exhaust manifold

[fush]

Anyone know of a good place to get information on exhaust manifold design, in particular for a turbo application. I am trying to figure out what kind of advantage/disadvantage there is between say a tubular style manifold or a box style manifold.

 

I want to weld up a manifold for my setup and I have few ideas on how I can do it. One involves going tubular for each cylinder and the other one would just dump exhaust into a box similar to the cast exhaust manifold thats on the car now. Here is a picture of one that is "tubular" style. I was thinking it may be easier to just weld one chamber the flange and into the collector rather than do it tubular but I cant really find any information on the pros or cons to doing it this way. Any ideas or sources of info would be appreciated.

 

http://palpatine.infinitedata.net/~jweber/exhaust_manifold.jpg

 

-jeff

[Lustalbert]

depends on your underhood clearances. A tube would be etter to keep the exhaust gasses moving faster and pull some heat away from the engine. HOwever, if you dont have enough room, a box or"log" would work. Also, with a tube, there is more distance for the shock wave or puse of your exhaust to travel so it dosent feed back into the other cylnders.

[Dave1647545494]

try to use tubes it keeps the port velocity up (scavenges better) an open manifold while ok for simply directing the exhaust into a pipe creates an area of intermintent high and low pressure depending on which cylinders are firing. in english the turbo will(or should) spool faster with tube headers vs a manifold becasue it directs the exhaust directly to the turbo without mixing with the pulses from the other cylinders

[SupraGlue]

The cast log style manifold is often just fine, and has advantages and disadvantages. Tubular manifolds can and do crack (just ask Kenny), but a cast manifold is unlikely to. Also, the shorter path and less heat loss before getting to the turbo tends to make up for the less efficient design in terms of exhaust pulse management.

 

To put some real world data to this, the aftermarket cast manifold for Supras has been dynoed to 600rwhp, and in back-to-back comparsions has spooled the turbo ~300 rpm sooner than stainless headers. The important issue is to have large enough ports to match your head ports, and to have a large enough internal volume with a cast manifold. Most stock manifolds adapted to turbo use will not have enough internal volume to flow efficiently at higher boost. They will also be heavier than tubular headers, and have a quieter exhaust note.

 

Also, keep in mind that any tubular headers for a turbo car must be made of stainless steel. Mild steel will not last long in this application. Expect to spend $500 or more in getting stainless headers fabricated. One can also fabricate a simple header from cast mild steel weld-els (pretty old school), which have the benefits of both cast manifolds in terms of durability, and tubular headers in terms of exhaust pulse management and flow. Such a header will also be VERY heavy and take up a lot of space, but be next to indestructible. Weld ells are also a whole lot cheaper than 304 stainless steel.

 

Cast manifolds lack any pimp factor whatsoever, though. Zero pimping with cast for sure.

 

My first choice for a budget (but not ghetto) turbo project would be to find a cast turbo manifold designed for the car in question. Used is fine. This is due primarily to durability and cost issues. Second choice would either be to fabricate a header using weld ells, or fabricating (or purchasing) one made of 304 stainless. My last choice would be adapting a stock cast manifold, and I would only do that if my boost and power goals were fairly low, if I ported the heck out of it, and it was kind of a junkyard turbo project. That's just my opinion.

 

Hope that there's some useful information in there somewhere. smile.gif