Jump to content
SAU Community

Recommended Posts

hey man just had search but i couldnt reli find what exactly i was looking for...i just need a quick answer...is it a big job to put a rb30de bottom end onto a rb25de? n will help me run higher boost more safely?

plz plz plz

The correct CR will help you run higher boost safely. so while u got the RB30 block apart, replace the pistons for lower CR, just grab a set of VLT pistons, they will be fine. if you read thru the rb30 conversions in the "forced induction performance" section, you will notice it isnt sucha big job.

if anyone is planning to do this, i have the stock R33 intercooler and piping for sale atm, for $80 ono. just pm me, its all in very good condition btw.

Don't be fooled gents. its not only the compression factor, but the piston itself, the N/a pistons are not Hyperputectic. therefore, even with low boost pressures, after a while you will melt a piston.

By all means, do this upgrade! turbo is 100% better effecient power, than most other mods. But do plan to change your pistons over in the near future.

Not really, my car ran fine for a over 50,000kms and as far as I know is still running fine without ever being cracked open to change pistons.

Melting pistons is from a poor tune, you can do it with any engine

the cast pistons will not tolerate the higher combustion temperatures associated with boost.

of course a good tune will help keep detonation to a minimum and the correct supporting modifications will ensure oil temps and water temps are kept low, but eventually the pistons will give up the ghost.

an example is my good friend who has a famous AE86 drift car here on the gold coast.

He had a stock 4AGE bluetop (bigport) bottom end which has the smallest rods, crank and gudgeon pins of all the 4AGE's and it took 6 months of punishment from a HKS GT2510 at 13 PSI pushing 150 kw at the wheels out of 1600cc.

It had a great tune from Adam from JEM and had all the supporting mods like a alloy radiator, great intercooler, big fuel system and oil cooler. The water temps never got above 82 and the oil never about 90 - 95. Eventually, the pistons gave up. But it goes to show that a motor can be pushed to nearly triple its factory power and still last for a while given that the correct supporting mods and great tune are applied.

Side note: I have read that the turbo RB30 pistons with the twin cam head will result in a 7:1 CR. too low

hey i just though i would go back a little bit and add something in, in relation to drilling the oil return line into the block a way of getting around this would be to buy an oil cooler and run the oil lines from the oil filter to the oil cooler to the turbo out the turbo then into the engine and around agian, this way you would have the best oil going to the turbo and you wouldnt have to worry about drilling holes in the block, and as a bonus it would be even easier to return to stock if needed

  • Like 1
the cast pistons will not tolerate the higher combustion temperatures associated with boost.

of course a good tune will help keep detonation to a minimum and the correct supporting modifications will ensure oil temps and water temps are kept low, but eventually the pistons will give up the ghost.

an example is my good friend who has a famous AE86 drift car here on the gold coast.

He had a stock 4AGE bluetop (bigport) bottom end which has the smallest rods, crank and gudgeon pins of all the 4AGE's and it took 6 months of punishment from a HKS GT2510 at 13 PSI pushing 150 kw at the wheels out of 1600cc.

It had a great tune from Adam from JEM and had all the supporting mods like a alloy radiator, great intercooler, big fuel system and oil cooler. The water temps never got above 82 and the oil never about 90 - 95. Eventually, the pistons gave up. But it goes to show that a motor can be pushed to nearly triple its factory power and still last for a while given that the correct supporting mods and great tune are applied.

Side note: I have read that the turbo RB30 pistons with the twin cam head will result in a 7:1 CR. too low

13psi in a 10:1 is asking for trouble that would have contributed to the death of that engine...I owned a blue-top as well and managed to melt the piston without a turbo.

under 8psi with stock pistons will see a reliable engine that won't need forgies and will live a long prosperous life.

ive got vacuum hose running straight from the compressor nipple to the wastegate actuator and its natural boost is .8 bar.

i do have a bleed valve in the line but its completely shut. i might delete this as it may still be causing a boost increase.

If you've got an RB20 turbo that's normal though, the actuator I put on my highflow from an RB20 was 13psi straight on the actuator, no bleed valve.

