Exhaust bellows & through hull exhaust question.

[Sidney073]

I have a 1976 Classic 18, Chevy 383 Stroker, TRS 280, 21P Laser II with Nicson through hull exhaust. The exhaust bellows is not present from the hull plate (?) to the outdrive since it's not used for engine exhaust, I know on boats where the exhaust goes through the outdrive instead of the hull this would introduce the exhaust through the Prop Hub. My question is does the bellows still need to be installed, mine is not and I was curious if it needs to be? Also is there any effect on performance with the exhaust not being directed through the Prop Hub, and the bellows installed or not?
Thanks,
Sid

[gcarter]

No effect what soever. It needn't be there, even it were in use.
In fact, Merc stopped using an actual bellows there some years ago.
They replaced it w/a harder rubber tube that's only attached to the gimbal housing.
If there's a block off plate on the inside (the case if there's no exhaust yoke inside the boat) then there's no need for anything outside the boat.

[MOP]

Our shop spent about a month testing flares ans converging rings with the OMC tech, the object of both was to induce a vacuum behind the prop to draw out exhaust. The flared props showed the most significant gains. There is a post kicking around one of these sites maybe OSO can't remember, but with through hull it is best to have the boot removed and also the flare cut off the prop. Just having the boot off which I did the next day after reading the post relieves the vacuum behind the prop, I have yet to cut the flare off. Those that have done both report nearly a 1 mph gain.

[Ghost]

+1 on that.

DISCLAIMER: I don't know about the TRS. I'd think it was just like the Bravo in this regard, but I don't know.

As I read the bravo installation manual, page 19, it says if you're not using thru-hub exhaust (aka: you have a blocking plate instead of a y-pipe), remove the exhaust bellows entirely to reduce vacuum-induced drag.

http://www.boatfix.com/merc/Install/gas/86017200.pdf

[silverghost]

The old TRS outdrives had NO exhaust, or exhaust passages going through them to the propeller at all.
And no provision for ANY exhaust, or exhaust bellows..
They also had no internal water pumps or cooling water at all going through them .

[Sidney073]

[ QUOTE=$originalposter]{$pagetext}[/QUOTE]

Thanks to all who answered, I didn't think it would need to be on since the TRS doesn't have exhaust through the hub (I saw this when I rebuilt the drive last year.), just wanted to be sure on the bellows.

L8R,
Sid

[VetteLT193]

[ QUOTE=Silverghost]The old TRS outdrives had NO exhaust, or exhaust passages going through them to the propeller at all.
And no provision for ANY exhaust, or exhaust bellows..
They also had no internal water pumps or cooling water at all going through them . [/QUOTE]

I'm pretty sure TRS has exhaust bellows and provisions for exhaust. you are correct on the water pickup though.

[silverghost]

Vette~
I owned, & ran, a TRS drive for 15+ years~~~In fact~~ it is still going strong today with my NJ neighbor.
It has never been opened nor apart.

The TRS does not have any provision for any outdrive underwater exhaust, nor coolng water going through it, nor internal drive waterpump.
It uses a Merctrans, or Velvet Drive, hydraulic transmisson and also has No clutch in the outer drive itself .
It is a very robust drive that Mercruiser originally built for racing, & the Big Block's horsepower.
You cannot kill these old outdrives!

[BUIZILLA]

The TRS does not have any provision for any outdrive underwater exhaust,

that would be wrong, my Criterion (as were several before and after mine) was delivered with thru prop exhaust, in fact mine has the block off caps inside the transom assembly in place now where they added the thru hull right after it was delivered new.. mine also had the original bellows in place when I bought it, but now has a block off cap that I installed when TNT rebuilt the original TRS drive. Mine is 32 years old and original....

[Conquistador_del_mar]

Sid,
I also agree that you don't need or want the exhaust hose connected on your TRS 280 since you are running through transom exhaust. Concerning the statement that TRS drives never had provision for exhaust is wrong.
You might find this interesting as I did. I ordered a new 1977 24' Excalibur with thru transom exhaust and the 370HP/TRS engine package. After Lightning boats (builder of Excalibur at the time) had built my hull with my dark green gelcoat preference, they called to inform me that the 370HP package was back ordered so I went with the 330HP package. I picked up the boat in Sarasota and saw it was installed with thru hub exhaust instead of thru transom as ordered, but I accepted it thinking I could have it changed later. After getting back to Dallas, I ran with a friend who also had a 24' Excalibur but with the 370HP/TRS package and thru transom exhaust. We were both shocked (me pleasantly) to find out that our boats were exactly the same in performance and top end speed - about 65MPH. We would run for quite a few miles at top speed together with no difference whatsoever. I found out later that the 370HP was a 4 bolt main 454 engine with horsepower rated at a higher RPM than the 2 bolt main 330HP so no real difference in performance in actuality. I also found out later that there is a scavaging effect of the exhaust with running thru hub so there was no effective gain with the relatively mild engines in running thru transom exhausts.
I hope you find my digression interesting. Bill

[olredalert]

----My 1974 Spitfire came delivered with 2 280/TRS set-ups, and thru the prop exhaust. I have made block off plates already and will go with thru hull, although I will have in-line muffs. I still have the Y-pipes. Guess you are wrong Silver Ghost.......Bill S

[joseph m. hahnl]

I tried it with out the bellows on the Alpha. I found it cavitated the prop .It would blow out way to early trimming up. I ended up putting a rubber plumbing cap on the drive leg. all is good again.

[silverghost]

Guys~~~
My mistake~~~
I forgot my old TRS outdrive on the old Formula 27 had a Race style Super Speedmaster II lower racing drive unit on it which had No provision for the thru-prop exhaust on my TRS set-up.
I bought the boat when it was only nine months old; & used.
It came to me set-up this way.
I just assumed ALL TRS drives had no through prop exhaust.
You ALL proved me wrong here.

I still like the old heavy TRS drive units as they were built like a tank.
It's almost impossible to kill, or grenade, them !
Beef-Up the TRS hydraulic transmission's forward clutch pack with new clutches from BAM and they will hold-up to very high hosrepower, & torque , and also take lots of abuse..

[Sidney073]

[ QUOTE=$originalposter]{$pagetext}[/QUOTE]

I haven't had a problem with prop cavitation, the 21P Laser II feels and runs about perfect. I may try a cap on the outdrive side next time out. I really appreciate the responses
L8R,
Sid

[MOP]

[ QUOTE I haven't had a problem with prop cavitation, the 21P Laser II feels and runs about perfect. I may try a cap on the outdrive side next time out.

Do a couple of back to back runs, I put $5 bucks it will be a slower capped.