Cyl No. 6 Lean Out - Theory Vs Practical

[MR331307]

there are theories that say bellmouths are no good and only increase turbulence and these same people support the chamfered edge runners as they come from factory. how do the bellmouths fix the problem ?

I would say that bellmouths work in pleniums

I have done tests there

Plenium Runner lengths and Bellmouths must be worked out varying on the type of engine

There are engine Simulation programs to work Runner Lengths ETC

As for the standard Manifold no 6 problem like stated Changed the no 6 % in the ECU

If people are serious and wish to get rid of these in the right method they will need to change pleniums

The problem in the Cylinder is lack of air flowing so a larger plenium with give more air flow

As for the EGTs in each cylinder will be an interesting test

might have to try this next to check AFRS in each cylinder

[R31Nismoid]

How do you know it isnt getting the air flow though?

Most others in this thread seem to beleive the fuel rail/cooling factors are the problem.

Not the plenum itself.

And when i see reasonable power (300rwkw+) on stock RB25/RB26 plenums, i would be saying that it therefore is not the plenum thats posing the problem at all

[Turbine]

Its a different story if you want 300+rwkw out of the RB20

[Warpspeed]

Wow, I have read some pretty strange way out off the wall theories in this thread.

First thing, cylinder temperature is not going to effect air fuel mixture, how can it ? If the same amount of air, and the same amount of fuel go in past the intake valve, how does cylinder (or head) wall temperature effect the mixture ?

It most certainly will lower the DETONATION threshold for the hot running cylinder, but that is quite a different thing to running lean. Perhaps someone could explain to me how temperature effects either airflow or fuel flow ?

Next myth. The electric fuel pump pumps almost a constant volume of fuel (at least if it a decent pump it will). This flows through the fuel rail. In the GTR it goes in at the back, and out at the front through the pressure regulator. Fuel flow through the rail will be pretty constant, and even if there was significant pressure drop along the length of the rail, cylinder six would always receive the HIGHEST pressure. It should be cylinder number one that runs lean if the fuel rail was the problem.

The real culprit is the plenum. At standard power levels and airflow the stock GTR plenum works fine. Nissan have carefully designed the runners and placed steps and ridges inside the plenum to get equal airflows over the whole operating range of THE STANDARD ENGINE. As soon as you start significantly increasing air velocity, the whole design goes to hell, because it was never designed to work at that power level. What you really need is a more suitable plenum. Fix the plenum, and the air fuel ratios should even up. The Trust plenums offer little if any power advantage, but I am told the flat out airflow distribution is somewhat better.

Cylinder six may still detonate first because it runs hotter, but that is not an air fuel ratio related problem.

The original post on this thread is only concerned with even air fuel ratios, not detonation, that is another quite different problem altogether.

[Shaun]

Yeah, sorry, i think i introduced the detonation problem in #6 to this topic; i understand its quite a different problem, especially in my case. I was just mentioning that i think i may have been the victim of several of these circumstances acting at the same time on #6. Still costs a sh1tload though!

Turbine, thanks for your input. Ill have to have a closer look at my gasket and block at home. I just dismissed the problem you mentioned because the super dooper head gasket goo (cant remember what its called) appeared to have an even and uniform thickness on the gasket when it came off.

I still dont understand about the exhaust manifold though.

Thanks,

Shaun.

[Sydneykid]

Sorry, I thought I was very careful in using both EGT (Exhaust Gas Temperatures) and A/F ratios. I don't think I am guilty of mixing them, I apologise if I was.

If I remember my fluid dynamics correctly (it was a while ago) the pressure is highest at the pressure controller (ie; the fuel pressure regulator) not the source. This overrules the Renolds number (pressure drop along a pipe length). Maybe the hydraulic engineers on here can clarify.

Not having used either, I can only go on what I see and the Nismo plenum (not the GReddy) seems to be used by the leading GTR exponents such as Mines. This is the road and circuit environment, when used with multiple throttle bodies, where throttle response is all important. In an all out drag environment, the usual double the engine capacity (minimum) plenum and single throttle body are the rule.

