RB25DE NEO into S30

[Dose Pipe Sutututu]

On 21/01/2022 at 4:17 PM, GTSBoy said:

Doesn't rev to 12k , by the way. Typical American cock throttling.

Always, like how they talk in fly wheel horse power to sound like they're making big numbers.

[GTSBoy]

On 1/21/2022 at 3:55 PM, vosadrian said:

I get that the RBs in NA form are not the best engines around. I'm not looking for the highest power NA engine around. We are really doing NA for sound and feel and we want to keep to the Nissan/Datsun family and we want to keep it straight 6. Obviously we could stick an E46 M3 engine in or something and that is a good NA straight 6. But we want to keep it in the family. Does that then leave just L series and RB series engines? Another point, is we want it EFI (I have worked a lot in aftermarket EFI and I enjoy working with it and tuning etc.). My take is that by the time you adapted an L series to EFI and modified it for good power, you would be down more $$ than doing the same with RB series. Have I got this wrong?

And we don't need huge power.... but we do want to optimise what we have. But not to 110%. I'm all for finding some easy extra revs with an oil pump upgrade and some decent cams and valve train... but I don't need fully lightened balanced for 12k RPM at very expensive $$. As I said, it is more about the sound and feel. But if we can spend a few $k on getting the bottom end to rev reliably and the top end to flow to good revs, we would go that far. Is RB the right choice for this? Is there another option I have missed?

As I said, I'm not trying to talk you out of it. Just pointing out that you should not get your hopes up that a small 6 cylinder twin cam is going to make it feel like a proper sports car. I have no doubt that if you pay someone big money they can be made to make good power. Look at the old Holden 202 - they are pushing well over 300HP out of those nowadays. But back in my day (the 80s) it was a struggle to get 200HP out of them. People learnt what to do to make them make power. But it costs.

There hasn't been a heap of development into making NA RBs make a lot of power, because.....the lure of the turbo reveals how poor the value proposition is. Yes, they sound bloody awesome revving to the moon through open ram tubes and long primary extractors. But the time taken to run from the bottom of the rev range to the top of the rev range reveals that they don't make a lot of power doing it. Listen too the Hakosuka video

 for the nearest example.

[vosadrian]

So if I want to build an RB based NA engine, which (reasonably priced and accessible) head option is going to give me the best result? It seems the RB25DE NEO has small ports and may not be easily ported for the best result. I believe the non NEO heads are the same casting between turbo and NA? So would either of those options be OK... or better to go turbo as perhaps the valve springs are OK for cams? Or are NEO turbo heads a better option due to solid lifters, so better for high RPM?

[GTSBoy]

If you're doing porting, it probably doesn't matter that the NA Neo ports start out small. It's just a bit more metal too remove - provided that the eater jackets aren't actually closer to the port walls, which is an unknown (at least to me).

Neo is simply better. Better combustion chamber shape, better valve train. Arguably better valve angle but I actually don't know what this does to the port shape around the short turn, so it could be a win-lose situation there.

But..... here we are talking about small differences. It's not as if there's 50HP available between your best option and your worst option. If it is more than 20HP I'll be very surprised.

[vosadrian]

Thanks for that. Who knows RB heads. Is Lewis engines a good option? Just looking for someone knowledgable who can set up porting and valve train optimised but at a fair price? Thinking I might send the heads somewhere to get them done. Possibly someone who might set up the bottom end also and supply a complete long motor. I might contact them first and make sure I am getting the right bits for them to work on.

[Dose Pipe Sutututu]

Try Rams Head Service, but also be prepared to pay.

I got a quote to machine my old NEO head and convert to shimless and let's just say it was cheaper to source and another head, fit new shims and buckets it to with plenty of change left for strippers.