Jeff92se

iTrader: (82)

Oh he has one of those Honda type flex sections with the springs. He never said that.

eric93SE

iTrader: (1)

Matt, I don't have that type. The one I have came out after they had problems with the flex section shrinking down to like 1 inch, so they made the flex section a heck of a lot stiffer, but its so stiff that it does not flex! (ie. no bolts to loosen up).

Wiking

Your solution looks great!
- About CAT: one day it has to be replaced, is it ok to buy any aftermarket or is there some reason for u to get 4gen CAT?
- Cattman/warp etc: Is there any measured differences in flow how the two pipes meet? I think I'll weld my own, and try to reach the 7 degree merge -angle that one sometimes meets in flow/echo -related litterature

If one could figure out the manifold heat/warp phenomena, (cooling it from the middle) maybe smtg could be done about it. Cut off some shield from middle?

Jeff92se

iTrader: (82)

The 4-gen was shorter. It didn't have any flanges on it (Carsound was the brand). Since I wanted a longer flex and it had to bolt up to the cat-back system, I had to make up for the longer flex with a shorter cat assembly.
The shorter cat doesn't seem to have affected anything. If this one goes bad, I'll have to cut the flanges off and weld them on to another one. As you can see, I'm using non-standard ball-jointed flanges (no gaskets and no leaks).

I don't think there is much of a diff inbetween the Cattman/Warpspeed Ys.

Your english is getter better and better.

Wiking

en glitch? Too mucho ? time on the .org....

The issue is in language structure: the word positions in a sentence vary depending on language. As one language is used more than others, it dominates word position fixation mentally before they 'come out'.

Take in typos and wrong word positions, the text becomes unreadable. The writer cannot see why o why 'cause all translates perfectly on the dominating language without noticing... Language starts to flow after thinking is done with that language.

To keep issues inside .org guidelines: its like cold engine TPS open/closed -loop

Minty91GXE

iTrader: (3)

i think it might be valuable to note which studs break most often.

for me: the 2 most-far-passenger side studs, both front and back manifolds. i've heard of other cars having the same issue where there were certain studs that were prone to breaking.

however: on both manifolds that had broken studs, twice, they both measured flat when checked for warping. my personal guess is the studs gradually become weaker each time the manifold becomes hot, the thermal expansion of the manifold pulls at the studs day to day, eventually 'popping' them. the break on the stud is always a flat, uncontorted break, not showing any evidence of twist or bend.

exhaust runs at what ? 1400 °F ? or so... and the rule of thumb is: cast iron shrinks 1/8" per linear foot from cast to cool

what are our manifolds made of? i dont even know.
tom

Wiking

- all say the same = ends.

(if rotten bolts dismissed) Problem has to be with uneven heat expansion. Both head and manifold, most of it goes probably to manifold. Y-pipe direct inevitably some force, maybe its minuscle as most argue.

What to do to succesfully compensate? If that could be figured out, maybe the studs could last as long as the car... If its only heat redistribution, then shield configuration might be one key.

edit:

Is the front stud (4) first to go? Check out, that is hotter than (5) rear 'cause of the shield is prohibiting it to cool.

Minty91GXE

iTrader: (3)

as far as the y-pipe theory goes:
it wouldn't make sense that the kinetic force it exerts would break the end studs. the pivot point of the manifold would segregate the possible shifting force of the pipe to either the top row of studs or the bottom row. there is no (left) or (right) variable and no movement that would have these studs breaking first. additionally, the end studs are furthest from the center, and therefore the last to break under that particular strain.
as far as the heat theory:
what confuses me the most is that i would imagine at least intuitively, that the center exhaust column would be the hottest, since it has ports on either side of it expelling exhaust.

mtcookson

iTrader: (2)

i still believe its the lack of support on the y-pipe. my car proved that to me due to not having any support of the downpipe. even though i had the turbo studs they still snapped.

Wiking

Thats the way it could cork out either end: the assy center balloons with the heat expansion, then surely with enough expansion/contraction, one end will be ripped off while center bolts have no stress.

