Flow test results of my Front Facing Plenum

[red900ss]

Now flow testing is new to me but wouldn't the best way to test it be at a common point in the runners with the runners attached to the plenum?

[B-Man]

Hi Guys,

I'm using these results as a baseline. As I have stated in the past I am no fluid/air dynamics professor - and am relying on the flow test ppl to do their job. I will try and find out the conditions of the testing so we have a baseline for the environment and conditions also. But I don't want this to turn into

Dino, I will endevour to find out where the flow readings were taken but at this stage I would assume at the end of the runners. Any other method of testing wouldn't be useful IMHO.

[Guest INASNT]

Bman

who made that plenum of yours and how much litres of air can it hold??

Also how hard is it to adapt the xf throttle body?

[B-Man]

Hills Motorsport

re: Volume - no idea, I suppose I could measure it - but the car is not with me right now. I'm prestty sure it's larger than the standard plenum.

Opps forgot about the XF TB. - I understand it wasn't hard to modify - just bolts on with a little help from Mr silicon hose. But there is no Throttle Position Sensor on mine (there is the ability to put one one, but mine, no have - I'll have to get one when the PFC goes in)

[Guest INASNT]

Hills Motorsport

Didnt Steve have a few issues with his hill plenum recently?

[Warpspeed]

I am a bit skeptical about all of this, how were the measurements made, and at what test pressure?

Is each runner flowed individually, or was there 1712 CFM flowing through the throttle body when these readings were taken?

I cannot see how flowing one runner at a time with a steady airflow is going to behave anything like six runners pulsing on a running engine.

I am not trying to put anyone down, please do not misunderstand me. Just trying to get my head around what it all actually means.

The only way I can see of doing this might be to blow high pressure air into the plenum, about the same amount as the engine would use, around 1.5 CFM per horsepower. And it should come through a similar pipe to the intercooler outlet pipe. Fit six identical orifice plates to the head face of the manifold, and measure the static upstream pressure at each orifice through the injector holes.

A better way might be to do a similar thing with a cylinder head fitted and rotate the inlet cam with an electric motor. You could measure the airflow coming out of each combustion chamber either with an orifice plate or an anemometer. This would be as close as you could really get to having similar conditions in the induction system to a running engine.

I would really like to try this myself someday, and probably will once my latest and largest flowbench is completed.

[Sydneykid]

Hi Warspeed, I have yet to find a flow bench (and I have looked all over the world) that measures flow under boost. They all operate under the same principle, ie; create a vacuum (usually 1 bar) at one end and measure the pressure drop through the item you are testing.

So in the case of B-Man's tests they would have connected the inlet manifold up to the vacuum source at the head flange on the inlet manifold for each cylinder and measured the pressure drop. This is then extrapolated into a flow rate (cfm) at 1 bar vacuum.

This all changes under boost conditions of course, where the air is being pushed through the inlet manifold. In addtion you introduce tuning frequencies into the inlet system. But I don't believe this matters to the overall validity of the differences between cylinders.

We have found by increasing the vaccum to 2 bar you get a better indicator of the flow capacity under boost, but the differentials don't change ie; a porly flowing cylinder (in comparison to the others) still flows poorly.

Hope that adds to the discussion

[Warpspeed]

Hello again Sydneykid.

On my flowbench I do most of my testing at 28 inches of water pressure drop, which is pretty close to 1 psi.

The induction system is measured at 28 inches vacuum, and the exhaust side at 28 inches of positive pressure. It is generally recognised that the flow figures that you get normally aspirated come pretty close to what you would get on an engine dyno, which is why that particular pressure differential is so popular.

Also, induction flow ends up near 1.5 CFM per BHP, and exhaust flow 2.2 CFM per BHP when doing flowbench work.

So when you say your cylinder head flows 380 BHP, that would equate to 380 x 1.5 = 570 CFM flow (total) at 28 inches of water pressure differential. That would be 95 CFM per inlet port on a six cylinder engine.

It does not really matter if you suck or blow, as long as the flow direction is correct, the exception being right at the beginning of the induction system, which may sits in (almost) still air. So if you have individual tuned n/a trumpets, you must suck. But a turbo inlet plenum is going to see some pretty turbulent air coming down the intercooler pipe, so blowing into the plenum with your flowbench is quite valid, probably even better.

The same goes with testing intercoolers. You must blow. If you try to suck, the incoming air has to see a sharp edged pipe on the upstream intercooler tank, and you get a false reading. You could fit a very efficient bellmouth to the end tank, but it is probably still better to blow.

But getting back to plenums, and air distribution, it would be pretty difficult to create similar flow conditions on a flowbench with steady flow. You really need the intake runners to pulse in the correct sequence, otherwise I think any flow distribution figures would be pretty meaningless.

Another thing people forget, it is actually fairly difficult to measure static pressure in a fast moving airstream. If you had a hose with a very sensitive pressure gauge on the end, and stuck it out of the window of your car at high speed, you could measure a positive or negative pressure depending which way the end of the hose faced.

It is not realised how high the air velocities get in a turbo engine, maybe half the speed of sound is high, but not all that unusual coming right out of a turbo. So the air is going maybe 500 Kmh, and the boost you measure might change rather more than you think depending on where and how the sensing line is fitted.

The fact that the poor old plenum struggles a bit to distribute the air evenly is not really surprising.

[Steve]

Thanks for posting up the results B-man.

Just for those reading, and to add a bit of interest, the plenum in question actually has the stock plenum's bottom on it, with radiused openings where it alignes with the runners.

