Rb26 iron block limit

[Curlyfred]

Hiya guys, 

 

i’m currently in the process of getting my rb26 built.

everything is being replaced with better/upgraded parts or oem when that’s good enough (which isn’t alot lol).

someone earlier mentioned to me that i’ll be screwed cause the iron block can’t take 800hp (to the engine, not wheels) which is what it’s being built for. 
what do you guys think about this, am I cooked or na?

The guy building the engine will also do the mapping as he is “the guru of old nissan engines” here in Belgium. I know the mapping makes a huge deal so i’m not concerned about that. 
 

I honestly he’s talking shit cause he’s that kinda guy but a second opinion never hurt anyone!

cheers in advance! 🫶🏻

[GTSBoy]

800 engine horsies is fine.

Will need all the obvious upgrades. Rods, pistons, oil pump, big sump, sump breathing mods. Build for revs because revs are power with less stress on the bottom end compared to boost.

Keep the torque down in the midrange, either by limiting boost or timing.

 

[Curlyfred]

1 minute ago, GTSBoy said:

800 engine horsies is fine.

Will need all the obvious upgrades. Rods, pistons, oil pump, big sump, sump breathing mods. Build for revs because revs are power with less stress on the bottom end compared to boost.

Keep the torque down in the midrange, either by limiting boost or timing.

 

Aye, everything is being touched and all the parts that are responsible for the oiling issues are also fixed. (Crank collar, billet prp oil pump, head return to sump, yada yada yada) 

Everything used is of reputable brands like greddy, prp etc.

My tuner did mention we’d keep the torque on the “lower” side.  

glad to read that my engine won’t blow up on me lmao 

[GTSBoy]

52 minutes ago, Curlyfred said:

glad to read that my engine won’t blow up on me lmao

Don't take it as a guarantee. It's all a game of statistics. And on top of that, smooth over a thick layer of "quality of spanner spinning" as a further Gaussian curve of probability of failure.

You play games at anything above ~400 HP, and you're using up margins in terms of engineering and luck.

[MBS206]

Make sure to have the block checked for cracking etc before doing anything.

[GTSBoy]

15 minutes ago, MBS206 said:

Make sure to have the block checked for cracking etc before doing anything.

Yes, important point. Watch the Motive videos with Herman thickness testing the bores and deck. You do not want to push the unlucky (thin) block as hard as you can push the average block.

[joshuaho96]

24 minutes ago, GTSBoy said:

Yes, important point. Watch the Motive videos with Herman thickness testing the bores and deck. You do not want to push the unlucky (thin) block as hard as you can push the average block.

https://dsportmag.com/the-tech/education/engine-tech-material-hardness-testing/

The PRP testing on block hardness I'm not sure how much it actually can be trusted. The thinner cylinder walls on RBs is a bit of a problem vs 2JZ but it really depends on the design goal. Siamesed cylinder bores like a 2JZ cause uneven cylinder wall temps too, which means a bit of distortion induced by that + the hotspot can affect knock margin. Something that actually gives me a bit of pause with the PRP block, whether super thick cylinder walls are going to keep it from being drop-in compatible on an otherwise OEM rebuild. 

[GTSBoy]

31 minutes ago, joshuaho96 said:

The PRP testing on block hardness I'm not sure how much it actually can be trusted.

Which is why I didn't mention that hardness testing, and specifically mentioned the bore and deck thickness testing.

31 minutes ago, joshuaho96 said:

+ the hotspot can affect knock margin.

Yeah, not really. The bore temperature will be a lot more even around the top half inch or so, where the material distribution is dominated by the deck, and which is the only place where the bore surface temperature heating any gas in the cylinder is likely to have any effect on detonation. Think about it. Another inch or so down the bore, you might have a hotter spot. The gas there might get a bit hotter, then the piston rises squeezes that gas away from there at high speed and mixes it with other gas from nearby. Instant dilution of the problem. I'd be surprised if it was an issue at any time other than in racing engines or OEM dev engines being run at the ragged edge of tuning.

34 minutes ago, joshuaho96 said:

Something that actually gives me a bit of pause with the PRP block, whether super thick cylinder walls are going to keep it from being drop-in compatible on an otherwise OEM rebuild. 

Say what now?

[joshuaho96]

25 minutes ago, GTSBoy said:

Which is why I didn't mention that hardness testing, and specifically mentioned the bore and deck thickness testing.

Yeah, not really. The bore temperature will be a lot more even around the top half inch or so, where the material distribution is dominated by the deck, and which is the only place where the bore surface temperature heating any gas in the cylinder is likely to have any effect on detonation. Think about it. Another inch or so down the bore, you might have a hotter spot. The gas there might get a bit hotter, then the piston rises squeezes that gas away from there at high speed and mixes it with other gas from nearby. Instant dilution of the problem. I'd be surprised if it was an issue at any time other than in racing engines or OEM dev engines being run at the ragged edge of tuning.

