Greddy/Trust Plenum

[Guest RedLineGTR]

thanks sydneykid

[GTS-t VSPEC]

Just to add my few cents to the debate:D

I have a Greddy plenum and have found gains across the board with it. Maybe it's due to my intercooler pipe setup, or maybe due to the plenum it's hard to know. I have better throttle response, more mid-range power, and it doesn't run out of puff at the top-end till much later. In WA my stock turbo made the most power from all the other stock turbo's, and the major difference was the plenum.

Make of that what you will:D

[benm]

What ECU are you running and what rwkw did you make ?

[GTS-t VSPEC]

I was running a Wolf, and made 296.6rwhp in shootout mode. I think the highest other reading for the day was 282rwhp.

[benm]

Very nice !

Anyone ever made over 300rwhp from the stock turbo ? I'm currently at 272rwhp still with stock ECU and for some silly reason i'd rather upgrade everything but the std turbo just as something different to do.

[Steve]

Thanks sydneykid, interesting reading.

Paul, thats insane from a stock turbo, what boost?

[GTS-t VSPEC]

It made 296.2rwhp from 14psi, and 296.6rwhp from 17psi, the torque gain was massive with the extra boost.

[Ronin 09]

sydneykid, your info is always extremely useful - particularly as i have only theory to back my suggestions, and you have actual bench experience. I already have a greddy plenum on order, so it is going on my car. To begin with i will probably run a adapter to use the factory throttle body, and run 65mm piping to the throttle from the FMIC outlet (it has a 65mm outlet).

I know that there will be flow turbulence behind the throttle when it is cracked open (due to the expansion to 80-90mm) but if anything this should in theory spread/disrupt the airflow a bit and instead of flowing straight to back cylinders (ie. no 5 and 6) there should be better distribution around the front of the plenum.

What do you think?

[Sydneykid]

Hi Ronin 09, how much power are you targetting? And what do you intend using the car for?

[Sydneykid]

Hi guys, I have seen 220 rwkw on a standard turbo in a R34GTT at 1 bar. But it only lasted 5 laps of Wakefiled Park on a suspension tuning day until it spat the turbine into the cat.

[Ronin 09]

hi sydneykid, currently on the car is:

*3.5" turbo back

*pod in inclosure

coming is:

*FMIC

*ProfecB spec II

*Greddy intake

next plan:

stage 1:

*Power FC

*Fuel pump

*Injectors

Stage 2:

*HKS GT3040

*HKS 1.2mm head gasket (and any other bits and pieces to support this, obviously)

So i would suppose i'm looking at around 280rwkW (conservative with around 1.2bar)

[GTS-t VSPEC]

Yeah, the R34 GTT's make much better power than the 33's, but the turbo's are always the weak point in both models:(

[Steve]

Isnt the RB25DET NEO rated at 208kw from the factory? or thereabouts?

[Sydneykid]

Hi Ronin 09, list looks OK but I would strongly recommend a set of camshafts, we find the Tomei 256's designed for working with VVT to be great. They don't add too much to the max power (10 or so rwkw's) but we found 30 rwkw in the mid range and brings the turbo on boost quicker. I am also a fan of doing some headwork while the head is off, again not much extra max power but much faster spool up and way better response.

I am not a fan of thick head gaskets, size the conbustion chamber to get the right compression ratio, o'ring the head and use a standard head gasket. That's my preference.

From my memory of the GT3040 compressor flow maps, I don't think you will get to 280 rwkw at 1.2 bar, certainly not without camshafts and port work. More like 1.4 bar with those done and 1.6 without.

What manifold are you going to use the GT3040 on? Wastegate? You will need a Z32 AFM at least, I personally prefer the Q45 AFM, at 90 mm they flow better and match up to the 100 mm GT3040 inlet diameter much nicer and saves using those expensive silicone reducer hoses.

Hope that helps

[Ronin 09]

Sydneykid, thanks for the info there.

I forgot to add that i'm also getting a adjustable exhaust cam sprocket, and i understand that i would idealy better to go with a a set of camshafts - probably best to do the camshafts when the head is off, while the adjustable sprocket is just there to try and bring on boost a little earlier at the moment.

I understand that most people don't like thicker head gaskets, can you ballpark what it would cost to size the comb. chambers and o-ring it? While it is off i would look to clean the ports up too. I know this is probably better and should hold boost with alot more reliability.

The power FC, injectors and pump will be done close to christmas, and i will probably do a Q45 AFM then too. I really want to get the PFC in soon, just so the mixtures are more optimum.

The turbo will be at least 6 months away, as i'm waiting to hear from a new job. It is the plan at the moment, but as we all know, plans change pretty quickly. Ideally i'd like to go with a HKS stainless manifold to suit, with an HKS external wastegate. But as funds allow, i may have a custom exhaust manifold made up by my exhaust shop - they do very good custom work.

Thanks again.

[Sydneykid]

Hi ronin 09, We have found ther Tomei 256's designed for the VVT don't benefit from adjustable camshaft pulleys. Their standard (un adjusted position) is optimal, they obviously did their homework.

