CFM query [SOLVED]

[shnazzle]

Someone who understands engine theory a bit better...

When I try to calculate the theoretical flow capacity of the 1zz I get to about 215 CFM.
Assuming 82% efficiency, should see a real world CFM of 185.

Now,when I average up my maximum airflow over quite a few drives, as measured by the MAF in a stock setup, I get a number of 114g/s,which equates to 215.

That means I'm running at 100% efficiency... Hmm... Not convinced...
What am I missing?

Edit:
Good explanation in the post below here:
https://www.mr2roc.org/forum/index.php?msg=822006

[Carolyn]

When it comes to flow capacity the engine is simply an air pump.

As long as there are no leaks, there is no reason why air in should not exactly equal air out.

[shnazzle]

How come that most cars sr said to run about 80-85% volumetric efficiency?

[Petrus]

How come that most cars sr said to run about 80-85% volumetric efficiency?

Because there are flow losses. It is after all ´driven´ by súcking in air through a filter and then pushing it out through another restriction. There is a pressure difference needed to drive the flow, hence the volume pumped is less than the swept cilinder volume.

How sure are you that the number indicated is the actual air mass? In other words is the value calibrated?

[shnazzle]

How come that most cars sr said to run about 80-85% volumetric efficiency?

Because there are flow losses. It is after all ´driven´ by súcking in air through a filter and then pushing it out through another restriction. There is a pressure difference needed to drive the flow, hence the volume pumped is less than the swept cilinder volume.

How sure are you that the number indicated is the actual air mass? In other words is the value calibrated?

I'm not at all. 

Could be aged MAF. But you would hope Toyota calibrated it. 
Hence my suspicion.

[Petrus]

I'm not at all.

Could be aged MAF. But you would hope Toyota calibrated it.
Hence my suspicion.

For the ECU and all tuning purposes it is all relative. X signal air means y fuel etc. 
Toyota will have calibrated that for sure.
How the signal relates to the real volume is basically irrelevant other than for an additional dial.

There are ways of extrapolating the swept air vuloume by calculating from the fuel used and the fuel air ratio.
It is not very important though other then for knówing.

More important is the effect of any modifications. Like the fuel flow rate increasing with the same ratio.
Or the CFM indicated increasing etc.
A 10% increase in fuel flow with constant ratio should equate to 10% more energy pushing the pistons down, the crank and eventually the wheels thus the car, thus basically 10% more performance.
And then you change the ignition advance, messing up the logic by adding a variable in the efficiency of both the burn and the push (effective duration) on the piston.

[jonbill]

My understanding is that you should be able to get to or beyond 100 volumetric efficiency at peak torque.
Where does that 80-85%  come from?

[shnazzle]

My understanding is that you should be able to get to or beyond 100 volumetric efficiency at peak torque.
Where does that 80-85%  come from?

It's a safe assumption, taking into consideration moderate tuning, aging, etc etc.


Theoretically, riding intake/exhaust pulses you COULD get 100% or more.
What I'm saying is that I find it unlikely this is the case for my stock engine, stock intake, 200 cell cat, zero mani and tte exhaust.

Unless it is... In which case; happy days

[jonbill]

It would be interesting to see a VE table from a 1zz.

[Ardent]

VE?

Volumetric efficiency?

All above my station, but every day is a school day.

[shnazzle]

It would be interesting to see a VE table from a 1zz.

If I could have one wish from Toyota, including free services for life and 20% discount on parts, I'd forego that for a copy or their calibration tables.

[ChrisGB]

With VVTi and 4 valves per cylinder, I don't see any reason why you shouldn't see something close to or slightly above 100% VE. Only the long stroke makes it difficult to get more. Peak VE will be where peak torque is.

[shnazzle]

With VVTi and 4 valves per cylinder, I don't see any reason why you shouldn't see something close to or slightly above 100% VE. Only the long stroke makes it difficult to get more. Peak VE will be where peak torque is.

That's just it. If I'm hitting 100% VE, it would assume that my 100k mile engine is still hitting factory levels of peak torque.

With normal wear and tear it just seems unlikely, even with my "performance" mods.

[ChrisGB]

With VVTi and 4 valves per cylinder, I don't see any reason why you shouldn't see something close to or slightly above 100% VE. Only the long stroke makes it difficult to get more. Peak VE will be where peak torque is.

That's just it. If I'm hitting 100% VE, it would assume that my 100k mile engine is still hitting factory levels of peak torque.

With normal wear and tear it just seems unlikely, even with my "performance" mods.

Wear will possibly reduce power / torque by losing a little compression and some increased blow by, but unless your inlet ports and valves are coked up, the VE should be mostly the same as when it was new. The inlet and exhaust gases move through spaces which, hopefully, don't wear out!

