hpi is THE ONLY way to go... standard on all new cigs fromthe factory,same for baja moast fountaind outerlimits etcs acctually increases hp on some applicationsmy buddies 51 OL went 2mph faster back to back after a same day install w/ merc reps on board w/ all the high tech monitoring equiptment on!!!

I am a little hesitant to get the HPI's after reading Troutly's experience with them... a hastle to install and not much noise reduction. Too old sells the Livorsi that look identical to the HPI's (on their website they list being a supplier to Livorsi). I was also looking at the GGB louver tips.

I installed a set of GGB mufflers on a 40' Scarab with twin Whipple Charged BBC's. It sounds really good. Not too loud at all. I can't attest to HP loss since this was done as a package, but he's very pleased with the performance. He lives down the lake from me and I can here him every time he goes by. He was running stock 400's with no mufflers before I built the new engines and my windows would rattle when he went by. I told him he HAD to install the mufflers when I built the engines. I can still hear him going down the lake and it sounds very good, actually better because it is a much deeper sound and not nearly as loud.

bobl- Did you install the extreme or the louver tip?

The HPI work dramatically on reducing Yves noise and no performance change.
His are the thru-bolted ones not a slap on.

What about Drew Marine shotgun silencer or Eddie Marines' version?

Don't care about quiet when on plane, but in no wake zones I want quiet.

Recommendations????

G.L - Did Yves install them himself or did he have someone do it. Difficulty?

I've have the HPI's on a 502/415 in the clamp-on style and like them. I wasn't that loud compared to alot of other boats but didn't want to get hassled needlessly! And no loss of performance. Steve

Steve - I wish that I could install the clamp-on but my tips only extend 1" from the transom so I need to install the tip version. I have stock 454 mag's so it is good to hear from someone that installed these on a stock non-blue mercruiser motor and had no power loss. Did you have your boat noise tested before and after

My formula originally came with the silent thunder box and it reduced the noise just enough but the box was coming apart and heavy so repairing the box and replacing just does not make sense.

livorsi are rebadged hpis