I think in this case, as long as all consequent testing of a totally stock plenum and trust plenum were conducted in the same manner, it would provide a basis for comparison.

Once again B-man, thanks for sharing the info:)

[Sydneykid]

Hi Warpspeed, have you tried it at higher pressure drops, say 56 inches?

For interest, we have tested an intercooler and found very little turbulence (smoke test) after around 1 metre of 75 mm pipework (what we run on a GTR). It comes out of the intercooler end tank a bit turbulent but the length of pipe straightens it up.

[B-Man]

Hi Sydneykid,

I was pondering plenums again, as one does on a Sunday - And wondered if honing & polishing the (inside of) cast aluminum standard plenum would add any significant flow to the RB25 ? Say for instance if one was geting some mild port & polish of the head - I suppose it woudn't hurt ??

[Steve]

B-Man, I have a friend who is very close friends of the guy who runs Signal in Osaka - cant remeber his name off the top of my head sorry.

I was told this yesterday (my friend came back from a trip to Japan) that he was in stiches when he was told about guys trying to use the stock runners and bolting on a new plenum chamber to increase performance, as it is according to him the stock runners pose restriction, not the plenum chamber itself - interesting.

[Sydneykid]

Hi B-Man, I think I have covered this a number of times before, but here we go ..........

I believe the task of doing any significant work on the standard inlet manifold is simply not cost effective. They flow perfectly well up to the limit of the standard internals (around 450 bhp). Since you are then going to spend a lot on doing up the internals, I reckon a complete RB26 top end is a far better way to spend the money than doing up the RB25 top end. In fact having done the numbers quite a few times, the RB26 top end works out cheaper when all likely things are taken into account.

This is because you can more easily and cheaply buy items like camshafts, exhaust manifold and injectors (especially second hand). Plus it gives you all inbuilt the RB26 advantages, stuff like stronger valve springs, better standard inlet and exhaust porting, no VVT, solid lifters, multiple throttle bodies etc

So up to 450 bhp I use the RB25 inlet manifold, maybe match it to the inlet ports, but otherwise standard. Over 450 bhp is RB26 top end territory for me.

Hope that makes sense

[B-Man]

Sydneykid - thanks for that info - makes sense - Must have missed the other threads that you covered that in - Thanks again ! I suppose, what I should have mentioned was that 'if it didn't cost me anything' honing/polishing the std plenum.. blah blah... ? No need to reply though now, as you said, this has been covered elsewhere.

Steve - V. Interesting.

OK, I have in my possesion a stock RB25DET plenum and throttle body. I'll get it flow tested using the same people and under the same conditions as my front facing plemum and I will post the results. It will take mabe 2 weeks or so.

I nearly was able to purchase a Greddy plenum (but got out bid and I didn't want to pay anymore) - So if I was able to get it, I would have flow tested it too - just for fun ! :)

[Roy]

Big prob with going to RB26 inlet setup is that you may have already spent money on a turbo setup which included an expensive exhaust manifold.

Also how does the RB25 ECU work with the RB26 setup? Do all the sensors match up/interchangeable.

If you planned your mods well enough this wont be a problem, but its not always that simple.

[T0nyGTSt]

The problem I see is not in the RB26 head - that in itself is not too expensive, however all the other stuff you need at the same time is probably the expensive bit.

You can't exactly get the head and slap on all your RB25 ancilliaries.

T.

[T0nyGTSt]

Originally posted by Roy

Also how does the RB25 ECU work with the RB26 setup? Do all the sensors match up/interchangeable.

It doesn't.

The 26 ECU has the i/o to control two of everything.

However the 26 PowerFC is about the same price as the 25 FC ECU.

IMO trying to make the RB25 into a hybrid RB26 is not worth it (I mean if you got the cash and patient more power to you).

However I see myself in an RB26 sooner rather than later so I don't want to convert this 25 into a 26 by proxy.

T.

[Sydneykid]

Hi Tony, we swap all the sensors over from the RB20/25 to the RB26. So the GTST Power FC work just fine. Recently I bought a complete RB26 with (the usual) damaged big end bearings for $3K. I sold off the bits I didn't need for $1.6K, so the RB26 top end only cost me $1.4K. That's less than a new Greddy GTST plenum.

It is going on an RB31 bottom end, so I sold a complete RB25DET for $1.5K and the RB26 top end cost me, minus $0.1K. That's a pretty good deal I reckon.

You gotta do the all up numbers, not just bit by bit.

Hope that explains better

[T0nyGTSt]

LOL

I didn't think about it that way.

I thought of it as buying RB26 bits by piecemeal - ie. $1,200+ for cams, plenum + TB + head... the list gets long and expensive.

T.

[Steve]

Originally posted by Sydneykid

Hi Tony, we swap all the sensors over from the RB20/25 to the RB26.  So the GTST Power FC work just fine.  Recently I bought a complete RB26 with (the usual) damaged big end bearings for $3K.  I sold off the bits I didn't need for $1.6K, so the RB26 top end only cost me $1.4K.  That's less than a new Greddy GTST plenum.

It is going on an RB31 bottom end, so I sold a complete RB25DET for $1.5K and the RB26 top end cost me, minus $0.1K.  That's a pretty good deal I reckon.

You gotta do the all up numbers, not just bit by bit.

Hope that explains better

Where do you get buyers paying that sort of money for RB25 bottom ends? Do you know any body that wants to buy some:D - whole RB25s sell for 2k privately