Exhaust Manifold Replacement - Marine Torq Stainless Steel

[maxfir]

My final parts arrived and was able to complete the install. They really are easy to install. I think the biggest surprise so far is how much better access to the engine and spark plugs there is compared to the old manifolds. A few notes:

 

1. You may order with either threaded port or hose flange for inlet. I got a threaded port and ordered Stainless flange adapter. The threads were 3/4" NPT to 1" Hose Flange

2. I was really surprised how bad the 4" Exhaust hose was bubbling inside the old hose. Will get a picture next time, but really glad I replaced the hoses. I would estimate the hose has been reduced by 1" internal by all the expansion bubbles. Makes me want to replace exhaust hose after muffler as well.

3. My Computer Box is touching the engine cover when down so will need to drill new holes to lower it. Consider this minor but do check if you have one. 

 

The Old:

 

The New:

 

 

[justgary]

Wow, those look great!  How much will you have to lower your control box?

[maxfir]

16 hours ago, justgary said:

Wow, those look great!  How much will you have to lower your control box?

About 1” in the stern section to have good clearance. Unfortunately the entire unit will need to lower and possible forward a bit rather than just lowering the back with how the front angles up.

[justgary]

53 minutes ago, maxfir said:

About 1” in the stern section to have good clearance. Unfortunately the entire unit will need to lower and possible forward a bit rather than just lowering the back with how the front angles up.

Is this something you could easily do by adding a small plate between the box and the bracket to get the offset you need?

[maxfir]

21 minutes ago, justgary said:

Is this something you could easily do by adding a small plate between the box and the bracket to get the offset you need?

I don’t believe so since there isn’t an overly large curve in the engine cover where it’s hitting. But will give it a try. 

[justgary]

13 minutes ago, maxfir said:

I don’t believe so since there isn’t an overly large curve in the engine cover where it’s hitting. But will give it a try. 

Is moving the box forward only a possibility?  Do you have enough cable to let it come forward?

What I meant by a plate is so you could move the box forward and down, not to the side.  Holes to pick up the manifold flange, other holes to hold the box.

[justgary]

Or you could just cut the flange off of the manifold and weld it back on at a different angle.

[AJwakedevil]

On 5/18/2022 at 9:23 AM, Woodski said:

And as with any heat cycled fastener, retorque them after a few heat cycles.

Heard some horror stories from my bro in the auto industry of heat cycled fastners breaking off and being a much larger chore. Should I be worried/ do anything to take proper care they come out cleanly?

[justgary]

20 minutes ago, AJwakedevil said:

Heard some horror stories from my bro in the auto industry of heat cycled fastners breaking off and being a much larger chore. Should I be worried/ do anything to take proper care they come out cleanly?

The auto industry uses uncooled manifolds, so they are a lot more likely to have stuck fasteners.  The manifolds on your boat may have rusted bolt heads, but they will probably come right out without much effort.

Stainless fasteners and some anti-seize is still a pretty good idea, though.

[maxfir]

On 5/20/2022 at 10:27 AM, justgary said:

Or you could just cut the flange off of the manifold and weld it back on at a different angle.

I was able to 1. Shorten the computer cover by 1.5” 2. Lower the stern edge  by drilling a new hole. It now also lines up with the exhaust hose angle.

 

Now fits under the engine cover and was least effort needed to make it work. I’ll say project complete! Started up in the driveway and sounds slightly quieter than old manifolds. Will get a full test in next weekend!

[TommyS]

On 5/20/2022 at 5:02 PM, justgary said:

The auto industry uses uncooled manifolds, so they are a lot more likely to have stuck fasteners.  The manifolds on your boat may have rusted bolt heads, but they will probably come right out without much effort.

Stainless fasteners and some anti-seize is still a pretty good idea, though.

 

[TommyS]

How much horsepower or speed or even RPMs did you gain with installing these manifolds?

