How do you read a compressor map?

[4sfed4]

Quote:

Originally posted by Vanquizor I noticed it mentioned several times that some are tuning by backpressure readings, I was just curious as to exactly where/how you were taking these readings. I've also heard a general rule of thumb that 2:1 backpressure vs boost is a good target for a street car// any thoughts?

I measured mine via the EGT port in the exhaust manifold.

And yes....2:1 is about right for a street/strip car! Thats ratio will generally give a good blend of spoolup to top end power. If your talking about a pure race car, youd want a lower ratio. Power SHOOTS up very quickly with reduced backpressure to boost ratios.

[Frank]

Quote:

Originally posted by 4sfed4 When I did the "reverse guessitimation" using dyno charts and the compressor maps, etc using your spredsheet, I am getting VE's well over 100%. For a 12 psi dyno run, here is how the numbers worked out--- RPM 7,000 6,000 5,000 4,000 3,000 2,000 VE 100% 130% 140% 145% 110% 100% I have no idea whether this is realistic or not!

This is kind of unwalked territory for myself, but let me take a stab at it.

100% VE of a n/a 2.0L engine is 2.0L of air. Normally stock tuning does not allow for 100% but a bit less, especially on heads like 2.2/2.5. You can achieve almost 110% VE on race n/a motors with properly valve overlap, head flow, exhuast flow, etc, etc, etc.

If you then factor in boost, say 12 psi of air of a 2.0L, and *lets say* it equals the equivelent of 2.3L of air at atmospheric pressure and you really had the equivelent of 2.3L of air in the engine, then it would be 100% VE. If you have 2.2L of air, then you would be at 95.6% VE.

This actually automatically compensates for air temps, psi, comp efficency, adiabatic efficency, etc to form air density and so your numbers seem right on if you were comparing it to your origional airflow. So to summerize it, if you are at these atmospheric conditions and I have this PSI, I should have this much air in my engine called X. But I really have Y. So now VE = Y/X.

With all that said, maybe something like this????
RPM 7,000 6,000 5,000 4,000 3,000 2,000
VE 82% 89% 93% 96% 84% 82%

Frank

[Frank]

Quote:

Originally posted by BadFastGTC Frank, Where did you come up with these figures?

guestimations, no more. hopefully between our collective knowledges coming together, we can get a good set of VEs for different types of engines/configurations.

Frank

[Frank]

Quote:

Originally posted by Vanquizor Finally on compressor maps I was playing with the utility on Ray Hall Tourbocharging's site, (http://www.turbofast.com.au/turbomap.html ) anyone use this tool/want to speak to it's accuracy? thanks!

It can be very accurate, but not as cool as my spreadsheet ;). I am currently working on making mine public. Really the only difference is that I cover a bit more compressor maps and have more detail of engine demand lines.

I want to make it so that my spreedsheet handles all the mitsu's also, but I will need to seperate things because its already 1.7MB with just the Garrett maps. Maybe make it more user friendly.

Frank

[4sfed4]

Quote:

Originally posted by fkatzenb This is kind of unwalked territory for myself, but let me take a stab at it. 100% VE of a n/a 2.0L engine is 2.0L of air. Normally stock tuning does not allow for 100% but a bit less, especially on heads like 2.2/2.5. You can achieve almost 110% VE on race n/a motors with properly valve overlap, head flow, exhuast flow, etc, etc, etc. If you then factor in boost, say 12 psi of air of a 2.0L, and *lets say* it equals the equivelent of 2.3L of air at atmospheric pressure and you really had the equivelent of 2.3L of air in the engine, then it would be 100% VE. If you have 2.2L of air, then you would be at 95.6% VE. This actually automatically compensates for air temps, psi, comp efficency, adiabatic efficency, etc to form air density and so your numbers seem right on if you were comparing it to your origional airflow. So to summerize it, if you are at these atmospheric conditions and I have this PSI, I should have this much air in my engine called X. But I really have Y. So now VE = Y/X. With all that said, maybe something like this???? RPM 7,000 6,000 5,000 4,000 3,000 2,000 VE 82% 89% 93% 96% 84% 82% Frank

What if we did this?

2.2L engine at 12 psi boost

= (14.7 psi + 12 psi) / 14.7 psi
=182%

Could one, in this very basic assumption, state that a 2.2L engine could theoretically have a VE of 182%? This assumes that the VE % is based on a perfect N/A engine.

Now, that 2.2L engine is actually acting like a 4.0L N/A engine would if it had a VE of 100%?

If VE cant be over 100%, then how would a turbo engine make more power than an N/A one? I am a complete novice at VE calcs, so I am just thinking out loud and trying to match dyno data with VE calcs.

[Frank]

Quote:

Originally posted by 4sfed4 What if we did this? 2.2L engine at 12 psi boost = (14.7 psi + 12 psi) / 14.7 psi =182% Could one, in this very basic assumption, state that a 2.2L engine could theoretically have a VE of 182%? This assumes that the VE % is based on a perfect N/A engine. Now, that 2.2L engine is actually acting like a 4.0L N/A engine would if it had a VE of 100%? If VE cant be over 100%, then how would a turbo engine make more power than an N/A one? I am a complete novice at VE calcs, so I am just thinking out loud and trying to match dyno data with VE calcs.

let me attempt to collect my thoughts together and try a different explination because I too am a newbie at this.

lets say this....
(assume made up numbers and a constant rpm)

#1 - 2.2L n/a achieves 89% VE with repsect to the 2.2L.
#2 - 2.2L t/c achieves 120% VE @ 12psi with respect to the 2.2L n/a that was mentioned in #1.
#3 - 2.2 t/c produces 89% VE @12psi with repsect to what it should be produce at 12psi.

