Did you figure anything out on the possible short?

Wildman,

No. As much as I'd love to, the shop that did the machine work gets $850 for a dyno session, and I just can't justify the cost. The builder has a preliminary base tune worked up, based on similar builds, and that will get it running on the stand. Once we get the engine back in the boat, it will have to wait until weather permits and we will go out, laptop in hand, and do final tunings, based on VE AFRs. This is fine, as I some need time to finalize the exhaust from the riser-elevated elbows to the tips.

One of the really cool features of the Holley HP is the self-learning function. As I'm told, you set the target AFR range, and the ECM works it out as you go. Once the tune is set, you save it and set the ECM to closed loop and disengage the O2 sensors. While I'm steadily wrapping my head around all of this, I'm leaving these aspects to the builder, who knows the Holley HP like the back of his hand.

Thanks. Brad.

Ryan,

Couldn't find anything tangible, so I'm running on the theory you were right; that it's a continuity, due to a persistent draw (stereo clock, etc.), not a short. As we discussed, nothing was changed that would lead to a short. We'll know when I hook a battery up. There are breakers and fuses in place. If something pops up, we'll know.

Thanks. Brad.

Guys,

https://cimg0.ibsrv.net/gimg/www.off...2ad48c8af.jpeg
https://cimg2.ibsrv.net/gimg/www.off...9db8d0056.jpeg
https://cimg4.ibsrv.net/gimg/www.off...e26108cf1.jpeg

We eliminated the intake manifold OEM integrated “PCV” that was inducing crankcase pressure whenever we were in boost condition. So, I made an intake snout extension for the ProCharger that will allow for a vacuum draw on the oil fill cap.

The hose that was connected to the oil fill cap was previously just hanging in front of the breather on the ProCharger. This always led to the breather getting all gunked up. The extension will also get the breather about 2” further away from the belt and its dust.


Thanks. Brad.

I ran into the same issue on a car project of mine that I turbocharged... I didn't love the idea of running the crankcase ventilation to be the turbo inlet and all that gunk going through the turbo so I ended up installing a catch can inline to try to eliminate as much of this stuff as possible.. It has worked really well so far.. Have you thought about doing something like this? You just need to remember to empty it from time to time.. I try to do it every oil change.

I agree, probably wanna put a catch can in line with it.

AShipShow,

I have not. I'm not all that worried about an occasional spit of oil going through the intake. I Think just getting rid of the positive crankcase pressure condition will all but eliminate it, given the height of the oil fill tube. And, if not, at least it will not get on the breather anymore.

Thanks. Brad.

If you`re sending oil vapors back thru the intake just know oil lowers octane , I think it`s a terrible idea. Unless you have a vacuum pump you`re not getting rid of "positive crankcase pressure".
Everyone uses a catch can, especially on a blower motor.

Dan,

Is it oil, or oil vapors, or both, that lowers octane? And by how much? Additionally, a catch can doesn't eliminate oil vapors, does it? Genuine questions.

I don't expect to see literally ANY oil. The fill tube is literally the highest point on the engine. I also don't expect there to be any crankcase pressure moving forward. If oil reaches that hose head, I've got much bigger problems than octane.

Mercury has been running a hose from the carb flange or flame arrestor to the valve cover for decades. The hose connection in the fill tube cap is OEM, although I don't know where it connects for vacuum in OEM configuration. Hell, even Whipple doesn't include or prescribe a catch can.

Thanks. Brad.

Oil vapors and oil lower octane obviously vapors less than oil.
Isn`t that on the suction side where it will be in vacuum?
A catch can takes all the oil and vapors to a remote location and keeps them at bay instead of making a mess.

On a supercharged engine?

Looks like you got it figured out then.



​​​​​​​"While not strictly "required," installing a catch can on a Whipple supercharger engine is highly recommended as it helps to prevent excess oil from entering the intake manifold, which can be especially problematic with high-performance engines like those using a Whipple blower; this is due to the increased crankcase pressure generated by the supercharger.

Key points about catch cans and Whipple superchargers:

• Reduces oil buildup:
  A catch can traps oil vapors and droplets that would otherwise be pulled into the intake manifold, potentially fouling the intake valves and reducing performance.
• Improves engine longevity:
  By filtering out oil, a catch can can help extend the life of your engine by preventing harmful deposits from accumulating.

