Exhaust Fab Continued

AKimball92

AKimball92

True Classic
A continuation of this thread:
https://xwebforums.com/forum/index....-2-exhaust-manifolds.32840/page-2#post-278925

I am getting the 4-2 manifold flange machined out of 304 SS hopefully in the next week.
Does anyone know what grade SS the OEM muffler is made of? I do know it is not magnetic. However neither 304 or 316 are magnetic and they are the most common SS options today. I would like to weld a new V-band flange to the muffler.

Unfortunately design plans have changed and I will not be able to make the cat fit while still keeping the lengths needed.

I will be including some flex into the system either through the use of 2 braided sections up top and one near the muffler or a long flexible section similar to Dominic's design shown in the above thread. I plan to use 16 or 18 ga, 1.5 and 1.75 tubes and making my own pie cuts to fit. I have the 7691880 4-2 manifold which does not fit directly to any OEM X1/9 muffler that I know of.
 
I get my exhaust fabrication supplies from a company that makes the systems for several of the big name exhaust companies. They do every aspect of system design, engineering, mock-up, testing, fabrication, and manufacturing. And they have been doing this for about 30 years. So I usually follow their suggestions when I want to create my own system. Their advice is to not use S/S for the flanges, but use it for all of the other components. Has to do with how mild steel seals better over time. I don't know the exact particulars, and it contradicts what I would have thought (I had the same idea as you, to use S/S for it). But I trust what they say on this. Naturally you need to make your own choices.

As for flex joints. There are a few types. In general they recommend using the type in the first picture (below) if it is to be located anywhere near the manifold flange/turbo/high heat item, and the type in the second picture anywhere else. Other types a best for other applications but I am focusing on what you are building. The number and location of them depends on many factors, so use your best judgement. Try to think how the weight and vibration/movement will act on the system.
YMEFJ404-2.jpg
80071_1.jpg
 
Thanks for the advice Jeff.

I don’t know how I feel about the mild steel for the flanges. Everything else being SS would be rust proof and then the flanges being MS don’t weld the greatest to SS and then rust a lot? Obviously I’ve never analysed the sealing properties of either or even know how to analyse it.

I’ve thrown around the idea of using a bellows joint up there and only had canceled it out due to lack of use in normal systems today. I don’t have a team of engineers optimizing this exhaust so can’t really compare this to that. I did see the comments in some pages that said the stranded joints fray under high heat loads oftentimes requiring bellows but many websites mention high heat like turbos so assumed the threshold to be higher. A lot of consider here but you’ve probably tipped me over the edge towards bellows at the top and stranded at the bottom.

I’ll still go with SS flange and VBand joints unless more research in the next day or so says otherwise.
 
Welding mild steel to stainless is not an issue, just need the correct shielding gas.

I agree with the desire to use all SS. But since being told that about using MS for flanges, I spoke with another performance exhaust specialist and he confirmed it. Flanges are thick enough that rusting shouldn't be an issue like it is for the pipes. However the MS recommendation might be more for flanges that attach directly the head (e.g. a header), or turbo outlet (e.g. down pipe) where temps are higher? If that is so then SS might be fine for this application (4:2 down-pipe). Not really sure, perhaps more research is needed.

Using flex joints toward the top of the down-pipe for a 4:2 junction is common on European FWD vehicles of that era. Below are two for VW's; the one on the left is the factory version and on the right a aftermarket version:
images (1).jpg
251.117S.jpg


I really like V-band connections. Look for the ones with either the offset flanges or the recessed/lipped flanges. They allow the pipes to remain properly aligned when attaching them and provide a better seal. Another good, simple, and affordable connection is the 'ball and socket'. It allows for some off-angle alignment so the system always fits. Also it seals well and is removable, similar to the V-band. Personally I'm not a big fan of the 'spring-loaded' connecting joints. They seem to be problem prone in my opinion. And bolted flanges (like on the bottom end of the above sample on the right) are really poor and leak.

Please share your down-pipe design when you figure it out. I'll be doing one eventually (but likely quite awhile down the road).
 
flex pipe should be used in short sections, and only in straight runs... it's quite restrictive to flow, and doesn't like being subject to bends very much. I know Dom's solution was because he had no welder available, but it would not be the recommended method.

SteveC
 
That solution on the right looks almost exactly like what i need. I will aim towards that. Fortunately if there is an issue with the SS flange (already underway) I can always cut it out and make a new one for not much cost. Its the Pie Cuts and collectors that will be the most time consuming part, especially since I do not have the welder in my garage but at work.

I will use two short bellows joints close to the top, come down underneath the frame similar to Dominic's design, a 90 degree bend, a 4 or 6 in stranded flex joint and attach to the muffler via Vband clamp.

Does anyone have an idea of what SS the muffler is? After 40 years of no visible rust, I only assume its a SS of some sort.
 
If you want to make it a little easier to construct, there are formed "2:1" merger ("Y") pieces available. That is the most difficult part to make and the formed ones have pretty good flow. But making one from scratch could allow you to make it flow even better if you create a long, gradual merge. Here is an idea of the one I'm referring to:
2-FORMED-COLLECTOR.jpg
 
Ive made exhaust manifolds before for a CBR600 engine for FSAE. Those are difficult. I'll see what I can find for cheap and see how much it ends up being.
 
Hey Andrew,

Where are you getting your flanges from and are they based on CAD, a master part, or other? I am kicking of a set of headers in the next week as well. I will spec 304SS.
 
The 2 port flange at the top I am having the shop at work or myself duplicate using 1/2 in SS bar stock. I will mill it down to about 3/8ths inch to ensure flatness. Gentle welding of the mandrel bends shouldn’t warp that.

The Vbands and clamp are off the shelf onmany websites. eBay seemed by far the cheapest which I am hesitating on.
 
Well I just ordered the mandrel bends, flex joints, and V-band for my exhaust 2-1 down pipe. It probably would have been cheaper to source a whole new 74/Euro exhaust had I not sourced the left of center, 7691880 manifold. Oh well, we all like to make our cars our own.

I purchased 2X 1.5 inch bellows flex joints and 1 6 inch 1.75 braided joint, a 1.75 in V-Band clamp and a bunch of bends to ensure I didn't miss anything. All but the flex joints an V-band are 304L.
 
just dont tell the lady. All this was bought on the credit card that goes under my name only :p Honestly though, this and trans and engine oil should be my only purchases left over 30 dollars to complete my build. I'm not going to say how many <$30 purchases I have left.
 
You must log in or register to reply here.
Back
Top