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Header design in Grassroots Motorsports article....


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I tried to follow as much as I could from that article.

By routing the exhaust the way he did, the exhaust backpressure was reduced so that the exhaust of 2 cylinders wouldn't mix. . . ?

The diameter and length of the tubes I get, but why do you need to bend them 180 degrees? Or is that in reference to the crank timing?

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180 headers are just like other headers, the tube length has to be right for them to be optimum. It's hard to say without dyno results, but I bet 40-50 hp is a little optimistic.

 

I wonder if he can get the pass side valve cover off?

 

That is a ton of work and some nice fab work. Is he a member here?

 

John

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Guest TeamNissan

I bet he can access the bolts by going from the rear under the tubes from 1+7 then slide the cover forward and up.

 

It is nice fab work but I really just don't like the rt at all. Looks how close it runs to the dizzy.

 

I too think 40-50hp is optimistic, VERY optimistic in fact. Still very nice though an I'm sure he is experiencing some nice gains besides hp and tq.

 

I hope he is a member here, I would love to hear that monster.

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180 headers are just like other headers, the tube length has to be right for them to be optimum. It's hard to say without dyno results, but I bet 40-50 hp is a little optimistic.

 

I was noticing this as well. In order for the 180º design to work as intended, ALL tubes must be the same length. In mid-engine cars, this is much easier to do than front engined cars because of the engine configuration. In the photo above, the tubes that are passed over to the opposite header bank appear to be longer than the rest of the tubes for that bank, which then changes the timing of the exhaust pulse relative to the other tubes in that bank.

 

I am attempting to attack the pulse timing issue using header tube length differences on my next set of headers, while keeping all left and right bank tubes grouped in a conventional sense. In other words, vary the tube lengths so that the pulses arrive at the collector in a more equally spaced timing rather than use the "equal length" method. It wont be perfect, but it should be an improvement.

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I have been gathering parts to build some 180 degree headers. Terry and I have an advantage because our motors are mounted using a front plate/ mid-plate. The advantage is that the entire under side of the engine is clear.

 

I plan to run the center two tubes from each side under the oil pan to the opposite side collector. By placing the collectors fairly far forward (about even with the starter), I believe that I can get equal length tubes. The tubes that cross under the pan will run parallel to each other in the space between the front and rear sumps of the oil pan. For ease of assembly, I plan to make the section of tubing that passes under the engine removable. The only real downside is that the tube may be a little long (36" -39).

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Intresting concept, although I have my doubts about the torque improvements he is guessing at. For me it would be more practical to just add more displacement to my engine to my engine and go from a 383 to 400 plus cubic inch engine.

 

I cringe having to work around those headers and the running the exhaust so close to the firewall. The interior heat will be nice and toasty.

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I was noticing this as well. In order for the 180º design to work as intended, ALL tubes must be the same length.

 

While that's an ideal goal in primiary pipe design, what's more important is to make sure the low pressure waves hit the exhaust valve when the valve starts to open during the overlap phase of the cam. Bends in the primary tubes slow down the wave so, theoretically, a shorter pipe with more bends would work the same as a longer pipe with fewer bends.

 

I am not smart enough to be able to calculate and build such a design so I try my best to make all the primaries the correct length, with as few bends as possible. But, if the packaging in the vehicle is such that unequal lengths are needed, you can still build an effective header with the above in mind while laying it out. It might take a few tries and a few tests on a dyno...

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