Oil vapors and oil lower octane obviously vapors less than oil.
Isn`t that on the suction side where it will be in vacuum?
A catch can takes all the oil and vapors to a remote location and keeps them at bay instead of making a mess.

On a supercharged engine?

Looks like you got it figured out then, 0 positive pressure is awesome , never seen an engine with 0% leakdown, that`s quite a feat. Please let me know what ring pack your engine builder is using :lolhit:



"While not strictly "required," installing a catch can on a Whipple supercharger engine is highly recommended as it helps to prevent excess oil from entering the intake manifold, which can be especially problematic with high-performance engines like those using a Whipple blower; this is due to the increased crankcase pressure generated by the supercharger.

Key points about catch cans and Whipple superchargers:

• Reduces oil buildup:
  A catch can traps oil vapors and droplets that would otherwise be pulled into the intake manifold, potentially fouling the intake valves and reducing performance.
• Improves engine longevity:
  By filtering out oil, a catch can can help extend the life of your engine by preventing harmful deposits from accumulating.

https://cimg7.ibsrv.net/gimg/www.off...f11f89ff6e.jpg
https://cimg8.ibsrv.net/gimg/www.off...d021483d80.jpg
https://cimg1.ibsrv.net/gimg/www.off...9fb34345b1.jpg
https://cimg6.ibsrv.net/gimg/www.off...11354dab47.jpg
​​​​​​​

Dan,

Yes. The hose will be connected to the intake side of the ProCharger. That's the whole point. The OEM intake included a vacuum tap on the bottom to do just that. All we've done is remove the potential for positive crankcase pressure due to intake manifold pressure. In other words, we've moved the vacuum tap to where it should be: Where there is always a vacuum.

Is the catch can not drawn to by intake vacuum? If it is, I get how oil would be filtered, but how are the vapors "filtered"? If not, where do you get your crankcase vacuum from? I'm not running a vacuum pump.

I'm not sure why a supercharger would make a difference, octane reduction aside (I didn't know this little factoid, BTW :ernaehrung004:). If oil in the intake is an issue, I'd think it would be an issue for a NA engine, as well. I would think fuel wash would do a sufficient job of keeping oil from building up on the valves. I could be wrong on that, though.

Where is the additional crankcase pressure coming from with a supercharger? Genuine question....

Again, I'm not anticipating literally ANY actual oil in this circuit. Vapors? Yes. Oil? No. I'm fairly certain, if we had any oil making its way to the breather via this hose before, it was only due to the positive crankcase pressure condition present while in boost. That potential is gone.

I appreciate the input. And I'm listening. I just want to try and understand, instead of just taking things at face value. It gets complicated when I get conflicting "absolutes" from voices I've learned to trust.

Thanks. Brad.

https://natrad.com.au/info-advice/wh...rged%20engines.
So where does the other end of the hose go , one side is intake of blower.. the other side goes ???

Two types of catch cans, remote like I have or inline like the above link.
The oil or vapors aren` "filtered" your other questions don`t make sense , google catch can or youtube it to understand how it works.
A supercharger creates more positive pressure leading to higher cylinder pressure leading to more blow by . Marine engines should be set up loose clearances especially on the ring package so to say I`ll have no positive crankcrase pressure is just not possible.

You`re going to have positive pressure at the engine and negative pressure at the blower opening (unless Im not understanding your set up) so ofcourse it`s going to suck all the oil and vapors in the intake .
If you think you`re not going to have positive pressure in the engine you`re dead wrong.
n/A engines do not have the octane requirement a blower does, they also do not have positive pressure in the intake so why we talking about N/A engines , has nothing to do with this conversation.

That being said here`s my N/A LS3 catch can I added because I don`t want all this **** in my throttle body/intake. I empty that can on the vette every 2 months and it`s full.


https://cimg9.ibsrv.net/gimg/www.off...af75b05695.jpg

Engines in an enclosed space will draw the local air and consume it, as the engine bay draws from the outside air.

Anything the crank case pushes out through a catch can...minor vapours etc will be diluted and also drawn in. No need to hook up the crank case to the intake vacuum.

My BMW 540 V8 PCv system used to fail and suck the oil into the intake like a straw. Failed process and system.

