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Old 08-08-2002, 03:02 AM   #1
mattjk
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Default My concern about the new HKS Downpipe

Ok, it's obvious HKS and omitted the factory donut
gasket that allows twisting and flexing.



It seems to me people are just BLINDLY installing this
to their stock exhaust, which needs a flex... something
is going to break.

The only exhaust I can see this working correctly
with is the HKS Carbon hiper exhaust which
has a built-in flex joint.

Does anyone know if the Stainless HKS Hiper exhaust
has the same flex joint?

I guess I'll be returning this and getting a PDE downpipe

Matt
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Old 08-08-2002, 03:05 AM   #2
KOBIR
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Default downpipe

hi to you i am using the hks downpipe and i dont have aproblem wite that but if you consider to switch the turbo to the sr40
try to find twin dump pipe to install

bye
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Old 08-08-2002, 03:42 PM   #3
mattjk
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Default Re: downpipe

Quote:
Originally posted by KOBIR
hi to you i am using the hks downpipe and i dont have aproblem wite that but if you consider to switch the turbo to the sr40
try to find twin dump pipe to install

bye
I'm not concerned with the bell opening or whatever, there is
no flex!

Matt
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Old 08-08-2002, 04:01 PM   #4
atomicapples
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Default

they all should have a flex joint on the mid-pipe. most aftermarket exhaust dont use that donut joint.
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Old 08-08-2002, 04:07 PM   #5
mattjk
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Default

Quote:
Originally posted by atomicapples
they all should have a flex joint on the mid-pipe. most aftermarket exhaust dont use that donut joint.
Every single exhaust I have seen, except for the HKS hiper
has a provision for the stock donut. Turboxs has a donut
also, although it is their own design and bigger than stock.

Am I missing something here, or are people not understanding
me?

Matt
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Old 08-08-2002, 04:21 PM   #6
RiftsWRX
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Default

Had a BPM for a year.... no flex there bud... was fine..


Flex is a lot less prevelent on any motor that is not transverse mounted... your have torsional strain... meaning the whole exhaust may wanna angle down a bit and twist on it's hangers... compared to a transverse mounted motor that's going to try and put the whole exhaust through the floor board, muffler first.

Lot's of things in life don't use flex joints... and they're fine... I have a 1000CC bike that makes enough torque to power wheelie my petiteness at 100MPH... and the Yoshimura exhaust I've had since 98 hasn't bawked once.

Think about it...

Jorge (RiftsWRX)
www.ProjectWRX.com
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Old 08-08-2002, 04:49 PM   #7
mattjk
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Default

Quote:
Originally posted by RiftsWRX


Think about it...

Jorge (RiftsWRX)
www.ProjectWRX.com
I did think about it, which is why I am concerned... you
can't compare a bike exhaust that is 3 - 4 feet long to
a car's exhaust that is over twice as long.

The WRX's engine twists a great deal in it's mounts,
and the first thing that is going to give are the
gaskets, then the welds.

I'd like to see how long your exhaust lasts before
you get leaks or cracks.

I studied structural engineering in college, it's dumb
to build an exhaust without a flex.

Matt
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Old 08-08-2002, 05:50 PM   #8
aardvark
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Default

Quote:
I did think about it, which is why I am concerned... you
can't compare a bike exhaust that is 3 - 4 feet long to
a car's exhaust that is over twice as long.

The WRX's engine twists a great deal in it's mounts,
and the first thing that is going to give are the
gaskets, then the welds.

I'd like to see how long your exhaust lasts before
you get leaks or cracks.

I studied structural engineering in college, it's dumb
to build an exhaust without a flex.
A tube which is longer will have less stress imparted into it during flexure due to a constant twisting motion. A shorter tube will have more stress under the same twisting motion.

Exhaust systems have been built without flex joints for like 90 years or so. It's not going to hurt anything by not having one. Besides, the tubing is bolted to a soft rubber joint, and the rubber will take most, if not all, of the movement.
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Old 08-08-2002, 07:24 PM   #9
ShaggyGT
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Default

Quote:
Originally posted by mattjk


I did think about it, which is why I am concerned... you
can't compare a bike exhaust that is 3 - 4 feet long to
a car's exhaust that is over twice as long.

The WRX's engine twists a great deal in it's mounts,
and the first thing that is going to give are the
gaskets, then the welds.

I'd like to see how long your exhaust lasts before
you get leaks or cracks.

I studied structural engineering in college, it's dumb
to build an exhaust without a flex.

Matt

So why did you even guy the HKS downpipe to begin with???? There were plenty of pictures availible of the downpipe that clearly showed that there was no flex joint. For $175 what do you expect????
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Old 08-08-2002, 08:02 PM   #10
mattjk
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Default

Quote:
Originally posted by 02_Scooby_WRX



So why did you even guy the HKS downpipe to begin with???? There were plenty of pictures availible of the downpipe that clearly showed that there was no flex joint. For $175 what do you expect????
When I ordered it, there were only pictures of the rear, and
they were not very good. The shop said it would have a
bell shaped opening, and would work with the stock midpipe.

