I took a look at a Greddy Elbow recently and noticed how rough the interior surface is. Looks like it has had minimal if no post treatment done to the interior after the part was cast (sand cast? looks rough!).

Would it be worthwhile to wet-sand/lightly polish the interior surface? Has anyone done this?

Also, would the Greddy Elbow be a good place to locate a bung for water injection or would it be better to locate the bung on the intercooler pipe that connects to the elbow from the IC? Assume that this will be on sequential twin set-up with typical bolt on modifications.

 

There was a long debate about this kind of topic:

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/polished-intake-manifolds-very-bad-554531/

In general, it seems a little bit of turbulence is desirable. I don't think it would be worth the effort to smooth it out, especially since your UIM and LIM will still be rough.

 

Unless I messed up the reynolds number calculation, it looks like you're pretty much in the turbulent flow regime anyway.
Roughness of the tube will have an impact on the pressure loss in the fluid flowing down the tube (ie rough tube = pressure drop down the tube). Also bends impact pressure loss, I don't have a quantified number, but I'd say the bends are the dominant factor!

 

I'm a mechanical engineer and I can tell you that fittings/bends will tend to dominate static pressure drop calculations.

Any post-turbo airstream is going to be well into the turbolent region of flow, no question. I'm not sure if I agree with the necessity of having roughness to induce mixing pre-throttle body. I may agree with the need for some airstream swirling just before the intake chamber, but only when the airstream is near the injectors.

Back to the Greddy Elbow... I have some spare time on my hands while I wait for someone to sell me a single Greddy Pipe... so I might play around with wet sanding the interior of the pipe some more. My thoughts are to reduce the huge suface imperfections and not really go so far as to pursue a "mirror" finish.

If anyone has a ballpark figure of what a typical bolt-on Hitachi Twin is flowing [CFM] in sequential mode at a pressure of 11-ish PSI and a guess of what the roughness factor of the original Greddy Elbow is, I can try to pull a pressure drop out of it.

 

 

^lol. Appreciate the Barney Style explanation.

 

I'm not sure if free-flow analysis really applies to pipe flow. Want to enlighten how it applies here? I am always up for learning.

As a follow-up, why dont bullet manufacturers dimple the casing of bullets to improve velocity through the barrel of a gun?

The fluid-flow through the Greddy Elbow will be deep into the turbulent region. I'm not sure if the same could be said for the aero of a golf ball.

 

I used to have that kind of time to do such things, now I don't worry about them





LAter

 

i love when people try to get into dick measuring contests via the interweb.

anyway, it was a joke. har har

 

i always keep the old v8 thinking... Keep the turbulence for intake and intake ports. most top builders do this

 

After I took some of the bend out of the Greddy FD elbow to work on my FC I went ahead and polished the inside of it just like the rest of my intake tract.

A couple of engine rebuilds later I went back in and roughed up the inside radius and just before the bend.

My thinking then was roughing the inside radius might help trip the flow to turbulent and help keep flow attached to the inside radius for more even distribution front to rear going into the throttle body.

I also used to spend way too much time thinking about such things...