Tim W

iTrader: (1)

Becasue on a hiper underneath the braid is a spring type flex joint...just like the one that splits on the up pipe guess where mines blowing [img]images/smilies/mad.gif[/img]

Nope slip joint is the way ahead I think...also means that other mounting flanges can be considered for other turbos

David_Wallis

hmmm... not sure theres an issue with these joints... but slip would be easy enough to do..

David

Pete Croney

The co-efficient of expension on stainless means the up pipe will expand 2mm when it is at 900degC. This expansion presses against the turbo, which sits on the up pipe and a soft mild steel bracket. You can bend the bracket up about 5mm with light hand pressure.

The downpipe has has no expansion joint and is much longer. It is rigidly bolted to the gearbox, so all of its expansion also goes back up to the turbo, neatly matching the expansion of a non flex joint up pipe

Tim W

iTrader: (1)

Pete, So if everything can move about at the turbo end, why did David TS, and a few others so I'm lead to beleive, have problems with his car regularly blowing the gaskets?

Is this some bizar anomaly only to be found on the MY01 on cars, or even an isolated incident?

David_Wallis

my replacement hks doesnt... (yet) have gearbox.. bracket... or back bracket like the scooby sport one.. Although I sheared off both my std ones... Must be something to do with 6000 rpm standing starts...

David

David_Wallis

tim I think what petes saying (could be wrong) but the turbo could move fine.. but as the downpipe is bolted to the box it holds the turbo in place.. and the weakest part is the non std up-pipe?

David

Tim W

iTrader: (1)

I see what you mean...

Therefore if there is no expansion joint and everything is so ridgedly mounted with the cast manifold then it seems obvious that something will have to give...hence the gasket failure(s?)

Dave T-S

Thanks Dave. I thought there would be

Do it yourselfers please note!






[Edited by Dave T-S - 7/19/2002 9:14:20 PM]

Dave T-S

And since my name was mentioned

I believe that in my case the replacement uppipe bottom flange was not ground flat after the welding process, and had warped, and this caused (if not fully, at least partially) the gasket blow.

On our other STi7 I had a centre pipe cut and repositioned next to the flange and the flange bent like a banana when welded - even with TIG. The oval flanges are much thinner in the centre and the welding heat path goes straight through this point.

As any of you with metallurgy knowledge will know, most metals have a memory - they will try and return to their state prior to having been worked. I have a suspicion that the bend in a solid up pipe causes it to try and straighten out and return to its former state - a piece of straight pipe - when exposed to 900c or so and this puts a sideways or twisting force on the flange which does the gasket no favours. A gasket is designed to take up minor imperfections in fit and will fail very quickly if these are exceeded or, worse, there are gaps between the mating faces - particularly when exposed to 900c.

Note this is all unproven, and only my own opinion, which may be wrong Nor is it a criticism of anybody's products.

All I am saying is tread carefully. If you make up any old pipe where the flanges are not an exact fit, expect trouble

Remember, Subaru went to the time, trouble and cost of putting an expansion joint in the OEM up pipe, and not for no good reason.

Interesting that both MRT and APS are putting an expansion joint in their replacement up pipes.




[Edited by Dave T-S - 7/19/2002 9:34:05 PM]

[Edited by Dave T-S - 7/19/2002 10:14:40 PM]

APS

Guys,

Obviously we are not here to design turbine inlet pipes (“up-pipes”) for you all!! However, a couple of additional observations.

1. Please note my previous comments re material specification. This applies to the flex joint also.

2. Flange flatness and gasket design are critical. Fabricated pieces require flange machining after manufacture (which again is not easy), minimum 1/2” thick.

3. The standard pieces work fine on a standard car at standard boost. Change anything and you better know what you are doing!!

Dave
APS

Rice Rocket..

i should be having my uppie fitted next weekend on my my01, scoobysport item, i have bought ne gaskets as well, shoul i have iy fitted or not. i keep reading treads and being put off having it fitted due to issues, i dont do track days or drive it hard all the time.

What should i do then.

RR

ps i already have a scoobysport downpipe fitted along with a blitz nur spec system (fitting next week)

Dave T-S

Dave (APS)

Thanks for your comments - just reinforces my views that this is a critical part that has to be constructed properly.

Re flange machining after welding - DIY'ers out there again please note - this does NOT mean 3 seconds on a belt sander/linisher which is guaranteed to leave it bowed -it means using a milling machine or surface grinder where the pipe is clamped in tight........