Grab one from a series 1 R33, it should be nice and tired and give about 6psi

  • 2 weeks later...

Absolute bullshit, my series 1 25de had the oil return just above the sump blanked off which simply unscrewed to fit my return line fitting. The same as the water return and oil feed, the only thing I had to source was a water feed which I t-pieced from a heater hose. Piss the rb20 crap off, accept a 25det stock turbo as a minimum.

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 will rebutt this and the preceding point from Dose....but without doing any calcs to demonstrate anything and without knowing that I am right or wrong. But... The flow capacity of a fluid transfer system is not limited by the smallest orifice or section of conduit in that system, unless it is drastically smaller than the rest of the system. OK, I use the word drastically perhaps with too much emphasis, but let's drill down on what I really mean. The flow capacity of the system is the result of the sum of the restrictions of the entire system. So, to make an extreme example, if you have a network with 3" pipe everywhere (and let's say a total length of only a few metres) and that 12mm ID restriction of the oil filter connection being the obvious restriction, then for any given amount of pressure available, the vast majority of all the pressure drop in the system is going to occur in the 12mm restriction. But.... increase the length of the 3" pipeline to, say 1000m, and suddenly the pipe pressure loss will likely add up to either be in the same order of magnitude, possibly even exceeding that of the 12mm restriction. Now the 12mm restriction starts to matter less. Translate this to the actual engine, actual oil cooler hose sizing, etc etc, and perhaps: The pressure loss caused by flowing through the narrow section (being the 12mm oil filter port, and perhaps any internal engine oil flow pathways associated with it) is a certain number. The pressure loss through, say, -12 hoses out to the cooler and back is negligible, but The pressure loss through -10 hoses out to the cooler, at the exact same length as the above, starts to become a decent fraction of the loss through the 12mm stuff at the filter port. Maybe even it starts to exceed it. I could actually do these calcs if I knew 1) how much oil was actually flowing in the line, 2) gave enough of a f**k to do things that I hate doing for work, voluntarily for a hypothetical discussion. Anyway - I reiterate. It's not the narrowest port that necessarily determines how much it can all flow. It is the sum. A long enough length of seemingly fat enough pipe can still cause more loss than a semmingly dominant small bore restriction.
    • To pick up what Dose is putting down. Not a lot of point running a huge hose if the motor is still restricted to the smaller size... It's only capable of flowing so much at that point...   *Waits for GTSBoy to come in and bring in the technicalities of length of pipe, and additional restriction from wall friction etc etc*
    • Hooley Dooley these things have some history! If i sell them they will need a certificate of providence to prove they have been in the hands of verified RB20 royalty! They have been stored in a plastic tub, away from sunlight and moisture. They are in mint condition. And they will stay that way, as i have sprung the money for a set of shockworks coilovers. I'm just working on getting them in at the moment, after rebushing the rear of the car, and while the subframe was out i welded in the GKtech reinforcement bracing as well.  They will get a workout at Ararat King of The Hill in November. I ran 48s on the short course there a few months ago, and i am hoping with new bushes and shocks in the rear i can launch a bit harder. There was a fair bit of axle tramp when i tried too hard off the line. a few of the corners had dips mid way which also made the car feel a bit unsettled, hopefully this will help there too.   
    • Food for thought, the stock oil filter thread is a 3/4-16 UNF, which has an ID of about 10 to 12mm (according to ChatGPT lol). Now compare than to an 10AN, which has an ID of about 14mm (Raceworks is 14.2mm, Speed flow is 14.27mm).  
    • Yep, totally get that. However hooking in for Generator back up is only a few hundred bucks for the wiring. You could put a couple of those in (for different circuits explicitly) and run a couple of baby generators. Bonus, you can balance them across different circuits, and now have backups in your backup. I'm looking at buying places that won't even have water etc, and I don't mind the idea of getting off the electric grid either, even with everything you've said. This country already has enough power outages that even the mains grid isn't that reliable anymore. I do agree though on spending a bit more to get better gear, and to add some extra redundancy in to the system too.
×
×
  • Create New...