How an Oil Catch Can Works, And Why You Might Want One


You want one. The blower will push air past your rings and pressurize your crank case with gas/air. That helps to break down the oil along with heat. The oil then vaporizes and leaves as a gas through your valve covers. Factory reburns this to be green. Performance people do not want to burn this crap. You can do a couple of things to keep from re burning it. Vent to atmosphere, vent to a catch can then atmosphere (cleaner engine bay), Send it to your exhaust using to principal you are and using the exhaust to draw a vacuum, Send it to catch can using a vacuum pump (some people even use old smog pumps), or add a catch can in line with what you are doing. It will still re burn the crap (Go Green) but will be filtered and cut down on a lot of the crap. A boat exhaust would be hard to use as extraction point for the most part. Pulling a vacuum in the crank case will give you power but not sure if the negative of re burn is worth the minimal vacuum. If you try yours with a can and do not like the re burn/ or lack of vacuum it provides you can simply pull the line from the can to the intake and put a filter and plug in place.

Dan,

The other end is attached to a fitting in the oil fill cap, which is in the top of a 6-7” tall oil fill tube, which is located in the mounting flange of the intake manifold.

If you’re pulling intake vacuum from your crank case, and you have positive crankcase pressure, you have something wrong. Like a broken ring. Hell, with the setup we had before, the only reason I think we had positive crankcase pressure is because we had oil bubbling out the top of the dipstick tube, but only after I’d run under boost.

My “other question” is, with a catch can, is there vacuum drawing on it?

I mentioned NA because you asked, “On a supercharged engine?” I can’t, for the life of me, understand why boosted or NA would be any different, other than the octane requirement and the potential for octane reduction from oil in the intake (as you’ve indicated). And, for the record, all the old school blower motors I grew up boating with had a vacuum port in the carb flange, with a hose leading to a PCV in the valve cover. Every single one of them. This is essentially what I’ve got, only my engine end connection for the hose is a country mile from any real exposure to incidental oil spatter, like what is present under a valve cover. I can say I’m not going to have any crankcase pressure because I’m drawing a vacuum on it.

At the end of the day, if we see any indicators of a significant amount of oil getting into the intake tract, I can add a catch can. In the mean time…

Thanks. Brad.

Tartilla,

Yup. I remember watching my dad change the PCV valve on the blower motor I grew up skiing behind. It had a vacuum line between the carb flange and the valve cover, where the PCV valve was. He would notice a loss of oil, and that was his sign it needed changed. I think he replaced it every year, regardless, but, once or twice over the years, they would go bad mid summer and he’d have to spend the 24 seconds it took to change it. Otherwise, we ran that engine for years and did nothing but change the oil and plugs every year. The first year we actually had to pull the engine (an unfortunate incident involving a log and a cracked hull at the prop strut), I can remember looking down inside the blower, and there was no sign of oil or any kind.

Thanks. Brad.

ZFrilly,

How does drawing crankcase vacuum increase power?

I’ve always understood it that a crankcase vacuum is to prevent excessive oil consumption.

Thanks. Brad.

HUH?? how can you have vacuum and positive pressure in the crankcase at the same time? What is intake vacuum in the crankcase ?
No need to answer,I`m done arguing with you , I got better **** to do.
3 people tried to explain this to you , I gave you all the info , pictures and links you needed and then some but I wasted my time because after all the proof you still are like you`re all dummies I know better because my dad changed a PCV valve on a ski boat .:rolleyes:

If you don`t understand why there`s more pressure in the cylinder of a blown engine vs. N/A I can`t help you .
How do you not get that you will have positive pressure in the crankcase and negative pressure in the intake and that means that all the oil and vapors will be getting sucked into the emngine , I mean this is 5th grade physics. Blow into a hose and it comes out the other end , it`s not rocket science.

Everything I referenced says put a fuking catch can on it but you know best so good luck.
​​​​​​​

Guys,

For the record, I am not opposed to using a catch pan. It’s just that we didn’t have one before, and the builder never mentioned one when we discussed this vacuum tap ProCharger intake extension. We are getting together tomorrow and we will discuss.

Thanks. Brad.

Dan,

You're taking this all wrong. I’m asking questions for a reason. As I said, I’m getting conflicting information from voices I’ve learned to trust.