Its #2 that your fuel calculations run off of. Its #1 or #3 that we need. So those VE's that you origionally calculated were the VEs that are found in #2.

So what does this tell us? That we have opened up a huge arse can of worms. See there is no way we can tell what we are really producing in terms of VE without tons of sensors/instrumentation. We can only assume based on fuel used, flowbenches, dyno charts, and reference points to other people's knowledge/experience.

My head hurts.

Frank

[glhsken]

Frank and Larry... I never realized you 2 were Bi (lingual that is)

All this Greek just went straight over my head... Please let me have the english translation when you figure it out... I might be mono-lingual.. but I can still learn ;)

[DakotaKid]

Quote:

Originally posted by 4sfed4 What if we did this? 2.2L engine at 12 psi boost = (14.7 psi + 12 psi) / 14.7 psi =182% Could one, in this very basic assumption, state that a 2.2L engine could theoretically have a VE of 182%?

Larry,

I think that is the formula for CFM Requirements of an engine.

-Bryan

[4sfed4]

Quote:

Originally posted by TrboVan Larry, I think that is the formula for CFM Requirements of an engine. -Bryan

It should be since VE addresses how much air makes it into the engine!

[4sfed4]

Quote:

Originally posted by fkatzenb let me attempt to collect my thoughts together and try a different explination because I too am a newbie at this. lets say this.... (assume made up numbers and a constant rpm) #1 - 2.2L n/a achieves 89% VE with repsect to the 2.2L. #2 - 2.2L t/c achieves 120% VE @ 12psi with respect to the 2.2L n/a that was mentioned in #1. #3 - 2.2 t/c produces 89% VE @12psi with repsect to what it should be produce at 12psi. Its #2 that your fuel calculations run off of. Its #1 or #3 that we need. So those VE's that you origionally calculated were the VEs that are found in #2.

What I am not clear on is this......

VE is a ratio. Thus, there needs to be a top limit and bottom limit. So, how do we find the top limit (i.e. VE of 100% under a given boost pressure)? How can one define the maximum amount of air one can get into a certain size cylinder without somehow referencing it to an N/A engine? Do we need to look at air densities, temperatures, etc, etc and see what volume of air the compressed air charge would occupy if it were allowed to expand back to 0 psig? If so, that might not actually be too hard to do.

Quote:

So what does this tell us? That we have opened up a huge arse can of worms.

Thats for sure! I say we just reference it to a perfect N/A engine and accept VE's of over 100% to relieve the headaches! Then, your spreadhseet will also work out just fine!

[4sfed4]

Quote:

Originally posted by glhsken Frank and Larry... I never realized you 2 were Bi (lingual that is) All this Greek just went straight over my head... Please let me have the english translation when you figure it out... I might be mono-lingual.. but I can still learn ;)

If you think I know what I am talking about I have some oceanfront property in Arizona I would like to sell you!
:big grin:

[turbovanman]

Quote:

Originally posted by Vanquizor I noticed it mentioned several times that some are tuning by backpressure readings, I was just curious as to exactly where/how you were taking these readings. I've also heard a general rule of thumb that 2:1 backpressure vs boost is a good target for a street car// any thoughts? Finally on compressor maps I was playing with the utility on Ray Hall Tourbocharging's site, (http://www.turbofast.com.au/turbomap.html ) anyone use this tool/want to speak to it's accuracy? thanks!

So for those of us without egt, what is an acceptable backpressure reading?????????

[contraption22]

An article in Hot Rod mag last month (which is fully available for free right now on hotrod.com) Recommends that you use a VE of 100% when doing these calculations.

Whether you're seeking to reach a desired power level (for racing) or a specific boost level (on the street), first determine how much airflow is needed to reach your goal at a given engine displacement and engine rpm. A normally aspirated four-stroke engine's cfm requirements are expressed by the classic formula: VE is at least 100 percent for a turbocharged engine, so use 1.0 for VE.
Next, you need to add boost into the equation. Turbo engineers use pressure ratio (the ratio of the total absolute pressure produced at the turbo outlet divided by atmospheric pressure) instead of an outright expression of boost pressure. Compressor pressure ratios corresponding to boost levels of 10 psi and 15 psi are 1.68 and 2.02, respectively; to find other pressure ratios:

[Frank]

Quote:

Originally posted by glhsken Frank and Larry... I never realized you 2 were Bi (lingual that is) All this Greek just went straight over my head... Please let me have the english translation when you figure it out... I might be mono-lingual.. but I can still learn ;)

I stayed at a Holiday Inn Express last night.


hehehehe

[Frank]

Quote:

Originally posted by 4sfed4 What I am not clear on is this...... VE is a ratio. Thus, there needs to be a top limit and bottom limit. So, how do we find the top limit (i.e. VE of 100% under a given boost pressure)? How can one define the maximum amount of air one can get into a certain size cylinder without somehow referencing it to an N/A engine? Do we need to look at air densities, temperatures, etc, etc and see what volume of air the compressed air charge would occupy if it were allowed to expand back to 0 psig? If so, that might not actually be too hard to do. Thats for sure! I say we just reference it to a perfect N/A engine and accept VE's of over 100% to relieve the headaches! Then, your spreadhseet will also work out just fine!

now you are starting to catch on. the density is the killer here. i dont know the best way to organize this into thoughts, so bare with me... partly because its me and secondly is because i am trying to explain it at the same time to even myself.

Here is what we know. VE is a ratio of air between what we have to what we should have volumetrically. If we have constant volume then that means we have a changing of density. Density is effected by temperature and pressure. Both of those are effected by cylinder and port characteristics.... that is another can on the shelf.

So what should be our next step? I dont know!

Its coming along though! "thumbs up

Frank