Safir

I have read these threads: https://honda-tech.com/zerothread?id=96443 https://honda-tech.com/zerothread?id=98528

And understand the theories and math behind most of what is going on, but how does Mr. BlueShadow decide on a Volumetric Efficiency of .95? 95% efficiency seems a little high to me, so I wonder, what is the usual range? what kind of numbers can i expect to see in the real world? And most importantly, what factors effect the VE of a particular motor? any help is appreciated.

BlueShadow

The reason I used 95% is so that it gives me some margin for error. To overly simplify my steps, what I do is find 2 RPM points (redline and 2/3 RPM range) for the "HIGH" point (redline) I use the highest % VE, for the "LOW" point (2/3) I use a lower % VE.

Some people say that only the enginers that built the car will know its VE. Since I dont know any Honda engineers, and since no one else knew the VE %, I just used a little common sense.

Look at the pis of the T04E 60" compressor,
If you draw a horizontal line at pressure ratio 1.8 at the right to the number 30 at the bottom. 30 is the flow rate in pounds per minute (LB/MIN)

lets say that at redline with a VE of 80% and PR of 1.8 the "point" will sit at the intersection of 1.8 and 30. If you increase the VE the "point" moves to the right, If the VE change is big enough you'll be sitting in the 50-65% range of compressor efficiency. see what I'm getting at? If you had used 80% for you VE, and your VE was actually 95-100% you would be sitting further to the right than you though you had been. Its a little exagerated but you get the point.

NOW for the other "point" I do the exact opposite, cause here we're not worried about compressor efficiency, we're worried about staying out of the "SURGE LIMIT" area. For low boost like 7-10 PSI, full boost is usually hit around 3500-3800 RPM, so at that RPM I use a low number like 80% or maybe even 50%.

If your "point" is sitting inside the "SURGE LIMIT" area you get compressor surge (not enough airflow too much boost), and you get this snake-like, che-che-che sound coming from the intake pipe.

BTW all my research is on T4/T3 Hybrids.

BlueShadow

And although I might have the selection part down (sorta) here is someting else that I thought about. It had to do with the Air/Fuel Ratio, altough it probably doesn't apply in actual conditions. I dont think people go "hmm.. I've got 25 Lbs of air moving at XXXX RPM's so I'm gonna need XX amount of fuel"

I quote BlueShadow,

I also noticed several things about that site, he said he used 85% as his number for Volumetric efficiency but I used 95%. I'll tell you my reason for using such a high number in a minute.

If you used a calculator and check over my work you'll notice a small discrepancy. I round all my numbers up. for example if my equation for airflow comes out to 35.123101 LB/MIN I will round up to 36 LB/MIN, same with boost/pressure ratio 1.6801347 will go up to 1.69 (1.7 would be better)

I did that to give myself some margin for safety, that way when you are trying to get the right fuel mixture your using a higher volume of air (36 vs 35.123101) .

that extra pound of air that I just rounded over might help against detonation because with an increase of 1 pound of air in the airflow we have to add XXX amount of fuel.

same thing goes with the Volumetric efficiency, its hard to figure out exactly what it is at a given RPM so I use the max 90-95% this means that we are accounting for more air entering the engine.

for example:
my car 2.2L(134.2cid) at 7000 RPM at 80%VE and 95%VE

80% Volumetric efficiency
(134.2 x 7000 x 0.5 x .80) / 1728 = 218 CFM with no boost
thats 368.43 CFM at 10 PSI or 25.91 LB/MIN

95% Volumetric efficiency
(134.2 x 7000 x 0.5 x .95) / 1728 = 259 CFM with no boost
thats 437.72 CFM at 10 PSI or 30.78 LB/MIN

So you see a 15% difference between VE means a 5 lb difference in airflow!
so think about it, your doing fuel for 25.91 LB/MIN (80%) but what if your getting mroe air then that? what if you were actually getting 30.78 LB/MIN (95%) but were only adding enough fuel for 25.91 LB/MIN?

BOOM! detonation!

EDIT
one thing I forgot to add, If I had to use my own methods for picking my own turbo I would only do it if I was boosting less than 15 PSI. above 15 PSI things start to get a little complicated when doing this stuff by yourself.




[Modified by BlueShadow, 2:53 PM 2/5/2002]

BlueShadow

I have a book that defines Volumetric Effieciency and gives an example.

It states that:

"After a certain engine speed is reached the VE efficiency drops rapidly. In general maximum VE efficiency is reached at approximately the same point where maximum torque is reached."

I'm assuming that that statement is referring to SOHC or maybe "NON-VTEC" type cars. Because If you apply the above statement to my car, Max Torque is at 5250 RPM (156 TQ), but that is roughly the same time my VTEC engages. My max HP is 200 at 7200 RPM and my redline is at 7400. The statement doesn't quite make sense to me, how can the car reach its Max VE when it has not even reached its HP peak?

oh well I guess thats a question for the engineers.

EDIT: also the VE of an engine is directly related to the cam design.


[Modified by BlueShadow, 3:11 PM 2/5/2002]

Safir

Thank you for the information, I am finding it extremely useful.

BlueShadow

Hey Safir,

here some info for you to nibble on. I was doing a search on yahoo.com for "Honda Volumetric Efficiency" and among the hits was this site.

Here is a quote that I found very interesting, It backs up what I said about VTEC having a higher VE than other NON-VTEC cars.

I quote autospeed.com,

"For comparison, the engineers also show the VE of the H22A 2.2-litre Prelude engine (still brilliant with 149kW at 7000 rpm) - has a peak VE of 'only' 102 percent, again achieved at peak power. So much for the traditional engine view that maximum volumetric efficiency occurs at peak torque!"

Its saying that a H22 VTEC has a VE of 102% at peak power (7000 RPM's)!!!

also the last statement
"So much for the traditional engine view that maximum volumetric efficiency occurs at peak torque!"

If you read my previous post, I posted this statement, but things didn't add up. peak VE after torque peak? (5250 RPM) it didn't sound right, but this here looks like proof. I'm gonna cross-check this with other sources and see If hey have the same VE# for my Lude.

http://www.autospeed.com/A_1127/page1.html