[mad_trbo]

Doing some reading and still trying to wrap my mind around the use of compressor maps.

My first question, CFM is definitely a measure of volume and not mass is this correct?

In calculating theoretical airflow for an engine, this number should not change based on the addtion of a turbo correct? Turbo or charger would cause the density of that volume entering the engine to change, is this correct? Volume should stay the same, the density of that volume will change.

If this is correct why in some cases am I seeing calculations that request an adjustment to airflow / volume for boost based on a pressure ratio calculation? As an example say I have a pressure ratio of 1.62 one of the books I am reading indicate to increase airflow found under n/a conditions by 62%. Plot this point on the compressor map and trace to the desired pressure ratio.

My thoughts are at a fixed RPM the airflow will not change for a particular application regardless of N/A or charged. When looking at the compressor map I need to know what my flow rate is at a particular RPM and then decide what kind of pressure increase over atmosphere I want to see. Plot this and see where I end up on the compressor map.

Where am I erring in my understanding.

[Robert]

Originally Posted by mad_trbo

Doing some reading and still trying to wrap my mind around the use of compressor maps.

My first question, CFM is definitely a measure of volume and not mass is this correct?

In calculating theoretical airflow for an engine, this number should not change based on the addtion of a turbo correct? Turbo or charger would cause the density of that volume entering the engine to change, is this correct? Volume should stay the same, the density of that volume will change.

If this is correct why in some cases am I seeing calculations that request an adjustment to airflow / volume for boost based on a pressure ratio calculation? As an example say I have a pressure ratio of 1.62 one of the books I am reading indicate to increase airflow found under n/a conditions by 62%. Plot this point on the compressor map and trace to the desired pressure ratio.

My thoughts are at a fixed RPM the airflow will not change for a particular application regardless of N/A or charged. When looking at the compressor map I need to know what my flow rate is at a particular RPM and then decide what kind of pressure increase over atmosphere I want to see. Plot this and see where I end up on the compressor map.

Where am I erring in my understanding.

This could be a very lengthy discussion but here's a couple sites that might help you. Check them out and let me know if you still have questions:

http://www.lovehorsepower.com/MR2_Do..._flow_maps.htm

http://faq.ef-honda.com/index.php?si...&id=20&lang=en

http://www.tunerfriends.com/forums/s...ead.php?t=5509

http://www.automotivearticles.com/12...election.shtml

http://www.cheresources.com/question...asics-100.html

[mad_trbo]

So I read through each one of the articles contained at the websites listed in your response. Thank you for takint the time to post them. The only one that really seemed capable of addressing my answer was the last one at cheresources. I got excited at the title but found myself a little disappointed once I finished reading. It really only explained the difference between SCFM and CFM indicating that SCFM meant all measurements were taken at a standard.

I guess I am wrong in my way of thinking. It appears you can change the volume through forced induction, I'll just have to follow the forumulas which I do understand which is fine.

I have a few other questions one of which involves varying pressure rates at the same CFM. I am going to do a little bit of homework first and post later. Thanks again for the information.