This is what I get for being impatient and trying to go cheap

Mat
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Old 08-08-2002, 09:24 PM   #11
lstepnio
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Default

I happy as I can be for $175.00 shipped.
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Old 08-08-2002, 10:23 PM   #12
Phailure
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Default

I have the Stainless Steel HKS HiPower CatBack and it does have the flex joint. Comes gaskets too ofcourse. Pretty nice exhaust, really quiet. Cant really hear it over 4k rpm cuz the engine is louder now after the exhaust.
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Old 08-08-2002, 10:51 PM   #13
ChrisV-FL
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Thumbs up HKS Down pipewith HKS CATback HI-Power

I just installed yesterday with the help of a good friend of mine my HKS Stainless HiPower Cat back, HKS Down Pipe and PDE Uppipe..... The car is a litle too loud for my taste but it feels AWSOME!!!!! Check engine light came on today.....What should I do about that???any tips????
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Old 08-08-2002, 10:59 PM   #14
Quick WRX
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Default

Quote:
When I ordered it, there were only pictures of the rear, and
I would never buy something, even if it is $175, without seeing a good picture of all sides. I have the GodSpeed DP with the HKS catback, it has no flex joint and everything has been fine. I am really suprised the HKS released this product, from all I have herd and seen it is substandard and HKS usually makes good products.
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Old 08-08-2002, 11:07 PM   #15
mattjk
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Default

Quote:
Originally posted by Phailure
I have the Stainless Steel HKS HiPower CatBack and it does have the flex joint. Comes gaskets too ofcourse. Pretty nice exhaust, really quiet. Cant really hear it over 4k rpm cuz the engine is louder now after the exhaust.
That was my thought also, I could get the HKS exhaust
with the flex...

Matt
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Old 08-08-2002, 11:08 PM   #16
subarud
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Default mil eliminator

ChrisV-FL

Buy a MIL (CEL) eliminator from
www.ponyexpresspeformance.com its $20

You splice this resistor at the O2 sensor at the last cat and you dont get a CEl from having no cats...

evan
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Old 08-08-2002, 11:22 PM   #17
mlambert
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Default

I got one cause they are so cheap, basically throw away exhaust if they get too bad.

no big deal imo, its better than stock
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Old 08-12-2002, 01:50 PM   #18
gqzboy
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Default For all ya'll in california

Hi, right now i'm currently in hawaii, but my car will be in cali soon... i'm running no cat.. how would i go about passing the smog and whats the minimum require cat in cali? someone give me a hand.. thanks
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Old 08-12-2002, 02:34 PM   #19
cdigerlando
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Default Flexing.

We had a discussion about this not too long ago for just the uppipe. I did not think you needed flex since the turbo moves with the engine. However, one member brought up a good point, that the pipes expand and contract a lot. This would be a good reason for flex on the upipe. More for expansion instead of for movement. On the dp, I think it would be foolish to think flex would not be helpful in this application. The hangers have some flex, but I think an in line flex joint would add to the reliability of the system.
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Old 08-12-2002, 08:47 PM   #20
Z1 Performance
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Default

A Flex is a nice thing to have in an exhaust..not a huge one, but some is good. relying on the hangers alone is foolish for long term, but fine for short term.

This is not a substandard HKS piece though guys....it is NOT designed for a street car, hence the no cats. Same goes for all HKS downpipes actually....all are really off road only.

As for the up-pipe flex, it is not needed at all IMHO...it will surely be the first thing to go wrong in the future. yes the pipes expand anc contract, but if the up-pipe is built properly to begin with fitment wise, it will be fine.
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Old 08-17-2002, 11:05 PM   #21
mlambert
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Default

so basically it would be best to make this downpipe to an hks catback (hipower or carbon ti both have flex joints)
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Old 08-18-2002, 03:04 AM   #22
Penguinking
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Default

Quote:
Originally posted by Z1 Performance


This is not a substandard HKS piece though guys....it is NOT designed for a street car, hence the no cats. Same goes for all HKS downpipes actually....all are really off road only.
im abit confused...what do you mean? im kinda concered b/c compared to the rest of HKS products, the dp is quite the deal, so are you saying its still high quality b/c its designed for "off road"?
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Old 08-18-2002, 09:37 PM   #23
mlambert
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Default

no hes saying that its high quality, but its illegal to run them on a car that is liscensed for street use

just like most every other exhaust that people talk about in this forum. TXS stage2 illegal, vishnu stage 0 illegal, cobb clubspec illegal, hks downpipe illegal...

about the only thing thats legal to do is change out the catback.
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Old 08-18-2002, 11:07 PM   #24
William LaPalme
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Default

I think that this is a moot point, anything can be legal if you pass. But back to the origional point, our engine flexs a lot less than many other turbo engines that have never had flex joints! So why should this one? Do you think the race car does? Do you think that a solid piece of high quality pipe would leak sooner than one with a point that is made of braided steel, and not truely sealed? If you think that for some reason turbo dp's "require" flex joints, on even such a low torque engine, maybe you should consult a higher power! Reeves Calloway, does not seem to think that it was necassary for the Sledgehammer. Porsche, doesn't seem to find it necassary for the GT-2! And NOBODY seems to think of it for the insane Supra, 360 Modena, F-40, F-50. But for those of you who are just paranoid, I think that they do have it on Semi trucks..... Which realy shouldn't help you at all.
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