Tim W

iTrader: (1)

Dave T-S, looking at my prototype flanges using float glass and water (any trapped water under the flange when looking from underneath, should show any surface problems) it looked fine...

Now I don't have the pipe to hand now (it's off being checked for angles) but it has been made by cutting a hole in each flange a little larger than the diameter of the OD of the pipe, the pipe has then been pushed in to the hole and welded on the reverse side...I know this is not as neat as others which, from the photos I have seen, are welded on both sides (and again as it's a prototype this may change!) but I wonder if this ahs some effect on the warping?

Oh, that and I think the flanges are mild steel...before you think it no they can't rust through, 10mm of steel? comeone, plus I'm told by various sources that it is better to use mild steel for flanges than stainless...but I can't remember why

Pete Croney

Just to confirm that Dave had one of the first up pipes we made and the flange was out of tolerance, hence the gasket failure. Production has since been changed to ensure that these are now perfect.

This has nothing to do with the pipe having a flex joint or not. When the 2 flanges and gasket are bolted tight, they become a solid member and the gasket cannot fail as it is crushed between the flanges. Its purpose is only to take up minute variations between the flange surfaces, forming a seal.

Fully anealed stainless is quite flexible in its nature and we not feel the need to fit a flex joint (see my earlier post about expansion). If a pipe does have a flex joint, it is the flex joint that will eventually fail, as is normally the case with the standard ones.

The standard up-pipe has to have a slip joint, because of the materials it is made from. Note (again) that the downpipe is ridigly fixed and doesn't have one, but the temps are almost the same between the turbo and its fixing point.

I don't know of one downpipe that has cracked.

They also fit a bright switch





[Edited by Pete Croney - 7/20/2002 11:12:37 AM]

Tim W

iTrader: (1)

Ah...the bright switch...re wire for use as Anti Lag control...then it has a use...plus it will certainly over a brightening effect for anyone following

Anyway back on topic, sod the expansion joint too complex and adds cost...maybe...

David_Wallis

LMAO at Pete...

Ill take my chances... if it blows.... I weld it to the turbo

Dave,

Note to Diy'ers... That doesnt mean three mins on a belt sander... That wasn't aimed at me was it???

I wouldnt like to do the flange on a milling machine (only cos I aint got one ) But do have access to a surface grinder...

But from what tim says it sounds ok.

David

Pete Croney

A table sander is the tool of choice, but I think what Dave meant is that it can take 30 minutes to get it perfectly flat. Also remember to keep quenching it.

Tim... great use for the bright switch

Pavlo

If you get the flange welded, see if you can't get someone with a gas axe or similar to heat the flanges till cherry red and cool in still air (normalizing). This should bring out most/all internal stesses.

Flaten flanges afterwards, shouldn't need to be 'critical' as that's what the gaskets are for. I would just do it with a large flat file, and check for flatness on flat plate with micrometer blue or glass and water.

If you want to bore out the flanges, put them in a 4 jaw chuck on the lathe (one with independant jaws).

Paul

Dave T-S

Pavlo said

Unfortunately this is NOT the case. The picture below is what happens to an up pipe gasket fitted to an STi7 that failed because the up pipe flange was out of tolerance. Note that this gasket is triple layer solid laminated steel 1.5mm thick, and the side blew clean out of it. The only thing holding it together was the central ring and sooner or later this would probably have burnt out too.



Pete, I remembered you mentioned a while back that ours was one of a batch of up pipes with flanges out of tolerance, but I couldn't recall where and didn't want to mention this anyway as it might have seemed I was criticising ScoobySport, which wasn't the intention.

BTW,
Our STi7's don't have a bright switch, but they do still have an expansion joint in the up pipe


Tim
Do you mean the flange was checked for flatness before or after welding? The warping during the welding process happens because the flange is thinner in the middle than the sides and this gives a different expansion/distortion rate whilst welding. As I am sure you are aware, if the flange is true before welding, it probably won't be after.


David Wallis

LOL - not it wasn't (and I actually said three seconds), but if you are feeling guilty......

The only way to get the flanges truly flat are to clamp them solid in either a milling machine or surface grinder.

In summary, my comments all along have been directed at DIY'ers - I am not having a go at anyone making their own - good luck to you - but just saying that absolute flange flatness is critical, and the photo shows what happens when it is not.

