999miki

Thermodynamic efficiency? No.
We want to have all parts of the engine and everything what we cram in at highest temperature possible without initiating preignition/detonation.
Right now, I´m looking at data from Honda RA168E F1 turbo engine and I clearly see, that lowest BSFC was achieved with intake air temperature 70°C and fuel temperature 80°C.

ken-x8

OK - that makes sense. Thanks for the correction. So the benefit of intercooling is avoiding detonation?

Where'd you get the Honda data?

Ken

Nubo

I'm not sure I understand where this is going. The engine keeps tabs with the MAF and keeps pace with fuel injection rate. You want more air, you increase the pressure beyond atmospheric, and/or redesign the path for the gasses. Yes, dealing with heat is part of that. So, now what?

Kane

iTrader: (1)

Now that we have understanding.... you can go forth and design your intake system to take advantage.

And tune accordingly...

And stop trying to compare power output of vehicles based on boost pressure - etc.

olddragger

iTrader: (3)

its all interdependent and interrelated.
never say all 6ft tall guys can jump 5 ft--

999miki

Of course, preignition/detonation suppression by lowering IATs, but also increasing charge density/mass-increase in mass flow-power.


I have many SAE technical papers, most of it is rotary engine development by NASA, John Deere...

arghx7

I think we all need to keep in mind total mass airflow (directly related to engine output) vs mass airflow per cylinder/rotor, which is directly related to cylinder pressure and all the other things that cause detonation etc. Both can be calculated using direct measurement (MAF sensor) or a speed density calculation (MAP sensor). Most modern GM ECU's do both mass air and speed density calculations and have both sensors (MAF and MAP).

The formula they used to relate the two is this:

MAF = (VE * MAP * RPM * Displacement) / IAT

total massflow of engine at a given point in time = (volumetric efficiency * manifold absolute pressure * rpm * engine displacement) / Intake Air Temperature

Generally speaking we can use the total mass flow of the engine to gives us an idea of how much power it is making. So at the risk of oversimplifying it, the more total air the engine is flowing the more power it's going to make all things held equal. We either directly measure the total mass flow with a MAF sensor or we calculate it using a speed density equation and a MAP sensor.

The other thing to look at is, how hard is the motor being pushed? That's what a lot of people are talking about here. I'm saying this in context of making fuel and spark tables. Qualitatively speaking, the more air we try to cram into each individual cylinder/rotor per revolution, the less spark advance we want due to all the cylinder pressure issues we've been discussing.

The two main methods to determine this is some kind of airflow per cylinder (or rotor) calculation or just a MAP measurement. If you look at all sorts of OEM fuel and spark tables across manufacturers and models, they all relate back to these two main methods. Each manufacturer uses different units and manipulates the overall equations differently though, so it's easy to get tripped up.

So let's talk about spark advance. The more air being crammed into the cylinder/rotor relative to its speed, generally speaking the later we fire the plug (less timing). Now here are two completely OEM implementations of this on factory turbo cars. The first is from a Subaru mass air system. This is the stock main ignition timing map from the turbo Subaru Legacy 2.5GT.



You can see that as we move across the X axis, we have measured more air being crammed into each cylinder at a given rpm (grams per rev). So we run less timing advance due to the cylinder pressure. If the measured mass air increases and RPM stays the same, our grams/rev increases. We have more cylinder pressure so we run less timing. If our measured mass air stays the same and our rpms increase, we have less cylinder pressure so we have more spark advance. That's what's happening as you move along the X axis.

Now here's a factory timing map from a 1992 GMC Typhoon. These were 4.3L pushrod V6 motors that came with a factory TD06-17C turbo. They only had a MAP sensor.



We have manifold pressure on the X axis here, in KPA where 100kpa is atmospheric pressure and 200kpa is 14.5psi boost. As manifold pressure increases (assume RPM stays the same), we can say that more air is being crammed into the cylinder, so we retard the timing. It's really no fundamentally different than our Subaru map, which directly measured the amount of air.

There you have it then. Pressure and mass flow can be easily related if you have enough informatoin. Both can both be used to measure what the engine's total output may be (total mass airflow), and both can be used to give a measurement of cylinder pressure and the potential for detonation etc. Keep in mind that part of what makes this discussion confusing is the units. There are so many different manufacturers and systems using different units, and it's very easy to get confused. When you start talking about compressor maps and intercooler efficiency and all that other stuff it makes it even easier to get confused.

Kane

iTrader: (1)

Good point arghx7,

But keep in mind the REASON that the timing is being retarded due to higher intake pressures is to combat the heat of the entire dynamic compression.

So once again we fall back to heating effects of compression, which while important do not directly correspond to the flow moving through an engine; otherwise known as the power output.

You can jump back and forth between flow and pressure in the terms of sensors because the size of the internal space is a known variable.... but a MAP based tune is only using the pressure to estimate the flow.

And you are right, the number of units of measure can make this whole thing very hard to understand.

arghx7

that's pretty much what I was trying to say--they are two different things but they aren't 100% unrelated because we can use the same instruments to measure either, provided that we have all the requisite data.

As more air flows into the cylinder relative to rpm (more mass air per rev or higher manifold pressure) the heating effects happen in the cylinder/rotor to some extent no matter what. However we can mitigate those effects by having cooler charge air in the first place. And cooler charge air can come from all sorts of things like intercooler efficiency, compressor wheel thermal efficiency, cooler ambient air, and methanol/water injection.

Kane

iTrader: (1)

Here is another way to look at the relationship that just popped in my mind.

Assuming you did not know what engine was in a particular car - which statement ACTUALLY tells you the power output?

"I boosted my car to 22PSI today!"
"I pulled 500g/sec of air today!"

Once is a more absolute statement that requires no conversions of pressure to power.