[shnazzle]

With VVTi and 4 valves per cylinder, I don't see any reason why you shouldn't see something close to or slightly above 100% VE. Only the long stroke makes it difficult to get more. Peak VE will be where peak torque is.

That's just it. If I'm hitting 100% VE, it would assume that my 100k mile engine is still hitting factory levels of peak torque.

With normal wear and tear it just seems unlikely, even with my "performance" mods.

Wear will possibly reduce power / torque by losing a little compression and some increased blow by, but unless your inlet ports and valves are coked up, the VE should be mostly the same as when it was new. The inlet and exhaust gases move through spaces which, hopefully, don't wear out!

I do mean the VE vs theoretical VE of course.

I understand that, as you say, unless those spaces have somehow been coked up, the theoretical CFM produced is the same. But, VE being a % of that theoretical, surely 100% means that compression is perfect as well?

Or am I getting that wrong?

[Call the midlife!]

Speaking from experience of having the engine in bits, pound to a penny your inlet manifold will be an oily mess inside and your valves and combustion faces will be carrying a film/coating of carbon so your available cc won't be "factory spec".

[shnazzle]

Speaking from experience of having the engine in bits, pound to a penny your inlet manifold will be an oily mess inside and your valves and combustion faces will be carrying a film/coating of carbon so your available cc won't be "factory spec".

Exactly. Hell even just going off the muck in the throttle body, the intake mani has to be a mess. 

Having said that, it gets a yearly intake clean with two cans of EGR cleaner so it might not be all too bad. How many people do that? 
That's why I had my catch can (before it just leaked everywhere). 

And having thought about it, I had my compression check done at AK and it was spot on. So, I guess it is POSSIBLE that my engine's quite clean.
Still not 100+ VE clean though so I still feel like I'm missing something

[Call the midlife!]

Speaking from experience of having the engine in bits, pound to a penny your inlet manifold will be an oily mess inside and your valves and combustion faces will be carrying a film/coating of carbon so your available cc won't be "factory spec".

Exactly. Hell even just going off the muck in the throttle body, the intake mani has to be a mess.

Having said that, it gets a yearly intake clean with two cans of EGR cleaner so it might not be all too bad. How many people do that?
That's why I had my catch can (before it just leaked everywhere).

And having thought about it, I had my compression check done at AK and it was spot on. So, I guess it is POSSIBLE that my engine's quite clean.
Still not 100+ VE clean though so I still feel like I'm missing something

I'll stand to be corrected here but dirty/carbon coated head and piston faces would probably up your compression values anyway, assuming your cylinder walls and rings were making a good seal?

[shnazzle]

Speaking from experience of having the engine in bits, pound to a penny your inlet manifold will be an oily mess inside and your valves and combustion faces will be carrying a film/coating of carbon so your available cc won't be "factory spec".

Exactly. Hell even just going off the muck in the throttle body, the intake mani has to be a mess.

Having said that, it gets a yearly intake clean with two cans of EGR cleaner so it might not be all too bad. How many people do that?
That's why I had my catch can (before it just leaked everywhere).

And having thought about it, I had my compression check done at AK and it was spot on. So, I guess it is POSSIBLE that my engine's quite clean.
Still not 100+ VE clean though so I still feel like I'm missing something

I'll stand to be corrected here but dirty/carbon coated head and piston faces would probably up your compression values anyway, assuming your cylinder walls and rings were making a good seal?

I believe you're right. My values were a bit elevated. So that would suggest the valves etc are a bit mucky

[ChrisGB]

And having thought about it, I had my compression check done at AK and it was spot on. So, I guess it is POSSIBLE that my engine's quite clean.
Still not 100+ VE clean though so I still feel like I'm missing something

Apologies for the delayed reply, been trying to salvage me business.

I'm wondering if you are confusing VE with airflow? Peak airflow would be at peak power assuming everything is set up correctly. Peak airflow = peak fuel burn = peak work done = peak power.

This will be a nominal figure and if numerically scaled on the ECU would probably be measured in grams / second or similar rather than CFM. The MAF sensor is highly unlikely to be calibrated to read from 0 to 100% where airflow is between 0 and 100%. The reading range will be a part of the full range of the sensor.

When everything is running optimally, your peak air draw should stay very close to the amount drawn when the engine is new. Things that could significantly reduce that figure could be a blocked air filter, blocked exhaust or severely coked up inlet valves (particularly a problem in direct injection engines). Assuming these things have not happened, your peak airflow should stay very similar to when the engine is new. I'm not sure that spotlessly clean and shiny inlet tracts flow any any better than slightly dirty ones. Very smooth surfaces can actually reduce flow slightly.