Say what now?

I was under the impression the reason why OEMs are going with solutions like relatively thin "right-sized" cylinder walls with technologies like PTWA and open deck is because they care a lot about whatever marginal knock margin benefits they get from that vs the structural rigidity benefits of a closed deck block and thicker cylinder walls. I also see some weird stuff like plastic inserts in the water jacket around the cylinders to try and equalize cylinder wall temperatures.

re: the PRP blocks and heads at the end of the day it's hard to know what is and isn't going to work there, just have to see what the initial buyers say about it.

[MBS206]

54 minutes ago, joshuaho96 said:

I was under the impression the reason why OEMs are going with solutions like relatively thin "right-sized" cylinder walls with technologies like PTWA and open deck is because they care a lot about whatever marginal knock margin benefits they get from that vs the structural rigidity benefits of a closed deck block and thicker cylinder walls. I also see some weird stuff like plastic inserts in the water jacket around the cylinders to try and equalize cylinder wall temperatures.

re: the PRP blocks and heads at the end of the day it's hard to know what is and isn't going to work there, just have to see what the initial buyers say about it.

They care about emissions, and cost the most.

Save weight where possible, and make manufacturing easier.

Less material also let's the engine transfer heat to water quicker, and bring the engine up to temp quicker, better for emissions and getting them past their warranty period.

[Curlyfred]

7 hours ago, MBS206 said:

Make sure to have the block checked for cracking etc before doing anything.

I shouldve mentioned that the engine is near being complete. I double checked with my mechanic but im pretty sure the machine shop did all the nessecary checks on the block.

i also won’t be driving on 800 all the doing doong pulls. Mainly be driving and cruising with friends on low boost maps occasionally opening everything it’s got.

[Curlyfred]

1 hour ago, Curlyfred said:

I shouldve mentioned that the engine is near being complete. I double checked with my mechanic but im pretty sure the machine shop did all the nessecary checks on the block.

i also won’t be driving on 800 all the doing doong pulls. Mainly be driving and cruising with friends on low boost maps occasionally opening everything it’s got.

Confirmed, the block was checked for cracks and was found healthy.  

[Predator1]

17 hours ago, Curlyfred said:

i also won’t be driving on 800 all the doing doong pulls. Mainly be driving and cruising with friends on low boost maps occasionally opening everything it’s got.

Why not? Since mines been built, I've used low boost maybe 5 times.

[Curlyfred]

On 14/05/2025 at 2:09 AM, Predator1 said:

Why not? Since mines been built, I've used low boost maybe 5 times.

Mainly being afraid of breaking something on something i've poured so much money into haha

[GTSBoy]

1 hour ago, Curlyfred said:

Mainly being afraid of breaking something on something i've poured so much money into haha

Yeah. OK. I'll say the same thing I say to everyone. You do not have to use 100% throttle all the time.

[Predator1]

2 hours ago, Curlyfred said:

Mainly being afraid of breaking something on something i've poured so much money into haha

Understood. If you dont have a ridiculous limit,  Tune, T's and P's are in check, and arent bashing it all the time and doing the due deligence for maintenance(inc oil analysis) then its pretty safe.

55 minutes ago, GTSBoy said:

Yeah. OK. I'll say the same thing I say to everyone. You do not have to use 100% throttle all the time.

100% agree, let your right food control it to some extent.

[r32-25t]

You don’t need to use full throttle all the time to break these blocks, 500kw at the wheels in more then enough to break them even with an occasional squirt. Hell I’ve seen them break under 400kw

[Curlyfred]

1 hour ago, r32-25t said:

You don’t need to use full throttle all the time to break these blocks, 500kw at the wheels in more then enough to break them even with an occasional squirt. Hell I’ve seen them break under 400kw

You can probably break everything and any point that's true.
But with the "precautions" of building the entire engine and everything around it and with a solid tune I wouldn't expect that to happen right of the bat. 😛 

[r32-25t]

Just don’t be silly enough to think it’ll never happen either 

[GTSBoy]

Meh, I think we're well into a new era of 90s JDM car.

The days when spare engines and parts were cheap and plentiful are long gone. Therefore the YOLO approach is now massively difficult to justify, use and maintain. One should start to ponder whether an 800HP build is really justified, using stock parts.

My thoughts? If you like/love the car and want to keep it and don't want to ruin yet another one, then be discrete about how much you ask from the stock parts. A 5 or 600 HP build is still a very fast car.

If you want to go silly, have to have the 1000HP territory, then just drop all your cash, buy billet everything (or PRP cast block, etc etc) and use a bigger/more modern gearbag, and put a massive retrofit diff and axles into it. If you ruin any of those things then you're either ham fisted and deserve it, or you're pushing waaaay too far for the stock stuff anyway.

The (presumably) young guys who are buying 30-35 year old busted arse Jap refugees and thinking they can live the life that was lived by others 20 years ago are deluded. Expectations need to be adjusted somewhat.