400i vs 412 Headers

blkprlz · Oct 29, 2012

I noticed that the 412 headers don't have the small pipe outlet at the bottom like the 400i, & that the 412 center section is only 2 units per bank instead of 3. I'm wondering if the small (balance) pipes were initially incorporated to relieve the back pressure from the 3 mid-section mufflers whereas the 412 mid section mufflers might possibly be more free flowing. Other than the small pipe port outlets at the base of the headers of the 400i, the 412 & 400i headers appear to be identical. I'm thinking the only reason parts catalogs show different part #'s for the 2 are because of the small pipe outlets. Oh, those small pipes in SS is a $600. option with Tubi, one I'd like to eliminate.
Thoughts anyone?

?? to Dave & Ken
Did you have your installer bolt a blanking plate to the small pipe outlet??
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180 Out · Oct 29, 2012

Somewhere along the line my California registered '83 400i had its six resonators (and the "horns") replaced with catalytic converters and a dual inlet-outlet muffler or resonator. The ports for the horns have plates welded over them.

A comment regarding exhaust system theory: when the exhaust pulse traveling in a header tube opens into a larger assembly -- like a header collector or a resonator -- the expansion of the exhaust gas creates a low pressure impulse which travels back up the header tube to the exhaust valve. At some point in the engine's rpm band, that low pressure pulse is going to arrive at an opened exhaust valve at the same time as the intake valve is also open. The low pressure pulse pulls the fuel-air mixture through the intake valve, adding to its velocity. After the exhaust valve closes the continuing higher velocity of the fuel-air mixture results in greater cylinder filling, and therefore more power. When the engine hits this rpm band we say that the engine has tuned. Another description you hear is that the engine comes on the cam.

Based on this phenomenon, my guess is that the Ferrari engineers found that the horns created some kind of "tuning" effect. If the horns open into a high volume chamber in the resonators, this would create the low pressure impulse that I described. Depending on where in the rpm band this pulse would be hitting the exhaust valve during valve overlap, the engineers could have been adding low end torque (which would be good in these heavy cars) or high end horsepower. With the 412 it may be that Ferrari engaged in cost engineering and decided the cost-benefit ratio wasn't there with the larger engine.

One other thing I have a $0.02 about is that exhaust systems do not create back pressure. If an exhaust is so restrictive that it is reducing the ability of the waste gases to escape the combustion chamber, in any way, then that is a problem. I think maybe people observe the better manners of an engine with header collectors, resonators, and mufflers, in comparison to an engine with straight zoomie headers, and conclude that the exhaust is adding beneficial back pressure. In fact the more complex exhaust system is adding the tuning effect during overlap.

blkprlz · Oct 29, 2012

180 Out said: ↑

Somewhere along the line my California registered '83 400i had its six resonators (and the "horns") replaced with catalytic converters and a dual inlet-outlet muffler or resonator. The ports for the horns have plates welded over them.
Click to expand...

Interesting. Probably took the easy way out because the cat isn't going to have the additional inlets to accept the balancing pipes, the cat replaced the 1st of the 3 mid-section mufflers, then fed to the original resonator at the rear.

180 Out said: ↑

A comment regarding exhaust system theory: when the exhaust pulse traveling in a header tube opens into a larger assembly -- like a header collector or a resonator -- the expansion of the exhaust gas creates a low pressure impulse which travels back up the header tube to the exhaust valve. At some point in the engine's rpm band, that low pressure pulse is going to arrive at an opened exhaust valve at the same time as the intake valve is also open. The low pressure pulse pulls the fuel-air mixture through the intake valve, adding to its velocity. After the exhaust valve closes the continuing higher velocity of the fuel-air mixture results in greater cylinder filling, and therefore more power. When the engine hits this rpm band we say that the engine has tuned. Another description you hear is that the engine comes on the cam.
Click to expand...

From what I understand, that requires a whole set of engineered calculations more than trial & error.

180 Out said: ↑

Based on this phenomenon, my guess is that the Ferrari engineers found that the horns created some kind of "tuning" effect. If the horns open into a high volume chamber in the resonators, this would create the low pressure impulse that I described. Depending on where in the rpm band this pulse would be hitting the exhaust valve during valve overlap, the engineers could have been adding low end torque (which would be good in these heavy cars) or high end horsepower. With the 412 it may be that Ferrari engaged in cost engineering and decided the cost-benefit ratio wasn't there with the larger engine.
Click to expand...

I'd say OK to that except the 412 finally achieved the 340 rated HP that the original 400 developed back in 1976 'thus fully redressing the retrograde steps taken with the advent of fuel injection' (to quote QV500), a full decade later. Remember, FI became big to help meet the demanding emissions requirements...everybody was scrambling to get their power back into their engines & I think these balancing pipes was a failed attempt.

SouthJersey400i · Oct 30, 2012

Bruce
Yes, the small pipe is blanked on my headers.

I read 180 Out's comments with interest. I think he is saying my straight pipes may be reducing power, at least at some RPM.
Ken

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