Thread: We made a 3`Stainless straight ultra quiet exhaust and WOW, what a difference...

I never quite understood people not finding out for themselves about upgrading cat back diameter. They just take a vendors words for it and figure its gold. Even though all the vendors have made mistakes. A simple read of David vizard exhaust science says alot. The formula for zero loss of 310hp calls for 2.75"... 2.25 is like 180 and it doesn't factor in bends which also cut down on flow. Then on top of that our factory exhaust is crush bent... so that just multiplies to a whole lotta fail.

Figure a stock fbody catback is 2.75 mandrel bent single and that's a restriction with their horrible flat y pipe... n they are around the 300hp level bone stock. Yet our crush bent 2.25 is good for 300hp.... I think not

Originally Posted by Reverant GTP

I never quite understood people not finding out for themselves about upgrading cat back diameter. They just take a vendors words for it and figure its gold. Even though all the vendors have made mistakes. A simple read of David vizard exhaust science says alot. The formula for zero loss of 310hp calls for 2.75"... 2.25 is like 180 and it doesn't factor in bends which also cut down on flow. Then on top of that our factory exhaust is crush bent... so that just multiplies to a whole lotta fail.

That's true. The lenght of the piping makes a big difference as well. A side exit straight shot 3" pipe flows a lot yet one that has to travel all the way to the back flows less.

But I would say that the other large restriction has to be the cat. It is huge in most application.
On my 1.8T removing the mufflers cat back with a straight through exhaust made a marginal difference.
When I took out the cat and replaced with the resonators, a approximate 15HP increase was noticed right away. I flowed more on the MAF as well...
The only reason the gain was only 15HP is because of the tiny turbocharger installed in those engines. The turbine side is so restrictive, it is a bottleneck in itself. Installing a larger turbo would make the exhaust gain even more noticeable.

Guess i didn't think about the forced induction, been up for 28 hours straight. Still though 2.25 inch exhaust crush bends down to around 2 inches i'm sure, plus two 90 degree bends and two 45 degree plus the curves to the muffler through 2 inch crush bent pipe that probably necks down to 1.75". I just don't see how that could be optimal for a 300 horse car... Obviously FI cars have made power on smaller exhuast systems... but is it optimal? I dunno just some food for thought... i know people claim "its been proven time and time again" I've never seen it proven on a dyno just like everyone says headers are needed for stock cars or 3.4 pulley or they will blow up... thats also "proven time and time again" supposedly, however GTPpower we both know thats not true.

I have a question, kind of off topic. Why do 3.4 pullied cars need headers to get rid of knock but turbo cars don't?

love that exhaust. build them and sell them

Installed a snow performance variable meth kit.
Just did 2 runs. 1 was a test and I had to retune the methanol (too rich a/f)
I'm now running 50/50 C16 and 91
The second a nice 0-100 mph run on my winter tires. Impressive numbers there.
The 2.8 pulley and modular pulley system from ZZP was easy to install and works great. No slip at all that I can detect, lots of boost now !
I am pegging the stock MAP sensor at 200kpa.

Also I am now peaking at 37.5 lb/min indicating a huge increase in performance from the 3.8 pulley obviously.
Pulls real hard...

The timing map needs work, I am still running the stocker and it is not appropriate for a 2.8 pulley. Too much boost for the amount of timing, especially at low rpm.
I'm getting a little knock but it's intermittent goes away but is never strong. I believe I can work it out with the timing map. It's not fuel or temperature related for sure.
It could also be due to false knock now because it goes away during a longer 3rd gear pull which isn't normal. When knocks starts it only gets worse on a longer run.
I am now running 104 plugs gapped at .045.

0-60mph is now improved from 4.9 to 4.7 on my first try. I had way too much wheelspin my guess it will do 4.4-4.5 easy on a good run. Pretty impressive for a heavy FWD on winter tires.
0-100mph is much improved at 10.9 seconds vs 12.0 seconds with the 3.8 pulley.

Mickeys E.T. street will bring this baby in the 4s flat if not high 3 secs 0-60mph and drop a good chuck of time off the 0-100mph too.
Can't wait. Just hoping this stock tranny will survive long enough for us to put the second engine in the back.

Videos and log should be up tomorrow !

Today it was nice a warm 80F and my log shows a good difference in power than from the cool 60F from last night
Cool weather was 37 lbs/min today's hotter weather 34 lb/min.

I went to our local track which is not a very good track for setting records but it gives me an idea of the potential on a good track.
The track was horrible for traction today my first pass was a disaster as I made a run like I do on the street and that was WAY too much throttle, I just stayed there smoking the tires.
Then I found I had to go 1/6 throttle for 20 feet then start roll slowly up to 150 feet when I would then lay into it.
That gave me a half decent start with an average 2.18 60 foot.

I ran 13.3 with a best mph of 103 and consistently ran 13.4 for the rest of the day.
Enough to beat a brand new Camaro SS with a close race as well as all the other cars that I raced. Only lost my first race when I smoked the tires against the same Camaro SS
Now the MPH is low but it is always the case at my local drag strip, 10hz refresh GPS datalogged shows 106mph crossing the finish line.
Anyhow pretty happy with the time, since I'm still on winter tires and on a slower track.

I made a test by disabling the methanol and running pure race fuel (C16), I had a good amount of the knock...
The engine NEEDS the methanol to avoid knock. That only means one thing, it desperatly needs an intercooler.
That is one upgrade that is necessary with that small pulley. No myth there.
With the methanol, it works, but it's dangerous in case the methanol fails.
I think the intercooler will boost the MPH up top by a long shot.

Now I have to decide if the front engine stays supercharged or not.
The price of a good intercooler set up is close to my cost on turbo parts with a self made kit.
Intercooler set ups are easier to do on a turbo, especially since I have no front bumper !

On another note, everybody loved the exhaust and the car. A 97 GTP still surprises people around here.
Maybe they forgot about them lol !
The comment everyone said is you almost can't hear the engine, only the supercharger whine.

Video of the drag racing today and you can hear the exhaust...or can't hear it...you choose.
Damn it's quiet. In person it has a nice OEM V8 tone. ON the video almost looks like a Electric Car.

<a href="http://www.youtube.com/watch?v=JKU47hKRIzk">

No most turbo guys run a front and rear plog, some guys will run a front manifold if they are cheap a-holes.