PRP RB26 cast block + head prototype running

[joshuaho96]

Something strange I noticed is the squish pads on the cylinder head are missing. This doesn't seem super wise to do for a relatively street-oriented build? The shot of it is at 6:42. Does it look like they just machined it out for some reason? Surface finish is visibly different so my best guess is yes. 

[r32-25t]

Most people building big horse power RB engines remove the squish pads and fit over sized valves

the prp head comes without the squish pads out of the box 

[GTSBoy]

If you really want squish back, you can have it put on the piston (at least to some extent).

[joshuaho96]

On 11/9/2024 at 1:08 PM, r32-25t said:

Most people building big horse power RB engines remove the squish pads and fit over sized valves

the prp head comes without the squish pads out of the box 

I thought the problem with doing this is the engine needs more timing and therefore is actually less efficient? Modern engines need very little timing to get to MBT, those super sharp edges on the squish pads are probably not the right way to get there but doing away with it entirely doesn't sound right either.

[r32-25t]

Is it a Prius or a race car? We are here to make power and have fun not drive grandma to bingo

[Dose Pipe Sutututu]

Most people that build big powered RB, are always building big powered RBs 🥲

 

[GTSBoy]

34 minutes ago, Dose Pipe Sutututu said:

Most people that build big powered RB, are always building big powered RBs 🥲

 

H8R

[Dose Pipe Sutututu]

11 minutes ago, GTSBoy said:

H8R

GT-R owners love drag racing, here's a S58 stock motor, stock turbos doing a 8.9s

 

https://www.instagram.com/p/DBq0s10pkx5/

 

[r32-25t]

Buy one

[WMDC35]

18 hours ago, Dose Pipe Sutututu said:

GT-R owners love drag racing, here's a S58 stock motor, stock turbos doing a 8.9s

 

https://www.instagram.com/p/DBq0s10pkx5/

 

That's not a cheap car though, well not in NZ anyway, either way 8s isn't cheap lol

[GTSBoy]

Johnny's just upset because he sees that he's spent mutliple BMW money on his dirty Datto over the years and wishes he'd put the money into a stocksbro business prior to the market explosion and then he'd be rolling in BMWs, dead hookers and coke.

[Dose Pipe Sutututu]

@GTSBoy you're not wrong 🥲

I'm stuck in a shit box Nissan for life, gone way too far down that rabbit hole.

[Duncan]

Sounds like you are trying to escape one abusive relationship by getting into an even worse one. It is possible to change your life if you want to

[joshuaho96]

20 hours ago, r32-25t said:

Is it a Prius or a race car? We are here to make power and have fun not drive grandma to bingo

I thought an engine that needs more ignition timing to make power is going to result in less power due to reduced knock margin? More time for the combustion to propagate -> more time for it to heat up the rest of the mix to detonation.

[Dose Pipe Sutututu]

31 minutes ago, joshuaho96 said:

I thought an engine that needs more ignition timing to make power is going to result in less power due to reduced knock margin? More time for the combustion to propagate -> more time for it to heat up the rest of the mix to detonation.

Food for thought, a longer stroke motor would need less ignition timing vs. a shorter stroke motor requiring more ignition timing.

[GTSBoy]

38 minutes ago, joshuaho96 said:

I thought an engine that needs more ignition timing to make power is going to result in less power due to reduced knock margin?

Nah, it's not the reduced knock margin. It is a direct mechanical effect of having to initiate the combustion earlier, while the piston is still rising, which starts to exert combustion pressure on the rising piston earlier, making the rest of the engine work harder to finish driving the piston up to TDC where the combustion pressure stops being a negative and starts being a positive.

Your modern engine that only needs ~10° to make MBT doesn't waste the other 10 or so degrees of crank rotation. That's almost all of it. The difference in knock margin might go either way. Remember that modern engines to which you are currently comparing the long tractor engine (the RB) are now running super high compression, direct injection, tricky cam control and maybe even cylinder pressure sensors. You're not comparing apples with other fruit. It's apples and sea weed, or some other evolutionarily primitive vegetation.