About vacuum and pressure…. Exactly. You CAN’T have positive crankcase pressure if you’re drawing a vacuum on it. From everything I’ve read, positive crankcase pressure is to be avoided. So a vacuum is applied. Or, at least, it’s vented. This is literally what a PCV is for. You draw on intake vacuum to pull any pressure from the crankcase. Like you said, it ain’t rocket science. It’s not like engines haven’t been set up this way since it was discovered that crankcase pressure was bad

Yup. A 900HP blower motor “ski boat”, that ran for years with nothing more than an oil and plug change in the off seasons. And that was set up exactly as I’ve described; drawing a vacuum on the crankcase from the flame arrestor.

I understand perfectly why there is more cylinder pressure in a boosted engine than NA. We weren’t discussing cylinder pressure. At all.

As I said…. I’m not opposed to a catch can. I will be discussing it with the builder tomorrow. He has two of them on his engine, but he also doesn’t have a full-on chimney where the vacuum will be applied.

Thanks. Brad.

I disagree. A boosted engine will see more pressure get past the rings and pressurize the crank case. What you are doing in not fully pulling a vacuum on it. IMO you will have more pressure on the crank case then your setup can get rid of.

What size line are you running from the valve cover to the air filter?

There was always additional power picked up when I increased the tube inlet size to the blower inlet, free hp. I would make the setup larger in diameter. You will have to get a larger diameter air filter setup though.

There are many benefits of running a vacuum pump. One is better ring seal/more hp.

vacuum in the crank case helps the rings stay seated and stable for a better seal

It helps to seal the piston rings and decreases effort required for the pistons to move. It has been proven over and over to add power. Thats why drag guys spend thousands of dollars for vacuum systems. Many of them have no engine bay to care about, they want power.

Under,

OK.... For context... The 496, in OEM configuration, has no vent to the valve cover. Never did. Not in the truck engine. Not in the Merc engine. GM's solution to crankcase pressure was to build a PCV of sorts into the underside of the intake manifold. It literally draws a vacuum on the crankcase, from the intake. This works great in the absence of a boost condition. In the presence of positive intake manifold pressure, this "PCV" actually induced pressure in the crankcase, in addition to whatever might already be there from ring blowby. This is one of many issues that ProCharger didn't address in their kit(s). In fact, after discovering the issue, by witnessing oil on top of the button at the top of the dipstick tube (that only showed up after I'd run hard enough to get into boost), I called ProCharger to see if they had any sort of fix for it, and they were apparently not even aware of it (at least, that's how it sounded over the phone). We have since eliminated this PVC circuit on the intake, so that issue has been resolved. As we bought the boat, there was also a port fitting in the oil fill cap, with a hose dangling in front of the flame arrestor on the intake snout of the ProCharger, which is down low on the port side of the engine. We did see SOME oil loss over time (a quart or so a season, maybe), but it was minimal, and I can't really be sure whether we were consuming it internally (rings, valve seals, whatever), through the vent hose and through the intake tract, or out the dipstick. I will say I never saw any oil to speak of in the bilge, so, while there was obviously SOME getting out the top of the dipstick, I don't think it was a significant portion of the little loss we saw. I know we hade a FARQ ton of oil in the bilge, front of engine and back of rear seat after the piston let go, so I'm very aware of what REAL crankcase pressure looks like. By the looks of the area of the bilge around where the ProCharger intake is (where the crankcase vent tube was dangling), there was no sign of a significant amount of oil, but there was a thin residue of what appeared to be oil vapor adhered belt dust. Nothing seemed irrational about it, considering the blower belt and vent tube in the area. There was also some of this gunk on the screen of the flame arrestor. This was actually where I initially came up with the idea of the extension that incorporated the port/hose barb in the pics above.

What we've done here is to move that PVC circuit from the intake manifold to the intake of the ProCharger. Whether there is any oil or oil vapor making it to the cylinders has not changed, outside the fact that it is less likely oil will make it to the port in the oil fill cap than there was it would get sucked into the PCV under the intake manifold (or, at least, logic would dictate). I have no doubt the current sitch is not drawing nearly as much vacuum as the OEM intake circuit was, but it's also never going to induce pressure of any kind. Essentially, what we have is a passive crankcase vent with some attempt to induce vacuum. Additionally, the OEM should have drawn less and less vacuum as the throttle body opened up, even without the ProCharger, as an engine at WOT is at zero manifold pressure; neither pressure nor vacuum, as I understand it. The current sitch should induce more and more vacuum as the RPM increases, to coincide with the potential for increased ring blowby due to increased cylinder pressures from boost. We have improved the overall setup by orders of magnitude, as-is, from my observation.

