Inerview with Chevy High Performance Magazine
and Dan Lemons, Owner of Lemons Headers
CHP - If there is an off-the-shelf header available for your motor/chassis combination, what is the advantage of running a custom header?
DL - If your motor/chassis combination is stock then an off-the-shelf header may be the way to go. The advantages of an off-the-shelf header are quick delivery and price. The advantages of a custom header are: correct fit, the ability to get the proper primary tube and collector size, better quality materials, workmanship and design.
CHP - What are the benefits and drawbacks of fenderwell headers compared to a more conventional header design?
DL - The benefits of most fenderwell headers are: lots of spark plug room, you don’t have to worry about oil pan or starter clearance and in most cases their very easy to install. The drawbacks are you will have to cut your inner fenderwells, tire clearance, limited turning radius and if the collectors are pointing down you’ll blow dust on your neighbors in the pits.
CHP - What are the advantages of stepped primaries and collectors over non stepped tubing?
DL - Some of the advantages of a step header are they will scavenge better than a straight tube header and broaden the torque curve. On our race collectors we build a transition cone inside which also assist with scavenging. We keep the flange opening larger than the head port opening to help with scavenging. When determining the proper tube size for an application we will sometimes use the step header as an in between size. An example would be if a 2 ¼” tube is too small, but a 2 3/8” may be too large then we’ll build a 2 ¼” stepped to 2 3/8”.
CHP - How does collector length affect the overall power curve, and how do you determine the proper length for a given application?
DL - A longer collector will typically make more torque. A shorter collector will typically make less torque but more mile per hour. If the car has an exhaust system then the collector length has less effect. With open headers sometimes we will use a larger collector and then use collector extensions to fine tune the torque requirements.
CHP - What is a good rule of thumb for properly sizing primary diameter and collector diameter for a certain power level or displacement?
DL - When sizing a header there are a lot of things to take into consideration. Cubic inch, compression and horsepower are the obvious, but we also consider the weight of the car, heavy cars need more torque, tire size, big tire cars need more torque. If it’s a 10” tire car then we may use a bigger tube to kill some of the torque and help manage blow to the tire especially if there is nitrous or a blower. If there is an exhaust system even a straight through muffler it will still add back pressure, so we may lean towards a larger tube or collector size. A lower converter stall setting will require more torque than a high stall. Nitrous and blower motors like bigger tube sizes. So to answer your question I don’t know that there is an easy rule of thumb formula, it may be more about experience as to what works in the real world. Engine builders and experienced header builders are usually a good source for answers. I’ll give you an example.
A 540 cu.in. Big Block Chevy 14-1 compression with good cylinder heads making 900 to 1100 horsepower on motor plus 300 to 500 nitrous on 10 ½” tires weighing 3100 lbs. with a 5500 stall setting and mufflers would typically need a 2 ¼” stepped to 2 3/8” header with a 4 to 4 ½” collector.
CHP - Some shops claim that ceramic coatings improve scavenging by improving heat retention. What’s your take on this?
DL - Heat retention does make horsepower according to the dyno guys, but I don’t know that there is any scavenging benefit. I do feel there is some benefit to a header that is well coated on the inside to help control rust and carbon build up inside the tube which would disturb the gas flow. Coating will also help these expensive headers last a long time.
CHP - Given the track abuse your products are subjected to, what features are incorporated into your headers to help them survive violent wheelstands?
DL - We started this business building drag race headers; where there are two high priorities, spark plug room and ground clearance. It’s a constant challenge for us. Most of our new Pro-Touring and Drag Racing designs have the primary tubes actually higher than the bottom of the oil pan. So if your wheelstand got the headers, it got the oil pan too. We put a lot of effort into improving and redesigning our headers. If we feel we can pick up a little more ground clearance or starter and oil pan room or better access to the spark plugs then we’ll redesign a header. On our Big Block headers we TIG weld silicon bronze on the outside of the flange to keep the tube from cracking, but keeping them off the ground is the key.
CHP - Mass-produced headers often have fitment problems. What measures do you take to ensure precise fitment?
DL - Production headers are designed so that the tubes can be bent on a mandrel bender from one end to the other. For this to happen, there needs to be enough straight between the bends for the bender to grab the tube. This necessity dictates the design. Our headers are hand made, so we can have bends anywhere necessary to properly clear any obstacles.
CHP - Headers designed for use strictly on an engine dyno can get away with not having nearly as many tight bends as headers designed to fit inside a chassis. How much of an impact can this have on horsepower?
