About VE, Flow Rates and Turbo Maps

[Tapage]

Hi all ..

I'm been reading more and more info about rubos and how get the perfect map for your engine .. I have plenty of question since I been reading info the hole weekend ..

But I wan to start this thread sharing that was I get for now .. and geting some info feedback from others ( Lost ! ) jajajaja mates with more experience acknoweledge than me.

Here ya go ..

The sat I make some adjust to my Turbo Intercooler Setup. I'm running KKK K26 turbo ..

This one ..

 

[Tapage]

I'm making now 14 PSI measured in the Throtle so I thought it's pretty acuracy reading. I'm running a small intercooler from a 2.5 turbo intercooler engine to minimize the turbo lag .. I'm very happy at this point ..

But I'm not hable to make 14 PSI at 2k rpm as I wish .. ( it's my goal )

when I buy this turbo ( new ) it come from a 3B turbo kit .. thinking ( as this time ) that in a 3B have less exhaust flow ( 4 bangger vs 6 bannger 2H ) In my 2H I will hable to produce boost sooner.

Now I get proper amount of fuel to make 10 - 12 PSI at 2,000 - 2200 rpm .. but to get the 14 PSI i need to rev up my 2H up to 2,800 - 3,000 rpm.

Don't get me wrong I'm pretty happy and when I run my Tencha at 3,000 rpm that means 140km/h ( pretty scary ) I have no mcuh more ooption to get it faster coz I'm pretty well geared for mud .. not for HW.

 

[Tapage]

Well I thought I have well adjusted my wastegate and actualy disconected and tapped teh hose. I tought I'm gonna re-check my wastegate spring to ensure I'm not loosing pressire at this poing ..

I also change all my gaskets ( head and exhaust ) for the 12H-T engine ..

Let start with interesting stuff ..

 

[Tapage]

K26 specs

Max Air Flow 35-36 lb/min ( that it's pretty impresive, seen the smal compresor housing ) 500 cfm and anounced 75% of eficience in this compresor.

It means .24 cubic meters/seg

Pressure Ratio 2.7 BAR ( 25 PSI )

I found som info in the Rennlist Porsche Forum about 300 RWHP in a 951 ( I had one ) that it's a 2.5 turbo ( K26.6 ) intercooled electronically injected and controled engine. This Porsche ( 944 turbo ) have 220 HP boosting 1.7 bar in stock condition ..

With straight pipe you will be hable to produce 250 easy with a chip also.

Ok back to the Turbo.

The Garret Equivalent it's the T04E-40

 

[Tapage]

K26.6

Compresor Housing ID of inlet = 1 13/16"
O.D. Of Inlet = 2"
O.D. of outlet = 2"

Compresor Wheel: inducer dim: 13/4" ( 44mm)
mayor dim: 2 9/16" ( 64mm )

- Turbine Housing #6: Inlet ID = 1 15/16"
outlet = 1 7/8"

- Turbine Wheel #6: Inducer Dim: 1 7/8" ( 48mm)
Mayor Dim: 2 7/16"

#6 cm2 Turbine = .36 AR ( that it's small than I suppose to be )

K26 will flow ( tested ) .212 cubic meters/seg some conversions
7.487 cubic ft/seg
449.22 CFM @ 1BAR ( 14.5 PSI ) 70% eficience.

How much CFM require at 2000 rpm 3B or 2H engines . ?

Keeeping in mind 1lb/min ( flow rate ) = 14.472 CFM

And thinking a little bit about this and if I remember well 350 chevys engines that are 5.7 lts engines uses 650 CFM aprox .?

making some cals it means to me 450 cfm aprox .. that it's in the range of K26 turbo able to produce.

 

[Tapage]

Aditional info and trying to read and learn about turbo maps ..

The lowest point it's 40,000 rpm

And the power range for K26 are between 105,000 rpm and 135,000 rpm ( pasing over 150,000 rpm can cause over sping with the knowed consequences )

All it's related to the exhaust flow, and pressure ratio .. and Just wondering if someoine here know the 2H pressire ratio ( not compresion ratio that it's other complete diferent means ).

I thought ( and just thought ) the 2H VE are about 76-80% ( with luck ) at sea level ( that it's my case most of the time ). With apropiated maped turbo we will dream in reach the 90-92% VE ( volumentric eficience ) in this engine.

The books calim the nice torque spot for 2H engines are at 2,000 rpm to produce 187lb/p that I't the reazon that I try to archive the 14 PSI at this point.