I just don't see the potential of a vacuum pump fitting into the current configuration. Not a belt driven one, anyhow. I suppose an electric one could be implemented, but I'm sure that opens up a whole new can of worms. FWIW... You'd be surprised how much vacuum can be drawn by venturi. Something very similar is used to empty waterbeds in a matter of minutes, even drawing the water uphill, and carburetors draw fuel by venturi principle. Once we get the engine running, I will check the draw on the vent tube. I'm betting it will hold itself to your thumb quite well. We'll see.

As it turns out, the builder has a couple catch cans he is willing to let me select from. We will be discussing the matter later on today (assuming we're still on). As I stated earlier, I am not opposed to the idea. We, the builder and I, just hadn't discussed it to this point. Someone asked if I was intending to implement one, I answered no, and the flame-on commenced. I think we had a fair bit of talking past one another. It happens on these forums. Meh....

I still can't wrap my head around the increase in HP from drawing a vacuum on the crankcase. But I'm certainly not going to argue against it, as I have no clue on the matter. My question on it earlier was a genuine one. That said, HP was never my interest in this specific venture. I was simply trying to do something with the crankcase vent and replace the crankcase vacuum draw lost with the intake manifold modifications.

To answer your question... It is a Ø1/2" ID hose, but there are ~Ø3/8" passages through the fittings on either end.

Thanks. Brad.

Technical Minute: Vacuum Pumps and Power - Automotive Tech Info

If you end up using the catch can, I would look at the Motion Raceworks one. I put them in my black thunder laster year and have been very pleased with them. There is a big difference between the cheap ones a good ones.

Brad everything you typed out about the stock 496 truck engine has nothing to do with a boosted 496 marine engine. It isn't even apples to oranges.

I'm curious how much "vacuum" do you think your new setup will put on the hose mounted between the tb and air filter?

UnderPSI,

No? The only differences between the truck engine and the Merc engine are the cam, a deleted fuel return line, the cooling plumbing, exhaust and ECM. That's it. Same rods, pistons, rings, intake... Literally ALL the components related to the topic immediately on hand are the same. Since my engine actually has the good crank, I suppose Merc might have had the presence of mind to actually address the main and rod bearing clearances while they were at it. I'm not holding my breath, because they chose not to address the valve springs while they were changing the cam (all this assuming Merc actually did these things rather than specing these changes from GM). Otherwise, ProCharger and their significant shortcomings with the kits they provide aside, not only is it, in fact, apples to apples, it's granny smiths to granny smiths. I was simply laying out what I had prior to the piston failure. Keep in mind, the ProCharger has been on the engine since LONG before I bought the boat. Prior to the piston failure, whenever in boost condition, we were actively pressurizing the crankcase, despite an open vent in the oil fill cap, enough to force oil up and out of the top of the dipstick tube. I'm guessing it's been running like this for 300+ successful hours. In the rebuild, we have converted from that condition of actually inducing positive pressure into the crankcase under boost condition to, at the very least, NOT. That alone is a MASSIVE improvement. With the hose connected on the intake side of the ProCharger, that port will always be in a state of vacuum until whatever blowby we have induces more pressure than that vacuum can overcome. Since that vacuum will be relative to RPM, I'm betting that condition is never reached. We'll see.

As for the level of vacuum that will be pulled at the intake port, I'm betting it will be enough at WOT to pull a blood blister on whatever you're dumb enough to stick the other end of the hose to. Are you familiar with Bernoulli's principle and Venturi effect? Your carburetors are.

At the end of the day, I'm working with what I have. I HAVE to draw a vacuum on the crankcase somehow (right?), and I CAN'T do it with the OEM intake PCV circuit. So, I'm relying on the success of the dozens (of dozens...?) of 496 Whipple setups out there that DON'T have catch cans, but, rather, a blower intake ported PCV circuit and a filter on the end of a passive vent hose that NEVER has any oil in it. I am simply combining the two into one circuit. If, by some happenstance, I see oil or oil residue in this vent line after initial run in, I'll address this topic accordingly.

Thanks. Brad.

