Tri y Headers?
01-17-2009, 04:01 PM
#2
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Join Date: Apr 2008
Posts: 504
Not necessarly
It has been my experience that the appropriate application for that pulse sequence will have an exhaust port that is too small relative to the intake port capability, say exhaust flow 70% or less of the intake. When you are unable to sht, you can not eat. Some circle track engines often find power with them due to limitations that are built in to the exhaust port they may have to run. When the exhaust pulse is increased at lower RPM applications it can help scavenge more spent gas which allows a greater intake charge to get into the chamber. Now if you have a good balanced head say with an exhaust port that flows 80% of the intake, this headder design can and will cause more of the incoming charge to be drawn into the exhaust or over scavenge. This will cause the exhaust to run hot maybe red hot and leave the combustion chamber with less trapped incoming charge. The best way to describe those unconventional pulse waves is that they are a crutch for a built in problem in the exhaust port by intent or accident. If your cam and exhaust port were not selected with these pipes in mind don't use them. They are very often misapplied and often never known by the user. This is my experience from years of welding headders. A step headder can be a hand bone too if the step is to close to the head. But that was not your question. I hope this info helps you make the best decision for you race program.
01-28-2009, 04:39 AM
#4
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Step primarys
The Step design headder extends the useful horsepower band higher than the band will be with a single diameter primary. This step magnifies the exhaust pulse going back to the exhaust valve from the collector to enhance the scavenging effect at higher RPM's. However like everything in physics there are side effects this causes at lower RPM,s. I use this style on engines that spend most of there time above the peak horsepower RPM. Drag racing engines often and circle track on longer tracks will benefit by extending the peak horsepower RPM 3 to 4 hundred higher. The bottom end will often be sour below sometimes 4 thousand RPM under full load condition. Where folks often go wrong is the step is too close to the head, which causes the sour rpm to be higher than your engine likes or can deal with. The step or steps need to be arrived at by the predicted exhaust velosity for the engine and cam profile and vehicle weight. The heavy car will not like a step unless the engine can rev freely to the tuned point. A light dragster with a big powerful engine will like a step closer relative to the head than a heavier car will. The converter or load will need to be higher in the rpm band to take advantage of this set up. It is not as simple as just stepping the primary one size larger, X dimension from the exhaust valve. Lots of factors must be taken in to account for every application. Not every headder builder will bother to educate there customers on the physics that are involved in a great set of working pipes and some don't even know them selves. They are just fabricators and could care less how there product works or doesn't. Most buyers are pleased if the pipes fit there chassis and if they look cool on there engine. The performance of the pipes are seldom checked and mostly presumed by the less knowledgeable customer's of the big well known builders. The cam spec's, rocker ratio, converter stall or trans gear ratio, weight of race car, type of racing, engine asperation, and fuel type are just some of the major factors that MUST be evaluated to estimate where a step might work best in any given race engine. This is why step pipes are a hand bone for second hand users. What are the odds that the step is in the best location for your engine? NOT GOOD I assure you. I have fabricated headders after the better known builders were paid to on some customers race cars and have fixed tuning problems that were built into the pipes from malicious step locations. Plagiarism is the ultimate sin in expensive racing engines and headders. If you don't know how to calculate the appropriate step location for your engine, don't do it, you WILL most likely loose torque, kill bottom end horsepower and tune-ability over a single diameter primary.
Good luck in 09
Good luck in 09
01-30-2009, 04:13 AM
#6
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Posts: 504
1 7/8" may be best in my opinion of the two choices for your application at or near 32" to 35"long . If the 1 3/4" pipes are real close to 30" they will perform very well in your application if you like torque and mid range horsepower. You have a lot of engine and RPM you plan to run, it will likely enjoy the shorter length of the two. Do not go shorter than 30", short is 30" long is 37" for your reference. The 1 7/8" will run better in the upper rpm range. Lots of racers in your sport change the pipes to suit the track they race on. Bigger for longer straight aways and shorter or smaller for shorter tracks.
