So what is the answer to my question then?? Am i right to say that the ideal range is 20-25psi?

Brian

 

<U>00SilverLS</U> The airflow calculated is the engine, not the turbocharger. The engine flows cfm into the turbocharger, cfm is a manner of describing the total velocity flow from the engine. In a way its describing how much energy is being able to "force" its way onto the turbine blades. So the cfm of the compressor is the flow that the compressor is putting out. The cfm that is calculated in the flow from the engine. The airflow calculation has to be loosely interpreted in that if you have turbo cams, ported head, optimum intake manifold, larger valves, etc you are going to increase the total cfm from the cylinder head.

The volumetric efficiency of the engine greatly effects the airflow calculations at different rpm's. If you have a lower rod/stroke ratio you'll have a greater volumetric efficiecy lower in the rpm band (ls/vtec). The rod/stroke effects the velocity of the piston speed traveling in the cylinder, so the lower the rod/stroke the faster the piston speed. The faster the piston speed at lower rpm, the greater the volumetric efficiency will be at lower rpm. The downside is that the volumetric efficiency dies at higher rpm (take a look at ls/vtec graphs if the head is kept stock you'll see what I mean they die around 7,500 rpm). The piston is moving faster in the cylinder, moving more air but the cylinder head cannot keep up in terms of total flow. If you increase the efficiency of the head (turbo cams, intake manifold, larger valves, etc) you'll raise the volumetric efficiency of an ls/vtec and have a greater total volumetric efficiency than a gsr over a greater rpm band.

<U>TurbodCX</U> I just did some quick calculations on your d16 engine, with a 98 CI displacement (1.6L) and you stop being efficient (I consider this lower than 70% efficiency) around 22~23psi.

 

Thanks alot bro!!

man you know your ****.. too much math for me............ lol

Brian

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">Boost: 6psi, Intercooler Pressure Drop: 1psi, Engine RPM: 8200, Post Intercooler Temp: 130 degrees, Displacement 110 CI (1.8L), Volumetric Efficiency: 90% and Underhood temps: 85 degrees</TD></TR></TABLE>


Are your assumptions on the I'C P-drop, I/C temps, VE, and Underhood temps pretty standard? I need to read more Maximum Boost, I know, but I don't know where to start for something like this. Also, I need to look at numbers for a b16, will something like the .50 trim appear just as beneficial as say a .57 trim for the smaller motor (in terms of cfm)? I don't know, I'm just asking some questions.


Modified by ricodemus at 3:53 PM 5/13/2003

 

i would also like to know more about the b16 and how much it flows

 

The assumptions I made are pretty much standard. Since its very hard to try and calculate the exact conditions, you have to just guess some values until you can either datalog, preform tests and solve a bunch of thermodynamic, fluid dynamic and heat transfer equations to obtain the raw data. I am working on a excel based program this summer that you can just change values for the things I assumed and come up with a very accurate model so you can plot on the compressor map chart.

As far as picking compressor maps alot of the maps will seem reasonable to pick. At that point you have to look at the cfm ratings of the maps, your low and high boost levels and go from there. That should narrow the selection down to one-two maps.

 

So what's the theoretical horsepower limit of a B18C1 with a 60 trim .63 a/r T3/T04E at about 22psi? Because of the airflow isnt the turbo a horsepower limiting factor if the engine is tuned correctly?

 

depends on how high you rev and displacement

 

Directly relating horsepower levels and compressor maps is a bit loose to interpretation. The larger the displacement the easier power will be made on the same size compressor map, but the quicker the compressor map will become unefficient. The larger the displacement the more total cfm an engine will flow, so the higher the pressure ratio and airflow numbers on the compressor maps. I would estimate that with proper tuning (which plays a very significant role) the horsepower level you could obtain using a relatively stock internal gsr block would be 450whp level. You are limited to the horsepower level with the .63a/r exhaust housing though. The higher you can rev the engine, the more horsepower you can make. This is directly from the equation: Horsepower=RPM*Torque/(5252). The goal to creating more power on the same compressor map is to have turbo cams to extend the torque powerband to redline, as well as have the head flow with the higher rpms (porting, efficient intake manifold, larger valves, etc) and running the largest exhaust housing you can possibly (Lag is the trade off).

 

Boosted Hybrid- I'm still not following you on something.

Say you have a 110cc motor, at 7000rpm at 90% VE. It will flow 200 cfm. Now if boosted say 9psi it will flow 322 cfm.

Now if two different compressors are making that 9psi at the same efficiency, say 70%. Then you are flowing 322 cfm at the same temperature. How does anything about the size of the compressor matter?

