First thing to do to get more HP to 99 Boxster?
 

On a 911, a cat bypass for $350 is usually the first thing you do. Is it the same for Boxster? Any specific brand?

Use the search function and spend a couple of hours being entertained....

I bought Topspeed Pro headers and cat delete pipes from Delubosparts out of Texas - good value - speak to John, I'm sure he will help you out.

A better bang for the buck is an underspeed pulley - again use the search function.

Sell it and buy a Boxster S

The 2.5 L 97-99 Boxsters only have one set of cats, and if you remove these you would have to deal with the CEL from not having them. (2000 - 2004 986 have 2 sets of Cats and only the front set is monitored so you can bypass the 2nd set with no CEL). Since you have no cats built in to the stock "headers" you can get some headers without having to worry about a CEL from them. I think Topspeed sells a complete exhaust with headers, mid pipe, and exhaust for an affordable price. You would have to solve or deal with the CEL by using spacers or some other solution. Some say that the low end grunt suffers when you do this but you get more power at the top end.

Underdrive pulley frees up a few HP that you can feel in the seat of your pants, but (in my experience) every time I get stuck in traffic, the car seems to heat up a lot quicker than it did before - one theory is that since the WP is turning more slowly, especially at idle, it isn't moving as much water. I never really drove in stop and go traffic before or really even watched the gauge before so it may just be due to my paying more attention to the gauges now.

Stripping some weight out of the car also can give an improvement to the HP/Pound ratio and make the car feel more powerful. Look at the Spec Boxster race series that uses the 2.5L Boxster as a platform.

Driver education - the car itself is probably faster than most of us can drive it - the more we learn the more we can appreciate and utilize the performance the car inherently has.

The general consensus seems to be that the Boxster is a fast car designed to be driven fast, but not necessarily designed to accelerate super hard from 0-60 like a "Muscle car" .

Steve

Steve is correct, there are mods you can make, depending on the state's air pollution regulations you live in, that can add minimal hp but when you calculate the $$$ per hp. mostly it is a waste on money. The only large hp gains I've seen, from the 2.5L, have been from turbocharging or supercharging, both expensive and controversial as to the potential damage they can do to the motor. You can always swap the motor to a 3.2 or 3.4L but then again it is expensive. The best advice, if you really crave more hp, is what another post recommended to sell it and buy an S and that way you get all the other brake and suspension upgrades as well.
You can also remap the ECU for another expensive for hp. gain. Typically around $800-$1200. I've known two people who did it and the hp gain was minimal and fuel mileage went way down.
I've been driving my 2.5L for six years and although I can't compete in a straight line put me on a winding, twisty road and I'll stay with just about anyone.

Your options. Almost all are $$$.

Maybe if you posted a description of when and why you wanted the increased performance we could better suggest a route to that end.

I raced motorcycles before I bought my bone base 99 986. The bike I raced for the last 5 years was a TZ250 (2 stroke Gp bike). Every 600cc and higher bike today can walk all over it in straight line speed. But nothing can match it in corner speed and handling. Not a fast bike but you can ride it very fast. That is what the 2.5 is like to me. Not a fast car but you can drive it fast.

If you enjoy the tinkering there are a bunch of things you can do, but if you just want the cheapest fastest route to more power then sell yours and get a 2000 S.

The money you will spend upgrading the older one will cost more that just buying an S, plus with the S you get the beefier parts and bigger awesome disk brakes.

Then once you get the S, spend a meager $500 for a Top Speed Exhaust and the 2nd cat deletes if you have 2nd cats and you will have a mean sounding, powerful beast of a 986 for minimal time and money, plus some nicer resale value.

^ Pretty much this.

My 99 tip came with a CAI that the PO did ? Basically cut the intake tube and stuck a KN on it. Amazingly it didn`t affect the MAF. I changed the filter and installed an Injen heat shield. When I had the IMS done at Mantis in Oakville I had them install one of their underdrive pulleys. It`s a 5" so same belt and very little effect on the p/s. I also installed a set of OBX headers. It does pull better but I find lags a tiny bit a low rpm but once its over 3 it really starts to pull and sounds great. My 99 has two cats without a bypass .:dance:

This or go buy a mustang. I can't for the life of me understand why people who equate performance to straight line stop light drag racing ability buy these cars.