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Log manifolds, Perrently not so crap

CAPT_BLOTTO said:
It's still a consideration. Maybe also the performance vs. cost benefits.
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we are all just shooting crap here about this. Without talking to the engineering and development departments at McL we all have no idea.

insert p1 engine (top of the line engine)

McLaren-MP4-12C-engine-left-front-three-quarter.jpg
 
If they can hit the targets they wanted with a cast log manifold why go to the expense of a tubular one? Also this engine will have to pass 500 hour durability which a tubular one may struggle to do.
 
84 Blue 240 said:
Another consideration for them is Cat lightoff. Headers don't perform as well on this.
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Cold (cast iron) manifolds suck up more heat than cold headers. That's why the heat shrouds for EFE are so much larger on manifolds. For the same reason, cat lightoff is faster on a thin header the same length as a cast manifold. Only when you move the cat twice as far from the engine does it become an issue.
 
mikep said:
Cold (cast iron) manifolds suck up more heat than cold headers. That's why the heat shrouds for EFE are so much larger on manifolds. For the same reason, cat lightoff is faster on a thin header the same length as a cast manifold. Only when you move the cat twice as far from the engine does it become an issue.
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That is absolutely true (as you note) when the header is the same length as the cast manifold. But look at this cast manifold and then compare to any header worth a damn. It's not really apples to applies.
 
Also a lot of modern engines with a tubular style maniflod are twin skin manifolds for the reasons described above. This I should imagine will drive up costs even more.
 
7mgtesup said:
Also a lot of modern engines with a tubular style maniflod are twin skin manifolds for the reasons described above. This I should imagine will drive up costs even more.
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True. I know the old LS7s and Gen IV/V Viper motors have them. They're pretty amazing pieces of manufacturing.
 
The first turbo setup I built was a log setup. It seemed to work really well.



I may build a nice 4-2 -1 style header for my 16 Valve build. I really want to keep the weight down. Something similar to this.

TurboManifold421.jpg
 
One of the problems with log manifolds is that they seemingly never have runners of equal lengths and very good flow figures, but these problems are not really that prominent unless you are close to the engine max potential. Long overlap cams, low flow narrow bend manifolds and narrow turbo exhaust housings create alot of pressure in the manifold. This pressure increases with boost obviously and when it reaches a certain point the exhaust pressure is greater than the intake pressure, causing the engine to take in exhausts instead of fuel air mixture (on greater overlap camshafts). On an engine boosting about 1,5 bars this is manageable and doesn't pose a big threat. Also with engines not even close to their maximum potential it's even lesser of a problem.

For example orginal 8v turbo manifolds on 1,5 bar boost create a exhaust pressure up to 2,5 bars which is pretty bad. Something close to 0,3 bar over boost pressure is easier to handle and normally what you see on a race-engine with a good manifold. Overlap won't matter as much then.
 
The cost-benefit of using a cast header far outweighs stainless for 99% of applications. I will take less horsepower if it means I'm not welding cracks and replacing warped headers. And if we're maximizing bang-for-buck with a certain budget, I would rather put that money toward engine work that doesn't need a stainless welded header to achieve my goals.

But I won't deny they're a work of art:

http://www.photo.gp/2012/MotoGP-2012-17-Phillip-Island/i-rsxrbbc/A
http://www.photo.gp/2013/MotoGP-2013-05-Mugello/i-sSbSmVw/A
http://www.photo.gp/2012/MotoGP-2012-18-Valencia/i-vGC4LBj/A
 
It does look out of place on a McLaren. After all they were the company that bragged that no expense was spared even using gold to insulate the carbon fiber panels from engine heat.
 
I'm just going to throw out there that as a gas expands it cools and loses energy/pressure, Boyles gas law I believe. I'm just saying, bigger isn't always better sometimes just right is what's best.
 
Mylesofsmyles said:
Who said log manifolds are crap??
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People that don't know any better. There's a 'just right' for every application, as is there a too much, or too little. While log manifolds absorb heat - they're also a poorer conductor of heat, and therefore will retain more heat than a tubular manifold will. More heat = more enthalpy = quicker spool. Also no need to wrap a log manifold. I'd also guess that the exhaust pulse tuning on the McLaren log manifold is 'just right' and equal length wouldn't be enough of an improvement to be noticeable.
 
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