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Motorbox Insulation


Headhunter 2317

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It made the cabin quite a bit more quiet when at idle. It eliminated the "ticking" noise that apparently comes from the fuel injectors.

However, I didn't find that it made much of a difference above 1500 RPM. Most of the noise comes from the exhaust pipes. I didn't measure it with a meter, but that's just my unscientific opinion.

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plenty...well worth it. I did mine last spring when Tracie did hers. Just follow her write up and you won't go wrong.

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I delayed putting the insulation on my SLXI cause I didn't think it would help much. I rode in a v-drive and noticed how much more quiet it was than my DD, so decided to give it a try. I took a different approach than most folks here. I used a "skinned" 1" thick foam from McMaster-Carr instead of the foil backed that most here have used. I think it looks better, you don't even notice that it is there when you lift the cover. The skinned has a slightly higher sound absorption coef. and I thought it would absorb the heat as opposed to reflecting it back to the engine.

I was very impressed with the results. I don't have any scientific results, but I know that we can hold a conversation at operating speeds when we use to have to scream over the engine noise.

I'd do it again, best $100 I've spent on my toy.

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Did you buy a kit or just go to the store and put one together?

I bought the insulation from McMaster Carr ($75) and a can of spray adhesive from Home Depot ($3-$4?). I used duct tape on the seams which held up fine, but some people bought the metal tape.

I agree with kb on the noise reduction at cruising speed. I noticed a big difference there too.

Edited by Dan P
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Doughickey could probably dig out the readings that he took. It won't take away your V8 rumble, the exhaust note gives you that. It does make a difference in our boat, it's definitely a bigger improvement at lower rpms, but we do see a difference between the observer & the driver even at ski speeds. The back seat is a different story though. I'm still thinking about the Silent Riders for that.

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Silent riders are high dollar from what I understand.

I could be wrong, but the parts themselves I've heard are only a couple hundred dollars. Putting them in is a big chore though, the entire backseat & gas tank have to come out. If I do it, I'll do the turn downs at the same time.

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We can tell a difference at the low RPM's, especially when talking to the people next to you if you're the driver.

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From Doug,

I added the insulation (2 double kits from Overton's) to the inside of my 1998 RLX motor box.

I did some sound tests with a dB meter from Radio Shack.

The sound drop at low speeds is VERY noticeable. The sound dropped about 12 dB at idle at the drivers seat (and passenger seat.) Sound was in the mid 60 dB range (A scale) I recall. (I did post all my measurements in an earlier thread.)

Unfortunately, at higher speeds (above 15-20 mph... when the exhausts are above water) there is virtually no drop in sound. The exhaust and wind noise is still in the 98-99 dB range at the drivers seat.... both before AND after adding the sound insulation.

Was it worth installing... YES. Having the lower level sound when idling along at low speeds lets folks have a normal conversation. Quite is nice sometimes.

At high speeds...we're usually too busy having a blast watching whoever is behind the boat. When I ski behind my own boat.... kinda nice to hear that deep V8 rumble pulling me .... gets me pumped!

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Thumbup.gif great mod - well worth it. Tracie sent me her a draft of her early write up and it helped a ton. I got a deal on the overtons kits at the time (needed two of the smaller ones). I think now it's cheaper to get the material from mccaster carr as a couple of people have suggested).
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I did it as well with self tac sound insulation and metal vent tape. kinda fun to do and makes a big difference for the front seaters. You still get the SAME rumble from the exhaust.

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Mine is not insulated and I've asked my son several times if the engine is running or if he shut it off. Hmmm..... guess it would be even better if I insulated it. ;)

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I bought the foam from McMaster. I can dig up the part # if you need me to. 3M Spray Adhesive, foil tape and a sharp knife is all you need.

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I bought the foam from McMaster.  I can dig up the part # if you need me to.  3M Spray Adhesive, foil tape and a sharp knife is all you need.

I used the same stuff only I got the PRE-adhesive version for a couple dollar more...I didn't have any sticky mess to clean up... did it in my living room!!! Biggrin.gif

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I went this route very cheap and very effective. I went into this thinking I would have $25 into it instead of the $130 for the kit from overtons. I couldnt believe the difference.

Reflectix from Home Depot $15

Actual duct tape (foil type) $7

3M Self Adhesive spray $3

2 hours in labor for cutting

Difference it made in sound. Priceless :)

post-33-1122007062_thumb.jpg

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Henken,

That ROCKS!! YOU ARE THE MAN. I am going tonight.

That is a huge savings. I am on a short leash now with the boat.

This is one that I think she will love however. Then I will be able

to hear her...... :(

Edited by Headhunter 2317
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I went this route very cheap and very effective.  I went into this thinking I would  have $25 into it instead of the $130 for the kit from overtons.  I couldnt believe the difference.

Reflectix from Home Depot $15

Actual duct tape (foil type) $7

3M Self Adhesive spray $3

2 hours in labor for cutting

Difference it made in sound. Priceless :)

I love that idea, but I just looked at the Reflectix product page and the operating range is -60 to +180 degrees. I'm sure the engine compartment goes over 180 from time to time, say after shutting the engine down. Thoughts? (I'd love to go this route- my boat is too old to justify even the overtons' kit)

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Reflectix is made to slow radiant heat, not sound, so I wouldn't think it would work as well as sound insulation. The foam I got from McMaster was basically a 1" piece of foam with reflectix on the outside and is made specifically to dampen sound.

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Reflectix is made to slow radiant heat, not sound, so I wouldn't think it would work as well as sound insulation.  The foam I got from McMaster was basically a 1" piece of foam with reflectix on the outside and is made specifically to dampen sound.

This is what I thought too, but It actually works. Regarding the temp concerns. These engines are running at temps around 160, so the ambient air inside the engine box wouldn't reach a temp Higher than that especially with the air induction tthrough the vents.

Believe me I had all these concerns going into this. After completing the project I was constantly lifting the cover for evidence of melting or the insulation getting hot.

I can also say that the insulation has not moved since the day I did it.

If someone goes this route make sure you cover the cut areas with the tape before installing them

If someone would like Pictures I will email them to ya. For some reason they are very small by the time I shrink them down to 100kb to post :)

Edited by Henken
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