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620 stock exhaust y-pipe

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I'm looking at Merge Collectors which are off the shelf parts and also trying to find the flange but so far no dice.


Another approach would be to run 2 separate pipes from the flange, around the torsion bar, and then merge where there is open space.  That extra length would FUBAR the exhaust tuning.  Probably get weird low end mega torque.


Also cannot find 1.5" exhaust tube thicker than 16 ga.  Some people sell 18 ga which is even worse than garbage and only .049 thick.


I think there appears to be a l20b exhaust manifold w/single pipe outlet, don't know if that is an option.


A header isn't a solution either.


My problem, I totalled my 87 Chevy Turbo Sprint and that was my Second Car.  Now I'm butt f**ked.

Edited by Cardinal Grammeter
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There were two L20B exhaust manifolds. One is co-joined or bolted to the intake but the '78-'80 is separate but has round ports. It'll work on a square port head but.... ? Both manifold s a 4 into one single down pipe. I think that would mess up any chnce of having any extraction tuning for the exhaust.


I used one of Mike Klotz's flanges and replaced the one on a twin 240sx down pipe.








Finished product is more like a long tube header....



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Thanks Mike for the info.


Let me see if I understand correctly, you did a 240sx exhaust, repairing the down pipe flange using Klotz's flange - or you put K's flange on a 240sx downpipe and used that on a 620?


What torques me is that I could weld up a beautiful exhaust but doing it on jackstands?  Homie Don't Play That!  I've welded under cars right over my chest and I swear I'll never do that again. 


If I had a lift, I'd pull that down pipe and since it feels very strong - just a couple pinholes, I'd go over the entire y-pipe with an oxy-acetylene torch welding up the holes and "reflowing" the entire assembly.  I think it would last a few more years if I did that.


I figure I'm going to have to Pay The Man which I don't mind if he does a good job and doesn't price gouge.


$64 QUESTION:  What would you do?  


Checking out exhaust shops:


I went to the local custom exhaust shop and talked with the guy and he started talking about if manifold studs get broken even though "you can get a torch on them" - that is not what I wanted to hear from guy I would hope was an expert.


I have another shop to check out 15 min from home.  I also want to find a shop that does stainless to see what that will cost.  I'm sure there is a "stainless tax" - but hopefully not a $500 y-pipe.


And I don't have a 2nd car to use just yet:


NOTE:  I don't have a lift and I'm "unburying" my 63 Studebaker Lark to use as a 2nd car if and when the 620 is laid up for repairs. 



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 This was for my 710 car, no torsion bars in the way. 240sx uses basically the same transmission so that clears nicely. The down pipes are too large so I slit them and squeezed them to fit the L16 flange and welded them. All three studs were rusted off so torched the manifold red hot and they twister out. New stainless studs and brass? nuts. Took a lot of on and offs to get aligned but the results were great. Took off again once for a/f sensor install. From exhaust valve seat to single pipe is over 30 inches. 

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2 hours ago, mainer311 said:

You mean like this?



Exactly.  Make a stubby separate y-pipe either out of .120 or .090 wall steel or stainless.  Then if exhaust pipe goes bad, no biggie.  would have to decide on what type of connection for the exhaust pipe - is yours one of those donut gaskets and a "V-band" clamp? 


I could fab that piece and then a friend could bend the pipe.  Question is can the stubby Y be symmetrical and perpendicular to the flange? - I'm thinking with the torsion "smack dab in the way" there should be maybe a 10* angle inboard on the stubby.  NOTE:  might way to see if could make exhaust pass outboard of the torsion bar - that way would be of the way for upcoming 5-spd trans swap.


The steel pipe will Git-R-Done too.

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16 minutes ago, banzai510(hainz) said:

is stainless harder to bend??????????????


I don't know if you were responding to my remark of a shop with a pipe-bender....   It is one thing to bend up some pipes, but to weld fabricate  the stubby Y is beyond the skills of some garages.  - like my friend who actually likes to bend pipe, but he does not even weld flanges on.  No welding.


As for is it harder to bend, I would say yes.  I've got pieces of stainless laying around and the sheet is massively stiffer to bend as well as "strap" sizes.




I good-guy country diesel machine shop referred me to a exhaust shop out in the sticks where "he only likes to work with stainless."  This alone puts him at the top of the "Leader Board" since if I'm going to pay for the labor, might as well get stainless.  Then I would hope the exhaust is Lifetime.  Only hitch is they are on vacation and won't be back for 6 days....  Argh! 

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Honestly man, the money I saved from doing it myself bought me my own Tig welder and I got exactly what I wanted as far as design.

I made it just how you describe. The flange has between a 5-10 degree cant to it, such that it clears the bell housing. This is critical! The two pipes need to point directly away from the block. The pipes are 1.75” merged into 2”.


I routed the downpipe to the outside of the torsion, however this is on a 521, which might be slightly different.


The V-band clamp requires no gasket. It locks up solid once the pipes heat up. What’s nice about these is that you can rotate the pipe segments to tweak the fitment.





I can send you the flange CAD file if you want it. I machined mine out of 304 stainless.


The entire exhaust was purchased from straights and mandrel bent 45’s and 180’s from Summit. I also used a set of pie cuts.









Edited by mainer311
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I'm 68 and I'm really warming up to buying a base price Carola.  I was thinking of the monthly payment which would be something like $325.


So for every $325 I pay for my new car, it is worth less.


If I was to put $325 a month into my 620,  in a few months, every single issue would be solved and the truck would be worth more. 