This has been something that I've been confused about for a while, and I hope you can help clarify this for me.

 

on a stock d16..what would be the best bet for a turbo???57trim .63 exhaust?or 60 trim.63 exhaust...10psi??this might also be put on a dohc later..b16 probably

 

To find the Airflow cfm of the engine you take it before putting pressure through the engine. The reason is that you must take the Airflow calculations before putting pressure through the engine is directly related to your questions. The cfm is rated pre-turbo so you can find the actual cfm of the engine that will flow into the turbine.

You'll not find two compressor maps that are the same, they might look close on the graphs but if you can get a larger plot of the maps you'll be able to see the smaller differences. The flow ratings between compressors as well will never be the same. If the cfm from two compressor maps were the same, as well as the efficiency ratings then you would have the same compressor map. To create a compressor is a give and take relationship. You have to give up total cfm for efficiency, or efficiency for total cfm.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by boosted hybrid &raquo;</TD></TR><TR><TD CLASS="quote">The volumetric efficiency of the engine greatly effects the airflow calculations at different rpm's. If you have a lower rod/stroke ratio you'll have a greater volumetric efficiecy lower in the rpm band (ls/vtec). The rod/stroke effects the velocity of the piston speed traveling in the cylinder, so the lower the rod/stroke the faster the piston speed. The faster the piston speed at lower rpm, the greater the volumetric efficiency will be at lower rpm. The downside is that the volumetric efficiency dies at higher rpm (take a look at ls/vtec graphs if the head is kept stock you'll see what I mean they die around 7,500 rpm). The piston is moving faster in the cylinder, moving more air but the cylinder head cannot keep up in terms of total flow. If you increase the efficiency of the head (turbo cams, intake manifold, larger valves, etc) you'll raise the volumetric efficiency of an ls/vtec and have a greater total volumetric efficiency than a gsr over a greater rpm band.</TD></TR></TABLE>


Great examples of motors that have peak VE (volumetric efficiency) early in the rpm band:
VW 1.8T----------144mm rod / 86.4mm stroke = 1.66 r/s ratio
Dodge SRT-4----151mm rod / 101mm stroke = 1.495 r/s ratio

Some say the turbo is too small on those motors ..thats why torque dies off in the highend. That is correct to some point, but torque will always die off in the highend even if you run a BIG turbo (unless you change the geometry of the motor). Peak VE occurs early on those motors and it dies out because piston speed is too fast for valving (there is a limit to how fast air can move, move it too fast and you'll lose its density).

When you plot on compressor maps, plot the airflow where peak VE occurs. Peak VE can range from 80% to 110% depending on the motor, and it rarely occurs at MAX rpm. (people get used to plotting max rpm airflow). Peak VE also follows the peak torque rpm rather than peak hp. %VE will move your plot along the x-axis (air flow in lb/min).
When you hit peak torque, you want the turbo to be at its best (efficiency) and not blowing hot air.

A very good compressor for your motor is one where both your: peak torque airflow, and peak horsepower airflow remain within the best efficiency island on the map, and thats kinda hard to find.

In the future, we might come up with custom size compressors, because some are "borderline". Dear precision..


Modified by Quick 200k Mile Motor at 7:15 PM 5/13/2003


Modified by Quick 200k Mile Motor at 7:17 PM 5/13/2003

 

We are not worthy....

Back to the point, I'm not very good at reading graphs so at what psi is 60 trim 63a/r most efficient then?

I know its probably a little vague is asking this, but if the turbo is operating at only half its maximum possible efficiency, am I correct in saying that its not making nearly the hp thats its capable of making if we were to compare it at the same psi?

Its late and so I might not be making any sense...

 

On the .60 trim map, find 2.1 for pressure ratio (y-axis)
That is 1bar (14.7psi), and I'd say that is where its most efficient, but this thing is efficient from 8 to 18psi for a 1.9liter

 

What about a Super 50 wheel? What makes it "super"? Is there better cfm? Why is it better than a regular 50 trim?

Art probably knows.

Thanks

 

The 60 trim will max out (fall below 70%) around 22-24psi. The peak efficiency of the 60 trim will fall between 12-18psi (76-78%).

If the turbo is at half its efficiency rating, its not making the maximum amount of horsepower at that psi level. Say for instance at 10psi you would be more efficient on the 57 trim, than 10psi on the 60 trim. Comparing the cfm ratings: 60 trim 52lb/min, 57 trim: 50lb/min. The difference in flow is pretty small, so you wont see a dramatic increase in power with the higher cfm flow. Now compare the 60 trim @ 18psi with a 60-1 @18psi, 60 trim: 52lb/min and 60-1:60lb/min. The 60-1 trim will own the 60 trim at 18psi, while both are in their efficiency range. The 60-1 is flowing 8lb/min more which is a noticable difference in flow.

