powerguy

Installed two sets of HPI mufflers on my Formula 336 yesterday. Would have completed it in an afternoon but UPS decided to deliver my mufflers at 6:30PM. Went down to the shipyard this morning and finished the install. The HPI mufflers seem very solid and the install was fairly straightforward. I used a trick heard of here to remove the old tips. First, remove the steel clamps connecting the exhaust tips to the hose in the engine compartment and remove the screws on the tips (use high torque drill) then scribe the silicone around the old tip with a razor knife. Second, (the trick) use a 2x4 about 4' long, trim a little off the end and stick into the exhaust tip. Third, pry up and down with the 2x4 and the tips should pop right off as mine did.

The only scary part of this install was drilling the holes in the transom for the muffler studs to go thru. I triple checked to make sure that nothing would be hit by the drill bit inside the transom. Once the drilling was done a little dishwashing liquid mixed with water to lube the rubber hose to facilitate sliding the muffler in, some silicone around the bolts and lip around the muffer, a little pressure and in they went.

After that back into the engine compartment to install washers and lock nuts and re-install of the hose clamps and my work was done. This took a little longer that I thought it because of all the bending to get at and tighten the 12 lock nuts and 8 hose clamps.

I decided to let the silicone on the tips cure over night so I will report back tomorrow with the results from the muffler install. So far so good. Some noise reduction and elimination of some resonance from the exhaust ( I had taken my silent thunder box off because it was rattling and found it to be almost completely delaminated) and was left with resonance at around 1000-1200 rpm and I will be happy.

powerguy

More pics

powerguy

Ran the boat today with the new mufflers as well as swap mirage plus for bravo 1 props. The mufflers definitely do the trick. They took the harshness out of the exhaust as well as my resonance noise but definitely left enough deep tone to the exhaust. I am very happy with the results of the mufflers. I should have ran the boat without changing props to see if there was any loss in performance from the exhaust. With the prop change from 23 mirage plus to 22 bravo 1 my rpm's increased enough so that I need to go to 24 bravo 1's and have them labbed. Overall lost 2mph or so top end with the switch which I relate to the props and not the mufflers. The bravo 1's definitely plane easier but I was finding that in the midrange that I was running the same rpm/1-2mph less thru the cruise range. I'll swap the props back later this week and post the results.

RLW

Thanks for the feedback. I am also interested in some performance mufflers.
What was the lead time needed to get a pair of HPI's?
Russ

powerguy

Russ-
I did not get the m directly thru HPI but a boat dealer/custom rigging shop. Give Dan a call at HPI and he can help you out.

Dave

powerguy

Swapped props back to original 23 mirage + and went out for a run. Hole shot was not as good as the 4 blades but midrange was back where it was and so was the top end. No noticable decrease in performance with the mufflers installed ,justl a noticable decrease in noise. Overall the boat still has a deep exhaust note and the noise level is less and my annoying resonance is gone.
I don't know if I am now legal buth here in Vermont they do not (YET?) test boats for noise. Thanks HPI, your product has worked for me.

GLH

Good thing!

Might be hard to warrant training and equipment for maybe 3-4 boats on the lake that would be illegal.

powerguy

My understanding is that all thru hull exhaust boats will not meet the existing noise laws which are 82dB at 50' in Vermont and 90dB at 3' at idle in NY. If Peter Clavell becomes governor of Vermont a 25hp outboard will be too loud.

Blade38

I've had the HPI's installed on my Cig with 525's. I was pissed when they put them on becaused I wanted silent choice. But now i love them. No performance loss, My ladies love them because they can still talk. They give a smother tone that still sounds badass. Best of all they dont clutter the engine compartment with the additional tubing,etc.