DL - In a perfect world a header would only have one bend, out and back. But we’re stuck with the confines of a stock chassis. To make things even worse we try to put too big a tube into too small a chassis and then we try our best to get them as close to the same length as we can. Not an easy task. We try to keep our designs as free flowing as possible, we use as large a radius bend as we can and we keep the tube square to the exhaust port without back cutting the bend at the flange.
CHP - What precautions must be taken when bolting off-the-shelf type headers to a tall deck block?
DL - A tall deck block is going to bring the header up and out usually causing a fitment issue. A raised port head will have the same effect. If an off-the-shelf header is used on a raised port head it brings the tube too close to the spark plugs.
CHP - How does primary length affect the shape of the power curve? What tricks do you use to maximize primary length in a limited amount of space?
DL - Primary length has an effect on the power curve, but in stock chassis cars to get all four tubes from the flange to the collector in a normal location we’re stuck with X amount of tube length, give or take a couple of inches. Having the ability to use different tube sizes helps greatly. Smaller tubes acts like longer tubes and bigger tubes act like shorter tubes.
CHP - For someone that has an uncommon set up, such as an 18-degree-headed small block Chevy that requires custom headers, how many hours does it take to fab up custom headers and what will it typically cost?
DL - In our jigs we have the ability to build the header for any cylinder head as well as different deck heights. We can make it in the tube size the customer needs in a step or non step configuration. But the engine needs to stay in the stock location. It takes us about 2 days to build a header once we start on it, but because we custom make every header we always have a lead time. Most of our customers understand that and give us plenty of advance notice. Any combination is the same price, about $1200 in mild steel.
CHP - Is mild steel or stainless steel preferable when building headers? What are the benefits of each? What gauge of metal is used?
DL - We build headers in both materials. Stainless costs about twice as much. It’s a stronger material and won’t rust, but it discolors and weighs more. Mild steel headers that are well coated inside and out make a lot of sense. We use 3/8” thick header and collector flanges, 18 gauge tubing and 16 gauge collectors. Both types are TIG welded.
CHP - Many enthusiast complain about installation difficulties with headers, but what challenges do you have to contend with to design a header system in the first place?
DL - To design a header and find that it installs easy is a blessing. But we won’t sacrifice performance or fit to make a header easier to install. Some of our headers are a pain to install, but when their in they fit good, have good spark plug room oil pan room and ground clearance and we don’t want to lose that. All of our race headers are made with individual tubes and slip on collectors, so you install one tube at a time and the collectors slip on and bolt in place. This makes all the difference in the world. Many of these headers can be installed with the engine and starter in place and be finished in about 15 minutes.
CHP - What type of collector gaskets do you recommend? Paper gaskets can blow out, while aluminum gaskets tend to distort over time.
DL - The collector gaskets we use are SCE copper. Since the copper can’t crush like a fiber gasket we use a thin layer of copper silicone on each side of the port opening. As for our flange gaskets at the head, again we use the SCE flat annealed copper. Any gasket that is flat will seal at the header flange. I never use the embossed copper type. Their made for the flange to match the port opening and won’t work with our headers.
CHP - Lazy installers sometimes dimple headers for clearance. How much does this compromise flow?
DL - Making a small flat spot in a tube probably has a minimal effect on performance, but I wouldn’t do it if you don’t have to. If your header is touching the steering column, there may be a way to adjust the column outward or if it’s the starter you may have to use a mini starter. If you are trying to use a header made for a stock configuration on a tall deck block and raised exhaust port head, then take a hammer with you.
CHP - How important is it for the exhaust gaskets and the openings of the primaries to line up properly?
DL - Again use a flat gasket and as long as the gasket is not obstructing the port opening, your fine. We normally use a gasket the matches the header flange, which is going to be larger than the port opening.
CHP - What are some features that can be incorporated into header design to maximize scavenging?
DL - We have covered some of this already, but again header flange larger than the port opening, step tube design, transition cone in the collector or merge collectors and an X pipe exhaust system.
CHP - What type of bolts are best in preventing leaks? What’s the best way to keep them from backing out?
DL - There are header bolts with locking washers that work well if you need them. We use ARP stainless bolts that are longer than a standard bolt because we have thick flanges. We find that the heavy flange and the flat copper gaskets don’t expand and contract like thin flanges and fiber gaskets do. Therefore we don’t have problems with the bolts loosening. Once the headers are installed and the engine is started always retighten the header bolts after the engine is warmed up.
CHP - What suggestions do you have for keeping under hood heat in check?
DL - Ceramic coatings do a great job of keeping the under hood heat down. Also a properly sized header can make a big difference. If your header is too small for the size of your engine, the header and the engine can overheat. This is especially true with blower motors.