Don't forget the bell mouths where the runners enter the plenum.
Worth about 10 HP more around 190 to 200 HP.

Paul Lamar

You keep writing this. But one source tells me that the rounded edges of
the bell mouths is the key here, not just the bell shape.

Finn

Possible I guess. Who is your source?
Does he have any comparison dyno data both ways?

I am just going on what Power Sport told me and what is common tuned intake
manifold practice in the automotive industry. I think Mazda would
use it if it was noticeably better than just a simple bell mouth which
they do use along with Mercedes, Ford, GM, BMW, etc., etc.. In fact I am willing
to bet if that is really true the difference is immeasurably over a simple
Bell mouth.

That feature would certainly greatly increase the cost of machining
the intake runners. In fact I see no way of machining it short of
an NC mill.

Paul Lamar

The source is Power Sport. You can't just quote the 10 HP increase from Power Sport without giving
the full picture. They say that the rounded edges of the bell mouths is what gives the 10 HP
increase. Not just the bell shape - that's been around forever. I think you even have a picture of
their intake with the airbox lid off.
Of course we only have their say so on this. Just wanted to make sure that if you quote their
number, that you also quote the reasons they gave.

Finn

We don't just have their say so on this.

Here is what Bill Jepson had to say on the matter.

Finn, I did a lot of webber tuning in my race days. They tested a bellmouth and radius and a
simple trumpet. The finding was if there weren't large obstructions close to the inlet one was as
good as the other. The full radius item was real exotic though, and was sold for several years.
The edge rolled all the way around 180 deg. The carbs with narrow bore spacing wouldn't even fit
them. The basic trumpet shape worked just as well. Mazda would have fitted a full radius if it
would have done anything. Check out the intake on the Le Mans engine on the acre site. If you are
going to all the trouble of building a varible intake you use the best possible shape! Bill Jepson

Also if you read any of these web sites you will see that simple bell mouths
greatly increase the air flow. More airflow more power.

Go to www.google.com and use the key words "fluid flow bell mouth".

Paul Lamar
 
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