So I'm really thinking of paying to get a bunch of work done on it like the exhaust, front cab mounts are cracking and the driver's door needs adjust up and will have to take the fender off.


I am so through with working under cars on jackstands and that was before being all banged up from totalling my sprint.  Besides, right now, I just don't have enough room in the garage to attempt the job if I wanted to.  Workbenches are piled as high as possible, parts on floor, and nowhere to put the car that stays in the garage - it is too long to park in my carport because there, too, too much stuff along the back wall.


I have all the equipment to do the welding.  I could fab the flange but would have to plasma cut it.  Would have to decide steel or stainless.


I'm also thinking about the L20B late manifold and a 720 down pipe - I don't know if that pipe is available but it might only need minor mods to fit.


Edited by Cardinal Grammeter
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RE:  Late L20B exhaust manifold w/single outlet on the L18: 


Any description on the mismatch?  I'm guessing if they didn't have more room given round ports, they could make rectangular for more cross sectional area.  It would be nice if it was possible to grind the L20B ports to match the L18 but I think it would probably be the other way around.  I'm guessing you'd have to use the L20B gaskets.


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Maybe you could show the shop what @mainer311 did to build his exhaust before they get started.


Stainless exhaust using mandrel bends gets very expensive. I know shops that charge $5000 for a stainless dual system. I charge $3500 for the two into one setup for my LS swaps. It's very time consuming, and if you can learn it yourself, you can save thousands. Enough to buy a TIG welder and a port-a-band saw.

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32 minutes ago, Stoffregen Motorsports said:

Maybe you could show the shop what @mainer311 did to build his exhaust before they get started.


Stainless exhaust using mandrel bends gets very expensive. I know shops that charge $5000 for a stainless dual system. I charge $3500 for the two into one setup for my LS swaps. It's very time consuming, and if you can learn it yourself, you can save thousands. Enough to buy a TIG welder and a port-a-band saw.

Are you talking about buying the bends???   


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On 8/3/2021 at 9:47 AM, mainer311 said:

You mean like this?



First thing, that RH pipe is an exquisite work of art and I fully appreciate the "stand alone" design and fineness of the welding. 


Unfortunately, I'm a "Philistine" since this is for a daily driver "work" truck with bare floor boards (because I'd destroy the carpet and mats make the floor rot.)


That LH pipe can be fabbed  just about as quick as putting a flange on a pipe:


1) Position bent up exhaust pipe just where you want it and weld to bolted flange on manifold.

2) Remove pipe and fit the "stubby" pipe, cut hole in bent pipe, and weld - 60 minutes tops.


I am acutely aware that some customers want the hole exhaust done like the RH pipe and are willing to pay for it.


RE:  Precision Welding:


When I first got my 620, I was so enthusiastic, I precision gas welded the end of the bed where the tailgate hinges bolted.  Most of that panel was gone.  When done, I hand filed the weld in a few places, sanded, filler primed, and painted.  No bondo, no glazing, nothing.  Granted it was an ideal position and about as easy a precision weld job could be - so I did it - just to exercise those skills.  I don't do that any more - don't have the time to waste at 68.   

Edited by Cardinal Grammeter
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RE:  Manifold Studs:  Breakage


Myself, if there is enough stud left to hold on a nut, I an get them out w/o breakage.  


But if any broke, I would remove the manifold and get the studs out using the various heat methods and install new studs, etc. etc.  However, it they broke the studs, they may still not get them out on the bench w/o damaging the manifold threads.


However, what are the odds of breaking bolts holding manifold to head?


Is it safe to assume an exhaust shop knows how to not break studs?  


Maybe not, the first words out of the local exhaust shop was "if the studs break" which was not what I wanted to hear.


What should I say to a shop?  Just ask them to be extra careful and "just not" damage manifold threads, or get into specific instructions what I would want done in the event.


NOTE:  The "silent approach" does not always work:  When I had my seat reupholstered, they put 4" foam in it so my head was up against the headliner.  It cost me another $150 for them to take the foam out even though it was their "fault" for "modifying" the seat.  In that case, "specific instructions" would have been in order.

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19 hours ago, Cardinal Grammeter said:

Are you talking about buying the bends???   


Yep. Buy them from someplace like https://www.summitracing.com/search?SortBy=BestKeywordMatch&SortOrder=Ascending&keyword=mandrel bend





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I know where to get them.  I just didn't think people actually paid people to do that kind of work.  Where I live, you want that, you learn to weld.  All my tuner friends weld up their exhausts.  If a guy is building a custom, they already know how to weld and the ethic is to do it all yourself.   I live near Pittsburgh and Work Ethic still is everywhere.  I suppose in CA or FL, things are completely different.


What I did years ago:  (about 30)

I did a 427/425 C20 with Hooker Comp Plus headers and wanted NO backpressure.  I wasn't concerned with beauty so I did miter cuts:  I went to a 3 to 3.5" exhaust (I don't remember but was equal to the collector diameter) then split each side into a pair of vertically stacked 2.5" pipes into 4 turbo mufflers (vertically stacked) and 4 tailpipes behind the rear wheels.  Back then there were no 3" mufflers other than a Walker school bus muffler.  I did miter cuts on straight tubing and didn't care about a 45* sharp bend.  If you looked under the rear bumper, it look like the RHS of a spider.  Exhaust was so massive (back then you could get some real heavy wall tubing) the tailpipes never got hot to speak of.  


A few years, 3" exhausts became common place.  Lesson learned:  avoid custom work at all costs (!)  LOL  

Edited by Cardinal Grammeter
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