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Exhaust Manifold designs and calculations

Discussion in 'Forced Induction' started by Mafix, Jun 8, 2011.

  1. Mafix

    Mafix Owner Staff Member Administrator Donated!

    Materials
    Cast - Is simply the best material when weight is not a factor. It lasts the longest, can be designed to fit any need, can be extremely compact, and it doesn't have the "flex" that other materials do.

    Mild Steel/302 Stainless - you should never have a turbo manifold made out of this.

    305/304 Stainless - This is the cheaper yet lighter stainless. depending on the application this may be the material of choice. This material flexs a lot and is more prone to cracking than 321. this can come in various thicknesses.

    321 Stainless - this is a very expensive and heavy stainless steel. it lasts the longest and doesn't flex as much as 304/305 stainless. the reason it isn't used nearly as much is because of the weight. typically these manifolds weight close to a cast counterpart.

    Runner Design
    Log - log designs work fine for close compartments. as i've discovered they suck at controlling boost at high rpm/load and high boost. log manifolds that are matched to a turbo yield better spool time.

    Tubular - believe it or not the stock toyota manifolds are tubular. just cast. tubular manifold work great and improve effefiency.

    Even Length Tubular - these style manifolds are even better than regular tubular manifolds. they to cost you in spool time due to heat loss but you gain better control over boost and improved effeciency.

    Uneven Length Tubular - or "tuned" as it would be. these will work the best for effeciency and control. these also must be harmonically tuned for each engine. and typically are horribly expensive.

    Ram Horn Tubular - the ram horm manifolds take tuning out of the process and focus more on reducing lag. these manifolds are made to get the turbo spinning as fast as possible. corerctly done these have proven to be one of the top 2.

    Wastegate Placement
    Runner - never have a manifold with a wastegate placed on the runner.

    Collector - typically used in logs. this is an OK design.

    Y pipe - this is the best design as it allows maximum flow through both the wastegate and turbo.

    Internal (turbo) - great for saving space.

    Runner Diameter

    Small - small diameter runners tend to yield better spool time but reduced effeciency and reduced top end power.

    Correct - or "tuned". these will give the best all around performance.

    Large - these are made for top end power.

    Runner Length

    Short - spools the turbo faster. bad for top end.

    Medium - best for an average.

    Long - less spool but greater top end.
     

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