Making log manifolds

Think this will be the way to go with the turbo v6 miata.  

How do i size this stuff? My first thought was use black iron pipe futtings, in 1 1/4.

But, can i do better?

Maximum flow rate at the lowest pressure drop with the lowest volume.

How big are the ports? 

This is one of those situations where "doesn't break" outweighs almost everything else. 

Match the ports or round down to the nearest size.  Do it smoothly and you will be fine until mega HP and mega rpm.

The ports are d shaped. 

Why would it be bad to make a d shaped flange that then transition to a larger round tube?

Just find the smallest round tube that completely covers the port.

Logs are simple, effective, and package well. Plumbing pipe and fittings means welding cast iron. Can you do that effectively? Also, that black iron stuff adds up quickly. Header tube is as cheap as a craigslist set of rusty ol SBC headers. Cut the straights and bends out that you need. Think this, but cheap steel and straight runners.

The hardest part will be getting a flange. If the factory manifolds are fabricated steel, you can just cut off the runners and weld to that. If the factory manifolds are cast, you might need a flange machined. Find a friend with a mill. and make it out of 3/8" plate or whatever you find in the scrap yard. Use the factory manifold as a template to trace and get the bolt holes and general shape correct. 

Once you have a flange, position a straight piece of 2"ish exhaust tube parallel to it. Cut and notch the 3 runners out of some other scrap tube that's the same or larger diameter than the head port. Yes, mild steel exhaust tubing will work if you don't mind the rusty look. Repeat for the other side. Tack it together with the engine in the vehicle to check for clearance issues. 

Weld a 3-bolt or whatever flange to each of the 2 logs for ease of assembly. Then it's just like making a custom exhaust. Pie cuts (or bends if you can find them cheap), route it to the turbine flange. Once you have a turbo, you can find mild steel turbine flanges cheap on eBay. Same process as the head-flange-to-log, but only 2 tubes. For your application, probably put the flanges on the log end facing forward, with turbo between engine and radiator, just like what's pictured above.

In reply to minivan_racer :

They make it look as easy as i thought it would be 

In reply to maschinenbau :

I didn't see your response until now.

Very informative and helpful. Thanks!

Dumb tangential question: should the turbo be over or under the exhaust feeding it? Most time i see it above, but with this one ill need to find every inch of space. 

I think it's just a packaging/maintnence issue. It just needs to be high enough that the oil drains downhill back to the pan. 

Yeah it's just packaging and maintenance, there's no inherent performance difference to turbo vs. exhaust height. There are performance advantages to keeping all the boost and exhaust tubing between the turbo and engine short though.

In reply to Dusterbd13 :don’t use black iron  exhaust tubing will work unless you have water flowing through it in which case rethink everything  

The real pipe is cheap.

I think I have 1 log exhaust manifold here for that engine.  Fieros had them.  Google it.  I'll get s pic when I can.

I built one for my 7, and will be building one in a few weeks (hopefully) for the Europa.

In both cases, I'm using stainless weld els (Amazon, oddly enough, has a pretty good price for 1.5" schedule 40 Weld Els @ Amazon).  I used schedule 10 on the 7, will use 40 on the Europa.  Not sure how much I'll regret having to work with the thicker wall tube.  Note, if you use stainless, you need to backpurge to prevent oxidation that will ultimately crack.  Carbon steel doesn't require anything special - just make sure you put a good bevel on the tubes so you get full penetration if you chose something thick wall. 

All that being said: I have yet to test mine...

Search googles for "Steel Butt-Weld Pipe Fittings"

How does egr work with log manifolds and a turbo?

Pick it up after the turbo exhaust.

on the Chrysler’s they did it right across from the oxygen sensor in the outlet.

it was phased out on later cars once they improved the electronics and idle control.

unless you need it for local emissions, I’d drop it, personally.

In reply to Stefan :

Obd2 compliant and street legal is one of the design goals. To do so, i need to retain all the emissions equipment from the donor (04 Buick rendezvous) which has egr. So....

Thanks!

Dusterbd13 said:

In reply to Stefan :

Obd2 compliant and street legal is one of the design goals. To do so, i need to retain all the emissions equipment from the donor (04 Buick rendezvous) which has egr. So....

Thanks!

I may have an 01 impala harness and computer too that you’re taking with you whether you want it or not 

In reply to Patrick :

You say that like it's a bad thing. I'll take every 60 degree part you want to give me