Heya,

Today I learnt about turbos.

As a result I want to know more about the VE of the engines I have at my disposal.

After searching for an hour I'm posting.

I'd really like a list of all Nissan/Datto engines with all their stats so I can play with compressor maps.

I made a lil excel spread today that will calculate cfm, lb/min and corrected flow 4 you if u input the cc's, VE, Psia and inlet temp.

Any one got anything?

Anyone also made a cool spread they wanna share??

I'm at home now but on Monday I'll upload mine.

Cheers, Jon

You can generally make a decent approximation of peak ve if you know the engine size and peak torque amount (or conversely you can roughly calculate any of the 3 if you have the other two). Which is why it probably surprises a lot of people that an F! engine only produces similar (all-right, it does make more, but not so much more as one might think) torque two a 2 valve production derived full race engine. - as in torque per litre.

Of course higher compression ratios increase torque, but it's not the biggest factor (and certainly a case of diminishing returns the higher one goes).

The formula 1 engines are 'quick' because they can make that sort of torque (and therefore good VE) at 3-4 times the rpm, hence they make 3-4 times the horsepower.

I've brought this up because typically you're going to find that each engine has different rpm range 'sweet spots' - or working rpm ranges, and as such the amount of torque they produce at peak torque might be similar, but if they do it at different rpms (or are different sizes) then the airflow required to make that torque is going to be dramatically different.

Or put another way, you've really got to look at a given engine's power curve (both in terms of peak power, and to a lesser extent rpm range) to start nailing what size turbo will do what for it, including spool up rpm, peak boost rpm, and when they get toward being inefficient.

Put yet another way - if the goal bhp was (hypothetically) 600bhp, but one person wanted to do it with a 2 litre motor and one with a 3 litre motor, and in both cases they had the same general maximum boost safe levels then the turbo to do it would actually be similar - though the 3 litre engine would do it all at a lower rpm.

And for the final 'other way' - turbos 'work' based on flow - per unit of time - lbs per minute, or more loosely cfm (though that doesn't include mass, only volume). Torque is a product of the force (and VE) 'per revolution' - so it won't apply properly. Horsepower is a measurement of force over time, hence it is the one to chase for turbo sizing. (well sortof)

Of course the beauty of turbos is they lift torque, and can do it at any rpm (within the scope of this discussion) so unlike the NA engine, we can make the same hp, and perhaps double the torque, without having to rev the engine beyond stock rpm levels.. This is where it gets a little 'grey' - because of course the ideal is to do that, but not all engines can handle heaps of boost (head gasket sealing, or pistons dealing with heat soak, whatever) but can handle a modest bump up in rpms.

I'm trying to remember (don't take this to the bank, but I think it was right) but I think an old rule of thumb was to look at the compressor maps in lbs/min flow and multiply by ten. I.E. if at a certain efficiency the compressor was moving 55 lbs/min of air, it'd be roughly good for 550bhp with decent efficiency (and probably handle 50-75 more without getting ridiculous.

It can occasionally get odd with mismatched turbos, where if you get them to spool too early they'll experience compressor surge, so on those occasions you are better off with an exhaust/cam/combo that didn't spool up quite as early in the rpm range. As damaging as such a situation might theoretically be, I can only think of one time I've seen anyone on a forum actually create a big enough mismatch that they got lower rpm compressor surge and damaged turbos.

I think from memory it is much more likely to happen using a 'big' (for the engine) compressor side and wanting to run a lot of boost, but having it spool too early with a tight enough exhaust housing to prevent lag. That's where it can be a pain, because faster spoolup is almost 'magical' on any sort of a competitive car - coming out of each turn harder, and quicker on boost is going to give enough advantage that someone following you out of the corner with the same basic combo, slower spool but more peak power is not going to get past you or even alongside, by the time they have to hit the brakes, and oddly enough if their corner exit speed is slower but they finally are quicker by 3/4 of the way to the next straight (but they'll still be well behind the other car) then they have to get on the brakes earlier. pretty much voiding any chance of an overtake being successful.

