I believe that catless exhaust without backpressure will indeed cost low end
torque. The method, I think, is that fuel/air mixture will blow out the exhaust
valve during the valve overlap period.
Tuning with an LPM can help compensate at lower RPMs but the engine is not
running correctly by just enrichening the mixture and adjust spark timing.
Catless can be an advantage at high RPM by reducing backpressure when
backpressure is highest. Tuning would be needed to take advantage.
Your engine could lose low end torque but gain in peak horsepower.
-Ron
Jon Heese <shotimes@jonheese.com> wrote: 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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