Off-Road.Com - Toyota Section - Downey V6 Headers Review

Feb. 01, 2006 By Scott Wilson

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3.0V6Headers By: Scott Wilson - swilson@off-road.com - 10/18/98

When it comes to bolt on upgrades for your engine, there are a lot of products that claim significant power increase, but few actually deliver as promised. I've found one that delivers just as promised... Downey's 3.0L V6 Headers. These headers aren't new to the market, but their recently acquired California Smog Certification, and their water cut header flange is new. Downey currently has the only V6 headers that are 50-State smog legal. This is big news for CA owners. This means you'll be able to drive into the smog station every other year, and never have to wonder if the technician is going to notice the headers. If the technician does notice, he'll also see the sticker under the hood (supplied with the headers) with the numbers that he'll need to legally certify your vehicle.

Headers replace the stock exhaust manifolds that came on your engine from the factory. Headers offer a performance gain because they are capable of moving much more exhaust than the stock manifolds. The stock manifolds and crossover pipe are very restrictive on this engine. (The cross-over pipe connects the exhaust from both sides of the engine, so the exhaust can then go out a single exhaust pipe.)

Here is a flow diagram to help you see how the stock exhaust system works. The 3 cylinders on each side of the engine dump their exhaust into a single exhaust manifold. The passenger side exhaust is carried around to the drivers side via the cross-over pipe, which fits snugly between the engine and firewall. Then the two sides of exhaust hit each other head-on, and flow out the exhaust pipe. As you can see, it is not a very efficient way of moving exhaust.

Here is a crude diagram of how the header works. Realize this is not to scale whatsoever. With a header, exhaust flows out of the cylinder into a header pipe (instead of the exhaust manifold). Each cylinder has it's own pipe. The pipes are routed closely together, and join up into a large diameter pipe. This way, the exhaust is not restricted, as with the stock system. Downey's V6 headers considerably increase both horsepower and torque. Used with 2.5" exhaust, Downey claims a gain of 14 HP compared to the stock exhaust manifolds and exhaust pipe. Their claim is absolutely believable. I added a 2.5" free flow exhaust (with a 2.25" tailpipe) along with my headers. The increased performance is undeniable. Since the addition of the headers I'm consistently seeing a 2-mpg improvement in gas mileage. If you can 'keep your foot out of it' better than I can, you may even see a larger improvement in mileage. There is significantly more HP in the mid and upper range of the RPM band. There is also a huge improvement in low end torque. My engine can idle the truck up-hill in 1st gear high range now, where before it would have stalled. The added low end torque helps significantly on the trail as well. The added torque will help the engine not to stall as easily when climbing an obstacle, and also means you will not need to keep the engine at a higher RPM to keep the engine from stalling. The bottom line is that you can wheel at slower speeds, which generally translates to safer wheeling, with fewer broken parts. INSTALLATION
Downey installation instructions in RED It's definitely worth mentioning that this installation will be SIGNIFICANTLY easier if your truck or 4Runner has a body lift on it. My 4Runner has a 2" body lift. Much of the work can actually be done through the gap between the frame and body if you have a body lift. This installation can be done with tools that most people have in their garage, however I feel that a 17mm S-Wrench should be on the required tools list for this job. It will also significantly help the installation if you spray all the bolts on the exhaust manifolds, crossover pipe, and exhaust pipe with Liquid Wrench (or WD-40, etc) a couple of days in advance. You'll also want to keep the Liquid Wrench handy the day of the installation...a shot of it a on a bolt or nut, just a few minutes before you're about to tackle it will save you considerable muscle wrenching.

1) Loosen Clamp and remove air cleaner duct from throttle body on engine. Unplug electrical cord from flow meter on top of air cleaner. Remove three air cleaner mounting bolts from inner fender panel. Remove air cleaner assembly from vehicle. 2) Remove 3 spark plug cords from drivers side spark plugs and tie or tape them out of your working area. To begin I chose not only to prepare the drivers side, but the passenger side as well. I completely removed my spark plug wires, to ensure they'd be out of my way. On the passenger side I also removed the battery, and many of the vacuum lines that would otherwise be in the way. BE SURE to draw yourself a map as to which vacuum lines go to which connectors, as by the end of this installation there is no chance you would remember. 3) Remove the outer heat shield from the left side exhaust manifold. 4) Unbolt and remove the Oxygen Sensor from the stock tail pipe (in front of the catalytic converter). 5) Remove the tail pipe between the left side exhaust manifold and catalytic converter. 6) Unbolt the cross-over pipe (behind engine block) from the left side exhaust manifold. 7) Unbolt left side exhaust manifold from engine.

