what is the most power increasing mod for a grand prix 3.8

Cold air intake and headers will give you the most bang for the buck. You will need to open up the exhaust to duals when you do this and you may want to go with a high flow cat. Total cost if you go with a cat back will be about $1500 if you do the work yourself.

As far as a simple bolt on mod, I'd add a ZZP or DHP re-programmed PCM on top of that. Without it any intake or exhaust mods will not be taken full advantage of. Cost for re-programmed PCM ranges from $79 - $99.

I would not waste any money on a CatBack exhaust. You'll get noise not horsepower. You'd be better off with the hp mufflers, doing the u-bend delete, hi-flow CAT and going to exhaust size better than the stock 2.25" via custom fabrication. Headers are highly recommended if you have the budget.

Another good bolt on mod for a L36 are 1.8 aluminum roller rockers which may add another 12 hp on a L36 and are relatively easy to install DIY. No other valvetrain mods are required for 1.8 roller rockers.

BTW - The most bang for the buck on a L36 would be a hot camshaft and the appropriate valvetrain mods like 1.9 aluminum roller rockers and heavy duty valve springs so sorry Lynn I disagree.

Loaded question anyways.

No problem Bob! I was looking more at bolt on parts rather than pulling the engine apart. A cam is always a good choice but the time and effort, especially in a transverse mounted engine, is usually more than the average person wants to put into their car. Headers, CAI and exhaust are relatively easy and usually will give the performance that most folks are looking for. Personally, I am not a fan of cat back systems either but they are relatively easy to install vs fabricating a new one especially on an SE. The rockers are a good addition as well and like you said not hard to put on.

No problem Bob! I was looking more at bolt on parts rather than pulling the engine apart. A cam is always a good choice but the time and effort, especially in a transverse mounted engine, is usually more than the average person wants to put into their car. Headers, CAI and exhaust are relatively easy and usually will give the performance that most folks are looking for. Personally, I am not a fan of cat back systems either but they are relatively easy to install vs fabricating a new one especially on an SE. The rockers are a good addition as well and like you said not hard to put on.

Same here Lynn. We all have different opinions and reasonable minds will differ. But you know I've been running into a lot of L36 owners that are pretty serious with their mods. This guy below is one example. Look at that mods list.....whew!!!! J.C. man!

http://www.automotiveforums.com/vbulletin/showthread.php?t=595830

All I know is I am glad I have a L67 GTP. All of my mods with the exception of the 1.8 ratio roller rockers is technically bolt-on.

I'm surprised someone hasn't weighed-in mentioning supercharger conversion or turbo. :lol: