Exhaust manifold design.

Competition engines and ancillaries - general discussion
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Joined: July 19th, 2006, 6:07 pm
Location: Crawley, West Sussex

Exhaust manifold design.

Post by cantfindausername » August 17th, 2006, 2:46 pm

Just thought it would be good to get a manifold design thread going to see what peoples thought and ideas are on them.

Obviously the application will determine the design but maybe we can discuss both in here?

I have heard that short straight runners are good for turbo applications as this gives the exhaust gases a quicker/easier route to go through from exiting the cylinder and entering the turbo.

We have links to a few pics in another thread, so I will copy them in later unless someone beats me too it.

This is a link to the man I have bought a manifold from. I am going for a "Top Mount Ram Horn" design with "Twin Scroll Wastegate".

However, I am having massive trouble getting him to chase UPS to get it delivered :x

I'm sure you'll agree that the work looks amazing! Just a shame I can't clarify :cry:


Guy Croft
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Post by Guy Croft » August 17th, 2006, 3:34 pm

Leaving tech things for a moment I just want to say that is some of the finest non F1 exhaust fabrication I've ever seen. Almost as good as JMC Power Automotive in Cyprus.
Thanks for publishing the link.


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Joined: July 19th, 2006, 6:07 pm
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Post by cantfindausername » August 17th, 2006, 3:43 pm

I'm sure you'll understand why I'm so frustrated at not recieving it.

I know that the design I've gone for isn't the ideal one for a turbo, but tie this in with the ceramic coating and it should be functional as well as awesome looking :D

If only I could get it.... :x


Post by Evodelta » August 17th, 2006, 3:57 pm


Many SS turbo manifolds fail (crack) due to poor design, SS expands a heck of a lot (I've stood and watched tail pipes contract back under the bumper after a hard used car is cooling down) so this must be catered for. Things like slots in the flange which attaches to the head and elongated stud holes are good ideas. Also, the flanges should be of 10mm min thickness and a good support for the turbo is a must. Other areas of design to look out for are equal length tubes and a pyramid collector, this blends the four tubes in gently before they hit the turbo.

Try to make contact with some customers of a fabricator before buying to see how the product has faired under duress, things on websites can often look very good but don't always perform in reality.

Internal tube diameter is also of importance, reckon on 1.375 - 1.75" on a two litre (note the spelling Mr Croft :roll: ) engine, the bigger the dia' the longer the spool up time for the turbo but better for high rpm power.

Hope this helps as a basic introduction and may I recommend a very good book which you must read: "Forced Induction Performance Tuning" by A G Bell, another one, although not as good is Corky Bells 'Maximum Boost'
Although It's about time somebody English wrote a modern guide on Turbocharged and supercharged engines......


Posts: 306
Joined: July 19th, 2006, 6:07 pm
Location: Crawley, West Sussex

Post by cantfindausername » August 17th, 2006, 4:09 pm

yes I do plan on making up a brace for the turbo to attach it to the head, not via the manifold.

I like the slots in the flange idea, I've not heard this one before on any of the many many manifold threads I seen!

I do have one book at home about turbo chargers, can't think of it off hand. Will dig it back out when I get home later.

As far as I'm aware, the manifold I've gone for is an equal length manifold, and will also have the pyramid you speak of. However, I have not yet seen pictures of the actual manifold :(

It was a rushed purchase as I wanted to get on the list, and I've gone for the same spec as a friend in the netherlands who is building a near identical engine to me.

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Post by Walezy » August 18th, 2006, 3:05 pm

Does anyone have any suggestions about exhaust manifold for 2.0l 16v TC with 4 x 44mm slide plate throttle body, 14,7cm long inlet manifold(modified Fiat coupe manifold)?

Ported head pistons from 1,8l engine (a bit higher CR).
Cams for now are standard but it will change soon.
For now I have 170HP at 6200rpm and 195Nm at 5200rpm.

What kind of ex manifold should I use, 4-1 or 4-2-1?

I would like to get about 200-210HP from the engine at about 7000rpm(of course I will need to change pistons to forged).

The best would be to know the diameter and length of the pipes. I have seen Ford Escort with BDA engine Gp.4 (owner claimed 230HP) that had very large diameter primaries (much more than 38mm) that is why I wonder if it will help in Fiat engine.

As for the cams for that engine I will ask in other post.

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