Silvia Club of NSW

I agree, its no biggie, but jampac is swearing black and blue that the world is flat.

props to Unigroup

You cant help yourself can you?

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Co-Founder
www.silviansw.com
snezy@silviansw.com
Why Drive When you can drift?????

The TSI might not be dead accurate on voltage, and the AFM never actually reaches exactly 5 volts output.
I'd be interested to see how long it was sitting at 4.8v. It might hit 4.8 and stay there for the whole top end of the rev range.



A restriction isn't a brick wall limiting you to a certain power output. It just means that you have to work harder to make the same power.
eg: You can make more power with more boost through a standard head, but it's more efficient to enlarge the ports, run cams with longer lift and duration, etc and make more power at less boost.
It's all about efficiency, and making all the engine's air pass through something much smaller than it needs to is not efficient.

One can also argue too that it's stupid for the factory to put in a meter that will only ever see half its potential in a stock setup.
All that does is reduce the resolution of the ECU, making it harder to tune accurately.


By all means keep the stock AFM, and make heaps of power with it, but for well under $100 you could get an RB20 one and suddenly there's no real restriction at all!
People will say the RB20 is no good cos it'll be maxed out, which is true - but the TSI will take care of that just as it does with the stock meter.

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The Engine Whisperer - fixer of things

I have to agree with dumhed here. Personally I think that people rely too much on more boost and bigger turbos to make more power while ignoring simple engine fundamentals. If it's easier to get the air in you _will_ make more power at the same boost level. I also can't see how the MAF isn't maxed out as the engine is taking in far more air than it can possibly measure.

As one engine has been presented as "proof" that I'll break my golden rule and post something about mine. At the same boost level as the engine in question and with a significantly smaller turbo I am making the same power (226kw atw). If a T25 frame turbo is getting the same power as a T3/T4 at the same boost then I'd say there is a hell of a lot of potential waiting to be realised before the boost is turned up.

Oh, and kudos to Nas77y for not turning up the boost on the stock engine to run a "number". Good to see someone who is more interested in doing things the right way rather than going for bragging rights, once he gets the engine built I think we'll see not just some big numbers but a well built complete package.

mate would you stay silent if I said a 180 chop-top ute is impossible?

Its obvious that unigroup have built a good setup, and NAS77Y is happy but i dont agree with what jampac is saying about AFM's




its exactly the same with karts.

I know exactly what you guys are trying to explain, and yes there is a pressure drop across the standard afm, which does increase with an increase in flow, up to a point. At this point air speed reaches mach1 and no more flow well occur. The reason for the pressure drop is turbulence at this point; with turbulent flow there is always an associated pressure drop. However this pressure drop in the big picture is not a concern. If you’re really concerned about pressure drops you better get stuck into your intercooler as they have a far greater pressure drop than any afm in existence. The only way to truly find out weather it is a "big concern" is to test it, or better still run a complete analysis on it in ansys. The web site I posted before has all the equations to work out the flow and even has some stuff about constriction coefficients. So I'll leave it up to you guys weather you want to find out the truth or simple believe what everyone else says.

I think the main point here is why have a pressure drop at all if it's not necessary?
Sure an intercooler has a pressure drop, but it also does an important job.

A small AFM doesn't do a better job than a large one.

BTW - why won't any more air flow past mach1?

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The Engine Whisperer - fixer of things

It appears you never read that web site I posted, its all there.

Yes, dumhed is right, we're questioning its necessity?

and whats the story with mach 1?

Gees make me do all the work

The mass flow rate of a compressible liquid, such as air, is governed by the speed of sound in that liquid. Once the flow velocity through the throat (minimum area) reaches the speed of sound (Mach 1) then the flow becomes choked. Pressure waves down stream of the orifice can no longer be transmitted through the sonic condition that exists at the throat and thus no more flow can be induced. Using isentropic flow theory for a perfect gas we can estimate the maximum mass flow rate that will pass through an orifice.

right ive read the material, and i think theres more to the mach 1 limitation than meets the eye.
this bit highlighted below says that there will be isolated points during the engine cycle that need to be looked at, not just the final choke point.

and back to the subject, there is still no valid reason for keeping it.
Formula SAE have set guidelines etc...

design must also consider the pressure loss that results from the restriction (figure 5.1). Another major consideration is the production of shock waves. There is a reasonable likely hood that there will be localised choking of the restrictor at various points in the engine cycle prior to permanent choking. Whilst we are necessitated to open the constriction up in order to recover as much of the initial pressure as possible we must be careful not to expand the cross section too rapidly. This will lead to an acceleration of the flow to supersonic conditions which results in shock waves and their associated pressure losses.

"Whilst we are necessitated to open the constriction up in order to recover as much of the initial pressure as possible we must be careful not to expand the cross section too rapidly. This will lead to an acceleration of the flow to supersonic conditions which results in shock waves and their associated pressure losses."

Have you had a look at the shape of the AFM??

Certianly not designed to prevent shock waves or turbulence...

Even if the flow doesn't reach supersonic speeds the pressure difference will be proportional to the mass flow, so the more power you're making the more power you're wasting...

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The Engine Whisperer - fixer of things

. Thus to approach a real scenario we must introduce a discharge coefficient, CD. This coefficient is a function of the constrictions shape, the Reynolds number and mach number of the flow, and the gas properties. This discharge coefficient is experimentally measured but for now we can estimate that with a near perfectly shaped constriction it could be as high as 0.9.

and as dumhed said, the AFM is nowhere near an SAE designed restrictor, so it wouldnt get near mach 1

Also, due to the partial flow design of the SR20 AFM it'll generate a huge amount of turbulence at the point where the measured flow comes back into the main flow at right angles. There are a lot of sharp edges involved and it's pretty ugly as far as laminar airflow goes.

Anyway, I'm going to do some measurements and see what I come up with

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The Engine Whisperer - fixer of things

Hi guys,
I'm a refugee from the 200sx forum, Just wanted to find out if the TSI unit is available in Melbourne or is it just Unigroup that is installing it at the moment.

Would it be a better option than say the UNICHIP or the CHIPTORQUE, as it seems a little bit more than the UNICHIP if you wanted to include boost control, But launch control would be a definite bonus.

At the moment my only mods are a CES dump and 3in cat back exhaust and a K&N Panel filter in the original airbox good for 140RWKW on a cool day

Thanks
Russ

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Russ