How much air flor need the 2H @ 2k rpm .? something like .11 cubic meter/seg ?

With the pressure ratio for 2H engine and multipliying it by 70% of the K26 eficienece give us the density ratio.

 

[Dougal]

The pressure ratio shown on the turbo compressor map is (boost+atmospheric pressure)/atmospheric pressure.

Atmospheric pressure is 14.7psi, so a pressure ratio of 2 is approximately 15psi boost.
A 0.36" A/R turbo equates to 9cm A/R. Is that what you've got?

There are many factors in turbo design that dictate whether a turbo will deliver better at high boost and low rpm or high rpm and lower boost. Blade outlet angle etc.

I would first fix your wastegate shut (i.e. wire it) and see how the boost goes, this will give the max boost your current combination is possible of at that rpm.

 

[Tapage]

Thanks Dougal fo r your answer and time .. I thought that thread will have many replys . but was wrong.

My first thought in the K26 was it have a .48 AR but reading info ( but I need to certify it with some code in the housing plate ) looks like .36 AR .. so if I thought about it, need to spool sooner and it measns for sure boost at lower rpm ..

But as you know it also depends in blades angle, and turbine are and olutlet.

I would try to compare it with CT-26 that look like a beast by me, when Tito with a manual boost controler was able to up 20 PSI at we first ride test.

My first step as you write, gonna be found a mecanical tensor to be sure that my wastegate spring it's working fine.

 

[brownbear]

two things Tapage

1; ensure the wastegate is firm closed. If you find no need to control the wastegate weld it shut...

2; to get the most boost out of a turbo you need lots of exhaust gas, so crank the fuel so that the maximum is high. 1250 or more. When under full throttle you should have to back off the pedal to not overheat. But this extra fuel will get your boost sooner too. As the fuel increases in the whole range.

 

[Tapage]

two things Tapage

1; ensure the wastegate is firm closed. If you find no need to control the wastegate weld it shut...

2; to get the most boost out of a turbo you need lots of exhaust gas, so crank the fuel so that the maximum is high. 1250 or more. When under full throttle you should have to back off the pedal to not overheat. But this extra fuel will get your boost sooner too. As the fuel increases in the whole range.

Thanks BB .. I would adjust this saturday my fuel again ( I already have 2 complete turns last sat )

And I will try to find an asjuster to tight the wastegate .. I'm trying to avoid the weld step .. coz it if make about 20 PSI I can blow my engine

 

[pioneer411]

Thanks Dougal fo r your answer and time .. I thought that thread will have many replys . but was wrong.

My first thought in the K26 was it have a .48 AR but reading info ( but I need to certify it with some code in the housing plate ) looks like .36 AR .. so if I thought about it, need to spool sooner and it measns for sure boost at lower rpm ..

But as you know it also depends in blades angle, and turbine are and olutlet.

I would try to compare it with CT-26 that look like a beast by me, when Tito with a manual boost controler was able to up 20 PSI at we first ride test.

My first step as you write, gonna be found a mecanical tensor to be sure that my wastegate spring it's working fine.

i using 12H-T and the original ct26 turbo boosted at 1.9bar quite a long time, and da engine still very great, the turbo are running now, but now i change another bigger, too big, thats why power a not too smacky. 1.9bar is around 28psi

 

[pioneer411]

anyone here can help me out some problem??
about the fuel pump, any kit or part to modify so it can get more power, more fuel to inject to engine, and also a bit higher RPM

 

[Tapage]

anyone here can help me out some problem??
about the fuel pump, any kit or part to modify so it can get more power, more fuel to inject to engine, and also a bit higher RPM

You can turn up your fuel .. but I'm not sure if the stock pump can compensate 28 PSI .

 

[Tapage]

Lets see tomething intereing ..

Making calcs .. my compresion after 14 PSI = 27.92 ( factory comp for 2H 20.7:1 )

10Lb/min = 144.72 cfm

I'm not clear at this statement ..

Absolutely manifold pressure
PSI = boost press + ATM press

So if I'm reading in my Boost gauge in my throtle body 14 PSI this is the absolutely press ( ATM press included ) or I need add the ATM press . ?

Found that the Engine Volumetric Flow = EVF

( engine CID / 1728 ) * ( rpm / 2 )

Making this calc asuming 2H 248 CID and @2000 rpm ( peak torque point )

2H EVF = 143.5 CFM @2000 rpm

That what I get in the turbine at 2000 rpm ..