If I remember right, this popup happens in cooling phase (?) meaning that ends cool faster than middle causing temporary warpage.

If that bend direction is to be minimized, it might be achieved by keeping mid assy hot from outside, cool it from 'inner side'. How...

I now agree/think that y-pipe cannot pop the bolts, but it might be the triggering force when the heat expansion, sudden engine tilt etc puts all bolts on notice... I think that force can be on any axis, but I could agree/guess that less on the ends.

Wiking

Can you illustrate the situations when/how that happened. How many and which kind miles the studs had experienced? Was the exhaust system heating or cooling, engine movement included etc...

First Hot drive, idle:
...exhaust starts to contract, outer parts most. Engine block water circ cooling capacity 'downgrades' as pump rev goes down. How and which direction heat travels in piston/cylinder/head masses, does it (ye it does) warp and how much? Is it compensating to exhaust manifold or working against the exhaust assy stress, magnifying the manifold 'ballooning' effect?

mtcookson

iTrader: (2)

basically, the turbo and downpipe on my car are all supported by the studs themselves due to no bracket connecing the downpipe to the engine. when the engine moves underload it puts tons of stress on the studs and eventually caused one or two to break and eventually a few more. i can see this happening with the y-pipe as well when the y-pipe is only supported by the exhaust studs.

the problem could be hindered with urethane motor mounts but i still wouldn't feel comfortable until the pipe was attached to the engine to take stress off of the studs.

Wiking

Plain turbo weight means stress, and also its inertia: its mass will not want to dance in tune with engine vibrations. Howabout flexpipe?

DanNY

iTrader: (14)

how heavy is one leg of the y-pipe...and how heavy is your turbo that pulls on the manifolds?

mtcookson

iTrader: (2)

its not really the weight, even though the turbo is heavy, its the fact that when the engine shifts around under a load it pulls and pushes on the y-pipe and the studs. there's only so much the flex section can flex... i'm almost positive if a bracket was put on the exhaust to move the pipe with the engine, there would almost never be broken studs.

if no one believes me that's fine, but i'm standing by my personal experiences with these things. i guess i should add in that we started having some stud trouble after the motor mount went on the gxe, which is just more proof to my theory.

eric93SE

iTrader: (1)

And an extreme case of that (agreeing with mtcookson) was when another org member bottomed out his max striking the y pipe, and thus shearing off his studs (an extreme case of course).


As an aside, lets all remember that the primary reason for studs breaking is the quality of the steel nissan used at the time (whether it was accidental or stupidity).

Minty91GXE

iTrader: (3)

but why would the end studs break most frequently? the studs that took the weight of those shifts would be the center studs, then the outermost studs on the backside of the engine, then lastly the end studs on the crankshaft pulley end.
honestly i believe it to be a combination of stress from the engine shift, which is pretty violent as i've seen on a dyno and the quality of the materials.

i did have one other thought today when i considered combining the two prevalent theories:

could it be, that the studs of the manifold are the first things to cool, before the manifold itself? that would allow them to shrink much more rapidly than the manifold, which is much thicker and has much more direct contact with the exhaust. that more rapid cooling would have them tightening themselves against the still swollen manifold.

-the holes for the studs in the manifold are MUCH wider than the studs that fit through them. they really dont contact at all.
-the gasket-edge of the manifold is MUCH thicker than the studs, thereby able to retain much more heat and dissipate heat far less rapidly.
-the studs would stretch themselves out if they cooled faster than the manifold.
-the stretched studs would be weak to hold up to the vibrations and physical force exerted on them by the exhaust system.
-if the studs on the end were the first to cool, then they could actually be the first to break, despite the fact that they bear the least weight from the y-pipe and exhaust.

that's where i'm at now

Wiking

If that is the issue, number 5 will ALWAYS go first (as it is non shielded, cools better).

Is it so?

Someone c/should make imperial test: add some shielding on the no.5 stud and waitwaiwait... and after 15 years come into conclusion that who cares...

What affects studs cooling is also its attachement to the internal head structure, its cavities, water circ and distance to heated exhaust channels.