Yoter

On 3.0 engines maybe others the passenger manifold goes around the back of the engine to meet up with the drivers side one. This not only creates in my opinion a hot engine bay aswell as fire wall but the way it goes into that drivers side manifold hold back on the ammount of flow. If the passenger manifold were to drop down I assume it would give the 3.0 alot more HP. The way it looks to be working right now is when the flow out of the pass. man. goes into the dr. man. it actually is pushing the flow into the dr. man. flow giving us lack of flow. Am I correct? I want to do as another guy locally found that a prev. owner did. They took that pass. side exh. man. and dropped it down the pass. side to the tcase and crossed over to make a Y pipe. Anyone ever heard of this or had it done? It would help me by doing away with that crossover pipe behind the eng. creating a coller eng and firewall temp, more flow, and no eng. rattle from the heat shields. Feedback?

Churnd

That angle coming off the passenger side manifold is nearly impossible to run a pipe off of like you're talking about. I thought about it before and realized it wouldnt work without a LOT of fabrication. You might be able to trim the manifold's end to change the angle but that's a big maybe. Why not just pop for a set of headers and some good gaskets to seal em up with?

You're right about the way the piping runs. The passenger dumps off into the drivers side head on and seriously cuts back flow. I have no idea why Toyota couldnt design it to where it would dump into the pipe more smoothly. I'm beginning to think Japs don't like power... or at least they didn't 15 years ago.

Yoter

i was checking out the owner of the Runner with the upgraded manifolds. It has been altered to drop straight down on the pass side as I previously said. On the drivers side manifold though where the crossover pipe entered you end up with a open hole when you take the cross over pipe out. The person that did the fabbing just took a cap and exh. gasket to coever it and kept the drivers side the way it was. All I see that needs to be done is to remove the cross over pipe and have the pass. side flange cut off and after taking maybe stove ducting to get a form of your pipe path have a piece welded onto the flange. Then you go to town on designing the exh. and how it will route out the rear. I like the idea and am going to do it. I figure its a $200 mod compared to $350 im assuming for hedders.

gwhayduke

Blue, I've always thought the same exact thing: get rid of the crossover and stop the upstream exhaust flow on the drivers side. I don't want headers...to noisy and expensive (about $800-$1000 from what I've read by the time you're finished plumbing). But the header crowd doesn't seem to gain much HP, so I have always questioned how much I would gain with this type of mod. I also wonder if these 3.0's were sent from the factory tuned for less HP simply to keep them from exploding...and since they were "detuned" there would not be much gain from headers.

With your body lift, it should be pretty easy to get a good muffler shop to fabricate everything fairly cheap.

Get yourself a good high-flow cat while you're at it.

williemon

Just a line on some things i have read and grown to believe. A few years back I saw a bit on the 4x4 wire forum from a member called Perfect Obsession. He was an engineer of some sort and talked about this some. I also read things from some other members, and from people elsewhere brought to me via links that seemed to advocate that the design was a way to tune the 3.0s for the proper powerband. From what I gathered from all this, and from Tim at DOA, is that the stock exhaust manifold, even though it looks restrictive, is set to provide a smooth flow and tuned frequency due to the 3.0s fireing order, to send a low pressure pulse out the end of the intake at a good proper operating rpm and the tail pipe would exhaust just right to exit the gasses from the cylinders with just the right amount of pull to make everything flow as well as the heads and intake path will allow. Im not an expert myself so this info helped make up my mind what I was going to do. I had (at Tim from DOAs recomendation)a 2.5" dia. pipe welded about 6" from the #6 junction on the stock downpipe. Ran 2.5" to a new free flow cat and dynomax muffler and out the 2.5" tailpipe. I had DOAs P&P heads and cams installed about a month or 2 prior. So I had a power boost with those mods, and a very noticable boost when I did the exhaust. The low end is still not what I really wanted, but once you hit 3000 rpm, you feel your head being pushed back. The power comes on strong. Anyway, thats what i have read about the stock exhaust manifolds.