Drilling Rb25 Head Out

[Franko07]

Hi im quite new to the forum and rb25s in general just wanted to double check something.

Im currently putting in a 25 into a31 cefiro drift car. The engine is getting freshened up before hand so the heads off and i had heard rbs have a problem of over oiling the head at high rpm. Bit of research said that theres some simple fixes like drilling out the drains in the head and block? Just want to confirm that its these 5 holes ive circled? When i lay the hg on the block the holes arnt central with the hg so do people just die grind on an angle so there straight with the gasket? And do they drill all the way down or just the entrances to open them up? Im planning on doing the rear drain through the welsh plug as well bought thought this couldnt hurt either... hope this makes sence was written on my phone so appologies

Thanks

[GTSBoy]

http://www.sau.com.au/forums/topic/110680-oil-control-in-rbs-for-circuit-drag-or-drift/

69 pages. There's a bit of useless chatter in the last few pages, but somewhere in the few pages before that the overall conclusion of the thread is summed up in a few posts.

[Franko07]

Thanks for the reply that post was interesting didn't quite get through all 70 pages though haha

It seemed to cover more what the problem was but I was looking for more of a how to?

From what I can gather I'm running a stock oil pump with VVT so that means that I leave the VVT oiling hole as that has its own drain, the middle oiling hole in the block, block that one off by tapping and threading in a screw? and the rear one fitting a 1.25mm restrictor? or is it the other way around?

Then the welsh plug drain I was just going to make myself by drilling and tapping two holes next to the plug and wind in fittings so then you can get them closer to collecting point on the head and the don't have a lip there, but is it alright to attatch the drain end into the turbo drain? I'm assuming as the crank rotates past there it creates a little vacuum and they are both gravity drains that this would be alright?

thanks!

[Blackkers]

The hose from the back of the head to the sump isn't actually an additional oil drain. It's just a breather.

The theory is that if crankcase pressure has another avenue to make its way to the head then it's less likely to interrupt oil flowing back to the sump from the head. That's also why you don't plumb it into the turbo drain, it needs to go to a fitting on the intake side of the engine above the oil level.

The general consensus is that it's redundant if you properly vent the head and sump to a catch can. Personally I'm going to do it anyway because I didn't drill out the oil returns so anything will help

It's all in the last 20 pages of that thread. I urge you to keep reading. There is a great summary post by a member called iruvyouskyrine or something similar.

[Franko07]

Yeah sure thing will do. Can someone quickly confirm that its this hole im pointing to in the picture that i block off? As i found a good post by sydneykid with good photos but in the beginning he says all rb's should block off the rear squirter as 26's have this standard but in his table he says that a vvt 25 with stock oil pump doing track work should block the middle squirter and leave the rear? Is this correct? I get a bit nervous when blocking off oil... thanks

[Franko07]

Its seems better to put two 1mm restrictors in as theoretically that should halve the oil flow to the head if they are a 2mm hole from standard?

But i read the rest of the post and it seems that alls you need to do is take the oil that comes out the rockers and make it go back into the sump and let the crank case breathe. So if i made a 4 fitting catch can and had both rocker covers going to the top, another line from the top of the can going to the turbo intake to create a vacuum and then a line in the bottom returning to the sump this would solve the problem?

Sorry to repeat things in the thread but im trying do things right.

Also where do people mount the return for the oil in the sump/block if i cant use the turbo drain? I dont want to make a weak spot in the block (photos would be great) i wanted to put it on the passenger side of the engine so i could use the turbo as vacuum so i dont have to run one way valves and stuff if i used the throttle body...

[Franko07]

Im talking about the stock sump too as those winged sumps cost like 1k which is more than the whole engine where im from. Not to sound cheap but surely it can be done.

[MJTru]

I never understood how the hose in the back of the head is a breather. ??? For me in drag racing it never breaths. Its always stuffed with oil. The oil has a had time flowing back to the front of the sump on hard launches. I tend to use the highest point for a breather on the block. We all try different things.

Edited June 5, 2015 by MJTru

[GTSBoy]

Its seems better to put two 1mm restrictors in as theoretically that should halve the oil flow to the head if they are a 2mm hole from standard?

Also where do people mount the return for the oil in the sump/block if i cant use the turbo drain? I dont want to make a weak spot in the block (photos would be great) i wanted to put it on the passenger side of the engine so i could use the turbo as vacuum so i dont have to run one way valves and stuff if i used the throttle body...

I know you have to dig through a lot of crap in the oil control thread with a lot of differing opinions etc etc....but one thing that we eventually agreed on was that the number and size of restrictors really depends mostly on how big the oil pump is. If you have a really big pump then you need to restrict the oil flow to the top a bit more. This is summarised in that one group of posts that has been mentioned before.

The side of the engine to put the sump breathers on is also clearly summarised there.

I never understood how the hose in the back of the head is a breather. ??? For me in drag racing it never breaths. Its always stuffed with oil. The oil has a had time flowing back to the front of the sump on hard launches. I tend to use the highest point for a breather on the block. We all try different things.

All pipes and tunnels running between the head and the sump are both drains and breathers. The reason to consider the rear additional ones as breathers rather than drains is also clearly laid out in the oil control thread summary. If you have a massive amount of sump gas that needs to flow up to the top and you only have the skinny little holes in the block for it to do so, then the oil and the gas are fighting to go in opposite directions, and the gas flow wins. Hence the oil stays up top. The additional drain at the rear adds more area, reducing the competition for cross sectional area. In drag racing (which is important to you, but not to most GTR owners, especially here in Australia), the acceleration forces is likely to make the oil head towards the back of the engine, and so it is well likely that the rear drain will end up acting more as a drain and therefore allowing the oil drains at the front of the engine to perhaps act as upward flow channels for sump gas. But that doesn't change the simple fact that it is just additional cross sectional area, rather than being ONLY a drain.

[Franko07]

yeah I understand the concepts fine, I just want a picture of someone who has done the correct catch can/sump vent set up on the stock sump/block, or even a drawing as the pictures are just of bays with pipes going everywhere and you don't really understand what there actually doing or places that they have tapped into.

and then I just want some one to confirm that its the hole im pointing to in the pic that I block off in my 25 as in Sydneykids chart it says leave VVT, block the middle one, restrict the rear with 1.2mm (this is for stock oil pump keeping vvt and drifting) but in his opening statement he says that 26's have the rear blocked off from factory, so which hole is it? or does it matter? does oil just get to where it needs to go and all the channels are connected?

[Franko07]

This is how I was going to set up catch can, excuse the crudeness of it, but you get the idea.

Right or wrong?

[MJTru]

Ive used on rb26 the front turbo drain as a vent for excessive blow by. I also have the head drain going to the rear turbo drain. Wonder how this will work. Thinking that now the rear head drain /vent will do its job letting oil drain or vent blowby in eather direction. Will see how it goes. I cant begin to see the nightmare these oiling issues would cause in drifting. Guys do it tho. I have heard of using a scavenging pump to aid in this phenomena but never really seen a clear depictions of it.

[MJTru]

Front turbo drian. Way up away from oil.

[GTSBoy]

Yeah, so 8 years later and seeing as this thread came back to my attention, I thought I'd stitch something on to the end of Marcus's posts above, to point out something important that he was doing (wrong) with a little evidence of how to do it right.

On 6/9/2015 at 12:05 PM, MJTru said:

I also have the head drain going to the rear turbo drain. Wonder how this will work.