Darien

I installed my H-pipe and already had a RMB. Do I lose HP with a straight exhaust versus some back pressure from a muffler?

m21sniper

Highly doubtful. What is more likely is that you shifted your powerband up to a higher RPM range, and are now making somewhat more peak HP...but in a range that's very hard to 'feel'.

Darien

Just curious, I re-installed my muffler. Man was it loud It seems to run better with the muffler back on. I might need to just get adjusted to the loudness It seemed a bit raspy and I don't want the Shark to sound cheap

m21sniper

Adding/removing a muffler can(and usually does) shift the power band up and down the rpm range.

A muffler in place will add some backpressure(depending on model), and that will tend to shift the power band to a lower rpm range and produce more low end power- but at the expense of top end power(ie, where all the real power is made- where races are won).

Conversely, a free-flowing race only exhaust will tend to lose low end power, but as a result of the decreased back pressure and increased overall flow potential will gain a significant amount of power where it's really desirable....high in the rpm band.

BrianG

Also, you might be running a bit lean with the stock A/F map, with all that freer breathing.

chaadster

Darien,
I had the exact same same sensation when I briefly ran my '88 with RMB and test pipe. It was wicked loud, and throttle response seemed sluggish. I drove the car 7 hours on the highway like that, from where I bought it back home. It might have been making more power up top as m21sniper suggests, but it was much too much of an earsplitting fuss for me to find out!

Anyway, I was much happier with the cats reinstalled, both in terms of sound and throttle response! I think the hot ticket will be x-pipe with high flow cats; I'm probably gonna pop for the 928 Specialists setup to install over the winter.

Darien

I installed the test pipe because the cats were suspected getting clogged due to the car struggling to reach top speed. It definately runs stronger with the test pipe.

I suppose the straight exhaust would result in a better dyno run? I'll have to wait and see what the SC will change after I get it installed I'm trying to get the Shark running best before I install it

RDS928S

Is anyone running this set up on a early 86 32 valve S:

X-pipe, no cats. bone stock exhaust including center resonator and final rear "pumpkin" muffler?.

If so can you please comment on the sound?

This is what I will be running on my daily driver once I install Dave Loma's Motorsport x-pipe.
I can't imagine the removal of the cats can make that much of a difference in sound with the stock exhaust.

RDS

mulik51

I heard that no pack pressure is bad on the valves. Is it just rumors or there is some underlining science behind it?

Klim

sublimate

Less back pressure can sometimes create a lean condition which causes a hotter combustion which can burn up your exhaust valves. Also I suppose the reduced bck pressure would allow more exhaust to flow up past said valves and thereby increase the heat they pick up.

tv

I have the goldylocks solution. High flow metallic cats and moroso race mufflers produce an incredibly PLEASING sound and immediate throttle response. As all who attended the boston shark party can verify the sound is just awesome, not annoying at all.

It seems to have whatever back-pressure is needed with great sound and elimination of the annoying highway drone at 2700 rpm.

mulik51

Thanks. I fell more educated now

Klim

Big Dave

Yes, that's exactly what I have on my '85 (which is identical to your 86). Here's a sound clip. Max RPM in the clip is 4K.

Ketchmi

Actually Big Dave, our X-pipe sounds different than the Ott. They are being shipped (and coated, then shipped) so there will be plenty of Motorsport sounding 928's soon.

I got the best compliment on them I could have gotten last night, Louie Ott bought one.

BTW RDS928S, we have one without cats on an 87' with the same mufflers as your 86' and with the rear muffler, it's really quiet. But it's also putting down 287rwhp.

Big Dave

Dave:

Do you have a sound clip of your setup? I'm curious to hear how the differences in the x-pipe shapes affect the sound. My clip isn't totally pure since I have the air pump still spinning and pushing air to the atmosphere (i.e., not into the exhaust). I've since disconnected the pump and there's no hiss from the pump.

One thing I have noticed is that during deceleration, I get the popping sound of small backfires if I've got the gear selector in something other than "D". I actually kind of like it.