Im almost done with the most unpleaseant install ive ever had, but I have one question that I cant seem to find an answer to:

my downpipe did not come with an exhaust hanger to replace the one on the pre-cat. I had initially decided to fabricate my own, but after bolting the system up, I am wondering if this is even necessary. It seems pretty rigid already (which sort of bothers me as I am used to some sort of flex pipe being used in a piston engine) but I guess with the lack of vibration it isnt needed? anyways, the info from this site has made an unbearable job bearable. many thanks to all those that contribute!

john

 

I dont know of any downpipes that come with a hanger. Its not needed.

Jason

 

I didn't bother with the downpipe hanger

 

thanks guys..

now I just gotta find a place that stocks the o2 sensor............

 

How many broken down pipes have I had in here or screwed exhaust flanges with striped bolts .I make a brace for each down pipe that comes here .Do what ever you like and listen to who you want,I know you need a brace to the tranny .

 

I was under my car and noticed the downpipe hanger was about 1" from the flange on the transmission on my car, with no bolt. It had been like that for at least 5 years, with a centre pipe and HKS superdragger. It's probably ok without a cat. I installed a Random Tech 5" "ultra high flow" metallic cat last year, and made a 1" spacer and got an appropriate bolt. I suspect when you have a cat the hanger is needed, but I have no proof - it was there so I used it.

 

I agree fully and fabbed up my own to help in the support of the pipe using the factory mounting on the tranny.

 

HKS downpipe have a support, but the factory bolt is too long to hold it tight. Some sort od spring or spacer should be used or find a shorter bolt. But my exhaust is fine without the bolt being 100% tight. Hell it might be gone by now cuz the clicking stopped.....

 

No need for a hanger on the downpipe, when you get the downpipe on it should be so snug you can shake the entire car with it. Its bolted to the engine.....do you really need more support? Anyways most auto parts stores will carry the generic O2 sensor for our cars, its bosch and works great, do yourself a favor and save the 70 extra dollars it costs for the same thing from the factory

 

Well the idea is to take load of the exhaust manifold/turbo housing

 

for o2 sensors check out www.oxygensensors.com they have OEM stuff with the right electrical plugs for cheap-cheap.

 

My thinking too, or to avoid exhaust leaks from over-compressing the gaskets from the leverage of weight down stream. Not sure what brand my DP is, it came with the car. But it's got a flange that allows it to be bolted up to the transmission. I've had it off a couple of times and with the weight of my cat it seems to make a difference on how solid the whole "assembly" is once I bolt it back up.

 

well, its easy enough for me to fabricate a new mount, so Im not gonna take any chances. also, Ive read on here that the generic sensor has different resistance levels, although I may have misunderstood the post. can someone clear this up? It would be nice to be able to pick this up at the local autozone, rather than pay 175 bucks and wait for mazda to ship it to me.....

 

or heres another way to look at it..... Can I install a wideband in the stock sensors place even though I am running a stock ecu? I plan on having a power fc installed (as well as some other things) this winter when I take the car off the road, so it would be nice if I didnt have to buy 2 sensors....

 

If you don't have the old o2 sensor, just buy a generic. Heck I might have a used on somewhere for you.

A wideband will not work with stock ECU, at least not properly. The only reason why people worry about generic o2 sensors is because you can add resistance by cuttning and reconnecting the wires. IMO it's no big deal - use a good crimp connection covered with tape and you're much less likely to have problems, which usually arise from cold solder joints. If you're really worried, check the resistance across the crimped connection afterward - it may not even register on your ohmmeter.

Dave

 

so I am off to autozone to purchase the single wire generic bosch o2 sensor!

thanks for all of the help!

 

Does it need to be solid mounted? The mount I fabbed up cracked (showes how many loading cycles these things are subjected to).

I was going to use a universal mount with the rubber link in it. I'm thinking this won't be stiff enough.

 

+1 Absolutely

The DP itself is a lever with approx 15:1 torque multiplication across the turbo flange bolts. How much torque do you think that it puts across the exhaust flange if you put a 10 ft/lb load on it? Yea,150 ft/lbs.... Now consider movement over the entire length of the exhaust system. It should absolutely be braced at the usual point, and this is why the factory did so.

 

have a pic or example of your mount?

 

Three years ago I fabricated and installed a bracket to support the back end of my Pettit downpipe, even though Cam said no rear support is needed. The original precat rear bracket wouldn’t fit because of the larger size and position of the downpipe, so I got 1.25” wide stainless steel strips in various gauges from a neighbor who worked for a fabricator. After a lot of trial and error, I made a bracket and a 2 piece clamp out of 14 gauge SS and installed it over the thermal tape. It seems to be holding up well. I don’t know if it is strong enough to relieve the weight on the front flange bolts of the downpipe, but it can only help. Sorry I don't have any pictures to post.

 

I think anything that limits the movement of the downpipe is better than nothing, but the more I think about it, the more it seems like it needs to be solid mounted.

I used a SS strip close to 14 gauge (~1/16 in thickness) and it's failing from what looks like fatigue.

I think the easiest way to do this is with a muffler clamp and something closer to 1/8 in thickness for better life and rigidity. Form the end of the strip/hanger so that a 3 inch clamp holds it against the pipe. Then adjust the other end so that it can be bolted to the transmission. Using both fastening points on the trans would probably be the way to go.

Anyone else?

 

Here's what I came up with using what was available. Not exactly a work of art, but hey...

It's not finished in the picture on the table. I ended up drilling a hole right above the bend for the u-bolt to go thru. Then I bent the tab to the pipe contour.

The only part I used from the hanger kit was the steel strap... and that doesn't really resemble the original part anymore. I cut out a slot between two of the holes for adjustability (read: crude fabrication).

Also, this is the 3rd iteration of my DP hanger... so you could probably make this easier.

 

I've never seen any issues as a result of a deleted hanger...... definitely never seen a hanger on a single turbo setup, but these exhausts also weigh a fraction of the oem setup when you consider majority of single guys aren't running a cat at all.

 

i thought i was the only one that wondered about the lack of a hanger when i was installing my dp... just was too lazy to do anything about it

 

Here's how I'm looking at it... the entire system has flexible mounts. That means if it's solid mounted anywhere, any movement has to be arrested by the solid mounting point. When you eliminate the transmission mount, you force that point to be the turbo to DP flange.

The DP flange between the twin turbos was designed to compress a gasket. Likewise, the studs (or SS allen bolts in my case) were selected to be strong enough to endure enough tensile force to produce enough pressure on the gasket to compress it and create a seal. Since there is an additional stock solid mounting point, I assumed that they did not factor in much, if any, additional force from movement when it comes to the DP flange studs.

There is probably a good amount of wiggle room in the design factor of the studs/bolts and that's why they don't fail right away when subjected to additional loads. However, these new loads are from movement of the exhaust system and the engine, so they are applied and removed repeatedly. Even though they are strong enough to hold the load, say 700 times, this could eventually cause them to fail from fatigue... if/when probably depends on how the rest of the system is mounted, engine mount type, road conditions, etc.

All that armchair engineering aside, I'd hate to pull the turbos again to remove a seized bolt half when I could have just put a bracket on there.