Heavy Breathing! Exhaust Questions

[Jay Herbert]

Borla Systems are 3"...... The size of the cat and header system will depend on extent of engine mods. Smaller diameter 1-1/2" header will actually be better for stock to light mods (roller rockers, K&N filters, smothe tubes) while a 1-7/8", stepped, or other would be better for heavier mods (bore/stroke, extrude honed intake and ported/polished heads, etc.)

 

[Brian Denham]

You might also want to give JonB a call at Parts Rack. They also sell the high flow cats and are claimed to have the highest flowing ones around. Im sure JonB could tell you MUCH more!

 

[Sean Roe]

Thanks for the recommendation.
The Borla cat-back is 3" except that the inlet to the side sill resonator is necked down to 2.5" ID, so the stock cat outlet will slip into it. For those that have 3" header collectors, we offer the service of removing the reducer and welding on a piece of 3" OD stainless.
Borla header #17112 have 1.5" primary tubes with 2.5" collectors and feature a factory style flex pipe.
Borla header #17113 have 1&5/8" primary tubes and have 3" collectors.
Both are Stainless steel and we sell them hundreds of dollars below retail at $1,199.
We have high flow 3" cats at $124.95 with a 5 year / 50K mile warranty. We spent the time to try different cats and dyno test them. Did the other guys......?
Regarding size recommendations, Jay's post is right on the mark in our experience.

 

[JonB]

Agree with most of the above!

Cats are not all created equal ! And, your mods often determine what bang-4-buck (if any) you will get. Just last week I talked 2 folks OUT of buying any hi-flow cat. It was wasted money, in an OEM exhaust setup. Do other stuff first!

PartsRack (Dan) has tested several cats, and found that some flow great, fit bad......fit good, flow bad......or fit right, flow right, the Goldilocks choice.

One thing we would NOT do again last week: Accept a "cheaper" set of the other guys cats on trade for ours! (The other guys fit so poorly in the sidesill!)

 

[Sean Roe]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by JonB - PartsRack:

Just last week I talked 2 folks OUT of buying any hi-flow cat. It was wasted money, in an OEM exhaust setup.
<HR></BLOCKQUOTE>

Hi Jon,

When you replaced stock cats with a straight pipes, did you see no increase in throttle response or power? That would be very unusual. Care to do a little dyno testing?

You must be registered for see images

Of course, removing the cats is not environmentally friendly and is really only legal for off road use, so lots of manufacturers make larger cats that flow better. There are converters out there that don't reduce the power on a Viper.

The stock cats are very restrictive (exhaust velocity is good, restriction is bad) and we've always seen improvements by eliminating them on otherwise stock cars in testing. I would not at all consider the improvements vs. cost (two high flow round cats with clamps and pipes costing about $250, total) to be a waste of money. If a customer pays too much from a vendor that has not negotiate a higher volume / lower price or has high overhead and a larger markup, I can see your point, $450 on up would make a little closer to a "waste of money".

I agree it is difficult to find that right mix of body size and internal substrate area, given the constraints of the side sill size. The fact that some aftermarket headers don't have flex pipes and if the collector comes into the side sill at an irregular angle (up or down) doesn't make it any easier to fit a larger body converter. Even I have one customer who is in the process of returning his cats because the Balenger headers he's using didn't have the collector pipe square in the side sill and the exhaust pipe was too high. We can't all hit the nail on the head 100% of the time

You must be registered for see images

As you said "all cats are not created equal". We certainly found that out during testing. It is very important to find a manufacturer that used techniques to retain the substrate in a fashion that would extend the converter life. In the Viper, the temperature and exhaust pulses can otherwise cause the substrate to move, fracture and eventually fail. Here's a picture of the ones we're using which shows the metallic O-Ring and retaining points in the body:

You must be registered for see images

You must be registered for see images

Because I haven't seen which ones Part Rack is offering, can you put up a picture?

 

[Sean Roe]

I just reread my post and realized I really beat around the bush.

You must be registered for see images

The bottom line is that our '96 GTS dyno tested 17 rear wheel HP higher when the stock cats were replaced with the high flow cats we now offer. The exhaust system was stock other than this modification.

 

[Jack B]

Jeff:

I just installed Balanger's with a 3" exhaust system and Sean's cats. It doesn't matter what you do with the Gen I, you have to do some welding. Sean's cats are tight in the sill and require some patience when installing. I was worried that the proximity of the cats to the sill would damage the finish. It is just the opposite the cats run so efficently the entire sill now runs relatively cool - night-and-day diff from the stock setup. If you look at the stock Gen I headers and exhaust, it is a wonder the car runs at all.

A side benefit is that I dropped aprox 30 lbs with the header and exhaust addition. Sometimes more is less.

 

[Sean Roe]

Before we dyno tested converters, we checked the flow restriction versus stock. With the test equipment we have here, we were able to measure restriction in terms of vacuum (read in inches of water) versus flow in CFM. That gave us a pretty good indication if a catalytic converter was worth dyno testing or not. The ones we have now pulled 1" of vacuum while the stock ones pulled 2.1".
It's a bit down the road, but the manufacturer we use is in the process of EPA certifying a new converter design that is a 4"x5" oval, as opposed to the 4"x6" oval we have now for the 3". The 2.5" ones we have are 4" round and stock is 5" round. I'd like to get as much side sill clearance as possible without, as Jon B. had mentioned, compromising flow.

 

[BurnR8]

Illy,

Next time you are up let me know....I have a 3" system from headers to exhaust tip and straight pipe "for racing use only"
;-) and then the adjustable mufflers welded in between...it works really well....I can be very quiet or raspy loud with the turn of a knob....Btreynor has a good post about the system....when you are up again let's hook up and I will show you the system...I have a lift so you can see the entire set up. Good Luck.....had to get the adjustables cuz I was waking the baby everytime I would start the car..hehehehe

 

[opnwide]

With all of this talk of high flow cats and stock exhaust systems, I have another question. I, too, would like to put high flow cats and muffflers on my RT/10, but I don't want to spring for the headers just yet. Can I get a 3" flexible coupler to go with my cats or do I have to wait until I spend the $2500 on the headers? (The headers do come with this coupler, I hope.)
thanks

 

[Jack B]

The headers should come with a three inch collector outlet pipe that will connect into your cat. If the cat inlet is three inch, your future install is simple. If the cat inlet is 2-1/2", you will need a transition/adapter. That also is simple. The problem could be the distance between the cat and the header-outlet pipe. If they are very close the transition could be tricky due to the proximity of the ninety. Welding might be the only solution. That also is no big problem

 

[Jack B]

Jeff:

Removing the excess seam from the top and bottom would definitely help. I don't think that specific cat would fit at all unless it is moved to the rear as far as possible (the sill flares out). If you put the muffler up front and the cat to the rear it definitely helps. You are correct the cat has to be angled at about 10:00.

I don't want it to sound impossible. I'm very happy with the results. Take your time and use clamps initially. When everything is aligned, spot weld, remove and seam weld. I started out using the stainless band clamps, however, they always seem to leak a little.

Sean has the right idea, the Gen I community should appreciate what he has done. My system was put together after a discussion with him. The only diff with my install is that my front end is governed by the Balanger headers configuration.