Now we use the EVF to determinate the Air Flow in lb/min

With

N = ( P * EVF * 29 ) / ( 10.73 * T )

where N it's the air flow in lb/min and P it's the absolutely press in PSI and T the absolutely ambient Temp in Ranking

At this point I have some questions .. like

P tis for me at sea leven 14 PSI ( that I see in my boost gauge ) or it's 28.7 ( ATM + boost press in gauge )

Asuming ( prentty of ) 180ºF

I have 2 options .. one with 14 PSI and other with 28.7 PSI

N1= 8.4839 lib/min

N2= 17.39 lib/min

That means that my K26 have plenty of capacity to fill my engine

 

[Dougal]

Firstly pressure.
Your boost guage reads "gauge pressure".
Absolute pressure is guage pressure plus atmospheric.

Then flow.
Your engine can only consume it's own displacement every 2rpm. The VE will reduce this further, but I prefer to calculate at 100% VE and add that factor last.

You need to know the absolute pressure in your intake manifold and the temperature of the air in your intake manifold to work out the volume of that air (ideal gas equations).
With 15psi and no intercooler, expect the air in your intake to be about 1.5 times as dense as with no turbo.
Perfect intercooling can get you to 2 times density, otherwise you're somewhere in the middle.

Then multiply out your engine air consumption by the density ratio your turbo produces (1.6 or whatever you got from above).

That'll give you volume airflow, from there at 20 deg C and a standard atmospheric pressure the air weighs approx 1.2 kg per cubic metre.

I didn't realise you had a 4L engine, I was using 3B figures.

In that case at 2000rpm and 14psi boost with no intercooler you get 12lb/min.

I have a spreadsheet I setup to calculate this. It saves a lot of time.

 

[Tapage]

Firstly pressure.
Your boost guage reads "gauge pressure".
Absolute pressure is guage pressure plus atmospheric.

Nice to know .. it means the absolute press in my intake come close to 28 PSI . ?

Then flow.
The VE will reduce this further, but I prefer to calculate at 100% VE and add that factor last.

I'm not sure if I need to use the VE with turbo and intercooler in this ecuation or without it ..

Coz with turbo it can archive 100% VE easy.

With 15psi and no intercooler, expect the air in your intake to be about 1.5 times as dense as with no turbo.
Perfect intercooling can get you to 2 times density, otherwise you're somewhere in the middle.

Asuming 70% eficiente con my intercooler ( I'm positive ) 1.7 times density.

In that case at 2000rpm and 14psi boost with no intercooler you get 12lb/min.

I have a spreadsheet I setup to calculate this. It saves a lot of time.

You can send it to me .. ?

My engine it's a 2H 6 cil inline 4.0 (3980) 91X102 ( bore and stroke )

Original in books claim about 105 HP@3500 rpm and 177lb/p@2000rpm

The turbo version ( 12H-T ) same bore and stroke but DI boosting factory 8 PSI come in books with 135hp and 231lb/p.

 

[gedrich]

Interesting thread guys, Dougal any chance of flicking that spreadsheet to me at gerard.richardson@ashcon.co.nz
I am in the long process of intercooling my 12H-t with a subaru intercooler and worked up own spreadsheet about 6 months ago and would like to see how we compare

cheers
Gerard

 

[Tapage]

Here ya come with some interesting stuff ..

CID = Cilinders Sweept Volume
CID = Cilinders * Bore * Bore * Stroke
CID = 308.36

CFM = (CID * RPM * VE) / 3464
CFM @ 2000 rpm = 178.03 CFM

1 CFM = aprox .0745 lb/min

13.26 lb/min ?

 

[Dougal]

Interesting thread guys, Dougal any chance of flicking that spreadsheet to me at gerard.richardson@ashcon.co.nz
I am in the long process of intercooling my 12H-t with a subaru intercooler and worked up own spreadsheet about 6 months ago and would like to see how we compare

cheers
Gerard

I've emailled it to both you and Tapage.

 

[Dougal]

I'm not sure if I need to use the VE with turbo and intercooler in this ecuation or without it ..

Coz with turbo it can archive 100% VE easy.

Some people think of turbos as increasing the engines VE above 1.00.
I prefer to think of a turbo as only increasing the intake pressure, with the engines VE not being substantially changed.

It doesn't really matter which way you prefer to work, but it does change the way you do the math model.