Pete Croney

Dave, no probs, I just wanted people to know that it was an early manufacturing problem, not a design one.

The reason why the gasket failed like it did is not the pressure blowing the metal away, even if the inner ring had failed, it couldn't do this. What happens is the leaking gas does the same as the thing we did as kids, blowing on a blade of grass which is held between the sides of our outstretched thumbs. It vibrates between the two surfaces, in the airflow. Its the banging against the flanges that wears the flange away and this is why its worse on the outside edge, where the movement was greater.

Pete Croney

Meant to add...

DIYers if you cant get use of a table sander, just use 2 new gaskets

Dave T-S

Pete
Blowing on a blade of grass - that takes me back.....

David_Wallis

Never did that as a kid... pavlo are you mad either that or you have big lathe I could get the up-pipe flange in our four jaw but wouldnt want to watch...

Mind you Ive just been and cut out the d/pipe flange with the plasma cutter and one of my dads mates workshops (on a railway.. (charity run)) and they have a suface grinder, a lathe big enough for a train wheel and a drill that is just undescribable (sp) oh and they also have three phase sockets for me to plug a plasma cutter in

Now just got to make it all line up and weld it up (and check flange flatness )

Run out of co2 though....

Have to wait till monday.

David

n5pug

C02 man, nooooooo get some argon/co2 mix in there (called argoshield, 18% co2) much better quality weld.

ustolemyname??stevieturbo

iTrader: (1)

DIYers... why use 2 gaskets.. A big angle grinder can be just as effective, and clean it up with a file. Filing may be a little work, but it does the job. I have also held the flange onto the disc of a 9" grinder to flatten. Using 2 gaskets would be a last option. Strictly speaking, if the 2 surfaces are flat, then no gaskets should be required. On another car, I have NO gaskets in the entire exhaust, from head to tail incl turbos, all with DIY made components ( altho I did have the manifolds machined on a surface grinder )
For those selling these up-pipes and downpipes etc... why do you even let these leave your shop with bent flanges. I have seen quite a few and I think it is absolutely ridiculous to sell something like that that isnt a perfect fit for the job. To have someone purchase one, and go to the trouble of stripping and fitting the part, to find out that it wont seal is a joke. Get your act together people. The customers deserve beter

David_Wallis

got to agree with stevieturbo on that one.. especially with the work involved changing them...

N Pug..

I know about argoshield helishield etc and how it efects the heat that you can put into the metal... but where do you get these from?? BOC gasses etc... which involves having an account and paying for a bottle.. then paying to have it filled.... when I could just use a pub bottle which are erm cough cheap

Thinking about it I might enquire about changing...

David

Tim W

iTrader: (1)

Pete, I have so many ideas for the bright switch that one day I'm bound to actually use one Anti lag, flamer kit, spot lamps, nitrous...I could go on...everytime I end up sitting in traffic I look at the bloody thing thinking 'I wonder...'

Anyway, Dave TS I checked the flatness myself once I got the completed pipe, so it looks like it survived the welding process well...maybe the guy who welded it (very neatly I might add) was carefull to make sure that it didn't warp...

If I had a mill at my disposal I'm sure I'd be using it...but I'll have to make too with the desk sander and some patience if I have to.

Dave T-S

Stevie
Using the flat of an angle grinder disc is not recommended - that's how they disintegrate

Agree if the flanges are finished to fine tolerances you wouldn't need a gasket at all.

Tim
Glad it's looking good

Rice Rocket..

Pete,

Do you mean using 2 gaskets at each end of the up-pipe?
I don't want to have the stripped by the garage and for it not to work.

I am not the most tech. minded person, so please bear with me

Thanks

RR

ustolemyname??stevieturbo

iTrader: (1)

Suppose the grinder bit isnt good advice. I just use argosheild 5 when welding. The bottle costs about £35-40 per year rental, and about the same to fill. I think mine is size G, but not sure. Its about 1.2m tall and about 250mm dia. Its the biggest 'small' bottle you can get, and it does last ages. Well worth it, I wouldnt even consider using the disposable bottles.
And no matter what gas you use, molten metal is still bloody hot, and it will caus ewarping iff too much heat gets in. I did mine about an inch at a time max ( opposite sides of pipe ) quenching in water straight after each weld. Warping was kept to a minimum