Civic EG

I am looking for a D15B manifold 4-1, the only one's I found are all 4-2-1 and the few 4-1 I found are 3 times expensive than the 4-2-1, do you guys know were I can find cheaper one's? Is there a big difference between them when it comes to a D15B Vtec?

You mean factory manifold or aftermarket?

If it's aftermarket then don't rely two heavily on the rule of thumb for 4-1 vs 4-2-1. In general it's said that 4-1 is better for peak hp and 4-2-1 is better for a street vehicle. However, a well-designed 4-1 can do whatever the manufacturer wants it to do. Perform miracles, whatev. And you'll know it because you're spending upwards of $600 for it.

As far as factory goes it seems to me like the JDM engines come with 4-2-1 manifolds and they don't match up to our USDM 4-1 down pipes. PITA

Really I want to buy an aftermarket one hoping for more bhp, but an aftermarket 4-2-1 will perform better than a factory one and a decat help help in the process?

Deleting the cat will do absolutely nothing. In fact, an article in Super Street years ago showed that you LOSE power. Cat converters cause almost no exhaust restriction, yet they burn super hot. Heat = energy

The only time you want to delete the cat converter is on a dedicated race vehicle when the engine is near it's maximum potential. The fuel mixture you're burning at that state of tune will destroy the cat converter anyway.