While Jon almost hit the nail on the head, I feel I should step in and add a
bit of clarity to my original statement before things start to get out of
control.
When I said that SHO engines do NOT require backpressure to make power, I
meant exactly what I said - backpressure does NOT make power, nor do we need
it to make or increase power on an engine like the V6 SHO. What we DO need,
however, is sufficient and effective exhaust gas velocity contained inside a
properly-sized and properly-designed exhaust system. I think it is these two
terms - backpressure and exhaust gas velocity - that have become crossed over
the years and subsequently caused a great deal of confusion. Crack open any
reputable high school physics book, flip to the section on fluid dynamics and
you'll see what I'm talking about.
For those who may still have doubts about what I'm saying and/or would like to
read more on this subject, I would refer you specifically to the posts made by
the long-standing and very knowledgeable Ted Breaux in this SHOForum thread
here:
http://www.shoforum.com/showthread.php?t=62722
As most of you know, Ted has more personal experience with this particular
subject than most of us combined (especially as it relates to V6 SHOs) and has
already expertly answered just about every question that could be posed on the
subject.
Adam
----- Original Message -----
From: Jon Heese
To: van Oss
Cc: Adam Parrott ; shotimes@autox.team.net
Sent: Tuesday, August 22, 2006 10:01 PM
Subject: Re: [Shotimes] new y-pipe purchase
Hmmm... Sounds to me like you two may not be in disagreement.
Adam says that SHO engines do not require backpressure to make power. He
doesn't actually say that removing the cats (and thus the backpressure)
from a stock SHO engine won't decrease the power output.
Put simply, I think he's saying that the engine doesn't require
backpressure to make full power, it requires agreement between the ECU
and the exhaust path.
Here's a quick breakdown of a potential situation that jibes with both
of your positions:
Stock ECU + cats = good power
Stock ECU + no cats = loss of power
Custom ECU + no cats = good power
Bear in mind that I'm just looking at theory here, but please correct me
if I missed something.
Regards,
Jon Heese
van Oss wrote:
> Thank you Mr. Parrott.
>
> It's been known for 1.5 decades that SHO engines (normally aspirated, at
> least) need some backpressure to make their full torque potential. If
> needed we can go back to the literature. Stop saying (a) like you know it
> because what you say is false. Most SHOs (outside perhaps of those blown
or
> turboed or maybe cammed) need at least some backpressure or else they lose
> torque.
>
> What you say in (b) might be true, I don't know. I do know that the fine
> for driving a catless car on the street (which is pertinent to the origin
of
> this thread), among other consequences, makes it a bad idea to drive an
SHO
> catless.
>
> But you do whatever you want.
>
> VO
>
>
> ----- Original Message -----
> While we're at it, I figured I would also add that:
>
> a) SHOs (like most gasoline engines) do NOT require backpressure to make
> power.
>
> b) any "loss" that is experienced or measured from the use of a catless
> Y-pipe
> on a V6 SHO can almost always be regained with a little bit of EEC
tuning.
>
> Adam
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