following from the Anti-lag thread, 30psi.
Turbo Mini Forums

"I think some people are confusing boost with airflow and fantasy with reality... "

Essentially what I've been saying on several other threads!!!

PSI is not air flow!

Alex

AlexF

I've plugged the numbers... but not kept any record of them and haven't had the time recently to do it again. Also I haven't been able to find my T2 compressor maps, which is the very thing I wanted to compair to a t3.

What formula did you use to calcule BMEP?

Break Mean Effective Pressure in case anyone is wondering its the force that actually pushes the piston down the bore and makes you power!

Alex

AlexF

As I recall Alex - What you've been saying is that the air flowing into an engine at 15psi is different depending on the turbo?

I still say that is wrong - the engine is what is dictating the volume of air to be consumed - how this falls on any compressor map is dictating the suitability (read efficiency) of that turbo for that boost pressure - unless I've misunderstood what you've been trying to get across?

Edited by turbodave16v on 30th Aug, 2005.

I still dont understand it myself, but 2 identical engines, but with different turbos can make very different power using the same boost. Just because the bosot guage says xx psi, the engine does seem to be able to flow much more air with better turbos.

Different turbos can make a huge difference.

Ive seen Subarus that will make say 260-280bhp with at 15-17psi a tiny TD04 turbo.
Stick something like a GT30 on it, and your talking 350-400bhp at that sort of boost, with the potential for so much more at higher boost pressures.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

Totally agree with that Steve, but again it's down to the turbine and compressor selection and how they work together.

Going back to that load of math I spouted at the beginning of a recent post - if you have

6000rpm = 100 revs / sec = 200 'ingestions' of air per second.

Each 'ingestion' of air = 1293cc / 4 = 323.25cc's

So that's (in pure airflow terms) 200*323.25cc's
= 64700cc of air per second at 6000rpm.

We?ll be completely theoretical and assume sea-level air-pressure for the baseline. Now, let?s up it to one bar of boost. Basically ? we?re doubling the amount of air squeezed into the same space.

With that ? let?s again be completely theoretical and say that in each single cc of un-compressed air, there is one oxygen molecule. Hence, boosted to one bar ? we have double the oxygen molecules in the same set volume of air.
Hence ? the number of oxygen molecules forced into that engine at 6000rpm, at one bar boost, can only be one fixed value - double the theoretically perfect needs of the nat-asp engine.


As is blatantly obvious, this is a dynamic situation ? but that still doesn?t change the optimal and theoretically perfect (100% efficiency) needs of our pretend engine at a fixed rpm and boost pressure. This is basically an adiabatic system ? one that will never reach 100%. Intercooling super-hot air isn?t the key either, as the inefficiencies lost in compressing and generating little more than heat will never be fully recovered, not matter how 'chavtastic' your intercooler looks.
I guess the point I?m making here is that whilst compressor selection will bring you closer (or further away) from the 100% target - the engine?s needs remain the same. Turbine restriction is another factor we won't even take into account.

I have a feeling we've all been saying the same thing, but in different launguages...

Makes sense to me Dave, and its ages since i last did something like that. Although with my pending degree course i should have oppurtunity to do some interesting assignements/projects

Some may even be interesting to the forum! who knows

Ha ha ha!
Been there done that. Never again!

Here's a tip for you - Buy 'Engineering mathematics' by 'stroud'.
This book - and the second advanced one were the greatest influence on me getting the grade!

ooops - OT alert!

Just for the record, I never confused psi and airflow.

All I was saying was that the conmpressor does not blow through the the turbine.

Wil

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Hear what you are saying on Stroud, Dave...!!! Spent many an hour scratching my head over that one...

My tip is "Mechanics of Fluids" by Massey...

Still got my 'massey' aswell ! LOL!

why are bigger turbos not used though on mini's i know this has probably been tryed by others but how come other engines such as starlets for example can use TD04 turbos with no problems? fair enough it does not boost up till 4000. but when it kicks in its like all hell is beaking loose.

A friend of mine has this conversion and recently racing a brand new evo which i saw with my own eyes he beat him.

so how come this is not possible on a mini? as the engine size is roughly the same, fair enough it is an efi block but there quickest car ive seen is running nearly 400bhp and 11's on the 1/4 mile.

Edited by lanxter on 30th Aug, 2005.

speed is the best rush i have ever had!!!

add me lanxter@hotmail.com

The cylinder head design ulitmately limits power/airflow.

You need to be able to get the air in and equally as important, out, regardless of what blower you use.

The minis siamesed heads dont flow very much air. I would think the more modern Starlet engine would flow loads more, giving it more potential, for similar boost used.

You could maybe try and make up for this with a radical camshaft choice, but it would take loads of testing to see what worked, and with wild cams, you will probably lose so much low down, it simply isnt worth doing if you intend to drive the car at all.

I actually tried a 286 Kent profile in mine years ago. It was just the basic n/a cam. Below 4000rpm, the car was a complete dog, horrible to drive.
But it did come on the power strong from 4000rpm to 8000rpm. Not enough to make up for what I lost. I reverted back to the MG Metro cam I was using after about 3-4 days with the 286, and it drove superbly from idle to 7500rpm, pulling very very hard from about 3500rpm. Once rolling you could easily go WOT in 4th from 1000rpm and it pulled faultlessly, and was actually surprisingly torquey despite not making much boost until after 3000rpm.

Perhaps such a radical cam with a different LSA might work better though. But as Minis are such a bollox to change cams, it isnt something I was about to experiment with, nor could I have afforded to anyway.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

I was thinking a similar thing Steve - stick a 'rad' cam in there, but open out the rocker clearances to epic proportions in order to reduce the overlap. Obviously it won't tell everythhing, but can reveal the point at which the overlap vs turbine back pressure / manifold pressure approach optimal - which could allow for a few cams to be ground working from what was established...


This kinda stuff needs to be done on a dyno really though - or by someone with a front-mounted rad and removable front end at least!

Or do you just spend the money on an 8-port, with 18+cc pistons and fit efi and have done with it?

The problem with thw tap/fire hydrant analogy is that you have INCREASED the PRESSURE of the tap to FLOW the same volume as the hydrant.

However, if you just change the turbo on an engine and you are running it at the same PSI then infact what you need to be thinking about is the restriction that the compressor is 'blowing' in to.

So, if the fire hydrant is exiting through a hole the same size as the tap then the pressure in the hydrant would increase massively. And to get it down to the desired PRESSURE you would need to REDUCE the FLOW RATE.

The actuator does a good job of this, effectively controlling the volume output by the compressor to achieve the desired pressure.

This still points to the same conclusion though.

That is: The turbo which is most 'efficient' at the desired pressure AND flow rate necessary will theoretically make the most power.

Wil

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

W are all almost definately talking about the same thing.

Just got it in are heads slightly different ways.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

well that's that figured out then. Does 1071 win the award for the longest post? LOL!