A 5.7 Liter LS1 @ 22PSI is a lot different than a Toyota Pruis motor @ 22 PSI. But 500g/sec is 500g/sec...

arghx7

in a speed density based system, we create an engine valumetric efficiency table to help us figure out the total airflow. then we use the airflow to calculate how much fuel is required for lambda=1 or 14.7:1 AFR. Then we directly use the manifold pressure reading to give us this measurement of cylinder heat/pressure and the potential for detonation etc. That is then used to tell us our spark advance and our target AFR.

On a mass airflow based system, we directly measure the total mass airflow. We use the total mass airflow to calculate fuel requirements for lambda=1 or 14.7:1. Then we take that total airflow measurement from the MAF sensor and directly calculate how much airflow is being crammed into the cylinder. When we know how much airflow is being directly crammed into the cylinder, we can use that to make a map of target AFR and our spark advance.

It's the same **** really.

remember that boost in analogous to grams/rev--the cylinder pressure and heating effects used to schedule target AFR and spark advance.

Boost IS NOT the same as total mass airflow as you have just pointed out. But if we know enough about the engine, we can use boost to calculate total mass airflow.

Mawnee

My LS1 made 660rwhp at 11psi(procharger)

Epic Flow > Epic lights on boost guage

Brettus

iTrader: (2)

Seeing as I get unfairly accused of not understanding this on a regular basis , I feel I need to chime in here .

Why people refer to boost so often as in ............. "how much boost you pushin' bro ?" Is because that is the background culture surrounding FI . People can relate to it .
Is it the "right" way to look at it ? No it isn't . but it's how most of the unwashed masses like to look at it so we are somewhat stuck with that.

So let's look at the RX8 with a turbo . We all have very similar setups when it all boils down . Very few of us have done anything with porting or modifying the intakes etc.
For the most part we all run turbos similarly sized as well .

Now if someone shows me their boost profile and I know they have a similar system to what i do and they have not fuxed up their install by forgetting to open a port or SSV or something like that- I garantee I can guess (within 5%) what their whp is going to be .

Does that mean I don't understand MAFvs boost ?

Kane

iTrader: (1)

I think people do it because it sounds cooler - and like you said in a small subset of vehicles, you can estimate power based on pressure alone.

Same engine, same compressor. However; we do have quite a bit of compressor variations here - a GT35 is going to flow quite a bit different than a TD06 at similar boost pressures.

Brettus

iTrader: (2)

Can we do the calculations on that to demonstrate the difference ?
Take a the stock Greddy and compare it with say a GT3071 at say 220 g/s (IE within the Greddy's efficiency map)

Kane

iTrader: (1)

Come on man.... the math is out there if you want it.

Let me see if have some old stuff.

Here is a 2871R at 13PSI

PR = 13 - 2 + 14.7/14.7 = 1.75
DR @ 85 Degrees = 1.75 * ([85+460]/[133+460]) = 1.61
VFR @ 9000 RPM = 80*9000/1728 = 417cfm
MFR@9000= (2.703*14.7*417*1.61)/(85+460)= 49 lb/min
MFR@6000=33 lb/min
MFR@5000=27 lb/min
MFR@4000=22 lb/min
MFR@3000=16 lb/min
MFR@2000=11 lb/min
MFR@1000= 5 lb/min

So to get 249.4758035 g/sec of air at 6000 RPM's this compressor needs to push 13 PSI.


Now do the Greddy one and post it.

Brettus

iTrader: (2)

I hate it when you ask me to do stuff that reminds me of scool exams!!!!!

Kane

iTrader: (1)

Sorry - I am editing my site (which I HATE DOING!) so I don't have a lot of time to play math guy..

Unless you wanna trade? You edit my grammar and I'll do math.

999miki

Kane, if we would run more timing without detonation, will it give us any benefit? Because as I see it, its all combination of IATs, dynamic compression-we want as small timing as possible and in the same time make max chamber pressure around 20° after TDC.
N/A peripheral ports are running around 20° total advance-Why?? They have very same IATs like stock port N/A rotaries which are running much more advance for optimal power. Some racing engines(N/A 4-strokes) are running around 10° BTDC advance-even at 10,000 RPMs-very fast combustion, very high CR ratio. With more timing, loss of power.
I really think its all about adjusting pressure to best crank angle. For that reason it seems to me totally contradictory that many people are running very rich-slower combustion and at the same time retarding advance and also when they tune with race fuel, they lean it out a little-faster flame speed but advance it even more... As I said, totally contradicting

Kane

iTrader: (1)

Well mechanical advantage is always the same - regardless of RPM and Load.

So in theory we always want to make the most chamber pressure at the same crank angle. However, heating, fuel and all that effects whether or not you can do that - in addition almost no one tunes timing with a pressure conductive spark plug - so they don't really know when they are making the maximum chamber pressures.

You can use a dyno or EGT's to guesstimate.

More timing (up to the mechanical advantage of the engine) will always yield more power, but detonation and pre-ignition are bad...so it may not always work out. Then we trade a lower brisance (more fuel, slower flame speed) for timing or vice versa. The perfect combination can really only be measured on a dyno or an in cylinder pressure transducer.

Kane

iTrader: (1)

Probably. But Captain Morgan helps me tune you out!

Brettus

iTrader: (2)

what just happened ?

dannobre

iTrader: (3)

Kane can't drive his car in the snowstorm...so he's resorted to rum drinking to keep sane

Kane

iTrader: (1)

Smithwick actually.... but yeah the snow sucks!

I am now reading Ray's ninja edit.

Kane

iTrader: (1)

All of that is true Ray. So would you agree that boost pressure measured post throttle body is still useless in determining the output of the engine?


As a side note - the snow just knocked a tree down in my backyard.... this is F*$king great....