Relation between CFM and HP

Discussion on general flowbench design
Post Reply
brandoracing
Posts: 103
Joined: Tue Nov 12, 2013 12:48 pm
Contact:

Relation between CFM and HP

Post by brandoracing »

Hi guys.
Yesterday I talk with one of my friend and talking about the relationship of CFM and HP.
I think is depends from the pressure test.
But for example,@28" where is the correct relation?
Is also to know and develop the correct size of a piece.
for example,this carburettor runner,enough for XXX hp?
And,this head,for a turbo engine,can support XXX hp for each cylinder?
Sorry for my English!
www.brandoracing.it
Alfa Romeo 75 owner
Hotz
Posts: 709
Joined: Thu Feb 25, 2010 10:37 pm

Re: Relation between CFM and HP

Post by Hotz »

My friend Brando, there is an excel spreadsheet forum here that makes this calculation if I remember, unfortunately I do not remember where this.

I think it was Jhon Holm who shared. (excuse me! how I not think in English many things are lost).

If you do not know, this is a place with lots of information.
http://speedtalk.com/forum/index.php
Sorry my english mistakes.
PTS Parts>> http://www.flowbenchtech.com/store.html
storm
Posts: 289
Joined: Mon Feb 23, 2015 6:10 am
Location: In the glorious Hunter Valley

Re: Relation between CFM and HP

Post by storm »

There are websites that have HP calculators, do a search for CFM to HP calculator and you can go from there.

From memory one of the well known Pontiac modification engines shops has one (Buttler performance maybe?).
Every job is a self portrait of the person who does it.
Autograph your work with excellence.
c.watson
Posts: 9
Joined: Tue May 14, 2013 12:13 pm
Location: Cumbria,UK

Re: Relation between CFM and HP

Post by c.watson »

CFM @ max lift and 28"wc x 0.257 gets you close, depends on transmission losses,hope this helps.
Clive
The more I learn the less I know
saltfever
Posts: 42
Joined: Tue Jul 30, 2013 9:04 pm

Re: Relation between CFM and HP

Post by saltfever »

Thank you Mr. Watson. I would like to look into that a little bit more. Could you suggest other sources or information about the HP/CFM subject?
Hotz
Posts: 709
Joined: Thu Feb 25, 2010 10:37 pm

Re: Relation between CFM and HP

Post by Hotz »

Sorry my english mistakes.
PTS Parts>> http://www.flowbenchtech.com/store.html
1960FL
Posts: 1338
Joined: Fri Jan 08, 2010 10:36 pm
Location: Maryland

Re: Relation between CFM and HP

Post by 1960FL »

CFM @ max lift and 28"wc x 0.257 gets you close, depends on transmission losses,hope this helps.
Clive
This formula X the number of cylinders is used to provide the HP Potential based solely on intake flow it is meant to be used based on the flow of the entire intake tract Head + Manifold + Carb + Air intake and is based on Crank HP. The details surrounding this one example can be found in Harold Bettes's book Engine Airflow in Practice and Theory. http://www.amazon.com/Engine-Airflow-HP ... 1557885370 He also has many other formulas and concepts toward HP estimation.

Remember just because your intake port can flow 300 CFM does not mean your engine will make 76 HP per cylinder. but conversely if you said you wanted to build a small block Chevy that made 800HP at the crank you could perform the inverse and say 800/8 = 100, 100/.257 = 390 thus your intake track will need to flow at least 390CFM per cylinder to reach this goal and that is only part of equation. Remember this is based on naturally aspirated combustion.

Rick
saltfever
Posts: 42
Joined: Tue Jul 30, 2013 9:04 pm

Re: Relation between CFM and HP

Post by saltfever »

1960FL wrote:
. . . The details surrounding this one example can be found in Harold Bettes's book Engine Airflow in Practice and Theory. http://www.amazon.com/Engine-Airflow-HP ... 1557885370 He also has many other formulas and concepts toward HP estimation. Rick
Thanks Rick. That is the information I was looking for. I forgot I had Betts' book. Great book! I want to understand it rather than just filling out a calculator field.
brandoracing
Posts: 103
Joined: Tue Nov 12, 2013 12:48 pm
Contact:

Re: Relation between CFM and HP

Post by brandoracing »

very interest post! I had the book of Bettes. All of this is awesome for naturally aspirated engine\heads.
But for we turbo guys?
I remember an incredible interesting topic on this forum,a guy very expert says the minimus difference of cfm from N\A and turbos,because CFM as an volumetric measure,in a turbos change the density.
So,I have interest to talk with they of this.
Sorry for my English!
www.brandoracing.it
Alfa Romeo 75 owner
Post Reply