Rb20/25/26/30 Redline Question.

[BHDave]

Hi guys,

Just something i've been wondering about the last couple of days:

How and why has Nissan decided the redline/rev limit in the different capacity Rb engines? For a start, the 20 with the shortest stroke has a limiter around 7500, the 25 (s1 r33) has the limiter around 7k (mine was at 6850 or so with the stock computer) with the next longest stroke and the 26 is up around 8 with a longer stroke again.

What i'm wondering is obviosly the stroke has little to do with it so is it the crank design (counter weighted vs not?), or is it the head design? the 20 and 25 share similar lifts, durations and hydraulic lifters so why the 500rpm difference, while the 26 has solid lifters and bigger cams (so more stable at higher rpm?).

Or is it the stock turbo?

How do people with rb30dets decide on a safe limit to use? And whats to stop me (other than increased engine wear) raising the limiter on my rb25 considering my power is still rising pretty rapidly at redline?

Thanks for any replys,

Dave

[Abo Bob]

I'm just making an educated guess here but isn't it to do with the rod/stroke ratio and side load on the rods?

[BHDave]

So there's more to it.

Though the difference between rb25 and 26 stroke is pretty small and they have rods the same length right? Though the 26 ones are stronger.

[The Mafia]

the rb26 is build A LOT better than the 25...

[Fitzpatrick Speed Works]

the rb20 has a higher limiter as it has a short stroke, and smaller capacity the shock loading, power generated by each revolution and some other factors is lower thus the engine can safely rev higher. The 25 has a relatively low limiter or a few reasons the main two are the rods are weaker than say an rb26, and the engine doesnt need to rev any harder as it is out of its effeciency range, the cams, cam timing, head flow dont work as effecienty above 7g so why bother reving it. Also the car was never marketed as a race bread car rather a good sports car, and a good sports car should have good low end response as well as up top go. The rb26 is a race bread engine. The bigger revs are a result of better engineering and the need to rev a short stroked engine to make the power, other factors such as head design solid lifters etc accomodate higher revs.

When building a rb30 with a twin cam head setting a limiter is really a mater of how the whole package is set up. What sort internals have been used, what is the head setup like??? However on a rb30 regardless of build you dont really ever need to take it beyond 7500RPM, as usually they have rolled over on the power curve anyway and alot of other strengthening work needs to be done to safely rev beyond 7.5-8g. This isnt a really technical answer but I am sure you will get the idea.

[Fitzpatrick Speed Works]

BH dave you can raide the limiter I have done it to 3 gtst, have raised the limiter to 8 because they where still making power till redline, However 2 of those cars spat rods out the side as the oil pumps didnt like that any rpms. The other we tuned with adjustable cam gear on the inlet to get it rolling over at about 7.2 with the limiter now set at 7.5k. Its a mater of the condition of the car as much as anything else, however rb25 do blow far easier in my experiece by making around with limters, boost and timing than the other rb series and it comes down to some of the stuff I mentioned above!!!

[BHDave]

Thanks for that.

I wasn't after a highly technical answer anyway, more of a general idea of what will effect the limit. I hadn't considered the oil pump or other anciliarys either.

[Abo Bob]

So since I am rebuilding my RB25 NEO (solid lifters) with RB26 rods and possibly some cams, does that mean I can safely rev it a bit higher?

I note that the NEO RB25 has a 7050 redline rather than the 6850 redline of earlier models however I can't say it does much with the extra revs in my experience.

[Abo Bob]

enewun?

[MountainRunner]

You also have to consider the upgrading the valve springs etc as all the gear in the head is under greater load as well when the revs go up.

[Butters]

One thing that bugs me is from what i have seen midly modified rb20's make peak hp bewteen 6200 - 6800 rpm. Engines without cams this is.

Then pretty much the power dies of.

So really not sure why people swing the rb20 beyond 7k in these states of mods.

[RNS11Z]

well here is my experience, first engine i had, rev to 7500, spat a rod. 2nd engine, built with gtr rods, revd to 8k+ never any dramas over 15k done.

[maximajim]

So since I am rebuilding my RB25 NEO (solid lifters) with RB26 rods and possibly some cams, does that mean I can safely rev it a bit higher?

I note that the NEO RB25 has a 7050 redline rather than the 6850 redline of earlier models however I can't say it does much with the extra revs in my experience.

<{POST_SNAPBACK}>

Unless somehow the Nissan FAST IPC is wrong, your R34 NEO engine already has RB26 rods.. rod p/n 12100-05u01

[Abo Bob]

Interesting. I had heard that the rods were the same but someone who had his rebuilt said they weren't. Well, we shall soon see.