Lekman
Lekman som man är så sa begreppet fullängdsgrenrör mig ingenting annat än att det var något jag borde känna till. Finns det korta grenrör? och vad är skillnaden? Vem vet, kanske Göran eller någon annan mentor redan har gjort en beskrivning av detta, men jag har inte hittat någon sådan tråd än. Men jag fann följande på
www.fullsizechevy.com som jag kopierade.
"Shorty headers will give you gains in hp in the higher rpm scale due to their short primary tubes, but will do less for torque production except for the gains found by removing the stock exhaust manifolds.
Longtubes will give you gains in low rpm torque due to their longer primary tubes thus allowing for better scavenging at low rpm. These gains will be over and above the gains normally associated by removing the restrictions of the stock exhaust manifolds.
You can raise or lower the rpm at which either header designs torque or power curve starts or ends by changing primary tube diameter and length as well as collector diameter and length. Obviously less can be done with a shorty header in terms of tuning ability.
on my Vortec 350 truck, a set of 1 5/8" primary and 2 1/2" collector headers markedly bolstered my low rpm torque, as well as improving the hp all around. The engine displacement and header pipe size, promote high exhaust velocities at relativley low rpms. This complimented my stock high torque camshaft, and relatively high vehicle weight. If I installed a header with a 1 7/8" primary and 3" collector tubing diameter on my same Vortec 350 and used the same stock cam in my 4000 lb truck, low rpm torque would suffer. This is because at low rpm, the larger header pipe will cause exhaust velocity to be low. I would have a cam setup for low rpm torque with headers designed for an elevated rpm level. If I installed the same large tube headers, with a racing cam, low rpm exhaust velocities would still be low. But as rpms increased both the headersand cam would start to work together giving strong mid rpm torque and high rpm power. As long as the longtube header will physically fit, its dimensions can be manipulated to outperform a shorty style header.
Shorty style headers more often are emissions compliant because with a shorty style header, the catalytic converter position will not be disturbed. The same cannot be said for all long tube headers. The EPA frowns on the catalytic converters are messed with as it MAY affect emissions. Shorty style headers are not used in racing because due to their short primary tube length, the tuning effects of the header are minimal.
If you select a proper sized long tube header for your vehicle, thats performance is optimized for the rpm that the engine will be used in, a phenomenon called scavenging will occur. Scavenging is where the momentum of exhaust pulses travelling down the primary tube of a header will actually PULL the exhaust pulse behind it, out of the combustion chamber, rather than the piston PUSHING it out. This ensures that a fresh air/fuel charge is burned in the chamber and it is not contaminated by any residual exhaust gas. If camshaft selection is NOT correct, scavenging can actually pull part of the next fresh air/fuel charge out of the chamber before the exhaust valve fully closes.
Exhaust tuning can be compared to intake tuning, except that the volume of gasses will always be higher in the exhaust side than the intake side due to the heating of the gasses through combustion.
on the intake side, short intake runners promote high rpm power(LT1/4 4" runners) whereas a long runner promotes low rpm torque(L98 TPI 21" runners). Having a setup that is somewhere in the is often the best for a performance street vehicle (LS1 14" runners), and you will get a nice balance of power and torque. Obviously this is an oversimplification of what an engine needs to make a nice balance of power and torque, there are MANY more factors which influence power and torque production.
Installing an H-pipe or X-pipe just after the header collectors can bolster low rpm torque by 15-30 lb/ft and NOT affect upper rpm power whatsoever.
My advice, if you can fit the longtube header into your setup, and wallet then that is what you should install. But sometimes longtubes just dont fit the bill, in this case shorties are better than stock cast iron exhaust manifolds."
http://www.fullsizechevy.com/showthread.php?218838-what-the-diffrence- . . . .
Peo.[/quote]
