A Bit Of Theory For Discussion

[Pisobiker]

since this thread is gone out of topic and it might also be a little too generic, what about starting a new one as for example "pressure pulses and turbo engines"?

Marco

[Lee]

Good Idea. No digression this time eh!

[Pisobiker]

Originally posted by S2central.net


1. Let's say I'm considering going for a 5-pot 2.5L conversion (the AEL engine) - what is the expected performance limit on a K24, RS2 or bigger turbo with that engine - using sensible boost values (max 1.4, 1.6 and 1.8 bar respectively for sake of argument) ? Assume we use an RS2 exhaust manifold in all cases.

First of all you have to consider your actual flow will increase (given all other parameters the same) exactly proportionally to the increased displacement.
It probably will actually not be perfectly proportional expecially on higher rpm because longer stroke engines "breath" less efficiently compared to shor storke ones so volumetric efficiency will decrease progressively more on the 2.5 compared to the 2.226 (but differences might be negligeble).
Given this, just looking at the turbo maps you'll immediatly find out how much boost at which rpm you can handle on the new setup with each of the turbines you have mentioned.

Just for an idea, take into account cold side has a max flow given by it's choke line, which implyes you will not push power higher than it can normally handle with the 2.226 block. It just will be obtained at a lower boost value.

Originally posted by S2central.net


2. I'd like as much torque available from low revs so how do I calculate the trade-off between say a K24 and RS2 turbo? Will a K24 have enough puff at 7000rpm in the 2.5 engine ? My gut feel would be NO - but I have no way to prove it ! So I think the RS2 turbo would be a good bet - as long as lag can be defeated properly. Who can talk me thru the compressor maps with the answer on this ?

Partially answered on the previous one. Will plot some rougly indicative curves for our engines on the K24 and 7200 (RS2) turbo maps for both the setups as soon as i find a little bit more time.

Originally posted by S2central.net


3. How do I determine which is the best camshaft choice for the AEL engine - for max torque down low, max power up top or the best of both worlds. Heck - what about considerations for compression ratio - dunno if the AEL engine has comparable CR to the ABY or ADU. That must make an impact on knock limits etc etc

I don't have a good enaugh answer for the cams.
2.5 L engine will not like to run as high rpm as the 2.226. This for sure. So best cams shouldn't be timed to give max volumetric efficiency at extremely high rpm. I would guess the RS2 ones could be good enaugh. 7A give even higher lift and something better breathing on high rpms. But should be seen on a dyno which is best for the stroker.

will take some more carefull mesurements on the block ASAP but it seems to me cylinders are 12mm taller. Will let you know what rod lenghts / piston compression hight approximate to get suitable CRs.

Originally posted by S2central.net

4. Lets say I throw a desire for a supercharger into the equation (to improve torque down low and counteract the lag effects of a larger turbo). How on earth does one select the right supercharger ? I would assume that mechanical boost control on the supercharger would be the simplest way forward. Custom mapping would of course be needed on such a setup to keep the ECU happy about increased manifold pressure at low/moderate throttle angles. Would the blower from (say) a G60 Golf/Corrado be suitable or would a larger item from a Mercedes be more appropriate ? Roughly how much power will a supercharger sap from the engine ?

Since best twin charging setup is a "parallel" (in my opinion, after having thought about pro and cons of all possibilityes), supercharger's flowing needs are actually only affected by the rpm at which turbocharger is supposed to kick in.
What I mean is that if monster turbo will kick in at 5k rpm, supercharger will need to drive it's boost (Roots tipe hardly do much more than 0.8-1.0 bar) only till then, then being bypassed thus spinning free up to redline or even with disengaged clutch using a boost triggered switch setup (for example).

I actually sourced a fairly small unit that could provide ~0.7-0.8 bar boost from nor much over idle till 4500 rpm.

Then where to place the device, and expecially way to connect mechanically, fluid-dynamically and electromechanically to engine is another task....

Could discuss of this in a specific thread if there is some interest.


Marco

[Dr H]

My older brother used to write for Car Magazine (now writes for EVO). When at Car he went to italy and got to drive a works S4 Lancia and wrote an article on it

[madmk4]

Long runners = torque is a very sweeping statement indeed.


For anyone who knows, in very, very veeeery short simple terms the idea of pulse tuning Is, when the air pulses backwards out of the inlet system, it'll refract back, if you can time this with the opening of the inlet valve you're onto a winner.

All engines do this, its just a trade off, and about harnessing the power where you want it, u8sing difference lengths and size trumpets. Sadly, you rarely get something for nothing. Might gain 10bhp beetween 5000-6000rpm but loose it somewhere else.

Ever see guys runnign silly long trumpets on their throttle bodies/carbs..Now you know why (probally the reason anyway)

People who say they have 'favourite' lengths for any perticular engine are generally talkin BS.

Cam timing, port diameter, valve sieze, port shape etc etc etc, anything that alters the TIME it will take the air to get from the inlet valve and back out, will alter what length will be to achive what you want.

This also works in the exhaust, but it pulls the gasses out, not pushes em back in, that'd be plain silly

Mart
www.designadubs.com/forum

[Pisobiker]

Originally posted by S2central.net


.....Let's say I'm considering going for a 5-pot 2.5L conversion (the AEL engine).....