This is your goal as far as disassembly. You want to have both exhaust manifolds, and the crossover removed. None of these part will be used again, so do not feel the need to be gentle with them.

8) Remove left side exhaust manifold, then remove the 6 mounting studs. Using two 10mm nuts included with the headers, jam-lock them together on each stud. The studs can then be removed by wrench. 9) Unbolt cross-over pipe from right side exhaust manifold. Remove cross-over pipe by pulling it toward left side of vehicle. Remove cross-over pipe by pulling it toward left side of vehicle. If the cross-over pipe binds between the engine and fire wall preventing removal, it will be necessary to put a jack under the transfer case cross member, unbolt the cross member from the frame, and lower the transfer case approximately 1.5 inches. After removing the cross-over pipe from the vehicle, remount the transfer case cross member.

I was surprised to find that nearly every bolt came off with ease, after being soaked in Liquid Wrench for awhile. One of the bolts that held the cross-over to the drivers side manifold was a huge problem for me. I worked at it a long time, and only proceeded to take the sides off the nut. Then I remembered that there is no need for the cross-over once the new exhaust is installed. I used a reciprocating saw, and sliced through the stock crossover in a matter of seconds. The cross-over itself came out from between the engine and firewall very easily for me because of my 2" body lift. I've talked with people who have no body lift, that had a terrible time trying to remove the cross-over, even after dropping the cross member as suggested in Downey's instructions. 10) Spray Coppercoat (or equivalent gasket adhesive) onto both sides of the left side header gasket. Install the left side header and gasket onto the engine using them 10mm bolts supplied.

11) Before removing right side exhaust manifold:

a) Remove spark plug cords from spark plugs and tie or tape them out of your working area. b) You may find it necessary to remove the power steering hose from the side of the reservoir and tie or tape it out of your working area. WARNING - If you lose fluid, do not forget to refill the reservoir before operating the vehicle. I was able to complete my installation without removing this hose, or removing the power steering pump from it's mount. c) Remove EGR valve and Air Suction Reed Valve from engine and exhaust manifold. Note - Some non-California vehicles do not have these valves.

12) Remove right side exhaust manifold, then remove 6 mounting studs as described in step #8. 13) Before installing right side header:

a) Bend coiled brake lines and fuel line closer to right side of frame, wire tie fuel line to brake lines to insure adequate clearance from header. b) Use wire tires to insure all electrical and plumbing have adequate header clearance. c) AUTOMATIC TRANSMISSION ONLY - Disconnect automatic transmission kick-down cable from throttle body and engine mount clamp. Reroute cable straight up firewall (vertically, away from header), the reconnect to clamp and throttle body. d) AUTOMATIC TRANSMISSION MODELS - Your transfer case has an oil cooler mounted to the right side frame beside the transmission. Remount the cooler slightly reward (in front of the transfer case) or remove both oil cooler hoses, remove cooler from frame, remount cooler to floor board behind transfer case using Downey hose kit #DOW32910. WARNING - You will probably loose some fluid during this procedure. Do not forget to refill the transfer case before operating vehicle. e) AUTOMATIC TRANSMISSION MODELS - It will be necessary to bend the transmission tube that carries fluid from the transmission to the front cooler inward toward transmission. Bend it inward far enough to clear header, but not far enough to interfere with the transmission shift linkage. These instructions are very VERY important, do not forget to check for adequate clearance for all fuel lines, brake lines, electrical wire, etc. before using the vehicle. I found it easier to install my headers, and then move (or bend) all the lines away from the header once I had the headers in place. f) Attempt to loosely mount the right side header to ensure there is adequate clearance (no interference) between front end of header flange and power steering pump. Trim if necessary! This step is ABSOLUTELY necessary. Most everyone I've talked to has needed to trim the edge of the flange slightly to prevent interference with the mount for the power steering pump. If you have access to an angle grinder it will make this step as easy as the rest. Notice the difference in shape between the two sides of the flange. I found it necessary to take approximately 4mm of one side of my flange so that it would not interfere with the power steering pump mount.