[justgary]

I would not buy these with some expectation of power increase.  You may get some, but the primary reason to buy these is the corrosion resistance.  I'm sure the power isn't lower.

They are definitely quieter.

[Woodski]

@TommyS - there will be a slight gain in power / torque when installing a set of exhaust manifolds that have runners v the older cast iron open chamber versions.  Your question does not reference what is being replaced so hard to give an answer.  Typically, the exhaust manifold is not the only limiter for those looking to boost power.  Other areas to get a bump include the input air side of the system - cylinder heads, camshaft, intake manifold, etc.   It boils down to specifying a system or combination of matched parts to achieve a significant power increase of which the exhaust manifolds are one (important) part of the system.

[TommyS]

On 2/25/2023 at 10:49 AM, Woodski said:

@TommyS - there will be a slight gain in power / torque when installing a set of exhaust manifolds that have runners v the older cast iron open chamber versions.  Your question does not reference what is being replaced so hard to give an answer.  Typically, the exhaust manifold is not the only limiter for those looking to boost power.  Other areas to get a bump include the input air side of the system - cylinder heads, camshaft, intake manifold, etc.   It boils down to specifying a system or combination of matched parts to achieve a significant power increase of which the exhaust manifolds are one (important) part of the system.

Took out old stock manifolds and put in new stainless ones . Same as in this thread just wondering because I bought at 1/2 price.

[Woodski]

@TommyS - congrats on getting at a great price.  I have a different set on my boat so can not answer the question @justgary can probably provide the closest answer from his experience.  I did get a power gain from a manifold upgrade although I also made numerous other changes along the path to what I have now.  There is a volume of data / dyno pulls on a small block GM engine showing exhaust manifold improvements provide a power / torque gain.

[skisky89]

How often have you guys needed to snug up the bolts on your manifolds? I've needed 3 follow up re-torqs since August '22. Seems the bow end bolts need the most correction on my v-drive.

[justgary]

1 hour ago, skisky89 said:

How often have you guys needed to snug up the bolts on your manifolds? I've needed 3 follow up re-torqs since August '22. Seems the bow end bolts need the most correction on my v-drive.

Interesting.  I have not noticed any need to torque them again.  I will admit that I have not checked....

You might try tightening them while the engine is hot.

[wakesetta12]

On 5/5/2023 at 3:16 PM, justgary said:

Interesting.  I have not noticed any need to torque them again.  I will admit that I have not checked....

You might try tightening them while the engine is hot.

I've had mine get completely loose.  Anyone find a good solution? Use some thread lock?

[justgary]

8 hours ago, wakesetta12 said:

I've had mine get completely loose.  Anyone find a good solution? Use some thread lock?

OK, I'll go out and check mine later today.

Did you use the supplied gaskets or goop to seal the manifolds?  My gaskets are hanging on the wall.  I used Permatex Copper to seal the manifolds.  Maybe I used goop on the bolt threads also. 

Aviation shellac on the threads would be a good solution to the problem.  I love that stuff for marine applications.

[justgary]

Anybody interested in reopening the group buy?

[wakesetta12]

On 5/5/2023 at 3:16 PM, justgary said:

 

I did use the supplied gaskets

[skisky89]

Interesting, I'll try to snugg 'em up hot. Also adding this to my pre-float. Yikes, completely loose @wakesetta12 ?!

[wakesetta12]

 I'm wondering if they just need broke in and I didn't get it hot enough when I tightened. Will check again next time I'm out. Anyone try locktite?

[justgary]

8 hours ago, wakesetta12 said:

 I'm wondering if they just need broke in and I didn't get it hot enough when I tightened. Will check again next time I'm out. Anyone try locktite?

I would not use Locktite on them.  If anything, aviation shellac (such as Permatex 80019) is the ticket.

https://www.amazon.com/Permatex-80019-Aviation-Gasket-Sealant/dp/B000HBM3QQ?th=1