Do exhaust riser extensions allow you to run hotter cams without water ingestion?

[mylesm260]

I was trying to answer a question for fabrimicator the other day, and it got me thinking.

We all know running too hot of a cam can cause water to enter the combustion chamber through the exhaust.

And we all know manifold riser extensions help keep water out of the manifolds in situations where the water line gets too far bellow the engine (like if you beach you're boat, or if waves are hitting you're outdrive)


My question is, do exhaust manifold riser extensions also help with hotter cams?

 

[WizeOne]

Re: Do exhaust riser extensions allow you to run hotter cams without water ingestion?

I would think not. Reversion would occur at the point that the exhaust gases and cooling water join enroute to exiting the system. Risor extentions do not effectively alter that point.

That aside, what advantage would a 'hotter cam' provide? The hotter the cam, the more the torque curve moves up and away from where it is most needed.

Many a people have tried it and been sorely disappointed. There may be some small improvements in marine cams that cam grinders have developed but they would not fall into the catagory of a 'hot cam' and they also respect marine torque requirments, valve overlap and lobe tip seperation; the latter two being critical for not creating reversion.

 

[TilliamWe]

Re: Do exhaust riser extensions allow you to run hotter cams without water ingestion?

We all know running too hot of a cam can cause water to enter the combustion chamber through the exhaust.

And we all know manifold riser extensions help keep water out of the manifolds in situations where the water line gets too far bellow the engine (like if you beach you're boat, or if waves are hitting you're outdrive)


My question is, do exhaust manifold riser extensions also help with hotter cams?

The two ways you list for water to enter the cylinders are two separate, unrelated things.

The answer to your question is "No".

 

[mylesm260]

Re: Do exhaust riser extensions allow you to run hotter cams without water ingestion?

I was thinking the same thing with regards to the point at which the exhaust and water meet up. You're correct, it would still occur at the end of the downward section of the risers.

What if you fabricated a set of stainless steal risers, with a longer up and down sections, and made them meet up with the y-pipe at the lowest possible point?

I'm more talking theory here, I don't actually intend to change my cam.

For those who DO want to change their cams, getting rid of the ingestion issue (or at least making the issue a lot less restrictive in terms of cam choices) would open up all sorts of new cam profiles.


Obviously whoever was doing it would have to consider bottom end toque and WOT rpms.

But in some cases, it may be acceptable to add 400 RPMS to WOT and loose 10% of toque @ 2000 rpms, in order to have about 15-20% more peak HP....

*just rough estimates for an example, obviously*



I'm considering swapping from a 4.3 to a 5.7 for example, I was thinking of starting with a vortec 5700 and rebuilding it while my 4.3 sits in my boat. I've been considering a few different cam profiles myself, but until I saw fabrimicators posts, I had only planed using the stock vortec or stock marine cam.


Reading his posts got me thinking. There are a LOT of valve train (cam's rocker arms, etc) options for the chev small block. And not all of them involve sacrificing a lot of bottom end torque.

 

[mylesm260]

Re: Do exhaust riser extensions allow you to run hotter cams without water ingestion?

I did some quick and dirty work in photoshop to show what the risers would have to look like.

A c+c flange and 2 stainless steel mandrel bend U's should work for each side.

I found this image on Iboats from a google image search.
It shows various riser designs.

I picked the one I liked and modified it.
Obviously my design would be heat exchanger only.
And would require a custom engine cover (but then so do riser extensions.)

I'm not saying it would eliminate ingestion from hot cams, but it couldn't hurt.

It would require much more vacuum to pull the water up that far. You would have a better chance of getting away with some low RPM vacuum pulses from a slightly hotter (than is currently allowable) cam.


Again, just theory and just an idea.

 

[mylesm260]

Re: Do exhaust riser extensions allow you to run hotter cams without water ingestion?

Another idea that would definitely work:

It would be a thru-hull only design though, and would have some transom installation/sealing issues that would have to be over-come.

The water and exhaust would leave in different directions, and a small piece of pipe outside the hull would be left un-cooled (altho at that point, it wouldn't get too hot)

And yes I drew this in paint.

 

[TilliamWe]

Re: Do exhaust riser extensions allow you to run hotter cams without water ingestion?

I can't see the pictures, but I have three words for you:

water jacketed headers

 

[Bondo]

Re: Do exhaust riser extensions allow you to run hotter cams without water ingestion?

Ayuh,... Do a search for threads Started by Me,...
A few weeks ago, I posted a thread, with pictures to Explain this same dilemma to Tailgunner....

You need extended dry pipe risers....

I posted pictures of Stock Merc. risers,+ several aftermarket 1s I have...
The longest of which don't introduce the water for 18", instead of 4" or so of the stock units...

 

[mylesm260]

Re: Do exhaust riser extensions allow you to run hotter cams without water ingestion?

Try again, (I forgot I Was hosting those pics on my own computer and turned it off last night, duh')

Bond-o, I think it's you're pictures I stole!

 

[TilliamWe]

Re: Do exhaust riser extensions allow you to run hotter cams without water ingestion?

While raising the dry pipe will help, its not a guarantee. For the money you would be better going with a through the hull exhaust or water cooled headers.

Exactly. And myles, you are trying to do all this thinking, and you are still using the stock manifolds. Well, they are part of the problem too. They are a tad restrictive. If you want to cam up a boat motor, you gotta run dry headers (very hot and makes the boat less user friendly) or water jacketed headers with open exhaust (the open exhaust part is like a prerequistie to building power. it doesn't do anything by itself, but you have to have it or everything after it is a waste of time and money.). Good luck.

