real world experiences/feed back from anyone who has personally ran a EFR7670 with a 1.05 exhaust housing or a .83 I'm leaning towards the .83 because its a street car used mostly for spirited driving in the canyons roads. I"m not looking for big numbers on paper. I want a responsive powerband that will be very linear to 8000 rpm. I dont mind if power remains somewhat flat but dont want power to drop off on top. The turbo I've purchased is a 1.05, although the mounting flange T3 vs T4 and internal vs external waste gates are different on both housings, I not concern about swapping parts or making fabrication mods to get what I want. Based on some of the research I've done with chat gpt, the 1.05 housing seems to be the way to go with slightly more lag and future proofing for more mods but recommends .83 for best response/street car setup. AI doesn't have the same emotions as real people driving a GTR so I think you guys will be able to give me better feed back 😀   
    • Surely somebody has one in VIC. Have you asked at any shops?  Is this the yearly inspection or did you get a canary?
    • This is where I share pain with you, @Duncan. The move to change so many cooling system pieces to plastic is a killer! Plastic end tanks and a few plastic hose flanges on my car's fail after so little time.  Curious about the need for a bigger rad, is that just for long sessions in the summer or because the car generally needs more cooling?
    • So, that is it! It is a pretty expensive process with the ATF costing 50-100 per 5 litres, and a mechanic will probably charge plenty because they don't want to do it. Still, considering how dirty my fluid was at 120,000klm I think it would be worth doing more like every 80,000 to keep the trans happy, they are very expensive to replace. The job is not that hard if you have the specialist tools so you can save a bit of money and do it yourself!
    • OK, onto filling. So I don't really have any pics, but will describe the process as best I can. The USDM workshop manual also covers it from TM-285 onwards. First, make sure the drain plug (17mm) is snug. Not too tight yet because it is coming off again. Note it does have a copper washer that you could replace or anneal (heat up with a blow torch) to seal nicely. Remove the fill plug, which has an inhex (I think it was 6mm but didn't check). Then, screw in the fill fitting, making sure it has a suitable o-ring (mine came without but I think it is meant to be supplied). It is important that you only screw it in hand tight. I didn't get a good pic of it, but the fill plug leads to a tube about 70mm long inside the transmission. This sets the factory level for fluid in the trans (above the join line for the pan!) and will take about 3l to fill. You then need to connect your fluid pump to the fitting via a hose, and pump in whatever amount of fluid you removed (maybe 3 litres, in my case 7 litres). If you put in more than 3l, it will spill out when you remove the fitting, so do quickly and with a drain pan underneath. Once you have pumped in the required amount of clean ATF, you start the engine and run it for 3 minutes to let the fluid circulate. Don't run it longer and if possible check the fluid temp is under 40oC (Ecutek shows Auto Trans Fluid temp now, or you could use an infrared temp gun on the bottom of the pan). The manual stresses the bit about fluid temperature because it expands when hot an might result in an underfil. So from here, the factory manual says to do the "spill and fill" again, and I did. That is, put an oil pan under the drain plug and undo it with a 17mm spanner, then watch your expensive fluid fall back out again, you should get about 3 litres.  Then, put the drain plug back in, pump 3 litres back in through the fill plug with the fitting and pump, disconnect the fill fitting and replace the fill plug, start the car and run for another 3 minutes (making sure the temp is still under 40oC). The manual then asks for a 3rd "spill and fill" just like above. I also did that and so had put 13l in by now.  This time they want you to keep the engine running and run the transmission through R and D (I hope the wheels are still off the ground!) for a while, and allow the trans temp to get to 40oC, then engine off. Finally, back under the car and undo the fill plug to let the overfill drain out; it will stop running when fluid is at the top of the levelling tube. According to the factory, that is job done! Post that, I reconnected the fill fitting and pumped in an extra 0.5l. AMS says 1.5l overfill is safe, but I started with less to see how it goes, I will add another 1.0 litres later if I'm still not happy with the hot shifts.
×
×
  • Create New...