As usual it depends on where you are on the power tree and what your uses are that determine the inlet system layout that best suites.

cheers

Edited June 20, 2006 by Sydneykid

[GTRgeoff]

SK you mean Bernoullis pressure/velocity conservation relationship of P1V1=P2V2. Reynolds number is a non-dimensional number to indicate an objects slipperiness or drag potential.

At the inlet to the pipe the fluid has a certain velocity (V1) and pressure(P1), but as it travels along the pipe turbulent wall growth occurs and the injector takeoffs add turbulence so the effective pipe diameter shrinks, so the velocity (V2) of flow slows meaning pressure (P2) increases as it approaches the regulator. This is fine for steady state but what about if the injectors outflow the pump capacity? Then it turns itself over.

[djr81]

This is getting very cofused in an awful hurry. To clarify (I hope).

Pressure is always higher at the pump than at the pressure regulator. It has to be otherwise the petrol will NOT flow towards the regulator. (At the end of the day you can be sure that shit don't flow uphill)

[Sydneykid]

This is getting very cofused in an awful hurry. To clarify (I hope).

Pressure is always higher at the pump than at the pressure regulator. It has to be otherwise the petrol will NOT flow towards the regulator. (At the end of the day you can be sure that shit don't flow uphill)

Nope, Geoff is 100% right and I was 99% ( I still reckon Reynolds has an effect in the rail).

Hence #1 cylinder gets the highest pressure, as long as the pump is up to the flow rate required of course.

cheers

[djr81]

The Reynolds number is a measure of the turbulence of the flow within the pipe (for a fuel rail). A low Reynolds number (<1000 or thereabouts) indicates laminar flow (less common for fluid in pipes) and a large number (>10,000) indicates turbulent flow.

The Reynolds number is dimensionless.

For our case (a fuel rail) we have:

R= fluid density*fluid velocity*pipe diameter/fluid viscosity.

[djr81]

Nope, Geoff is 100% right and I was 99% ( I still reckon Reynolds has an effect in the rail).

Hence #1 cylinder gets the highest pressure, as long as the pump is up to the flow rate required of course.

cheers

Here was me saying we had to be careful & then wasn't careful enough.

There are two similar sounding terms which have two distinct meaning when related to fluid dynamics.

Pressure loss & pressure drop.

Pressure loss is a measure of the energy loss per unit volume of fluid. It is also known as the stagnation pressure loss. It represents the loss of energy per unit volume of the fluid that it suffers when being transported from one end of a piping system to another.

The pressure drop is a measure of the change in pressure between two points. This can be either positive or negative. A typical example is flow moving from a smaller pipe to a larger one. Typically the pressure downstream is higher than that upstream on the back of a lower kinetic energy (ie velocity) component of Bernoulli's equation.

In a pipe system comprised of different diameter pipes the pressure loss will be different to the pressure drop.

So, in summary.

EVERYONE is correct.

The fuel rail will have a pressure loss over its length, but can also have a negative pressure drop (ie a gain) due to different pipe diameters at the different measuring points.

I think I need to have a lie down now.

[dangerous_daveo]

Deadset after reading that a 2CV is looking like a stella car right about now!

Is there an english version of the above?

[djr81]

Damn, I thought that was in English.

[Turbine]

This thread has definately brought out some good reading.

Back to the Lean Out issue.

Because No. 6 cylinder is so far from the cooling system pump, We have fitted some extra plumbing into the cooling system to remove the steam out of the engine. Has enybody done the same to thier RB engine?

[Swiper the Fox]

This thread has definately brought out some good reading.

Back to the Lean Out issue.

Because No. 6 cylinder is so far from the cooling system pump, We have fitted some extra plumbing into the cooling system to remove the steam out of the engine. Has enybody done the same to thier RB engine?