 

[Bondo]

Re: Do exhaust riser extensions allow you to run hotter cams without water ingestion?

I picked the one I liked and modified it. Bond-o, I think it's you're pictures I stole!
Again, just theory and just an idea.

Ayuh,... That's My driveway,+ those are My pipes....
The Gil's on the right, I stole on ebay,...
On the left is the stock Merc. 4",...
Center are the stock aluminum,+ SSteel for my Kodiack aluminum manifolds,..
Being Eddiemarine knock-offs, the SSteel Eddie's bolt right on... I bartered for them...

Go to someplace like GilMarine, or EddieMarine,... You'll get All kinds of Ideas....
Btw,...
Either of those places will Custom build whatever you want or need,...
For a Price....

 

[Bt Doctur]

Re: Do exhaust riser extensions allow you to run hotter cams without water ingestion?

This link is a well written article about reversion and includes riser cut-aways.

http://www.michel-christen.com/ExhaustElbows.pdf

 

[mylesm260]

Re: Do exhaust riser extensions allow you to run hotter cams without water ingestion?

Ayuh,... That's My driveway,+ those are My pipes....
The Gil's on the right, I stole on ebay,...
On the left is the stock Merc. 4",...
Center are the stock aluminum,+ SSteel for my Kodiack aluminum manifolds,..
Being Eddiemarine knock-offs, the SSteel Eddie's bolt right on... I bartered for them...

Go to someplace like GilMarine, or EddieMarine,... You'll get All kinds of Ideas....
Btw,...
Either of those places will Custom build whatever you want or need,...
For a Price....

I'm a bit of a part time fabricator myself, a good friend of mine has a shop with a C+C machine, he makes manifold flanges and turbo header manifolds all the time.

For all the @#$#ing around though..... I doubt it's worth it... I don't particularly want thru-hull exhaust.

My boat's a 21' open bow, I use it for relaxing on lakes, I like it quiet.

If it were a cigarette boat, and I used it to go super fast, then maybe.


This post was more for theory and conversation....

 

[wca_tim]

Re: Do exhaust riser extensions allow you to run hotter cams without water ingestion?

imco powerflow manifolds (or some of the others mentioned above, The imco's make more power than the others, aside from headers) with long risers will get you to the point where you can run as much cam as you could possibly want to for all around performance - that's if you go with through hull exhaust. You can run mufflers and even turn downs with them to make it much quieter than you might realize.

If you're dead set on running your factory exhaust manifolds and if you have the room, you can extend the center tube of the risers a foot or even more to get the water far away from the engine, and then run mufflers after that. I will say that the factory manifolds are a big barrier to performance and should be one of the things that gets changed pretty early in the process.

Just my two cents...

 

[fabrimacator21]

Re: Do exhaust riser extensions allow you to run hotter cams without water ingestion?

Interesting thread.... Myslem... I missed your pm until now.

The only problem I see with the aftermarket stuff is the price. Through hull is a great idea especially if you have some fabbing skills... could be done real cheap. However I like a quiet boat too, especially when trolling. I also like a somewhat throaty boat though. Problem is my regular passengers include a 2 1/2 year old so I think the through hull pipes are out of the question(for me at least). I do have some ideas for helping water ingestion though. Seems like a simple internal valve would do the job... much like some 2 stroke engines have. (see pic)


Also anything that you can do to increase the amount of space in the the manifold will help with sucking up water... just a basic can shape would work. It's just that much more air that has to be sucked out before vacuum is created. I think when you put these theories together with longer/higher then stock manifolds it may be possible to run alot hotter cams. Keep in mind this is just theory.

I also want to say that the whole idea that cams don't raise tq, they just move it is arguable... since grinding tactics and ramp rates have come a LONG way from older technology. For me, any new cam would be a 30 year leap in ramp rates/grinding improvements which does help alot with power everywhere. Also I'd like to add that while playing with the dyno program I've noticed that certain cams can make more power up top AND down low then "torque" cams. But those cams do have a border line duration.

And yes theres other things you can do to gain tq... Full roller block REALLY helps. Roller rockers really only give you high rpm gains. If you can get your hands on a roller motor then go for it. Port matching your intake manifold, cleaning up the heads (port and polish) and windage trays are all good ways to get cheap power. EFI is also a nice step up in low end tq compared to carb.

 

[mylesm260]

Re: Do exhaust riser extensions allow you to run hotter cams without water ingestion?

IF you read the article posted above on stock mercruiser designs it looks like there is a lot of potential for improvements.

Looking at the stock design, it's no wonder these motors suck up water on occasion. I don't understand why thy don't mix the water and exhaust lower down.

I mean I understand the design is to make the bellows and elbow joints serviceable, but if they could just keep the water and exhaust separate until the actual Y-pipe starts, it would make a huge improvement.

 

[fabrimacator21]

Re: Do exhaust riser extensions allow you to run hotter cams without water ingestion?

IF you read the article posted above on stock mercruiser designs it looks like there is a lot of potential for improvements.

Looking at the stock design, it's no wonder these motors suck up water on occasion. I don't understand why thy don't mix the water and exhaust lower down.

I mean I understand the design is to make the bellows and elbow joints serviceable, but if they could just keep the water and exhaust separate until the actual Y-pipe starts, it would make a huge improvement.

Well I guess so the more of the pipes are cooled which reduces heat under the engine box... but mine is completly different. The water enters at the front of the exhaust manifold. Looks like the exhaust manifolds have water jackets in them. Not sure exactly where the water ends up.

Looks like all you have to do is drill a hole and weld on a fitting though.