Why are you trying to re-invent the wheel on a 496? Just finish the thing and go boating. I can't imagine driving my self crazy like you seem to be on a simple engine build that isn't exotic or high power.

With all due respect.

Pasquesi,

The simple answer….? We’re not.

Very early on in this thread, Ryan asked if I was going to address the potential causes for the piston failure. With damned few exceptions, everything I’ve done has been to do just that.

The thing that most people who have not gone down this road don’t realize is that there’s a lot to be desired about both the Merc 496 and the ProCharger kit that came on the engine when I bought it.

The engine itself is fine, but was initially designed as a truck engine that would spend 90% of its life at 1700RPM, would rarely see 3500, and almost never see 5K. A boat engine spends 90% of its life at 3500, is ran extensively at 5K and literally NEVER sees 1700 other than sweeping past it getting on or falling off plane. Pretty much NOTHING that is going to take issue with these differences in design directive was addressed when Merc marinized the long block for marine use. Those differences have now been addressed.

The ProCharger, while the unit itself is fine and does its job perfectly well enough, the kit they sell with it leaves a LOT to be desired. These issues have all been addressed.

Damned little else has been done. Yes, we swapped to roller rockers. Who is going to argue this decision? The decision for 1.8 ratio was superficial, admittedly. So was the decision to drop 1/4” on the blower pulley diameter. Otherwise, I suppose we could have just ordered all OEM parts, slapped it all back together and started counting backwards from a number, waiting for a piston to let go again. Would that have been a better route to have gone? :faint2:

Additionally, this is a ProCharger, NOT a “supercharger” like most of us refer to. While a Whipple or a Roots pulls air through the throttle body, the ProCharger pushes it through. There are pros and cons to both, but these differences make approaching the various issues different. Changes had to be made for proper setup.

We aren’t reinventing the wheel. We’re making a square wheel round.

Thanks. Brad.

Guys,

So, looking toward the finalization of the exhaust from elbows to tips while recalling some specifics discovered on "demo day"....

For context, and believe it or not, this is all connected in my train of thought....

When I pulled the remnants of the exhaust, I found that the exhaust had gotten hot enough to actually melt and extrude some of the nylon (I'm assuming) reinforcement from its encasement in the rubber exhaust tubing on both ends of sections between the SilentChoice diverters and the exhaust tips. I also discovered a 1/4" ID check valve at the top of the pickup on the fuel tank that seemed VERY restrictive by the old hillbilly flow-thru test. Additionally, the builder found the oil to be black as black gets, and suggested it was from fuel contamination from running too rich. With the nature of the failure in mind, it's hard to reconcile all these details. Short of any conclusive evidence of some culpable failure that led to the perforated piston, the only realistic conclusion I can come up with is that we were, indeed, running fairly rich at idle and cruise (as is typical for the Merc 496 tune), but lean at WOT, caused by the restrictive check valve and a fuel pump that fell short of the prescribed 65-75lbs of pressure the ProCharger kit (I don't believe I ever saw anything over ~53lbs). This doesn't really explain why just ONE cylinder went lean enough to cause what we found, but I guess one of them had to go first. We have since rebuilt the entire fuel delivery system from tank to intake manifold, including 80lb/hr injectors. Assuming we've eliminated any and all potential systemic fuel delivery shortcomings...

Is it normal for the exhaust hose to get that hot; enough to, at least over time, melt the nylon reinforcement in the exhaust hose? Or will ensuring we are always delivering sufficient fuel as to not run lean correct this?

As I work out the details of the exhaust routing from the elbows to the tips, I'm inclined to use as little exhaust hose as possible, based on what I found, but this complicates the fabrication of what will replace the SilentChoice diverters after the choice was made to not reinstall them upon reassembly. If we remember, we've made elbow risers that elevate the elbows ~2-1/2" and tilt them 8°, and I intend to extend the elbows an appropriate length to bring the terminus back to original height and fill in the gap left by the removal of the diverters. As I see it, I have three choices:

1) Just use exhaust hose to fill the entire gap between the elbow extensions and the tips, allowing them to account for the difference in height and angle. A smooth sweep would obviously be the goal.
2) Fully fab the extension, including an 8° incorporated elbow at the appropriate point to precisely line up with the exhaust tip, using a short section of exhaust hose to couple them together.
3) Terminate the elbow extension wherever works out the best, fab up a separate elbow to recover the 8° tilt of the elbows, using two short sections of exhaust hose on either side to couple it all together.

