Post by ajmopar on Apr 27, 2004 8:24:59 GMT -5
I just read the article in Mopar Action by Ricardo Ignorantbooger about the 496 inch eddy headed big block they built for their 69 runner. Nice piece, like everything Ray Barton builds. Anyway, Ricardo couldn't figure why when he jetted the carb to what should be optimum, he lost power. He said it seemed to him like some cylinders went lean and some went rich when he changed the jetting. Okay, here it comes, I am going to talk about header size, length and function.
He has a set of the TTI headers on the big block. These are nice quality, fit nicely in the car and have a nice shiny coating on them. They even have a nice bolt on exhaust system to go with them. Nice, shiny, bolt on. Unfortunately, and I seem to be the only one to notice, they are FAR from being equal length. They are as bad as the cheapie 1 3/4" headers you always see at the swap meets. I measured the cheapie jobs and found an 18" (!!!!!) descrepancy in tube length between the longest and shortest tubes. Now imagine trying to get an engine to function properly with one intake runner 18" longer than the others or one shorter than the others (I know, dual planes use different lengths, but it is done in a logical manner to spread torque production over a wider rev range).
"What the hell is this Loogan getting at?" you asked emphatically. Well, booger boy can't figure out why he has problems jetting his carb to make max power and he has VERY unequal primary tube lengths on his nice shiny photogenic headers.
Lets look at the theory of header function. A properly sized (diameter) and proper length tube connected to the exhaust side of a cylinder will reflect a sound wave back towards the cylinder, creating a scavenge. This scavenge, or suction, if you will, pulls the exhaust out of the cylinder instead of the piston pushing it out. As well, during the overlap period of the cam, the suction actually pulls the intake into the chamber, to a smaller degree. The main effect is that the cylinder gets filled better with air and fuel with less combustion resudue. This is increased volumetric efficiency. This is why a header with a SMALL enough tube to keep velocity up and LONG enough tubes to create the scavenge at a usable rpm makes big improvement in torque and thereby horsepower in a range of rpm that helps throw a car down the track or the street.
Now, getting to my point about e-booger's big block, do you think it would be difficult to tune an engine for max power that was making way more power in 6 cylinders than the other 2? Might the range overlap where you are leaning out the strong cylinders to get the others right or overrichening the weak cylinders to get the strong ones right?
I know on most street applications, fit and not burning plug wires is more of a consideration than proper function, and that's a tradeoff you have to weigh when choosing your parts. But if your goal is a crisply tuned, all the power you can get for your money engine, you need to take proper header design into account.
He has a set of the TTI headers on the big block. These are nice quality, fit nicely in the car and have a nice shiny coating on them. They even have a nice bolt on exhaust system to go with them. Nice, shiny, bolt on. Unfortunately, and I seem to be the only one to notice, they are FAR from being equal length. They are as bad as the cheapie 1 3/4" headers you always see at the swap meets. I measured the cheapie jobs and found an 18" (!!!!!) descrepancy in tube length between the longest and shortest tubes. Now imagine trying to get an engine to function properly with one intake runner 18" longer than the others or one shorter than the others (I know, dual planes use different lengths, but it is done in a logical manner to spread torque production over a wider rev range).
"What the hell is this Loogan getting at?" you asked emphatically. Well, booger boy can't figure out why he has problems jetting his carb to make max power and he has VERY unequal primary tube lengths on his nice shiny photogenic headers.
Lets look at the theory of header function. A properly sized (diameter) and proper length tube connected to the exhaust side of a cylinder will reflect a sound wave back towards the cylinder, creating a scavenge. This scavenge, or suction, if you will, pulls the exhaust out of the cylinder instead of the piston pushing it out. As well, during the overlap period of the cam, the suction actually pulls the intake into the chamber, to a smaller degree. The main effect is that the cylinder gets filled better with air and fuel with less combustion resudue. This is increased volumetric efficiency. This is why a header with a SMALL enough tube to keep velocity up and LONG enough tubes to create the scavenge at a usable rpm makes big improvement in torque and thereby horsepower in a range of rpm that helps throw a car down the track or the street.
Now, getting to my point about e-booger's big block, do you think it would be difficult to tune an engine for max power that was making way more power in 6 cylinders than the other 2? Might the range overlap where you are leaning out the strong cylinders to get the others right or overrichening the weak cylinders to get the strong ones right?
I know on most street applications, fit and not burning plug wires is more of a consideration than proper function, and that's a tradeoff you have to weigh when choosing your parts. But if your goal is a crisply tuned, all the power you can get for your money engine, you need to take proper header design into account.
