RB 25DET coarse OEM intake manifold cast ..

[Torques]

Would there be any benefit in smoothing the rather coarse intake runner (lower part) on an RB25DET?

I think possibly not, but what's your opinion?

 

That picture is for the last cylinder ..

 

[Rusty Nuts]

You are only going to be able to get at a small amount of the intake runners, not the whole intake manifold unless you extrude hone it. That will cost a fortune. Dry intake systems should benefit from smoothing, whereas fuel loaded systems benefit from a courser finish. Will the time and money spent give you an economical gain is more the question. Positive pressure dry intake systems maybe inherently turbulent, I seem to remember that they have an insanely high Reynolds number which would make the flow inherently turbulent, but ive forgotten more than I remember about laminar flow.

 

 

 

Light travels faster than sound, that's why some people appear bright until they speak!

[Torques]

Yes, I agree .. removing these 'barnickles' might be more of a cosmetic procedure. (I'll still give them a quick smooth over)

Extrude honing would be the way to go, but as you said 'it will cost a fortune' and is economically not viable.

I'm not sure about the Reynolds number, after the air has passed through the FMIC and long subsequent piping it might not be that turbulent anymore?

Btw. I have seen better casts on WWII engines ....

 

 

Edited May 4, 2018 by Torques

[Rusty Nuts]

3 hours ago, Torques said:

Btw. I have seen better casts on WWII engines ....

 

Me Too Andy, I also would not be able to resist removing those crusty bits, just because they look awful. The Neo head on mine was cast and finished so badly at the rear oil drain that half of the gallery was blocked, I spent a couple of hours on that.

[GTSBoy]

I would say that the benefits from waving a die grinder around in there will be unmeasureable.  There may be some benefit to keeping the finish on the inside of the bend a bit rougher to hold on to the flow for longer, thus reducing separation and thereby using more of the cross section for actual flow.  Luckily, this is he hardest bit to reach with a burr.....so, win.

The runners are not small on a 25, so there's little point in trying to make them bigger.  The single biggest benefit available would be to ensure a good port match, and even that advice would be subject to knowledge about how the port itself works and whether a small mismatch at the runner-port interface can actually help (which it sometimes can, to force flow to bias a little to one side or the other to set it up to make better use of the downstream port shape, short turn, etc).  But I don't know, so am not going to say.

And one very important thing for you all to remember.  I cannot imagine any flow, at any point in an automotive intake tract that will not be fully developed turbulent flow with Re well above the minimum.  Usually Re> several tens of thousands, even at low revs.  The velocities involved are simply too high.  And boost has nothing to do with it, because as the velocity goes down (because boost) then the density goes up at the same rate and they cancel each other's effect.  You'd have to have the air velocity down into the single digit m/s range to even hope to get the Re below 10k.

There is pretty much no such thing as "laminar flow" in any part of anything real.  The best you can hope for is "well conditioned turbulent" flow, where the flow is fully turbulent, but it has had time in a straight duct to develop an even velocity profile

[Torques]

6 hours ago, Rusty Nuts said:

Me Too Andy, I also would not be able to resist removing those crusty bits, just because they look awful. The Neo head on mine was cast and finished so badly at the rear oil drain that half of the gallery was blocked, I spent a couple of hours on that.

Yes, the crusty bit will have to go ... just for esthetic reasons

Funny, I thought on the Neo things would have improved ..

 

[Rusty Nuts]

7 minutes ago, Torques said:

Funny, I thought on the Neo things would have improved ..

Nope, mine was cast by an orangutan on work experience and there was clear evidence of a permanent pool of oil  having existed for the engines first life ie a big brown "bathtub ring"

[Torques]

6 hours ago, GTSBoy said:

I would say that the benefits from waving a die grinder around in there will be unmeasureable.  There may be some benefit to keeping the finish on the inside of the bend a bit rougher to hold on to the flow for longer, thus reducing separation and thereby using more of the cross section for actual flow.  Luckily, this is he hardest bit to reach with a burr.....so, win..................

Yes, all valid and true what you write. Without proper fluid dynamics simulation I suppose we'll never know for sure what's going on there. Possibly back in the day Nissan used trial and error designs to figure the best flow out.

I'll possibly go for a different manifold at some point but I don't want to loose low to mid range which seems to be the case with the Greddy style intakes

 

 

 

 

[Dose Pipe Sutututu]

Plazmaman has released a billet, CNC machined runner intake manifold and plenum kit.

I might just get it for the sake of it, bring on no power gains and more lag! Lol

[Jordy32]

2 hours ago, Dose Pipe Sutututu said:

Plazmaman has released a billet, CNC machined runner intake manifold and plenum kit.

I might just get it for the sake of it, bring on no power gains and more lag! Lol

Baller life! And you give me shit about my pink salt and brunch habits

[Dose Pipe Sutututu]

7 minutes ago, Jordy32 said:

Baller life! And you give me shit about my pink salt and brunch habits

Decided not to upgrade my car to something sensible because I came up with a great idea to get the missus a Golf R as a daily

So... R33 might get more mods before it even sees the dyno (if ever) lol

[Torques]

On 5/5/2018 at 10:49 AM, Dose Pipe Sutututu said:

Plazmaman has released a billet, CNC machined runner intake manifold and plenum kit.

I might just get it for the sake of it, bring on no power gains and more lag! Lol

OK, I didn't know that ... I only knew about their 'set on top' bulb which looks a bit funny

That plenum costs serious money and I like my fuel rail ...

https://plazmaman.com/product/rb25-r33-and-neo-inlet-manifold-full-billet-runner-6-injector/

 

Edited May 7, 2018 by Torques
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