14) Spray Coppercoat (or equivalent) onto both sides of the header gasket. Install the right side header and gasket onto the engine using the 10mm bolts supplied.

15) MOUNTING REED VALVE - Remove the original plumbing from the bottom of the reed valve. The 2 bolt aluminum mounting flange on the reed valve can be removed with a hack saw (optional), since the reed valve will no longer remount onto the cylinder head often it is mounted onto the header plumbing. Cut the original plumbing to remove the original compression nut that screws up into the bottom of the reed valve. Slide original compression nut onto copper tubing toward the flared end. Screw original compression nut and crush sleeve onto opposite end of copper tubing. Position copper tubing down into rear fitting on header and screw crush nut onto header fitting. WARNING - When tightening crush nut, ensure that copper tubing is tightly pressed into header fitting and fully seated. If not, the crush sleeve will not crimp the copper tubing and form a seal. After completing installation of the reed valve, ensure that rear spark plug wire does not come into contact with the copper tube. Tie back if necessary.

As you can see, the supplied pipe will not connect to the header with the Reed Valve in its stock location. Downey's instructions call for the Reed Valve to be mounted atop of the supplied copper pipe, and no longer attached to the passenger side head. I decided to see if I could come up with a solution that would allow me to keep the Reed Valve in its stock location.

I purchased more 5/8" copper pipe, and attempted to bend it into the S-shape I'd need to make the connection. None of our MANY attempts succeeded. I ended up using the supplied stainless steel flex pipe for my Reed Valve instead of my EGR valve. This way I was able to leave my Reed Valve in it's stock location. 16) MOUNTING EGR VALVE - Remove original plumbing from bottom of EGR valve. Position EGR valve back into its original mounting position on the engine, do not tighten. Hold stainless flex tube (supplied with headers) up to fitting on EGR valve and front fitting on header. Determine exact length flex tubing should be when fully seated into the header and EGR valve, trim tubing to proper length. Position crush nut and crush sleeve onto one end of the flex tubing. Fully seat flex tubing into front fitting on header and tighten crush nut finger tight. Cut original plumbing to remove original crush nut. Install original crush nut and crush sleeve onto top end of flex tubing. Fully seat EGR valve down into flex tubing and tighten crush nut finger tight. Before fully tightening crush nuts, position EGR valve back into its original mounting location and tighten original mounting nuts. After determining flex tubing is still fully seated at both ends, fully tighten crush nuts.

For my EGR valve I used the existing EGR pipe. The pipe does not fit in it's stock form...we had to severely modify the pipe to make it fit. It took CONSIDERABLE effort, but I'm very pleased with my installation. If I had to do it again I have no doubt I WOULD NOT try this same method. I would stick to the Downey method, and mount my Reed valve atop the supplied pipe. 17) Reconnect spark plug cords, both sides. 18) Reconnect power steering hose to reservoir if disconnected earlier. Check fluid level. 19) Reinstall air cleaner assembly. 20) Connect new tail pipes to new exhaust system. 21) Install Oxygen Sensor into the fitting on the new exhaust system. As instruction #20 states, you will need a new exhaust system, or at a minimum a new cross-over. To get the maximum performance from these headers you should consider installing a high-flow 2.5" exhaust system. I chose to have a completely new and custom exhaust system made to compliment my Downey headers. The new exhaust system includes a 2.5" high performance Car-Sound catalytic converter with flanged ends, available from Downey. The only drawback I've found is that the new cross-over must be routed under the front driveshaft. This is not a problem is the sense that the front driveshaft does not move on IFS vehicles. But this is a problem in the sense that the crossover may be susceptible to damage on the trail. I currently have plans to modify my transfer case cross member with a skid plate that will protect this new cross-over. Special thanks to Eric Stegall and Jim Brink who helped considerably with this project. Please tell Downey you saw their V6 header review here at Off-Road.Com!!