header or manifold

Mad Fabrication

Mad Fabrication

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May 12, 2013
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At what point is a header better then a exhaust manifold? Or is the manifold better. I see some who where running header go back to a manifold why?
 
With a runner that is to big the velocity slows down right? Changing the way the turbo will respond to rpm and fuel? Would a properly sized header run any better then a manifold? I was just wondering you see high end gas and alky motors with header making huge power and some diesels. Read a article about a back to bsck test of a turbo manifold vers header on a gas power car and the header made more power. Wondering why not as popular in diesel.
 
Agree with Kjp. We're all too chicken to build a set with 1.25" tube. I have a hunch they need to be that, or maybe smaller.
 
motorwood said:
Agree with Kjp. We're all too chicken to build a set with 1.25" tube. I have a hunch they need to be that, or maybe smaller.
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Who are you calling chicken ive already built one with smaller diameter tubing. 1.625 id is great for 4500krpm+ but not needed for a street truck.
 
If you want that info you need to spend the money and time and try it yourself.
 
We built a header for a 05 cr with a s475 single. Had no bottom end what so ever but was an animal after 3500rpms. Lets just say its in the scrap pile now haha. We all run stainless diesels manifolds.
 
Thank you r-rated diesel for your info. Answered my question. Wasn't trying to get any bodys spec or if if made 50hp more. Just wsnted to know if better or not and why.
 
Simply posting headers dont work doesnt show the whole picture. Primary size makes a huge difference. Thats why i said try it yourself because you will get nothing but poor info on here.
 
I an going to take a educated guess from what I have read that primary tube size and length plus collector design all play a part in how a turbo is going to work. A smaller diameter and shorter primary would work better for a low to mid range set up. Would keep the velocity up from the smaller diameter and with a shorter runner have less area to fill before will build pressure behind the wheel to drive it harder. With a larger diameter primary will flow more air. So with a larger diameter and longer primary can get a better flow when you are running higher rpms and you are looking to move more air so it doesn't chock off or hinder new incoming air. I feel a header as to be built for your set up to work properly.
 
With turbocharger you want as short tubing as possible before turbine. That is because of backpulses from turbinehousing. NA manifold makes negative pulse that suck out gases from cylinder when timed right, but turbocharger is like end of 2-stroke exhaust chamber and makes positive pulse which pushes gases back into cylinder. When the tubes are short enough, the pulse reaches cylinder when the piston is still quite far away from TDC and at that point negative effect is minimal. If you make equal length manifold with tube length calculated like optimised for NA engine, you get positive pulse just the worst time, when piston is close to TDC and intake and exhaust valves open at the same time.

Tube diameter is calculated from wanted rpm range, nothing else.

So, log type manifold is always the best for turbo engine, equal length header the worst.
 
Tube diameter is calculated by rpm range and cubic in of a cylinder. The same size primary doesn't work on every engine for the same power band. I understand the length of a primary and the collector are very important in a na motor. Scavenging there are motors that are 100 plus percent valumetric efficiencet because of there set up and they are na motor. I see what you are saying about the back pulse too. What I dont understand is why a high output gas or alky motor make more power with a tuned turbo header then with a log manifold.
 
Mad Fabrication said:
What I dont understand is why a high output gas or alky motor make more power with a tuned turbo header then with a log manifold.
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They don't, they just don't know what they are doing.

I have even seen a test about NA prostock engine with short stubs ending to common log and the power difference to hitech manifold was maybe 15 horsepower, so exhaust manifold is not so important at all. NA Formula one engines had exhaust manifolds optimised for aerodynamics, not power because aerodynamics was more important than a couple of horsepower from 100% optimal manifold.

Trying to get the strongest pulse, highest velocity and heat to turbine is most important when designing turbo manifold.
 
Leiffi said:
They don't, they just don't know what they are doing.

I have even seen a test about NA prostock engine with short stubs ending to common log and the power difference to hitech manifold was maybe 15 horsepower, so exhaust manifold is not so important at all. NA Formula one engines had exhaust manifolds optimised for aerodynamics, not power because aerodynamics was more important than a couple of horsepower from 100% optimal manifold.

Trying to get the strongest pulse, highest velocity and heat to turbine is most important when designing turbo manifold.
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I'm more of a drag racer that plays with gas engines than I am a diesel guy, I'm okay with that.
Did I just read you saying that the type of collector on a header found on something like a 500" pro stock mill making around 1800+ doesn't really matter?
I'll disagree, myself and many engine builders with years of dyno experience would argue that the collector and how the gasses are merged is more important than primary diameter or length. I could go on here but it's probably wasted effort.
On the F1 car, I think the level of heat created from hours of extreme exhaust temp is more of a reason for manifolds than aerodynamics. Why were the craftsman truck series 364" motors 9:1 but ran race fuel?? High temperatures from hours of WOT condition and heat build up.
 
Grudgeguy said:
I'm more of a drag racer that plays with gas engines than I am a diesel guy, I'm okay with that.
Did I just read you saying that the type of collector on a header found on something like a 500" pro stock mill making around 1800+ doesn't really matter?
I'll disagree, myself and many engine builders with years of dyno experience would argue that the collector and how the gasses are merged is more important than primary diameter or length. I could go on here but it's probably wasted effort.
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Those stubs in the picture lost maximum of 18 hp at 9800 rpm. A GM PS engine that could qualify at the time: he said.

So, pipe diameter is the most important, length not important at all if it's short enough to cancel out all pulse tuning. Well flowing collector is important of course if it is used.

Using compact manifold with turbocharger makes it possible to use larger turbine side which makes more power than any exhaust pulse tuning would if it was even possible.

This 1300cc Busa used compact manifold principle, they said it would never spool that S400 if they used larger volume manifold. I heard they later did 800 hp so it must be working. [ame="http://www.youtube.com/watch?v=_oU3gTR8ebY"]http://www.youtube.com/watch?v=_oU3gTR8ebY[/ame]
 

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