Of course, the older engine can be down on power, but this is mostly going to be energy lost to blow by, reduced combustion efficiency from tired ignition components, or ignition timing being pulled due to head / valve / piston crown fouling induced detonation.

Volumetric Efficiency or VE is something quite different. Imagine a cylinder of 500cc. If your intake cycle gets 500cc of air into the cylinder (at STP or Standard Temperature and Pressure) that is said to have achieved 100% VE. With two valve per cylinder road engines, they tend to top out at around 85% VE, so your 500cc cylinder will ingest up to 425cc of air at peak torque. Four valve per cylinder engines can, if well set up, achieve up to 125% VE, so your 500cc cylinder could ingest up to 625cc at peak torque. This is achieved by clever intake and exhaust pulse control that effectively uses resonances in the system to cram more air in than natural airflow would allow, hence the term tuning! For an easy to read grounding in how this stuff works, I'd recommend "4 Stroke Performance Tuning" by A. Graham Bell.

Hope this clarifies!

[shnazzle]

And having thought about it, I had my compression check done at AK and it was spot on. So, I guess it is POSSIBLE that my engine's quite clean.
Still not 100+ VE clean though so I still feel like I'm missing something

Apologies for the delayed reply, been trying to salvage me business.

I'm wondering if you are confusing VE with airflow? Peak airflow would be at peak power assuming everything is set up correctly. Peak airflow = peak fuel burn = peak work done = peak power.

This will be a nominal figure and if numerically scaled on the ECU would probably be measured in grams / second or similar rather than CFM. The MAF sensor is highly unlikely to be calibrated to read from 0 to 100% where airflow is between 0 and 100%. The reading range will be a part of the full range of the sensor.

When everything is running optimally, your peak air draw should stay very close to the amount drawn when the engine is new. Things that could significantly reduce that figure could be a blocked air filter, blocked exhaust or severely coked up inlet valves (particularly a problem in direct injection engines). Assuming these things have not happened, your peak airflow should stay very similar to when the engine is new. I'm not sure that spotlessly clean and shiny inlet tracts flow any any better than slightly dirty ones. Very smooth surfaces can actually reduce flow slightly.

Of course, the older engine can be down on power, but this is mostly going to be energy lost to blow by, reduced combustion efficiency from tired ignition components, or ignition timing being pulled due to head / valve / piston crown fouling induced detonation.

Volumetric Efficiency or VE is something quite different. Imagine a cylinder of 500cc. If your intake cycle gets 500cc of air into the cylinder (at STP or Standard Temperature and Pressure) that is said to have achieved 100% VE. With two valve per cylinder road engines, they tend to top out at around 85% VE, so your 500cc cylinder will ingest up to 425cc of air at peak torque. Four valve per cylinder engines can, if well set up, achieve up to 125% VE, so your 500cc cylinder could ingest up to 625cc at peak torque. This is achieved by clever intake and exhaust pulse control that effectively uses resonances in the system to cram more air in than natural airflow would allow, hence the term tuning! For an easy to read grounding in how this stuff works, I'd recommend "4 Stroke Performance Tuning" by A. Graham Bell.

Hope this clarifies!

It most certainly does. First and foremost; I sincerely hope your business is ok, or will be OK. It's tough times for the self-employed or business owners. Definitely wishing you all the best.


So taking what you said, really 100% VE, on our engines with VVTi and 4 valves per cylinder, is quite bad.
But, that's based on the MAF signal, which as you say, may not be calibrated for the full VE range. So, 100% VE might actually be higher. The only way to measure VE then is to have a calibrated device that accurately measures the actual airflow.

Why is the MAF no calibrated to be true?

[Ardent]

Putting head briefly above the parapet.

I think CGB is saying it will be true, for the range it is calibrated for.
If 0 = no air and 100 = air.

Not much point calibrating to measure a vaccum. If there is no air. Engine starting will be the least of your worries.

So anything below a set target does not need to be measured. But between whatever the range is. Will be accurate.

Ducking back down quickly.

[shnazzle]

Putting head briefly above the parapet.

I think CGB is saying it will be true, for the range it is calibrated for.
If 0 = no air and 100 = air.

Not much point calibrating to measure a vaccum. If there is no air. Engine starting will be the least of your worries.

So anything below a set target does not need to be measured. But between whatever the range is. Will be accurate.

Ducking back down quickly.

On that note, how does the car measure manifold pressure? Is there a sensor I don't know of? That shows vacuum on the "gauge"

[Ardent]

Part of the PCV system?

[Call the midlife!]

I'm sure there's a vacuum hose comes off the inlet manifold to the small assembly that clips into the air feed pipe, near the MAF.