4TEC engines... louder at ~5000 rpm?

[Michael211_2000]

Something I've noticed for awhile now, my engine's exhaust get's significantly louder at just over 5000 rpm's and I feel a slight vibration increase... but once into the upper 5K or low 6K the sound level (from the exhaust at least... wind screaming past my ears get's mighty loud though hehehe!) quiets down (I think) and the vibration I felt goes away. Has anybody else observed this?

I think it may get louder as the hull's OEM exhaust outlet comes higher out of the water, hard turns and accellerating from stop at ~5K+ rpm's I don't notice the sound increase until I get fully on-plane and up to speed. There is however a slight vibration increase in the 5K rpm range no matter what though IMO. Thoughts?

Everything seems to be running fine, no oil consumption antifreeze level has been stable... it just bugs me that's all. Since this is the only 4TEC PWC I've ever ridden I wondered if other's have noticed this???? Below 5K it's quite as a kitten purring...

Thanks!

- Michael

 

[470]

You are correct with the sound. I found playing with the trim at all rpms changes the sound, even idling out of the harbor. As far as the vibrations I won't worry about it. Rotax has made a lot of engines over the years that have had some serious questionable harmonics. The 650 single cly Rotax motor in my BMW cycle has vibes below 5000 rpm then smooths out.The 1200 triple cly Rotax motor in my sled has harmonic vibes between 4000-4500 rpm. My sons parallel twin 800 (Rotax) in his BMW GS buzzes every where. The worst one is their 800 twin used in their sleds. Great motor (stump puller) but you would think it was a single cly thumper.

 

[Michael211_2000]

My year model RXT doesn't have adjustable trim VTS (something I'm looking to add to it in the future, though).

Thanks for the info.

- Michael

 

[Superbadz]

Check the metal exhaust box, there are 2 rubber pad under the box. Both of mine pads were came off, and i had same problem as you.

 

[Coastiejoe]

I found a sticky rubber pad in my driveway and had no idea what it was, though it did come from my GTX after I had cleaned it. Hmmm,,, they are at the dealer getting the oil changed and winterized right now. Once I get them back I will take a look there.

My RXT-X which is supercharged is over-all MUCH quieter ride. I have always been shocked to hop on the GTX and find how loud it is. Not loud enough I felt there was a concern, just louder than my RXT by a considerable amout.

 

[Michael211_2000]

Check the metal exhaust box, there are 2 rubber pad under the box. Both of mine pads were came off, and i had same problem as you.

Thanks! How do you check these pads without removing the exhaust box though?

Winter's almost here in my area, I'm only planning a few more weekend outtings with mine as soon as we get a forecasted overnight freeze I'll winterize and then have all winter long to explore this possibility and/or replace the pads if needed.

What you say does make sense though, those pads would likely wear over time and/or slip out from under the box possibly. That is kinda what it sounds like to me at ~5K rpm's in fact, like something is vibrating loudly in the stern and the ~5K rpm range is where this engine seems to have it's highest vibration levels so....

- Michael

 

[Superbadz]

It will be easier if you remove the box.

My rubber pad slipped out, i saw both flapping around. I manage to put it back without disconnect the pipes. Remove the tie down cable. Run a robe around the tank, pull it up about 1 cm, tie the robe to the trailer. Then refit the pad.

Hope this help