Just a comment on where the "efficiency" rating of the compressors. The efficiency is determined by: n(efficiency)=W actual/W ideal.

The W actual is Work Actual

The W ideal is Work Ideal

You are comparing the actual work to the ideal work of the compressor to get a ratio. Once you have the ratio multiply by 100 to get a the efficiency % as on the compressor maps. If you guys are really interested in compressors, turbines, etc pick up a thermodynamics book that is user friendly. You will learn a tremendous amount worthwhile information.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by boosted hybrid &raquo;</TD></TR><TR><TD CLASS="quote">Comparing the cfm ratings: 60 trim 52lb/min, 57 trim: 50lb/min. The difference in flow is pretty small, so you wont see a dramatic increase in power with the higher cfm flow. Now compare the 60 trim @ 18psi with a 60-1 @18psi, 60 trim: 52lb/min and 60-1:60lb/min. The 60-1 trim will own the 60 trim at 18psi, while both are in their efficiency range. The 60-1 is flowing 8lb/min more which is a noticable difference in flow.</TD></TR></TABLE>


Grrr I'm still not understanding how a different turbo will put more air into the same engine.

 

If you have compressors A and B. A flows 50 lb/min while B flows 65 lb/min, B will out flow the A compressor.

The airflow, or cfm of the engine is a calculation based upon the engine without forced induction. Its the total amount of airflow that flows out of the engine naturally aspirated. You need to have pre-turbo cfm ratings since its the actual airflow of the engine that matters. The cfm of the engine with boost is still based upon the actual engine flow (cfm) + the actual compressor flow (cfm). You must use the actual engine flow when you plot on a compressor map since the cfm rating of the compressor flow would be neglected since its an external part of the exhaust system.

 

2 things

1) Isn't the engine flow rate the amount of air that the engine intakes not how much goes through the exhaust.

2)When you plot a compressor map you correct for pressure. you take NA cfm x pressure ratio.

Heres a quote I found in Maximum Boost "The trick to choosing optimum compressor size lies in positioning the point of maximum efficiency at the most useful part of the rev range." and "Larger or smaller compressors do not have a huge effect on turbo lag or boost threshold."

What hes saying is that it all depends on efficiency, not size. Again, in the same motor at the same rpm, 9psi at 100deg is 9 psi at 100 deg no matter what its coming out of.

 

someone has been studying for finals

good stuff jeff!

after all is said and done, the thing that really limits you is the availability of an "ideal" compressor. Becuase we can not choose exactly what we want in a compressor we often have to compromise. I personally have a very math-less method which works well for street cars. Pick a HP # you want (flywheel) on race gas OR on pump gas. Take that number, find it on the chart via CFM and then size a turbo according to what the car is going to spend most of its time doing

More street driving? Use the turbo that is super efficient at 15 psi, falls out of efficiency around 25 psi (60-1 is great for street cars b/c of this)

More racing and high boost? Use the turbo that is super efficient at elevated boost levels.

Also remember that a GM 3 bar map can only read up to 30psi...

 

Also a thought to take into consideration for choosing an efficient turbo as quoted by Corky Bell...

"I believe the reasonable balance between low-speed response and top-end power is to size the turbo such that it begins producing boost at about 30% of the redline rpm."

That means for a B18C1, a turbo that has good low-speed response and top-end power should start producing power at around 2,700 rpm. But I bet you guys would be saying a turbo like that would be too small.

 

just depends on your transmission ratios, and redline.

if you have a 9k redline, power coming on at 6k isn't going to matter, since you have 6-9 to put it to the ground.

boosted hybrid owns this thread. jeez.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by boosted hybrid &raquo;</TD></TR><TR><TD CLASS="quote">If you have compressors A and B. A flows 50 lb/min while B flows 65 lb/min, B will out flow the A compressor.

The airflow, or cfm of the engine is a calculation based upon the engine without forced induction. Its the total amount of airflow that flows out of the engine naturally aspirated. You need to have pre-turbo cfm ratings since its the actual airflow of the engine that matters. The cfm of the engine with boost is still based upon the actual engine flow (cfm) + the actual compressor flow (cfm). You must use the actual engine flow when you plot on a compressor map since the cfm rating of the compressor flow would be neglected since its an external part of the exhaust system. </TD></TR></TABLE> so my question is does anyone know around the ballpark of the total amount about of air that flows out from a b16

 

I'm also interested in knowing the most efficient boost level for a B16 with 57 trim..

Also does the size of AR make a lotta difference? mine is .48 BTW.