Re: back presswure

[Scott Hinojos <lightsplicer@xxxxxxxxx>]

It's good to see that "You need backpressure" myth finally start to
die. Thankfully, the folks on the GM forum helped put it to rest:

"...'you need backpressure to make power'. This is not true. What is
needed is velocity. This is where we get back to pipe size. Often a
smaller system will make more power than a larger system as the
exhaust leaving is kept at very high velocity in the smaller pipe.
This is what creates the very important scavenging. If the pipe size
is increased the flow slows down & power is lost whether in the
primary tube of a header, or the exhaust system behind the header or
manifold. As seen above, increasing a pipe by 40% will make a HUGE
difference in velocity & scavenging. With most cars being operated 90%
of the time in the under 4000 rpm range it is better to err on the
side of smaller instead of bigger."

I think it's important to note that velocity is maintained in a
properly sized exhaust system because the exhaust charge isn't allowed
to cool much before it exits the pipe. The reason an exhaust system
that is too large hurts velocity is that the charge cools and
contracts, which slows it down, which causes a "train wreck" of a sort
with the exhaust pulses, which simply kills the scavenging effect.
Explained like this years ago, it made more sense to me than simply
saying a large exhaust slows down the exhaust charge. Maybe I just
need to know things in too much detail. hehe

Of course, scavenging is also a product of the exhaust pulses being
placed in the exhaust system at the right time and place, which is due
to a header/manifold being made properly, according to cam specs and
so forth....

-- 
~S~
'64 Chrysler 300, AKA: "Leon", 383, push-button 727, 8 3/4"
'62 Mercury Comet Custom wagon... a work-in-progress for too many years.

On Sat, Jul 21, 2012 at 6:43 PM, Gary H. <62to65mopar@xxxxxxxxxxx> wrote:
> There is a discussion at this link that may or may not be helpful. Read through it and think of what is discussed.
> http://www.hotrodders.com/forum/exhaust-diameter-formula-49188.html
>
> Generally, too big of an exhaust is a trap many fall into.  See for example the first post here:
> http://www.gm-trucks.com/forums/index.php?showtopic=67798
> (Yeah GM , but generic, as in generic motors. LOL)
>
> Maybe you can call TTI and see if they have a tip / formula as to matching a motor to exhaust pipe size. Or call up the cam mfg for suggestions.
>
> Thanks,
> Gary H.
>
>>  -------Original Message-------
>>
>>  --- On FRI, 7/20/12, JACK CHEEK _< >_ wrote:
>>
>>  From: Jack Cheek
> ...
>>  > a 440 bottom end with max wedge top end with the max wedge manifolds.
>
>>  > what size exhaust pipes would be best from the max wedge manifolds though
>>  the mufflers. 2 inch pipes-- three inch pipes--- with 3 inch flow masters
>
>>  > would this be to much pipe and would it effect the back-pressure
>>  > or run like crap--motor was bored 30 over and the cam is mopar 484 lift
>>  with
>>  > 284 duration-intake and exhaust-not sure of the compression
>>  >
>>  > running flat top pistons they are about .125 below deck..
>>  thanks inadvance for the thoughts.
>>  thanks jack>
>

-- 
--
Please address private email -- email of interest to only one person -- directly to that person. That is, email your parts/car transactions and negotiations, as well as other personal messages, only to the intended recipient. Do not just press "reply" and send your email to everyone using the general '62-'65 Clubhouse public email address. This practice will protect your privacy, reduce the total volume of mail and fine-tune the content signal to Mopar topic. Thanks!

1962 to 1965 Mopar Clubhouse Discussion Guidelines:
http://www.1962to1965mopar.ornocar.org/mletiq.html and http://www.1962to1965mopar.ornocar.com/general_disclaimer.html.
-- 
You received this message because you are subscribed to the Google Groups "The 1962 to 1965 Mopar Mail List Clubhouse" group.
http://groups.google.com/group/1962to1965mopars?hl=en.