Port, polish, size combustion chamber and O'ring head on a 6 cylinder shouldn't be more than $1K.

I am not a fan of HKS stuff, it is simply too expensive for me. I personally don't see the value in the product, but I am only interested in the function not the look. Plus I am not a fan of top mount manifolds, turbos are heavy and sticking them up in the air does nothing for the centre of gravity.

Hope that helps some more

[Ronin 09]

Thanks Sydneykid, that is great help. I think i've hijacked the thread enough, but will keep you posted closer to the time i'm looking at turbos. Cheers again.

[Gradenko]

A lot of interesting points brought up in this thread.

Originally posted by Sydneykid

You are right about losing pipework being better for response, it's a worthwhile target.  The important thing here is the volume of air in the pipework, not the length of the pipework.

Volume of pipework and volume of plenum, for those who are moving to a front facing plenum for response, are the important factors. The 80mm vs 63mm comparison is a good one. Another one is the 5L+ most of aftermarket plenums consume vs ~2.75L for the factory one (caluclated, not measured, so may be inaccurate). Not to say 2.75L is ideal, it isn't, but it should perform better from a response point of a view.

(Warning: Uneducated fluid mechanics ahead)

I don't agree with the factory throttle body location. Runners for cylinder 3 & 4 are undoubtly favoured in my opinion. The design just seems too ameaturish to feed air evenly. I don't believe the stock fuel rail can be blamed for cylinder 3 & 4 running lean either. According to a local injector cleaner, the design seems ok and it's not as flawed as, say, one from a wrx (ej20).

Originally posted by Sydneykid

On turbo inlet systems flow bench comparisons are a bit nebulous at best.

I had originally planned to do flow bench tests on the stock plenum to see how good (or poor) its design is, but as you said, flow benches can't be used to test plenums accurately. While its possible to the test how much each individual runner can flow, this figure means little when all 6 runners are in use. The real difficulty is in trying to predict flow after reversion from adjoining inlet tracts cause pulses along the plenum. In truth, its pretty damn difficult without megabuck instrumentation that only engine designers would have.

The only thing I can do is question Nissan's design and try and improve on it. Thats what led me to try a modified factory plenum. I wanted good response with a factory sized turbo with fmic and that meant shorter piping distance, low piping volume, no increase in plenum volume and standard 60mm throttle body. A modified factory plenum would suit very well in this situation. (Before big turbo ppl jump on me, I said stock sized turbo )

I didn't have a hand in the design of my cut'n'shut (one of GTS-t VSPEC's friends made it), but it does have a bit of thought put into it. Off the top of my head:

- Throttle body isn't mounted perpendicular to the plenum. It enters at an angle so charge disperses against the side wall of the plenum and doesn't favour cylinder 5 & 6 or neglect cylinder 1.

- Wall between throttle plate and cylinder 1 is smoothly radiused to encourage flow.

Should have the piping finished early next week and I'll be keeping a very close eye on the detonation threshold of individual cylinders. I'll call it a success if it gives a noticable increase in response and doesn't increase the tendancy to ping. Extra power is not a goal.

Pic of plenum in attached. Excuse the quality, it was taken with a film camera and scanned poorly.

[Steve]

Nice work, will be really interested to see the results of this one.

Cheers

[Sydneykid]

This is S of S here...

Before I start, I am not trying to shoot you down Granenko. Just one point confused me. IF you can explain exactly why a front facing throttle body is better, please go... I didn't really see any reason it would be from your post... but

Originally posted by Gradenko

I don't agree with the factory throttle body location. Runners for cylinder 3 & 4 are undoubtly favoured in my opinion. The design just seems too ameaturish to feed air evenly.  

Lets put it this way; I reckon having the throttle body closer to all of the cylinders is way more intelligent than having a throttle body close to cylinder 1, but miles away from from 5 and 6, which is what is causing a few people problems with air distribution. Sure #3 and #4 are favoured, but then so is #1 and #2 in a forward facing manifold... but #5 and #6 don't get ANY air... I personally don't see how a forward facing plenum could have any positives - sure, it might shorten the amount of pipework, but maybe not decrease the volume on air in the pipework and plenum chamber. I am no fluid dynamisist (sic?!?!?!) but my in my logic, after some thought (hours and hours), the standard inlet just seems way more efficent. Or maybe I should say the position of the throttle body is more efficent - that way i exclude the modified standard inlets... I also think that Nissan have an R and D budget three times the amount of money I will make in my lifetime..... prolly more. So i think nissan spent more time with inlets, and prolly knew what they were doing. And it seems to work pretty damn fine just the way it is.

BUT, if I have 6 throttle bodies, then hella yeah... but if I had 6 throttle bodies, I would prolly have an RB26, so I wouldn't be changing it - Just found out that the Apexi V-MAX GT-R (did an 8.45 1/4 mile no less) uses the stock inlet - pretty interesting. To add to that, most of the really fast curcuit GT-Rs also use the standard inlet... i don't see a reason to change.

Son of Sydneykid