This month's circle track magazine has an article on header-exhaust design. I scanned it at the bookstore and in the article, they have a graph that relates exhaust diameter to exhaust flow cfm at 28 vacuum. They report that the linear relationship between diameter and flow can be described by the equation:

square root [ (cfm x 1.27) / flow density]

They say in big V8 racing engines, a typical flow density is 80.
The exhaust flow has to be measured ...usually during headporting on a flow bench.

Anyone here know what the typical flow density is for a modified Honda 1.8-2L engine?

As you know, SMSP stated that he uses 60 crank hp per square in. cross sectional area on the exhaust to determine the optimal exhaust diameter for an engine.

I've always wondered what the assumptions were to achieving that relationship and how was it arrived at. Hopefully Dave can shed some light onto the topic.

cheers

PS BTW the Circle Track article also stated that bigger diameter, shorter collectors make more upper rpm power whereas longer, smaller diameter collectors make more midrange power.

 

Yes, I`ve had a long discussion with TUAN about that.. You may ask him too.

BTW,
congrats! 1000 posts

Michael Delaney
Honda-Tech Member

1000 posts [100%]
Toronto On






[Modified by Maijk190, 6:40 PM 2/20/2002]

 

Same Person....

 

Ummm... I thought...

 

LOL. LOL.

 

I don't have the answer to your question but wouln't the density of the exhaust flow vary depending on
1- what are the modifications of the engine (aggressive camshaft, higher compression ratio, better exhaust port design)

2 - the header itself. The more restrictive the header the higher the density will be ( and vise versa). What I mean by that is the density wont be the same if you take the measurements at exhaust port or at the end of a test header.

So what is the goal of a good header design? Is it to take the density at the exhaut port and try to keep it constant or try to reduce it gradualy or try to reduce it quickly. And then what is the effect of the rest of the exhaust system on that header?
I think most tuner work by trial and error when it comes to optimizing the complete exhaust package. It is not easy to mathematically schematize.
Just my small input.




[Modified by JPP, 3:01 PM 2/20/2002]

 

... and then there's turbos !

 

LOL - I knew someday Tuan was going to confuse someone with that.

 

Posts By Tuan - Gets

 

really ? didn`t know

 

It should also correlate with engine rpm right?

 

You are correct. The higher the RPM is, the higher the density of the exhaust flow should be.