Header design
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====Equal primary tube length==== | ====Equal primary tube length==== | ||
| − | =====Argument | + | =====Argument for equal primary tube length===== |
If the length of the primary is part of the tuning equation, how well does an engine run with different primary tube lengths? Try and jet that carburetor without pulling your hair out! Most of the commercially available headers out there have a large variance in tube length. Check out a set for a big block mopar in a B or E body for an example. The variance between longest and shortest tubes on these units can be as much as 16". | If the length of the primary is part of the tuning equation, how well does an engine run with different primary tube lengths? Try and jet that carburetor without pulling your hair out! Most of the commercially available headers out there have a large variance in tube length. Check out a set for a big block mopar in a B or E body for an example. The variance between longest and shortest tubes on these units can be as much as 16". | ||
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In the header photograph above, the short primary tube would scavenge at a higher RPM and the long primary tube would scavenge at a lower RPM for the respective cylinder. Therefore the cylinder with the short tube will be running lean at low RPM and the long tube cylinder will be running lean at the high RPM and would require different jetting and timing than the others. How do you do that with a standard kettering distributor and a simple carburetor? That's why equal length is important: so you can tune your car. | In the header photograph above, the short primary tube would scavenge at a higher RPM and the long primary tube would scavenge at a lower RPM for the respective cylinder. Therefore the cylinder with the short tube will be running lean at low RPM and the long tube cylinder will be running lean at the high RPM and would require different jetting and timing than the others. How do you do that with a standard kettering distributor and a simple carburetor? That's why equal length is important: so you can tune your car. | ||
| − | =====Argument | + | =====Argument against equal primary tube lengths===== |
Equal length headers are good for a certain part of the RPM range of a typical engine. However, when buying an equal length header you are left with the length the manufacturer wanted to use, NOT the correct length for the engine you are building. How do you know if its the right length? | Equal length headers are good for a certain part of the RPM range of a typical engine. However, when buying an equal length header you are left with the length the manufacturer wanted to use, NOT the correct length for the engine you are building. How do you know if its the right length? | ||
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==Collector== | ==Collector== | ||
| − | + | ===Argument for small collectors=== | |
| + | Ever see a car header with 1 5/8" primaries that had a 2 1/2" collector? Hooker makes them for trucks, but you don't see them for cars. But that is the optimum diameter for many street headers. Run that right into a 2 1/2" exhaust and you have a sweet system with lots of torque where you need it, and better fuel economy to boot. The collector should have a smooth, gentle shape from the four tube area down to the final diameter to keep things moving smoothly. | ||
| − | + | If you have very healthy big block, are running a blower, some turbo, or have a ton of nitrous, a 3" header may be appropriate. However, about the only street application of the monster 3" diameter pipe is when you count on having an engine with large gobs of top-end power. Otherwise, velocity is king in exhaust and 3" is probably too big to keep the speed of the gases up in the exhaust, and there goes that bottom end torque again! Many recommend either 2 1/4" or 2 1/2" diameter pipe for street V-8's. | |
| − | + | ===Justification for larger collectors=== | |
| + | A larger than needed exhaust won't necessarily "kill" your low end torque. Any respectable engine that makes low end power will continue to make low end power regardless of the sewer pipe exhaust. SOME power may be lost, yes. Usually not enough to make a difference on MOST V8 engines that are even close to being tuned right. Even a stock big block can make complete use of a 3" single exhaust system. Some even come with that size STOCK. | ||
| − | + | The majority of "lost" torque is now in the midrange of the engine's powerband. This will help with highway driving and towing, and provide better passing power when needed. This more powerful midrange will always make the low end seem less powerful, simply because the engine pulls better in a different part of the RPM range. Most people that "think" they lost low end power are simply noticing that the engine pulls better in a different way, even if NO low end power was ever lost. | |
| − | + | ==Summary of header design principles== | |
| − | + | #A "shortie" or a "block hugger" flows better than a stock manifold, and helps to produce more power than stock. However, it's sometimes not technically considered to be a header. However, they are also typically easier to install since they bolt up to the rest of the exhaust system. | |
| − | + | #Bigger diameter primary tubes are NOT better in most street applications. | |
| − | + | #Longer tubes are better for torque ''(this claim needs to be confirmed and expanded upon. Top end torque? Low end?)'' | |
| − | + | #Equal primary tube length is very important for tuning and power output, but not to the point of obsesing over it. A regular Tri Y or 4-1 header will work wonders over the stock manifolds. | |
| − | + | #A long and smooth collector is a good thing. | |
| − | + | #Just like header tube size, be reasonable with the size of your exhaust system. | |
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[[Category:Engine]] | [[Category:Engine]] | ||
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