converting to through transom exhaust

  • 7 Replies
  • 4183 Views

steves86ta

  • Join Date: Mar 2013
  • Location: Beaumont
  • *
  • Macho Member
  • ******
  • Posts: 2,325
  • Karma: +38/-0
  • Registered User
    • View Profile
  • Liked:
  • Likes Given: 27
« on: April 03, 2013, 06:47:21 PM »
Hi guys,

Im in the process of planning an engine build for my 21 bahner and i was throwing the idea around about doing through transom exhaust while im in there. Now im on a budget of 1500 and that includes my engine build so if i cant make it happen for that i wont do it now.

My stock mercruiser has the old "exhaust Logs" that have the rear mounted risers like seen here


With the way it currently works i would be unable to run the exhaust straight back off of the logs through the transom, i dont have the room and the risers are to tall for that. Could i swap the sides of the logs then run long exhaust pipe back? I dont think the angle will work.

Does anyone have anyother ideas? Maybe run an "S" shaped pipe? anyone have experience doing this with this style of header? If it cant be done ill just put it back stock and switch to the center riser style later when funds are available?

Heres a picture i found of what the logs and risers look like. ill get pictures of how then sit in my boat later.



Thanks! and if anyone has stock center riser maniflds for a SBC for sale let me know if they dont fall out of my budget
1980 Bahner 21' Mini Day
1968 Rogers project



GT Jets

  • Join Date: Jan 2007
  • Location: Morgan Hill CA
  • *
  • Informative Member
  • *******
  • Posts: 11,704
  • Karma: +191/-0
  • Team Evil Weiner
    • View Profile
  • Liked:
  • Likes Given: 137
« Reply #1 on: April 03, 2013, 09:18:13 PM »
Hi guys,

Im in the process of planning an engine build for my 21 bahner and i was throwing the idea around about doing through transom exhaust while im in there. Now im on a budget of 1500 and that includes my engine build so if i cant make it happen for that i wont do it now.

My stock mercruiser has the old "exhaust Logs" that have the rear mounted risers like seen here


With the way it currently works i would be unable to run the exhaust straight back off of the logs through the transom, i dont have the room and the risers are to tall for that. Could i swap the sides of the logs then run long exhaust pipe back? I dont think the angle will work.

Does anyone have anyother ideas? Maybe run an "S" shaped pipe? anyone have experience doing this with this style of header? If it cant be done ill just put it back stock and switch to the center riser style later when funds are available?

Heres a picture i found of what the logs and risers look like. ill get pictures of how then sit in my boat later.



Thanks! and if anyone has stock center riser maniflds for a SBC for sale let me know if they dont fall out of my budget


Hate to do this to you, but......

You will have about $1500 in exhaust worthy of going thru transom on that deal...
Spoiler number two... Plan on replacing your prop. The 228 is a 305 Chevy and you are probably going to build a 350 (I would), you gear ratio in that drive should be a 1.50:1 and you are probably turning a 17"pitch prop, you will probably need to jump to a 21" pitch to get the RPM to stay in the acceptable range.

Keep your eyes peeled for the later style center riser exhaust, I just picked a set up for my neighbor for $150 and we converted it with some copper pipe (you could use galvanized steel conduit, but it don't live long because of rust).

Good luck, sounds like an awesome project.

A lot of out drives lately...  :-\

GT
  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
  • Boat #2: 19' Bubble deck Jet BBC Berkeley
If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:
Ray

carlitos

  • Join Date: Sep 2012
  • Location: lake elsinore
  • *
  • Full Member
  • ***
  • Posts: 119
  • Karma: +1/-0
  • Registered User
    • View Profile
  • Liked:
  • Likes Given: 2
« Reply #2 on: April 03, 2013, 09:39:07 PM »
i have some center riser manifolds for a 350 chev but the risers them self are missing i can take some pics if your interested
  • Boat #1: 86 bahner

steves86ta

  • Join Date: Mar 2013
  • Location: Beaumont
  • *
  • Macho Member
  • ******
  • Posts: 2,325
  • Karma: +38/-0
  • Registered User
    • View Profile
  • Liked:
  • Likes Given: 27
« Reply #3 on: April 03, 2013, 10:28:35 PM »

Hate to do this to you, but......

You will have about $1500 in exhaust worthy of going thru transom on that deal...
Spoiler number two... Plan on replacing your prop. The 228 is a 305 Chevy and you are probably going to build a 350 (I would), you gear ratio in that drive should be a 1.50:1 and you are probably turning a 17"pitch prop, you will probably need to jump to a 21" pitch to get the RPM to stay in the acceptable range.

Keep your eyes peeled for the later style center riser exhaust, I just picked a set up for my neighbor for $150 and we converted it with some copper pipe (you could use galvanized steel conduit, but it don't live long because of rust).

Good luck, sounds like an awesome project.

A lot of out drives lately...  :-\

GT

Thanks for getting back to me, yeah i figured i wont be able to do it with this budget which is fine no biggie.