Similarly at the drags, although a slow spooling turbo can produce fast times (since the timer itself doersn't start till the car leaves/through the starting line beams) they are slow to spoolup, and often they sit there spooling up just to run a decent time. In a real race, where they have to leave on the go, as their opponent will, they can't get that ideal spool and end up losing the race. Similarly overtaking on a highway - instant boost is a 'must', it's dangerous to be on the wrong side of the road waiting for the bliding acceleration to kick in.

Anyhoo, point of that long detour was that for smaller engines in particular, there's more of a conflict of interest with regard to exhaust size selection (and compressor spec too of course) - on the one hand quick spoolup is a huge factor, but at a risk of compressor surge if it is boosting already whilst near or at the surge line.. In those 'odd' or more extreme cases where one needs quick spoolup but also to avoid surge, it might be a scenario whereby you have two similar compressor maps, one (in practice) might make a bit better peak power (less heat, better flow, whatever) but would be closer to the surge line, so far safer (and productive overall) to choose the compressor wheel/housing/spec with a bit less peak efficiency but also doesn't put you into surge at lower rpm.

On a larger engined car, you'd typically be able to go conservative with rpm and still make enough power to destroy any street tyres, and even drivetrains for that matter.

Awesome info Jmac, cheers.

I have been trying to think of ways to get the turbo to spool up quicker on a suck through setup, too many beers and nothing else to do makes for some silly ideas.

But have no idea if they are feasible. Here's a couple of them, and be warned they are whacky!!

1) Use the vacuum created by normal engine operation to increase suction through turbo inlet at low rpms.

2) Turbos look like electromagnets. Design turbine housing that functions as such (copper wire etc) and use coil pulses to spin turbine wheel, or conversely use turbine wheel to power something else (to get really out there remove the petrol engine replace with electric motor pumping air??)

Anyway the point is, if I follow you correctly, that you run into the surge line the quicker you spool up with a given turbo/engine combination.

This is dictated by the lb/min rating of the turbo.

So stupid big turbo with "somehow" assisted spool could get you in a nice efficiency island much earlier??

Also to get ve is it displacement(engine size)x torque (nm?? ft/lb???)

fast spoolup - in general - cam selection (usually not going too big, as that can slow spool (in a sense anything that reduces off boost torque will slow spoolup). The other is of course the exhaust housing spec. Tighter the better (but of course with the penalty of more restriction up higher once fully underway)...

One that isn't usually mentioned - the exhaust manifold. If it's an adapted factory cast iron manifold, they keep the heat in (or don't drop as much heat) and more heat energy for the turbine (ex wheel) so ok spoolup. With custom 4 into 1 pipes, keep the i.d. of the pipes down (aim for similar or just ever so slightly larger cross section area as the exhaust port at the manifold face, not as big as extractors for a decent NA option) and use the thickest practical wall thickness you can find (and wrap them with that insulation tape stuff too. Once it's through the turbo exhaust section, run the biggest pipe that is practical and realistic for such a setup. Consider 2 1/4 a minimum, and 2.5 good. You'd probably be able to make a case for 3 inch but it'd have to be at some monstrous boost levels. Point being, as little back pressure as possible. Thankfully the turbo itself acts as a noise reducer, so a single muffler of largish diameter is usually able to be done without making the car the centre of attention for police within a 20km radius whenever it is driven.

Jmac,
You really should write a book mate. I (like to think) I know more about motors that the average bloke. But everytime I read one of your essay like posts, I'm left thinking omg I don't really know anything.
You're a clever bugger! Keep those essays coming!

The only other "reasonable" way to get a quicker spooling turbo (while still having a big turbo) is a variable geometry one. In these turbo the exhaust turbine is surrounded by a number of small vanes that are actuated via the "wastegate" diagram canister. They work as such, low rpm, low boost the diaphragm canister is basically off and the vanes are shut which in essence makes the turbine have a small housing (only a few millimeters clearance to the turbine) which will allow the turbo to spool fast as it has at this point a very small A/R number.

Now as boost rises the actuator moves the vanes proportionally and expose more and more of the cast exhaust housing. Allowing the now partially spooled turbo to use a bigger exhaust housing and flow more with its now greater A/R ratio.

