Monthly Archives: November 2011

bowtie6‘s Muffler

Looks like my last post about the muffler and exhaust has drawn some interest..

I’ve been asked for more info about the muffler.  Well here is the skinny:

Since the entire tubing is all stainless (this stuff was pricey) I figured the muffler should be stainless also.  The tubing is all 2.75″ and the muffler is stainless too.  This bad boy came from Speedway Motors and is called a “bullet muffler” (CLICK HERE for more info).  They have several options on finish.  Mine is the “non-polished” version.

Something to keep in mind:  as nice as this muffler is, it is not quite enough to tame the Ecotec.  When the VVT kicks in, the Ecotec really starts to wail.  That is why we are running the Supertrapp tips at the end of the pipe.  Speaking about the Supertrapps, I have been experimenting with the number of discs.  With Supertrapps, the more discs you add the less restrictive the exhaust is, at the expense of noise.  With less discs, it gets more muffled but backpressure increases.  Right now, I am using 12 discs – six on each tip – and this puts one hell of a smile on my face past 4500 revs.  I’ve ordered more stainless discs and plan to add at least two more per side.  We shall see how they turn out.


Exhaust Changes…

Yesterday we took the exhaust pipe apart for a modification.  In the previous post, I made mention of what the exhaust system looks like and I had the picture on the left showing the SuperTrapp tips.  As you can see, the whole affair ends underneath the trunk floor.  We did this for several reasons, but mainly because it hid the exhaust from sight. However, even though this was with the V6, somehow exhaust “smell” would end up in the cab.  So we had to make a small change.

Since I dropped the whole thing, I thought it would be nice to document the way it looks in its entirety.  First, the following pictures show the flange that is bolted to the flange on the header’s collector.  This is where the bung was welded to hold the O2 sensor.

A copper gasket fits between the two flanges – the one shown above and the one on the header.  Why put the bung and 02 sensor on the exhaust side rather than the header?  The exhaust is much easier to remove than the header.  These four bolts holds the front part and at the rear two tabs fit inside two rubber hangers (see the picture at the very top), so the whole tube “floats”.

Moving along, this is the mid section:

There is a bend right below the O2 sensor, followed by a section that “swells” up a bit.  That is an inline resonator to reduce noise.  At first, on my cousin Jim’s TR4 we ran the exhaust without the resonator – just the SuperTrapp tips – and the thing ended up being way too loud.  The Ecotec has a killer shriek at around 3500 RPM’s when the VVT kicks in.  That is why we used this resonator. Here is another picture showing the area aft of the bend:

This section is between the elbow and resonator.  It looks crushed.  And yes it is.  I am sure questions will come up as to why this is done this way:  we wanted to make sure nothing was below the frame line.  This section of the exhaust had to clear some crossbracing on the frame and the transmision mounts.  Does it restrict things?  Not really.  This is 2.75″ stainless tubing.  Yes, we decided to make the whole thing out of stainless.  The tubing was a bit pricey, but this way we do it one time and not have to worry about it ever.

Finally, the end of the pipe looks like this:

Look close at the picture above.  Several things:  on the mid-left is one of the SuperTrapp ends.  On the top right (standing up) is the tube extension that we added to make the ends stick out a little further back.  And in the center is the tail end of the exhaust with the end flanges cut off.  You can see in the tube extension standing up, the flange is on the end resting on the work table.  Finally, you can see underneath the two split pipes the “hanger” that fits in the rubber donuts mounted on the frame that is used to hang the whole affair.

That is all that holds the pipes in place.  Simple and effective.

The picture above shows the new extension before being welded.  You can see the flange on the left where the SuperTrapp ends are affixed.  These are a bit of a pain to put in place since each has 8 screws, lockwashers and nuts.  Taks a little time but all good things do too.

So what does this all look like on the car?  Take a look:

We added about a foot to both ends of the exhaust.  Now, it sticks past the roll pan of the trunk and is a little more prominent.  We still clear the whole frame since the new frame follows the curve of the body and has a bit of a slope “up” past the diff.  Sure, not everybody is going to like it but then again it is my opinion that matters and I really dig it.

Practically speaking, the result of this small alteration turned out well.  No more scent of eau d’Smoked-T-Rex in the cabin and things are a bit quieter too.  With the exhaust now past the body instead of underneath the trunk, the exhaust note is a bit more muffled.  This is still loud under WOT though and that is the way I like it.


400 Miles and Counting…

Well, I’ve got about 400 miles on bowtie6 with the new frame and the Ecotec.  Simply put, this thing rocks.  I expected an improvement, but damn!  This thing is awesome.  And I have only scratched the surface.

Where to begin?  Well, the coilovers are amazing.  The front coilovers have made an incredible difference in the steering “feel”.  Before, with Richard Good uprated springs and SPAX adjustable shocks the steering was very “heavy”.  At parking-lot speeds it took quite some effort to turn the wheel.  Perhaps it had something to do with the 205/55-16’s up front or the extra heavy springs but now, this thing turns as if it had power steering.  At speed, the steering response is very quick; point and shoot actually.  What does this look like?  Take a look:

The front suspension towers were designed in such a way to accommodate the TR6 front suspension pieces but also the front coilovers.  Some things to note:

  • Yes, those are “stock” rotors.  They are cheap, and this allows me to use a very aggressive pad compound on my Wilwood calipers.  I am not racing this car so there is no need for the extra unsprung weight of “vented” rotors.  Contrary to popular opinion, these rotors along with the uprated calipers offer plenty of stopping power.  Remember, the master cylinder is from a Vette so this offers more than adequate clamping power.
  • Take a look at the sway bar end.  It has a blue SuperFlex bushing.  All the rest of the front suspension uses SuperFlex bushings – I ordered these from England.  They are amazing; a bit pricey but certainly worth the expense.
  • The coilovers are adjustable for rebound.  That is the little knob on the top, right below the top “A” arm.  I’m still trying to dial them in.

This is what the Wilwood caliper looks like:

Just like a good looking super-model, bowtie6‘s backside is just as sexy…

  • The rear coilovers are similar to the fronts; these are also adjustable for rebound.
  • The exhaust is a single 2.75 pipe.  We have a single resonator just past the bend off the headers and then at the exhaust end, a pair of SuperTrapp mufflers.  The basic principle with SuperTrapps is their adjustable baffles.  This works by adding or subtracting discs that add or subtract backpressure and noise.  The less discs the more backpressure and less noise.  With more discs, less backpressure and more noise.  I added quite a few discs but this made for a very high shriek anywhere north of 4500 revs.  So, I had to tone it down.  Right now we’re running eight discs – four on each side.

I’ve already started messing with the ECM a little.  HPTuners is an awesome tool to dial in the engine and I am just getting started.  With the new redesigned intake, headers and above mentioned exhaust things are flowing very “freely”.  I noticed the airflow mappings were way off and this has been the first thing I’ve started to modify with pretty good results.