Yes

[RB30-POWER]

this is a little off topic, however...

remember that fastest GTR in the UK as tested by jeremy clarkson in one of his car movies (cant remember which one). 1000hp yellow thing it was R33 built in Japan.

the car had a water temp guage for the front, middle, and back of the engine, (3 guages total) plus extensive coolant system mods, id be guessing.

so some engine tuners must take the coolant issue fairly seriously.

animal of a car too

Edited June 20, 2006 by RB30-POWER

[ISL33P]

have to agree with turbine and dirtgarage and this was what i was looking for when typing up the original thread.

r31nismoid - flow test results would show that the rear runner has an inability to flow the amount as the other 5 cylinders do in a rb26. even more on a evident with a rb25.

standard rb25 runner flow from 1-6 at 25" is below and this pattern is typical of all plenums with a centre feed throttle body. just look at 3 & 4 compared to 1 & 6, well over 10% variance which can not be good in my eyes.

1 256

2 260

3 283

4 290

5 259

6 260

sydneykid - please dont assume a simple rule of thumb for plenum volume based on engine capacity. it is more dependant on individual port sizes of the head. an overly large plenum can have a negative effect and a smaller than expected plenum can still be a restriction in terms of overall flow available to the engine. i still dont have a formula but a decent idea what is required from different port sized heads. engine bay dimensions and application may not necessarily require the optimum sized plenum which is also something that needs to be taken into consideration.

i like the idea of modified water plumbing and certainly something i will look into when i am putting my engine together.

[Sydneykid]

sydneykid - please dont assume a simple rule of thumb for plenum volume based on engine capacity. it is more dependant on individual port sizes of the head. an overly large plenum can have a negative effect and a smaller than expected plenum can still be a restriction in terms of overall flow available to the engine. i still dont have a formula but a decent idea what is required from different port sized heads. engine bay dimensions and application may not necessarily require the optimum sized plenum which is also something that needs to be taken into consideration.

Does that mean less than 5.2 litres is OK on an RB26?

cheers

[Sydneykid]

have to agree with turbine and dirtgarage and this was what i was looking for when typing up the original thread.

r31nismoid - flow test results would show that the rear runner has an inability to flow the amount as the other 5 cylinders do in a rb26. even more on a evident with a rb25.

standard rb25 runner flow from 1-6 at 25" is below and this pattern is typical of all plenums with a centre feed throttle body. just look at 3 & 4 compared to 1 & 6, well over 10% variance which can not be good in my eyes.

1 256

2 260

3 283

4 290

5 259

6 260

I thought we had previously agreed that the test methodology for that result was erroneous. It did not allow for the opening/closing of valves and was done using negative pressure at the cylinder head interface. Both of which mean it doesn’t duplicate the real world.

I should add that we have done primary exhaust pipe EGT testing on an RB25 running a standard inlet manifold/plenum and it shows very little temperature difference at 315 rwkw (~500 bhp). That is without any fuel correction being applied to individual cylinders. A 13% differential (256 versus 290) would stick out like the proverbials.

cheers

[ISL33P]

Does that mean less than 5.2 litres is OK on an RB26?

give me an engine and i will show you

I thought we had previously agreed that the test methodology for that result was erroneous. It did not allow for the opening/closing of valves and was done using negative pressure at the cylinder head interface. Both of which mean it doesn’t duplicate the real world.

I should add that we have done primary exhaust pipe EGT testing on an RB25 running a standard inlet manifold/plenum and it shows very little temperature difference at 315 rwkw (~500 bhp). That is without any fuel correction being applied to individual cylinders. A 13% differential (256 versus 290) would stick out like the proverbials.

cheers

it shows the ports ability to flow air when the inlet valves are fully open, although not spot on since i have not tested using a head and plenum on a bench. this will be around the corner once i have the bench setup for the rb's head and plenum sorted.

what was the actual egt degrees or % difference/variance ?

your comments seem to contradict themselves. on one hand #6 requires correction (upto 6% someone mentioned - which is massive considering the the afr's you are talking about) and one would assume this would bring it more closely inline with the other cylinders, if tuned correctly. yet without correction there is "very little temperature difference" which is directly related, amongst other things, to the amount of fuel in the mixture. figures will usually shut me up. maybe a copy of a egt log or fuel map from a computer.

this is the whole idea of the thread, theory vs practical and all this from real life experiences go a long way to helping find out the cause of the problem so many people suffer from.

thanks again for your input, your posts are always read with much interest.

Ariel