With a properly sized variable vane (variable geometry) turbocharger a waste gate would not be needed as when the actuator opens fully the vanes in the fully open position allows extra exhaust gasses out. In saying that, if it isn't apparent already, variable vane turbos don't have waste gates - they rely on the vane control for exhaust gas control.

With all this sounding good and like its the holy grail for big turbo situations with lag, it begs the question "Why isn't it already being used these days?"

Simple fact is that they have used this technology for years but on diesels as diesel have a far lower exhaust gas temperature than petrol engines so turbo manufactures can get away with steel vanes in their turbos. However, if you were to use a steel vaned turbo on a petrol motor you would seize the vanes to the housing because of raise exhaust temperatures.

For this reason I didn't go on an use the Garret GT22U turbo I got for free - despite being the perfect size, in good condition and easy for me to machine up the parts for the carbon seal conversion - I wasn't going to risk it. In my case running water injection to cool the air charge; I may have been able to get away with the steel vaned diesel turbo due to lower exhaust temps but I wasn't going to find out. I'm holding out for a TD04L-13T of a rexxy.

In addition, Porsche has just recently started to use a variable vane turbo on one of their new (petrol) cars but they are using a turbo with ceramic vanes which will withstand the petrol engines higher EGT's.

So NO ONE KNOWS?

I don't either. But the stock A12 dyno chart, with torque is here

If a 1.2 liter engine fills with 1.2 liter air (at ambient density) per 2 revolutions, that is 100% VE.

* Many car engines achieve about 85%
* Supercharged or turbosupercharged engine often reach 100%
* Naturally aspirated engine can acheive more than 120%

Cheers guys, I've set VE to 80% in my spreadsheet already but I was interested to see if I could get more specific information.

80% seems like a reasonable number but if I can change the ve at specific revs independently well... garbage in garbage out.

It would be interesting to see the efficiency of the engine used by one member here
for long distance economy runs compared to a standard a12 or a12gx motor.
If somehow power torque and economy can be used in some calculation we could tell
which a series combo is the most efficient or satisfying to drive.

I can only imagine if Nissan decided to develop the A series by keeping it pushrod
like Chev has done to the small block, that its would still be and engine to compete
with other small capacity ones out there.
Eg. using heat proof and friction coatings, distributorless ignition, intelligent EFI,
better manifolding and roller tip rocker tech.
Even 3 valve head using pushrods like Chev was developing and eventually alloy block.
To think Topgears simple drawthrough tubo setup made 100kw atw shows that it can be
as good as it baby brother e15et or even better with no belt to worry about.
The third party parts profit wouldnt be good for Nissan though hence the constant changes.

You can look at the late VW 1.4 or 1.2 litre supercharged/turbo engines.
They have amazing power and torque compared to a 3 litre NA car.
They copied the Nissan March concept of the past where the supercharger
assists the turbo for a no lag arrangement and very good efficiency.
They are very complicated setups and I wouldnt be surprised if VW makes
a zillion in owner servicing costs these complicated thing represent.
A friend of mine had a Rav4 crap box nudge him when it reversed into him
and it activated the front drivers airbag and damaged the supercharger
piping not to mention intercooler and radiator. 3 months later with part
from Germany he was back on the road and with the other driver forking
out big time for the damage and rental car my mate needed.
I guess this is the reason for yuppies driving these things which say
touch me if you like but its going to cost you in German parts / labour.

Have a look at how complicated these Vortex VW are its stupidly complicated
just to have efficiency that is lost in servicing or keeping them any length
of time similar to a datsun which you obviously wouldnt. This diagram makes them
look simpler than what they really are full of hoses, sensors and wires everywhere.

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The only real way to know is to run one on a dynomometer equiped with an air flow meter. Then you would have a graph of CFM of air vs RPM. This is then easily converted to a VE table.
It is possable to get very close by knowing injector pulse width and air fuel ratio. But its time consuming maths.
You also have to know injector dead time, Barometric pressure , Air temp and exact injector flow rates to be acurate. It will obviously have to be injected aswell.

The other way is to measure exact fuel flow though carb and air fuel ratio. You still need a dyno for this.

I`d be interested to know aswell.


Good luck with your search.