Log Vs Tuned Mani

[JayRome]

was researching for a new manifold design and came across this.... interesting read but pritty much dyno sheet says it all.. (its an old post though)

http://www.sr20forum.com/745652-post1.html

 

[GSR]

i would love to see boost graph and what happened to it between 4750 and 5000rpm..

 

[brisvr4]

Jesus, that log thing barely qualifies as a manifold, holy turbulence! :lol:

 

[evopwr]

Shortest runner length = faster spool
Equal length = top-end power & torque.

complies with basic thermodynamic laws

A good test to conduct would be tuned equal length manifold VS tuned split-pulse manifold

 

[TMAK]

A good test to conduct would be tuned equal length manifold VS tuned split-pulse manifold

Agreed! that would be very interesting to read...

 

[D3bb4]

boy, i think you need to speak to an engineer.

Exhaust pulses in log manifold would interfere with each other at high rpm with that design, to the extent that the direction it's pointing to is completely wrong!!!!!!!!! it's going horizontally, not vertically!!!!! Would be less lag, but top end would screw itself over and then some.

Is gas/fluid dynamics, not thermodynamics.

Split pulse will get a better spool than an equal runner length manifold, won't have the top end though.

 

[JayRome]

...
Split pulse will get a better spool than an equal runner length manifold, won't have the top end though.

just depends on the size of the rear end on the turbo, but then gain top end loose bottom end.... and vise versa...

 

[evopwr]

boy, i think you need to speak to an engineer.

Exhaust pulses in log manifold would interfere with each other at high rpm with that design, to the extent that the direction it's pointing to is completely wrong!!!!!!!!! it's going horizontally, not vertically!!!!! Would be less lag, but top end would screw itself over and then some.

Is gas/fluid dynamics, not thermodynamics.

Split pulse will get a better spool than an equal runner length manifold, won't have the top end though.

Your paragraph doesn't make much sense, apart from the 'log design will (produce) less lag but (loss in top end)' which is what the test proves.

Last time I checked, Thermodynamics covers gas & fluid dynamics. Unless Cengel & Turner had it wrong for the last 20 odd years :lol:

 

[LWNSLW]

ive seen a log mani on a eb falcon 6 banger it worked awsome BUT it had 6 pots for low down and it also had a massive turbo. also it had more room under the bonnet too. when it hits 3000 fark me it hits hard and pulls to 7000 all day...

 

[iluszn]

The log design itself isnt great, perhaps with a little refinement it would work better ie; putting output of cylinders 1 and 4 not going straight into the outputs of cylinders 2 and 3 on the manifold. Perhaps having them angled in to flow inline with them would help. but pushing exhuast gasses into the side of flowing gases is just silly. turbulence would be terrible.

 

[D3bb4]

Your paragraph doesn't make much sense, apart from the 'log design will (produce) less lag but (loss in top end)' which is what the test proves.

Last time I checked, Thermodynamics covers gas & fluid dynamics. Unless Cengel & Turner had it wrong for the last 20 odd years :lol:

Thermodynamics does not cover exhaust pulsations, and will not teach you how to design a decent exhaust manifold. I can recommend you a few books if you're interested.

The test is proving something that is commonly accepted/known. Split pulse manifolds have been around for a long time.

With that particular log manifold design, it's not so much turbulance that is the factor as much as the lack of directing the gasses. By having them horizontal, the pulses would clash and negate the exhaust gas velocity, (this part is thermodynamics)... the energy lost in the velocity would then produce excess heat in the manifold, and lower velocity gasses will pass through the turbocharger. Even stock manifolds are similar to a log design, but at least they run internal guides for the gasses to force them down through the turbo rather than together.