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Review:
Downey 3.0L V6 Headers

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Author: Scott Wilson December 1999
50 State Smog Legal!
Toyota 3.0L V6

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.


Downey 3.0L V6 headers 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 E.O. sticker under the hood with the numbers that he'll need to legally certify your vehicle.



Header & Manfold

Headers replace the stock exhaust manifolds that come 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.)



Manifold Flow Diagram

Here is a flow diagram to help you see how the stock exhaust manifolds 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.



Header Flow Diagram

Here is a crude diagram of how the header works. 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.


I have had the Downey Headers on my 3.0L V6 engine for more than one year (more than 30k mile also), and am still as happy with them as the day I finished the installation. Though I have changed my exhaust once already to better suit my needs, I have not had to even tighten a loose bolt on the headers. They are working as advertised, and have had no leaks. If I ever begin building up another truck with the Toyota 3.0L V6 engine, these headers will be on my 'Must Have' list.



Follow this link to see the header installation


 


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