And remember, squish only really comes into play at the very end of the stroke. It certainly does good things, but it is not the biggest contributor to what's going on. It is quite possibly much less important in 4 valve head than 2 valvers also, because there is so much less squish available to a 4 valve anyway.

Edited 23 hours ago by GTSBoy

[TurboTapin]

21 hours ago, Dose Pipe Sutututu said:

GT-R owners love drag racing, here's a S58 stock motor, stock turbos doing a 8.9s

 

https://www.instagram.com/p/DBq0s10pkx5/

 

That's my local track! A lot of fast/record holders come out of it presumably due to our cold air in spring and fall. 

[joshuaho96]

1 hour ago, GTSBoy said:

Nah, it's not the reduced knock margin. It is a direct mechanical effect of having to initiate the combustion earlier, while the piston is still rising, which starts to exert combustion pressure on the rising piston earlier, making the rest of the engine work harder to finish driving the piston up to TDC where the combustion pressure stops being a negative and starts being a positive.

Your modern engine that only needs ~10° to make MBT doesn't waste the other 10 or so degrees of crank rotation. That's almost all of it. The difference in knock margin might go either way. Remember that modern engines to which you are currently comparing the long tractor engine (the RB) are now running super high compression, direct injection, tricky cam control and maybe even cylinder pressure sensors. You're not comparing apples with other fruit. It's apples and sea weed, or some other evolutionarily primitive vegetation.

And remember, squish only really comes into play at the very end of the stroke. It certainly does good things, but it is not the biggest contributor to what's going on. It is quite possibly much less important in 4 valve head than 2 valvers also, because there is so much less squish available to a 4 valve anyway.

Is the RB26 actually that far off the mark? Honestly from where I'm sitting a VR38DETT is not actually that much more advanced than the RB26. Yes, there is a scavenge pump on the VR38, it's smarter in a number of ways but it's not actually jumping out to me as alien technology. Something like a B58 or V35A-FTS on the other hand has so many surprising little design features that add up to be something that just isn't comparable. 

[GTSBoy]

Well, yeah, the RB26 is definitely that far off the mark. From a pure technology point of view it is closer to the engines of the 60s than it is to the engines of the last 10 years.

There is absolutely nothing special about an RB26 that wasn't present in engines going all the way back to the 60s, except probably the four valve head.

The bottom end is just bog standard Japanese stuff.

The head is nothing special. Celicas in the 70s were the same thing, in 4cyl 2 valve form.

The ITBs are nothing special when you consider that the same Celicas had twin Solexes on them, and so had throttle plates in the exact same place.

There's no variable valve timing, no variable inlet manifold, which even other RBs had either before the 26 came out or shortly afterward.

The ECU is pretty rude and crude.

The only things it has going for it are that the physical structure was pretty bloody tough for a mass produced engine, the twin-turbos and ITBs made for a bit of uniqueness against the competition (and even Toyota were ahead on the twin turbs thing, weren't they?) and the electronic controls and measuring devices (ie, AFMs, CAS, etc) were good enough to make it run well.

Oh, and it sounds better than almost anything else, ever.

The VR38 is absolutely halfway between the RB generation and the current generation, so it definitely has a massive increase in the sophistication of the electronics, allowing for a lot more dynamic optimisation of mapping. Then there's things like metal treatments and other coatings on things, adoption of variable cam stuff, and a bunch of other little improvements that mean it has to be a better thing than the RB26. But I otherwise agree with you that it is approximately the same thing as a 26. But, skip forward another 10 years from that engine and then the things that I mentioned in previous post come out to play. High compression, massively sophisticated computers, direct injection, clever measuring sensors, etc etc. They are the real difference between trying to make big power with a 26 and trying to make big power with a S/B50/54 (or whatever the preferred BMW engine of the week is).

Edited 20 hours ago by GTSBoy