Engine data for turbo selection

crankbender · 03-26-2004, 03:55 AM

Ok there are as always a lot of people asking about turbos. Well I made it a little bit easier on everybody...

Below are the graphs showing the flow rates (in CFM) as well as some representitive flow rates (in lbm/min) with a few different configurations.

Hope this really helps everybody out. Keep in mind that these are very conservative figures and will overestimate your flow at higher RPMs. These do not take pumping losses into account...Unless you have a very well designed system take the flow rates and multiply them all by .85 or so to convert the volumetric efficiency. I used 1 so that everybody would be able to convert easily for different set ups.

crankbender · 03-26-2004, 03:56 AM

I really need to learn to post more than 1 pic per post...

Anyway the 2 liter engine.

crankbender · 03-26-2004, 03:57 AM

crankbender · 03-26-2004, 03:59 AM

The 2.3 L stroker motor

crankbender · 03-26-2004, 04:00 AM

crankbender · 03-26-2004, 04:01 AM

The 4G64 motor

crankbender · 03-26-2004, 04:02 AM

crankbender · 03-26-2004, 04:04 AM

There ya go!!! That will allow you to use any common compressor map to select the appropriate turbo for your car.

If there are any questions, comments, or suggestions please post them here. Also if want info like this to keep comming please post it here.

kpt4321 · 03-26-2004, 08:50 AM

What calculations did you do to estimate this? I'm just curious.

This is how I rock it:

Also, if people want to do their own calculations, there is a tuning guide on this website that will do some basic ones for you:

Tuning Guide for the Beginner to Intermediate Tuner

Great thread!

Groomz · 03-26-2004, 09:19 AM

Very nice. I like how the lb/min flow drops with a rise in intake temps. Something to think about.

98RedGs · 03-26-2004, 10:52 AM

Dam nice.

DaveSM · 03-26-2004, 10:07 PM

Crankbender: Did you just multiple displacement by RPM to find CFM? What about volumetric efficiency...

and then for the other charts, you set VE = 1, what about when VE increases with boost pressure?

Groomz · 03-26-2004, 10:40 PM

Quote:

Originally posted by DaveSM
Crankbender: Did you just multiple displacement by RPM to find CFM? What about volumetric efficiency...

and then for the other charts, you set VE = 1, what about when VE increases with boost pressure?

VE on boosted engines is still calculated sans boost. VE peaks at the torque peak, usually around 95% on our engines. VE changes from engine to engine and is dependent on many variables, so 100% VE is just a rough estimate. What's interesting is that most OHV V8's only get about 60% VE. 4G63's are nice motors.

LordDigi · 10-19-2006, 06:35 AM

These charts are very good info

Not that I don't believe you, but I think it would be more informative if you were to post the formulas behind your calculations as well

EL13EVIL · 03-05-2007, 11:49 PM

Real Nice!!!

DarkStarMenace · 02-08-2008, 01:33 AM

Actually that would be stock V8s. I built a 383 Chevy that screamed to around 8k RPMs. I got its max VE to about 85 %. now thats peak. average about 70-75. And when boost comes into play the VE exceeds 100 %. Just my 2 cents.

123bobby123 · 05-06-2008, 09:22 AM

Quote:

Originally Posted by DarkStarMenace

when boost comes into play the VE exceeds 100 %.

Hi,

Sorry to bring this back from the dead, but this is an incorrect statement. Whenever you talk about the VE of an engine, you should always talk about it when the engine is in its naturally aspirated form. As I'm sure you all know the turbocharger is used to increase the mass flowrate of the engine, and the reason you go through all these calculations is to match the turbocharger with the engine, through pressure ratio and mass flow rate. The mass flowrate is dependent on density ratio caused by the turbocharger, atmospheric density, and volumetric flowrate of the engine. In other words mass flow rate is dependent on density ratio and how much air the engine would ingest under naturally aspirated conditions. This is because the density ratio is how much the turbocharger will increase air flow through the engine on a mass basis over when the engine is naturally aspirated.

The amount of air that the engine will ingest on a mass basis when it is naturally apsirated is only dependent on atmospheric air density, engine displacement, engine speed (rpm), and engine volumetric efficiency. Say that a certain turbocharger we will use gives us a density ratio of 2.0 (this depends only on turbo inlet temps, pressure ratio, and compressor efficiency). This means that the engine will now bring in twice as much air (on a mass basis) as it did when it was naturally aspirated.

The reason why you have to go through the trouble of matching a turbo to an engine is becasue a given engine can only ingest a certain volume of air. Now it can ingest any amount of air on a mass basis, because you can use a turbocharger to raise the inlet density to basically whatever you like in theory. But the amount of air the engine can ingest on a volumetric basis is only depenedent on engine displacement, engine speed (rpm), and volumetric efficiency.

Another much more simple way to think about it is that a turbocharger only effects the mass flow rate of air moving through your engine. The volumetric efficiency is just that. It expresses how efficient the engine is at filling its cylindes every four strokes, based upon the volume of air the engine draws in and how much it should be drawing in. Based on this it can be seen that there is no way for the turbocharger to effect the volumetric efficiency of the engine, becasue it does not effect the volume of air being delivered to the cylinders.

Hopefully this helps to clear this up. Also, I hope that I was clear enough.

Bill