OK, here's some pics of the HKS DP. It is mild steel and at least twice as heavy as the stainless. It comes thinly painted with heat coat (not more than 1300 degree).

 

The O2 sensor bunge is in the exact same location.

 

has the hanger thing the pre-cat did and basicaly is the exact same thing as the pre-cat but without the cat.

These were done with my web cam. If I can borrow a digital cam, i'll take some instillation pics.

 

Repost: When I uploaded the last pic, it got corupted. Yes I took more of her, but I can't post those here

 

I couldn't get a dig' cam and I can't drive the car upstairs to my bedroom. So no step by step pics. The HKS can "easily" pass for the pre-cat! Only a rotary mechanic with a flashlight could tell.

If you don't have a O2 sensor socket, you need to have the O2 sensor installed first, but be extremely careful as you can easily break off the wire. Does anyone know where it plugs in to?

 

so with the HKS so you still get the benefit in HP as the other downpipes...most test I see gain about 20hp. just concerned that I installed a downpipe removed the heat but am not getting the hp gains. how much are owners gaining in hp with the hks (if any at all). If no gain then I am ripping it out!!

 

That's one hell of an egt hole! The hole for EGT(Greddy, DEFI, Apexi guages) are all 3/8 npt sizes...MUCH smaller than an o2 Bung.

 

With the HKS you get the benefit of a DP. The pipe is an exact copy of the pre-cat, less the cat (only piping). The crimp is exactly the same as the OEM precat and so is the O2 senser bunge/hole location. It does widen to make up for the crimp, as someone called it a Cobra head. Whether that offsets the restriction, I couldn't tell you. I can tell you that the silver paint is not a 2000 degree heat coating but it's free (comes painted). I can also tell you the down pipe is a no brainer and apparently I had no brains for waiting!

The benefits are: Price, looks deceivingly like OEM pre-cat, ease of fitment/no stud isues. Lighter than pre-cat by 40lbs and less restrictive.

Cons: Heavier than stainless steel DP. May be more restrive than M2 or similar DP.

Pre-cat = bad & down pipe = very, very good!

Best bang for the back ...stupid, stupid, stupid me!

Oh btw: If you need to replace the nuts for the studs, they are 8mm and 1.25 thread.

 

GoRacer. The studs on a stock 3rd gen turbo manifold to precat or downpipe are 10mm and 1.5 thread not the 8mm and 1.25 reported above.

 

ive heard good things about the HKS or the M2

either way, a DP is a good thing to get!

 

Well it seems it's not an exact perfect copy. On the corner stud that allways has problems. There is a wall around where the nut goes instead of being flat and open.

Sorry that is not the nut size. I brought the wrong one to the auto parts store.

 

has anyone had experiences with the Bonez downpipe? I tried searching but apparently its been disabled.

Do you have to replace the studs? how about quality,

 

I have pettit and really like it---the old butt dyno really notices the differenece. But the o2 sensor is up by the turbo manifold and is a real pain to work with. I would have gone with m2 but they are always back ordered. Found out too late that Shane at Aim carries them in stock. Here's a link if you are looking for an M2
http://aimtuning.com

 

If Laminar flow is the flow which will make the exhaust gas exit faster. Why would those race cars tuner wrap their headers and downpipe with thermal wrap. For example the RE amemiya race car has their WHOLE exhaust system wrapped with those thermal wrap. I believe the purpose of thermal wrapping is to trap the heat inside the exhaust pipe and that will cause a turbulent flow of the exhaust gas. So which flow is better?

 

Wrap is to keep heat away from places you dont want it to be. Laminar flow is fluid flow in which the fluid travels smoothly or in regular paths. The velocity, pressure, and other flow properties at each point in the fluid remain constant. Laminar flow over a horizontal surface may be thought of as consisting of thin layers, all parallel to each other, that slide over each other. It is common only where the flow channel is relatively small, the fluid is moving slowly, and its viscosity is relatively high. Examples include the flow of oil through a thin tube. Essentially friction at the walls of the pipe grab at the material passing through it and stir it up or slow it down. Exhaust gasses due to the nature of the combustion cycle are not particularly inclined to have good laminar flow. Intake air might... in a nice smooth pipe. and I though i'd never use that physics class in real life lol

 

Yeah, I took the wrong nut to the auto parts store for them to match a replacement.

Nut part # JE10-40-355 $5.70(ea)
Stud part # 9YA9-01-002 $4.20(ea)

 

Here is a pic of the M2 DP uploaded by JimmyJimoJet

 

My DP is a Bonez, at least that is what the guy who sold me the car said it was. It looks to be really nice quality and when I removed/reinstalled it to replace my turbos it wasnt that difficult. There is one bolt that is a tight fit, I had to grind the flange off of a factory pre-cat nut to get it on. No studs need to be removed or replaced unless there is another problem with the stud.

 

I have the Bonez downpipe and it is an excellent fit. Just throw out the studs they give you and use the stock studs. A little hard to get the 4th stud in - need someone under the car to jiggle the pipe when putting it in. All flanges line up perfectly.

 

thats weird that you said that because i just picked up my DP from M2 and i saw 20 more polished.

 

that looks nothing like m2's

 

It's not. He said it was but I beleive it's a Pettit (unless i'm wrong again). I think Pettit is the only one with three bends. I copied the pic from another thread but forgot to correct my post on this one.

 

oic its all good, but slipspeed i hope you get your correct m2 downpipe.

 

ok, i noticed a few comments in the earlier pages, that im going to comment on, i kinda got bored after page 2 so i skimmed over the rest, so if i repeat what somone has already said i apologize.

one 3" tube will flow more then two 1.5" tubes. (not nessarliy refering to any downpipes in particular)
i think somone said the split downpipe was to match the exaust ports pulswidths. thats a good idea, except the downpipe starts at one then goes to 2 then back to 1. i personally dont see any advantage to haveing 2 tubes rather then one. somone said it would be pointless to have a 4" downpipe unless u had 4" exaust, this isnt true....although i personally believe a 3" downpipe is plenty for most anything, the downpipe being the closest to the turbo, has a bigger part in turbo spool up. plus the down pipe has some different bends going through it, where-as the rest of the exhaust is fairly straight and therfore has better flow.
anyways, thats just my personal feelings, in no way am i an exaust thermodynamic specialist

 

OK, maybe I'm not looking at this right, but why do the DPs like the M2 mate up with the turbo manifold with a rectangular flange but with a circular pipe? The exhaust port on the turbo manifold is rectangular. That's like pushing a square peg through a smaller round hole.