Question for all you Greddy/Trust plenum owners ?

[B-Man]

Hi Guys,

I just received my Greddy/Trust RB25 plenum kit from Japan.

I was sort of surprised to see how rough and daggy the inside of the plenum chamber and runners are.

Understanding that the thing is cast aluminum , I thought the factory would have smoothed / ported / polished the chamber and runners ??

Did you guys who fitted these plenums do any extrusion honing, porting, polishing before you put them on ??

Or did you simply remove the cast dags an bolt it up ??

Cheers,

[grepin]

Hi Guys,

 

I just received my Greddy/Trust RB25 plenum kit from Japan.

 

I was sort of surprised to see how rough and daggy the inside of the plenum chamber and runners are.

 

Understanding that the thing is cast aluminum , I thought the factory would have smoothed / ported / polished the chamber and runners ??

 

Did you guys who fitted these plenums do any extrusion honing, porting, polishing before you put them on ??

 

Or did you simply remove the cast dags an bolt it up ??

 

Cheers,

Just had it bolted on. Sort of considered cleaning it out. However maybe a little turbulance may keep things even within the plenum. I might be waffeling however.

[Guest INASNT]

For a $1000 plenum i would expect the inside to be nicely ported and clean, especially something from japan

[Merli]

For a $1000 plenum i would expect the inside to be nicely ported and clean, especially something from japan

Why? $1000 is cheap as chips for a CAD designed plenum chamber...

If you want all that, step upto the $4000 JUN GT Surge Tank (Plenum Chamber), and pay for the man hours it takes to get that kind of loving

Brendan, sorry I can't help, my car came with a GReddy plenum, although I bought one for my silver GTS-t before someone prematurely ended that project. You're right... The insides are quite rough and don't look perfect for smooth airflow, but they're not THAT rough. When I looked inside the one that I bought, although it had a slightly rough finish, there weren't any protruding cast marks inside that would really disrupt the path air would take...

Also notice that the runners are tiny!! But with a lot of meat cast into the runners. I believe they've been cast small to promote faster air velocity, but give you the option of boreing them out more if you're running high boost and need more airflow...

[B-Man]

Thanks Merli,

Don't get me wrong - the thing is a work of art ! When you look at all the angles etc - you can see that a lot of R&D went into this.

I guess to get the most out of it, a bit of machining / hand luving with a dremel tool (in the right hands) would be beneficial !

I'll see if I can take some pics for reference while it is off the car !

[DoughBoy]

Have to disappoint you, but the Jun plenum for the RB26 isn't smoothed out as much as you think. The only part which has been finished after casting (besides the bolt holes) is the outside. Go Go rice factor!

After saying that, there is plenty of meat in the runners for them to be ported out. Jun may feel that anyone going to spend that kinds of dosh on a plenum will pay someone to matchport/ enlarge the runners anyway.

[Merli]

Have to disappoint you, but the Jun plenum for the RB26 isn't smoothed out as much as you think. The only part which has been finished after casting (besides the bolt holes) is the outside. Go Go rice factor!

After saying that, there is plenty of meat in the runners for them to be ported out. Jun may feel that anyone going to spend that kinds of dosh on a plenum will pay someone to matchport/ enlarge the runners anyway.

I had a look inside Mario's JUN plenum chamber, and let me tell you, it's about 5 trillion times more advanced than the GReddy plenum.

The way the internal bellmouths have been crafted is just mindboggling, and just by looking inside it, you can tell how much care has been taken in it's design and fabrication.

It was flowtested to a 0.4% flow difference across all cylinders. If that's rice factor, then I think I need to find a new hobby

[Ronin 09]

mine had no really big cast dags, but like anything flow related, if you can be bothered polishing etc it will be better. But time vs an extra couple of k-dubyas?

[DoughBoy]

Gah, don't make me pull out the cam and start taking photo's again. Wasn't discussing the performance, design or flow characteristics of the Jun piece, just the fact that the internal parts of the manifold are not machined from factory, and that the only polished part is the external.

[Sydneykid]

Hi guys, good machinists in Japan charge like brain surgeons. So there is no way that you should expect any hand finishing of anything. If it comes off the cast that way, then that's the way you will get it.

[B-Man]

Hi Guys,

Well I've had a bit of a better look at the plenum/intake and I did imagine that the finish internal to the unit would be better - maybe I got a newby casting engineer or something - I got BIG dags there..... Nothing that can't be fixed mind you ....

SK - I do understand that manual labour in Japan is expensive - but when I looked at the Greddy plenum/intake, I thought to myself - yup, designed in japan, made in China or Korea....... I expected better.

OK nuff said on the afformentioned problem.... what am I gonna do to fix it ??

Well I had a crack at removing some dags and gave up - this is a job for the pros -

Since I paid good dolllar for the unit (more than $1000) I've decided to spend and extra 200-300 to get it extrusion honed, ported and polished. Mirror finish on the inside (used to know a girl like that once..... he he)

Here's some before pics.... (i'll post after pics too)

[B-Man]

[mambastu]

I got my GReddy plenum a few months ago and mine hasn't got the casting marks yours has in picture 3 and 4 but it has the casting marks in the runner side walls. Must admit I was a bit surprised it wasn't smooth inside.

I also bought the GReddy throttle body adaptor and when I bolted it onto the plenum I found it wasn't aligned very well either so port matched the plenum to the TB adaptor plate and matched the runners to the manifold gasket and smoothed the runners as far up as I could go with the porting tool.

The plenum water ways were much worse than yours so I smoothed those out as well.

[mambastu]

While we're on the subject of GReddy plenums, it doesn't have a takeoff for the turbo water return like the standard plenum.

Where have people plumbed the return into ?