bbarbulo

iTrader: (2)

Ok, in your experience, is cast iron better than tubular steel for turbo applications. I know cast iron is better in the long term, but does it flow as well as tubular? What makes the tubular ones unreliable in the long term (do the welds crack, and why?). Also, equal length or no for the manifold runners? What size primaries are best for small turbo IHI off the stock WRX? Any manufactureres you know about for turbo manifolds?

imported_SW20 MR2

I can't help you with all your questions, but here goes. Turbular is the way to go for bigger hp setups. Cast manifolds seem to be common for most of the "kits" available on the market, but that's probably due to cost. Turbular units are used for cars making big hp. Cracking is indeed a reason why many prefer a cast manifold, especially for street/longer term use. Here are some manufacturers for the most common manifolds and turbo kits:

http://revhard.com
http://www.maxrev.com
http://www.f-max.com

KS-R

Well, basically what I have to say is pretty much what SW20 MR2 said already.

Cast manifolds are more a mass produced product, so performance may (not necessarily) not be as good for performance.. Due to the cost of production and flow characteristics.

Now, tubular is suppose (not necessarily either) to be a more well designed manifold to produce as much flow as possible.. Plus, you have the freedom of many different designs to cater to whatever engine and placement you need. There isn't really any right or wrong way to designing a header or turbo manifold.. basically... whatever works.

Oh.. and to answer your questions with the reliability and durability.. The reason the tubular ones crack is due to the excessive heat and stress. The tubular ones are quite thin, unlike the cast ones which are almost always at least 3-4 times thicker.. So.. therefore the cast ones are somewhat more durable and last longer.

So... You have a trade off.... to get durability.. to get less performance.. and vise versa..

But then again.. Stock cast exhaust manifolds crack as well... So.. Go figure.

To me.. it sounds like you're trying to piece together a turbo kit yourself. The IHI off the WRX are fairly small and wouldn't need very much to spool it up.. nor will it generate much power in the top end.

If anything.. I would suggest you get ahold of a stock HF/VX exhaust manifold and just adapt the turbo to it. It'll provide more than enough flow to spool that up and it'll save you time/money compared to buying another manifold for it.

bbarbulo

iTrader: (2)

Excellent....thanks guys. I ask because I will be doing my own manifold design and build, so I'm just looking at initial info. I have over a year to study exhaust pulse dynamics in order to design a good manifold, but I thought I'd see what knowledge is out there in the general public. I figure I'll buy pre-manderel bent sections and weld them together to a thick flange, then mill the flanges perfectly level for a good seal, and have it ceramic coated.

imported_SW20 MR2

Hytech Exhaust is considered to be one of the best header/manifold designers:



http://www.hytechexhaust.com/

Max Rev log style tubular manifold:



Cast Greddy manifold:



Kiwi turbular manifold:



Kooks tubular manifold:



Hope that helps. Check Honda-Tech.com for more information.

KS-R

IMO.. Unless you're going full race.. I wouldn't worry too much about the flow difference between a cast manifold or a tubular one...

I give you props for attempting such a task in designing and building your own manifold... I'll be attempting to build my own full race side exit header.. That alone will take a very LONG time to design and build, let alone a turbo one.

Mind you.. depending on your design and how elaborate you want to make it... It'll take quite a few mandrel bends to build one. I suggest you use stainless steel bends which are thicker and stronger, but those are about $40-$50 each bend... It'll probably end up costing you quite a bit to build this one manifold.

Just a heads up. Good Luck.

bbarbulo

iTrader: (2)

Thanks again. The pics were an inspiration! Well, KS-R I figure my spare time is free So why not do it. As for the price...I can get bulk bends and then take pie cuts out and weld the angles in for the right radius. I believe this is how titanium bits are made...pie cuts all the way, since Ti cracks when bent (kinda like Alum. but even more so). Perhaps I will break down and buy it, but I have all the time in the world...my car isn't really driven much, so having it down for a few months won't be a huge problem. Or I can just use the stock manifold to scan all the points into AutoCAD or similar software, then produce a design from that, and proceed with fabriaction, w/o my car being down at all. It will ensure perfect fit, since I'm reproducing the exact shape of the stock flange, but with different tubing. Both my dad and brother are mech eng, so I have quite the talent pool to draw from. Too bad I decided to do an Economics degree instead of mech eng.

KS-R

Bah.. Don't sweat it.. You're the smart one by taking the economics.. See.. you know how to finance the project.. That's the smart way of doing it.

imported_SW20 MR2

Good luck!

bbarbulo

iTrader: (2)

Thanks boys!! I'll let you know how it turns out in a couple of years