You have a good knowlege of exhausts.What changes have you made to your Vmax
especially the exhaust system.There is an ongoing discussion of Kerker vs
Hindle.Do you have a preference?
>From: "Sat Tara S. Khalsa" <[EMAIL PROTECTED]>
>Reply-To: [EMAIL PROTECTED]
>To: V-MAX TECH LIST <[EMAIL PROTECTED]>
>Subject: Re: Insulated Exhaust Systems
>Date: Thu, 30 Mar 2000 14:26:04 -0700
>
>Hi Kelly,
>
>How's the leg test going?
>
>on 3/30/00 11:20 AM, Kelly Cash at [EMAIL PROTECTED] wrote:
>
> >> ...Don't get me wrong, I think coated pipes are preferable to
> >> chrome ones due to the frictional argument mentioned earlier,
> >> and increased corrosion resistance. I just think the scavenge
> >> due to heat retention argument doesn't make any sense.
> >
> > Well, I'm not a flow engineer. I was basically quoting
> > the info from the coating companies. But I've got some experience
> > with auto/bike mechanics, and how they explain it seems plausible
> > to me. I also know that some back pressure is GOOD.
>
>Umm well, are you sure? Why is that? I agree that in some cases, in the
>real
>world, engine designers design valve timing assuming some back pressure,
>and
>that removing that back pressure can result in poor performance
>(particularly for mileage) due to over scavenging and, in effect, moving
>the
>fuel/air mixture through the cylinder rather than having the close of the
>exhaust valve perfectly coincide with the arrival of the mix in the
>cylinder. This results in loads of unburned hydrocarbons in the exhaust
>mix.
>But that's not because back pressure is good, just that engines are
>designed
>for less than perfect conditions. If you remove the back pressure and alter
>the valve timing and intake parameters to match, the volumetric efficiency
>of the engine is increased, and the engine makes more power. Motors are
>just
>big gas powered air pumps, after all.
>
>But, more to the point, scavenge is the RPM-dependent science of using the
>timing of exhaust pulses from one cylinder to, in effect, suck the exhaust
>from another cylinder. That's why an engine with headers can, in most
>circumstances, outperform individual pipes. But it's not because
>backpressure is good. Scavenge is NEGATIVE backpressure.
>
> If I'm
> > reading your posts correctly you're saying that the more you
> > reduce back pressure, the better it'll run. Not so.
>
>That's not exactly what I'm saying. I'm just saying that I think increasing
>scavenge by insulating the header pipes is a nutty idea, and that
>increasing
>the volumetric efficiency of an engine is always a good thing.
>
> (which is
> > evidenced by the fact that the 18" can on a Hindle slightly
> > outperforms the 16" can)
>
>Are you sure that the TBR 18" can outperforms a TBR 16" can because it
>produces higher backpressure? I doubt it.
> >
>snip
>
> I do know
> > that the Airborn and JetHot people claim about a 1.5 horsepower
> > gain after coating the pipes. Considering what we saw in Laughlin
> > at the dynos, I wouldn't argue with it.
>
>As I mentioned, I'm not arguing with a horsepower gain after coating. I
>just
>doubt the insulation theory. My own guess is that reduction in
>boundary-layer frictional losses is more important. Also, I wonder what the
>nature of the horsepower gain is. Is it an across-the-board, good for every
>RPM gain, or a peak power gain w/o changing the RPM peak? Or is it a gain
>at
>say 5000 rpm and a drop at peak? Or a gain at peak and dip elsewhere?
>Inquiring minds want to know.
> >
> > Back to the sidelines,
> >
> > -K
> >
>Best,
>Sat Tara
>
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