2. I'd like as much torque available from low revs so how do I calculate the trade-off between say a K24 and RS2 turbo? Will a K24 have enough puff at 7000rpm in the 2.5 engine ? My gut feel would be NO - but I have no way to prove it ! So I think the RS2 turbo would be a good bet - as long as lag can be defeated properly. Who can talk me thru the compressor maps with the answer on this ?

.......

Ok, I didn't even take into consideration keeping the k24 after the 2.5L conversion. Let's directly talk about top RS2 configuration: 7200 turbocharger, RS2 EM, IC, injectors, ex-cam, 3" turbo back exhaust, nice 380 hp chipset.

How will behaviour change between 2.2L and 2.5L?

Pushing the k24 7200 next to its limits you should get something that looks very close to this:

[Pisobiker]

On previous map P2 is calculated assuming average P1 being in the 950 mbar range.

This would produce some torque and power figures that should look about this way:

Torque

[Pisobiker]

And power:

[Pisobiker]

As stated before peak power will be the same and determined by turbocharger max flow capabilityes, while peak torque will be higher (about proportionally to displacement increase) but produced at lower rpm.


Marco

[APNess]

"My older brother used to write for Car Magazine (now writes for EVO). When at Car he went to italy and got to drive a works S4 Lancia and wrote an article on it " - Leigh
=============================

Off topic, but is this ..

http://www.bbc.co.uk/london/travel/f..._webcast.shtml

your brother, Leigh? (Hilton?) Does he ever bring anything decent around for you to have a go in?

On the other topic of my garage, they've said they'll sort it out next week. *****. The baseball bat is all polished up anyway, and I've got a couple of bin liners, some bricks, and string, for the bodies.

Apologies for hijacking the thread ops:

PJ

[Mihnea]

Marco, I beg to differ here, the graphs you've done simply don't work with a 2.2l engine.

I've BTDT a few weeks ago and found out that in order to be able to plot the air flow on the compressor map, you have to know or to assume the volumetric efficiency at the various RPM points.

The correct formula for working this out is:

Assuming second and third order influences are negligible.

cid = cubic inch displacement
cfm = cubic feet per minute (need to convert to cubic meters/second for KKK maps).
Ve = Volumetric Efficiency.
AFu = Unboosted Airflow
AFb = Boosted Airflow
Pr = Pressure ratio

1) AFu = (cid * rpm * 0.5 * Ve)/1728
2) AFb = Pr * AFu

Once you have the boosted airflow in CFM covert it to Cubic Meters/Second and with the Pressure ratio - you can get the RPM and Compressor efficiency of the turbo from the KKK compressor maps.


Thus, after doing the homework, there's no way a 20vt engine with about 80% VE at 7000 RPM can draw enough air inside in order to be able to run the turbo at those high speeds.

Plus, by running the turbo at such high speeds, without a 360 degree thrust bearings, I think it's a matter of weeks before it goes totally kaputt, and we also have to take compressor efficiency into account, which makes it that the curves you've plotted make the turbo run way off its efficiency range, thus decreasing HP with a given intercooler....

That's just a thought,


Mihnea

Originally posted by Pisobiker
Ok, I didn't even take into consideration keeping the k24 after the 2.5L conversion. Let's directly talk about top RS2 configuration: 7200 turbocharger, RS2 EM, IC, injectors, ex-cam, 3" turbo back exhaust, nice 380 hp chipset.

How will behaviour change between 2.2L and 2.5L?

Pushing the k24 7200 next to its limits you should get something that looks very close to this:

[Pisobiker]

I assumed 0.85 as VE, that of course was a guess. If you have better values we can keep them into account.

What you have on the map is P2/P1 not pressure on the manifold.
Then box show P2 which is pressure on cold side outlet NOT MANIFOLD.


Marco

[Pisobiker]

Anyway the map and the figures (apart being in my opinion pretty realistic: 380 hp and 540 Nm look fair enaugh to me....) where only meant to give a good indication on how things would change from a quality stand point going from 2.2L to 2.5L, given all other parameters the same.


Marco

[Mihnea]

Originally posted by Pisobiker
I assumed 0.85 as VE, that of course was a guess. If you have better values we can keep them into account.

I wish.... I guess the only way to know this for sure would be to run a 20vt engine as totally NA and to measure the air mass being drawn inside it with a MAF, previously calibrated so we know the exact amount of air that it measures at various voltage output points....

What you have on the map is P2/P1 not pressure on the manifold.
Then box show P2 which is pressure on cold side outlet NOT MANIFOLD.

**** me, how do you want to measure that without a nipple for a separate boost gauge right at the compressor outlet??? you're right though, the measured pressure in the IM gives no indication of what's being lost through the intake tract and the IC....

[Mihnea]

Originally posted by Pisobiker
Anyway the map and the figures (apart being in my opinion pretty realistic: 380 hp and 540 Nm look fair enaugh to me....) where only meant to give a good indication on how things would change from a quality stand point going from 2.2L to 2.5L, given all other parameters the same.


Marco

Agreed

Except that an ADU motor running 1.7 Bar and about 19 degrees BTDC advance at 3500 RPM will produce 600 Nm, not 540