robert What is the date for street machine nats. Richard had to be having trouble if Russell won. Im pretty sure the mav runs low 11s in the 1/4. Did you get you car runnng yet. I would like to check it out.
Probably all depends on what you are gonna do with the car......I'll use my setup as an example. I'm running a 347 with Vic Jr. heads. I originally intended the motor to be a street/strip car and was running a hydraulic roller cam. The 1 5/8" primary headers were probably OK for that but not the best. I have since changed to a solid roller with over .600" lift so th e 1 5/8" headers were definitely not enough header. The 1 3/4" primary headers are, in my opinion still not big enough for my application but anything bigger would mean a custom set. I got a couple estimates on custom 1 7/8" step headers at about $1200 - $1500 . The 1 3/4" are kind of a "band-aid" fix and were in my budget. What would be nice is a set of Kooks custom headers but they only build stuff for mustangs and the most popular drag applications but they will build you a one off set for the right price!!
Step tube headers I wonder if if would be easier to take your 1 3/4 and after you clear the shock towers go up to a 1 7/8 tube. I dont know if it would be worth it or not.
I spoke with a local shop owner who told me he could make me 1-7/8" headers for $1k or less (buying the tubings/collectors from Jegs and Summit). But then, I'd have to add the cost of coating ($200+) and adapter plates (mo money). Again, all it takes is money! (which I seem to be depleting at an ever incresing rate lately). Please send your donations, old batteries, and used oil, to www.rick's in the poor hose.com.
. Someone fill me in here. I've heard all kinds of crap about exhaust and how it affects torque and horsepower. I think it's pretty common knowledge that small pipes and exhaust manifolds make it harder for air to flow out of the engine, which kills horsepower and torque because it limits the amount of fresh air an engine can suck in, plus you're reburning a portion of that exhaust if it can't get out of the manifolds and pipes fast enough. Where it gets interesting is this. I've heard people claim that if you take a car with straight headers and you take a car with headers and a good, free-flowing exhaust system, that the car with the exhaust system will have more torque than the one with straight headers. I have a hard time buying that. In theory, it seems like the biggest diameter, straightest, and shortest headers would produce the most power because exhaust would flow so easily through it. Hell, no exhaust at all would probably be even better, but you can't have that because your valves would probably get warped from the extreme temperature differences. Correct me if I'm wrong here, especially the racers out there who aren't concerned with steetability and everything that goes with that.
I have heard that same thing mavman....something about "back pressure" helps build torque? :confused: I am going to put a good exhaust on my car next year, after I make some open header passes with my new gear and headers, I know its a long way off, but I will have a answer next May 2004?
Re I know racers who have a full exhaust and the car is quicker than with open headers. There are some very good mufflers out there now. NOT FLOWMASTERS
I gained half a second by adding a 14" collector extension . Made them with two flange's and 3" bus pipe!
THe reason it works better is exhaust scavenging. A 4 into one open header will make more power at a higher rpm but will lose power down low. X pipes and H pipes will also help in scavenging. I never ran my car on open headers(Cracked the main webbing rebuild #1 Should have new motor in feb) I tuned mine to run with full exhaust on a chassis dyno. I made Headers and Fabricated exhaust for 7 years. It is a dying art I was one of the few young guys who wanted to learn so the old exhaust dogs in the shop taught me of course I had to show them how to use the scanner '
I am no physics major but here goes. Scavenging is a vacuum effect where the cylinder that is on the intake helps pull the exhaust from the cylinder that is on an exhaust stroke. Now having explained that as simple and best as I know how. I will move on to why that would hurt low end power. No scavenging creates chaos ,for lack of a better term, The exhaust gas expands and then cools rapidly and loses velocity. The scavenging helps keep the pattern in order. An x Pipe or H pipe adds to this effect by tying both sides together which in turns causes even more scavenging in a more evenly fashion as now all cylinders fire in sequence effectively. WHich in turn equals more useable HP and torque. However, depending on the actual motor this will also lose its benefit in the upper rpm as things get to crowded. That is why most drag cars are tuned to run open headers they are in the higher rpm band most of the time. Street and occasional track use benefits due to the lower Rpm and powerband. Point in case My dad's neighbor has a chevelle with a well built 350 that ran 12.70 all day with full exhaust went to open headers expecting an improvement and ran 13.30's. Then again cork up John Forces funny car and see the his times drop dramatically. I hope this helps..........LATER
There is a lot of science involved in an exhaust system application for each engine. It is never a matter of bigger is better. The reasons are many. Gas temp., gas speed, internal wall surface finish, shape, pipe size, length, exit shape and the valve overlap of the camshaft. Basicly to keep torque, the pipe diameter needs to stay near port size and be on the longer side for length. In the reasons above, you need to optimize many of the actions that are taking place in order to see substantial gains. The two main actions are pulse reversions up and down the pipes and length that have to be timed with the valve opening point to improve the power over a narrow rpm range. So the pipe size controls the speed as well as the temp of these actions. Generally tuning will only be optimized over a short RPM range but there are other tricks that can be used to widen out the band and make exhaust tuning more useful. The pulsing get into deeper action like acustics, temp. , size, positive and negative pressure point reflection from one end to the other and is how a negitive point creates a vacuum in the cylinder to pull gas out and in some cases even pulls fresh charge out the exhaust in the cases of large valve overlaps and blower applications. Back pressure does have a use in certian systems and is used a lot on motorcycle engines with adjustable intenal exhaust system features. For quite a few years now, adjustable intake tracks are being used to widen the power band of engine and uses many of the same principle as the exhaust system uses. Longer smaller tracks for low end and shorted larger tracks for higher RPM power. So there is much more to this than meets the eye. Without any way to measure power vs change except time slips and seat of the pants it often becomes a guessing game as to what will help over what you already ay have. Going from old stock iron header to more free flowing tube header is extreem and always results in a gain.