As far as the prop i know ill be looking for another one. I currently have two, a 17 pitch aluminum prop and a 19 pitch stainless steel prop. With the engine plans i have, i am thinking ill be needing to lean towards a 21 or possibly a 23 pitch.

heres the outline for the engine, should be an honest 350+ horse
1998 Vortec shortblock (all new rings bearings etc)
Stock compression 9.3:1
Stock vortec heads for now (until i can afford an aftermarket set)
Custom cam that i dropped off at my grinder today. 224/224 @.050 503" lift on a 110 LSA (he has one in his boat which is a stock 350 mag, and has done hundreds of them. It is a monster of a cam tons of lowend and midrange plus pulls all the way to 6K with the right prop)
Performer or Performer RPM intake if theres room
and a 650 marine carb yet to be decided

The shortblock i have is out of an old truck i had, less than 40K on it but its getting freshened up. It should be a decent running setup though nothing overkill. And if im lucky it will push the boat quite a bit harder than the 305 thats in it.

Then down the road i plan to build a 383 with another block i have sitting around
1980 Bahner 21' Mini Day
1968 Rogers project

steves86ta

  • Join Date: Mar 2013
  • Location: Beaumont
  • *
  • Macho Member
  • ******
  • Posts: 2,325
  • Karma: +38/-0
  • Registered User
    • View Profile
  • Liked:
  • Likes Given: 27
« Reply #4 on: April 03, 2013, 10:30:50 PM »
i have some center riser manifolds for a 350 chev but the risers them self are missing i can take some pics if your interested

Please do, are they the factory Mercruiser style? Would all i need is the risers?

Thanks
Steve
1980 Bahner 21' Mini Day
1968 Rogers project

GT Jets

  • Join Date: Jan 2007
  • Location: Morgan Hill CA
  • *
  • Informative Member
  • *******
  • Posts: 11,704
  • Karma: +191/-0
  • Team Evil Weiner
    • View Profile
  • Liked:
  • Likes Given: 137
« Reply #5 on: April 03, 2013, 11:02:22 PM »
Thanks for getting back to me, yeah i figured i wont be able to do it with this budget which is fine no biggie.

As far as the prop i know ill be looking for another one. I currently have two, a 17 pitch aluminum prop and a 19 pitch stainless steel prop. With the engine plans i have, i am thinking ill be needing to lean towards a 21 or possibly a 23 pitch.

heres the outline for the engine, should be an honest 350+ horse
1998 Vortec shortblock (all new rings bearings etc)
Stock compression 9.3:1
Stock vortec heads for now (until i can afford an aftermarket set)
Custom cam that i dropped off at my grinder today. 224/224 @.050 503" lift on a 110 LSA (he has one in his boat which is a stock 350 mag, and has done hundreds of them. It is a monster of a cam tons of lowend and midrange plus pulls all the way to 6K with the right prop)
Performer or Performer RPM intake if theres room
and a 650 marine carb yet to be decided

The shortblock i have is out of an old truck i had, less than 40K on it but its getting freshened up. It should be a decent running setup though nothing overkill. And if im lucky it will push the boat quite a bit harder than the 305 thats in it.

Then down the road i plan to build a 383 with another block i have sitting around
Sounds pretty stout, you literally cannot turn that drive more than about 5000 rpm and have it live long.

Drive shower, good synthetic gear oil, oil reservoir, and double check the upper gear clearances and it will live for a lot longer.

Let me know when you get to that point.

Those heads are awesome. Do you have the early ones or the late ones?

I have one with the early and one with the late, using the gmpp hot cam in my Carrera with the late heads, dyno says 385HP at 5100 rpm. Can't wait.

Got a Bravo I when your ready to go hard core.
  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
  • Boat #2: 19' Bubble deck Jet BBC Berkeley
If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:
Ray

steves86ta

  • Join Date: Mar 2013
  • Location: Beaumont
  • *
  • Macho Member
  • ******
  • Posts: 2,325
  • Karma: +38/-0
  • Registered User
    • View Profile
  • Liked:
  • Likes Given: 27
« Reply #6 on: April 04, 2013, 10:01:23 AM »
Sounds pretty stout, you literally cannot turn that drive more than about 5000 rpm and have it live long.

Drive shower, good synthetic gear oil, oil reservoir, and double check the upper gear clearances and it will live for a lot longer.

Let me know when you get to that point.

Those heads are awesome. Do you have the early ones or the late ones?

I have one with the early and one with the late, using the gmpp hot cam in my Carrera with the late heads, dyno says 385HP at 5100 rpm. Can't wait.

Got a Bravo I when your ready to go hard core.

Thanks for the heads up on the drive, i do plan on having to baby it atleast for this season. The plan is to buy a new one i was looking at the SEI 106  which comes with a 3 year no questions asked warranty for 1300. However depending on cash flow i would really like to upgrade to a Bravo 1 so i dont have to worry about it. Are you saying you have one that you may be able to get for me? How much work is it to swap over to the Bravo from the current drive? And how costly?

As far as the heads go i have the "906" castings. The plan is to run these with LS6 beehive springs so there is no machining then if/when they pull a stud (more than likely when) im going to throw a set of aftermarket heads on, either E-Tec's or something along the lines. I dont have to stick with vortecs because i have an extra performer intake for centerbolt style heads.

Let me know about the Bravo
1980 Bahner 21' Mini Day
1968 Rogers project

carlitos

  • Join Date: Sep 2012
  • Location: lake elsinore
  • *
  • Full Member
  • ***
  • Posts: 119
  • Karma: +1/-0
  • Registered User
    • View Profile
  • Liked:
  • Likes Given: 2
« Reply #7 on: April 04, 2013, 09:24:26 PM »
Here's a pic. It's still on an engine
 
  • Boat #1: 86 bahner

 


Website Security Test
Powered by EzPortal
Null

Website Security Test