What is the best choice of header primary tube inside diameter and length for my application:3300 to 3500 lb,462 ci 12 to 13:1 comp.,TE heads,4500 intake,nitrous. Should I go after 2 1/4 primary 2 1/8..will 2" kill it? Rick went into tube length in another post..and I want to go into it further..thanks...fish
I don't think that you'd "kill it" with 2 1/8 or 2 1/4. Remember that nitrous is being rammed in, so the bigger the tubes, the easier it is to get it out. On my 470 nitrous motor, I had custom headers made, 2 1/8 to 2 1/4 step, and a 4 inch collector. Good luck Fish. Gary G.
Fish depending on your exhaust port 2-1/8 is the smallest I would go.2-1/4 would be best.On my heads a 2-1/8 killed exhaust flow by 30 cfm but my exh ports are quit big.The motor may not be as strong on hp alone but when you hit the can it will fly.As for length I would say 26-34 inches You can use fomulas but when it all comes down it's a compromise with a stock frame you kinda have to go with what will fit.The long header tube will make more torque(do we need any more on a 10 wide) shorter tubes favor higher rpm hp.I like to keep the header as short as I can make it.
More thoughts on it all.... Big tubes.....Short tubes...... On tube size, I don't think you can go wrong with 2 1/4" with a nitrous 462. Even though it may hurt some torque on motor due to the loss in velocity, you will pick up that lost velocity with the spray and pick up extra HP at higher rpm where the nitrous motors tend to lay down at. It will help the peak hp from shifting as far below the Naturally Aspirated peak. Basically you are designing the header to make the motor work on nitrous instead of naturally aspirated and it will help keep the exhaust duration from needing to be excessive. The more you design the motor around nitrous, the less you have to make it up with cam duartion split and the more effective the nitrous will be. On length, if you can't get 2 1/4, at least make sure to get you tube lengths short. YOu want to do what you can to shift the rpm band up and shortening the tube will help shift the power above peak torque. Tube size/diameter determines at what rpm peak torque is looking to occur and length shifts the power above and below peak torque. Yes, 2" will kill it unless you cut the tube length in half. Just as a note, I don't believe is excessively sized cams if you building the header for nitrous. Your motor is a combination, not the sum of one part or idea. If you build the header for nitrous then don't put a cam in that works with a restrictive exhaust/Naturally aspirated. Also look at what you heads flow in comparison to tube size you don't want to oversize the header too far over what the exhaust port will flow. You will want to shorten the tube length over going larger in header size if the head won't support the flow. This is mainly a consideration for guys running stg 1 style heads. On compression, I would stay as close to 12.0 as possible. YOu will make all the cylinder pressure you need with nitrous. Plus it will be easier to tune and less sensative on larger shots of nitrous where bad things tend to happen. On a max effort nitrous setup, I have yet to see or hear someone go faster from higher compression. Unless it was needed to make up for lost cylinder pressure from cam timing. Don't read into all this too much or think you have to change everything just for nitrous. You can spray a naturally aspirated setup just fine, but if you are looking for ever last HP for a serious nitrous combination, want to keep your rpm band in the operating range, don't want to deal with too much torque, and are building something from scatch then it is something to consider. :TU:
Thanks Bad,10 and Rick... To answer Rick,yes I am building for nitrous,we'll see how far the pistons sit in the bore, but I bought the 12:1 wisecos,but I can always get a thicker head gasket. I plan on o-ringing the block for copper head gaskets anyway.I will have to get the heads and intake here and get em flowed,they are ported with a ported intake so i'm hoping or the best.I really dont mind spending the money in the right places,and if I have to,I may get get my machine shop to work em over a little more if they need it....thanks guys for the encouragement and the knowledge...fish
Copper Head gaskets.. SCE makes a Titan copper gasket that has the rubber beads around the water ports so you no langer need to mess with sealants and possible leaks. :TU:
You bet ya it will. Interesting post just some added info. I'm not running nitrous. On the dyno with the TE heads the engine dynoed about 750 hp. We were using hooker 2" headers. On the very next pull the only change we made was to install 2 1/8 " headers (custom made) the dyno numbers on that next pull jumped 29.8 hp! Gained 30 hp on just a larger primary tube size and no other changes were made. Pulls after that were were all consistantly 778-780 HP so it was no freak, it was a real hp gain! No doubt with what you are doing that either a 2 1/4 or 2 1/8 will help. I wish I had a set of 2 1/4 to borrow at that time to test and compare the results. Best of luck and keep us posted.
thanks for the help Martinez cinched it...and I think 2 1/4 will be the deal on the gas. I'm gonna be patient and find some used...fish
