>>>*Well, I have some opinions myself on this subject.

The factory exhaust was designed to be quiet. It has to be, the vehicle might be driven by a little old lady to the market.

If her new 4Runner rattles, I bet you can guess what she will do.

So the factory passed on a large amount of potential power output, sacrificing that for sales. From their point of view, sales are all that matter.

I am getting very good reports from you folks out in the field from the Thorley setup. I believe they have the "no-fit" concerns solved.

But I will say this, and this is from my own testing, admittedly some 7-8 years ago.

The stock manifold really does not reduce power, a header may help but at that time it was not proven to me. I found the stock manifold to be a pretty sweet and well designed piece with the advantage of sound dampening. It holds the exactly correct amount of backpressure at the port.

After the port, there is just one goal for the exhaust: Get it OUT of there!

The REAL gain is in the pipe, so we tested 2" all the way back through the Cat into the muffler, and 2 1/4" on exit, using the plain stock factory manifold as best of everything.

That worked, it worked well, and it was far less hardearned out of the jeans to do.

A good header doesn't hurt, if in the budget go for it and that Thorley is hard to top. They have been around a long time, I had one of their setups on my 1964 327 Impala and it worked well. And yep, that was IN 1964.......*EB

And pretty much, I agree 100% with everything you have stated. It does make sense that Toyota would mildly sacrifice some things for sales.
At first I wasn't even going to purchase a header for this truck until I read an in-depth article on Thorley and it's "180* Firing sequence math" and how it showed What their headers did and smoothed out the exhaust flow. Which im sure the Toyotas OEM manifold does reasonabley well (Am very impressed with many of Imports stock setups, RSX-S being my #1 Fav) So, I figure i've got a little cash to throw around and already have the performance exhaust on it...Mild upgrade in power but too quiet for my taste.
I figure too, technology is always being upgraded, and im curious to see how effective a full performance exhaust on the little 4 banger would be <img src="/forums/images/graemlins/smile.gif" alt="" />.
It's funny you mention porting too, I need to call you some day or PM you since I want to build up a new engine for my truck and need to talk to some one who can explain, in depth, porting polishing gains/boreing/compression ratios and all that fun stuff to me so I can do it strategically instead of going down the lego effect and "Hope" it works.

You mildly remind me of my father too w/ the Impala, He loves his blackjack headers on the '56 Bel Air (Hedmen I beleive)