#1 is the simplest, but will result in what I see as excessive exhaust hose in the final install.
#2 is the most complicated, but is the least amount of exhaust hose.
#3 is a middle ground between the two.

I won't really know if any of these are viable or not until we get the engine back in the boat, but I would like to have my options fleshed out before we get there.

Thoughts?

Thanks. Brad.

Draw us a picture of the side view and you will probably get more response. I can tell you this for sure, if you are putting rubber hose where the exhaust exits the elbow or riser or whatever you are using, it must be in a straight line for several inches. If you try to tilt the hose up or down very much at all the hot exhaust will burn a hole right through it. I have typically extended my tails to within an inch of the thru-hull tips and used a 4" rubber or silicone coupler to join them together.

I know you don't want to do this, but it's what we did when I redid the exhaust. Fit it up, put screws through and marked them. Then sent to CMI and had them make up some dry to tip tails. Fit perfect.


https://cimg1.ibsrv.net/gimg/www.off...25a19371ff.jpg
Result:

https://cimg3.ibsrv.net/gimg/www.off...faadc2d1d3.jpg

Snap,
https://cimg6.ibsrv.net/gimg/www.off...971b5bc3a7.jpg

These are obviously for reference only. Reality will dictate final dimensions. The plan is to cut the trumpet off the OEM inner tube of the elbow and weld the inner tube extension to it. It will be telescope fit over the OEM tube, full seam welded at the base of the dam plate and tack welded through holes in the extension tube to the OEM inner tube. Then the new dam plate and outer tube will be welded to the outer body of the OEM elbow and the new dam plate, extending the water jacket and exhaust passage. A, 8° elbow with then be welded to the end.

Looking at it, I'm not at all a fan of option #1, for a couple reasons, including what you mentioned. It was a concern when I asked, for the reason you mentioned, and based on what I saw with the melting nylon reinforcement oozing out of the original exhaust tubing. I suppose I could use a straight filler tube and two sections of exhaust hose per side.

#2 is, in my opinion, the best option for functionality, but obviously the most complicated to get right. It would most likely require tack welding in the boat to ensure alignment of the 8° elbow at the downstream end of the extension and the exhaust tips.

#3 will be much more forgiving, as it will allow for adjustment at assembly.

FIW... I also just realized I hadn't represented the exhaust hose for the OEM configuration that included the SilentChoice diverters like I did the others. There obviously was, though....

Thanks. Brad.

Wildman,

I don't hate the idea, but I certainly don't want to go to the expense. I could be talked into incorporating the flex coupler at the joint between the elbow and the extension, however, If I could find either a weld-on flange or work out the dimensions and make them, but how is the inner tube connected? I will admit I am a little bit concerned about the welded-on extension.

I'm also never going to get dry exhaust past the CFO. She's already kinda peeved we ditched the SilentChoice. She's not as keen on the cackle and rumble like we refined folk are. :ernaehrung004:

That looks sweet, BTW...

Thanks. Brad.

You know after looking at your drawing the one thing you can take away is using the PVC to mock it up, and since it is wet exhaust much easier to weld up yourself or any competent shop.

I like 2, only one rubber coupling.

Wildman,

The OEM SilentChoice setup had two coupling joints per side. That doesn’t worry me so much as the exposed length of the exhaust hose at the joints. I’ve been thinking I’d be trying to keep any gaps to 1/4” or so, but Snap mentioned he’s had 1”, so it’s good to know I’ve got some leeway there.

#2 was the initial concept from the start, but the complications of it has led me to ponder and consider other options. I’m still leaning that direction, but haven’t ruled anything out.

The whole idea behind the 8° tilt of the riser was to bring the C/Ls back together somewhere near the inside end of the tips without an S-bend. Given I’m having the welding done on-site, I really think I would have as much time in a PVC mock up as I would just welding it as I fab it. I’m very sure if I were going the S-bend route, my tune would be much different.

Back to the discovery that led me to this particular line of questions…. Is it normal for the exhaust to get hot enough to melt the nylon reinforcement inside the exhaust hose? Even with fully wetted exhaust?

Thanks. Brad.

The only time I've blistered the inside of the rubber exhaust hose is when I had a seawater pump/flow issue.