Improved Mercury Water Intake

Carl Guffey · Jul 27, 2009

Improved Mercury water intakes


I am following some advice from wrechin2 about lowering the chances of sucking air when running WOT with my 200 EFI and a hydraulic jack plate. I have closed the top five water inlets on both port and starboard leaving only the bottom three open with a slight modification to these holes to improve their intake capacity. The project itself is not very difficult, just requiring some personal time and patience. 


1. Mask bottom three inlet holes with duck tape to avoid cutting the wrong holes and to keep some of the excess material out. Also I taped a vacuum hose to the opposite side of the foot as I worked, which keep most of the debris out of the air and off the ground.
2. Using a Dremel tool and a coarse bit begin by relieving (opening the interior wall and removing the paint) each inlet.
3.After all inlets have been relieved, rotate the bit around each orifice forming a bowl.
4.Rough sand or grind an area around the inlets that you intend to close off to hold filling materials in place. I used a brass wire wheel brush and a drill to buff the adjoining surfaces.
5.To fill the inlet holes I used a short fiber fiberglass mat and two part West Marine 105 A & B epoxy resin. Begin by cutting two patches per side. A smaller patch to match the concave surface of the inlets and then a larger patch to smoothly blend into the surrounding area.
6.Make sure to have all patches cut and ready before mixing the epoxy resin because the pot or set up time is usually four to five minutes. Begin by wetting the patch area and then stick the smaller patch making sure that the fiberglass material is completely wet and devoid of air bubbles. A auto body filler wedge and a small paint brush make excellent tools. Hold the patch in place with the wedge and brush lightly in all directions to remove any imperfections. Working quickly, re-wet the surface and apply the second patch following the same method as the first patch to complete the installation. You should be able to complete both sides of the project before the resin sets up. Do not worry about runs, they will sand off.
7.Let the epoxy set over night and sand with a coarse paper (80 grit) the next day. I also used a coarse rasp and carved the top of inlets to resemble the original configuration of the factory Mercury foot.
8.Next, apply a good grade auto body filler to fill in sand and pock marks. After the body filler has set sand with varying grits of sand paper from 120 through 400 grit to achieve a smooth surface,
9.Use several coats of a good quality spray primer, sanding between each coat.
10.Finish with a quality epoxy paint (color of your choice).

AThornton · Jul 27, 2009

Nice work Carl!! emoThumbsup

NRG · Jul 27, 2009

I hope you used epoxy mat on that Carl, reg fiberglass mat the epoxy cant melt the bonding agent used on reg mat intended for polyester resin.
You could also do that with Grey Marine tex, using fiber glass cloth with larger holes it the cloth so that the marine tex can push thru the holes in the cloth.. then after cures, sand smooth, then fill with poly filler, then paint
or you could even have the holes welded shut, but that requires taking the foot off and apart .. boy is that ever fun

wrechin2 · Jul 27, 2009

Carl,
Looks good! Don't give all my secrets away!!!!!!! Did that bit work well that I gave you?? I ususally use short hair bondoglass and have never had any come out even on the faster boats. It always raised the water pressure. Doc's went from 14 to 18-19 with that modification. We had a baseline to compare to.

NGR,
Have welded them. If you noticed the lower on that shadow was welded. I done it. Was a PAIN to do. With aluminium being so porus and absorbing the oil, it makes for a trashy weld from being contaminated with oil. Takes alot to clean it. Just my opinion.

sdfd504 · Jul 27, 2009

Why not just use a tap and screw and have it done in a 1/4 of the time?

http://bbcboards.zeroforum.com/zero...master-lower-unit-blockoff-plug-install-wpics

Also I hope you have low water pickups on the lower unit?

wrechin2 · Jul 27, 2009

I do it this way for the cost and looks. Alot cheaper to fiberglasss them up and looks alot neater.

Why do you ask about a low water pickup???? Only the 3.0L torque masters have dual water pick ups. Side and bottom. This is off of a 2.5L. If this had a bob's on it all would be filled up on the inside and outside. Most people can't believe you can fill this many hole up and still have good pressure. You are feeding a tube with a 1/2" diameter. 6 of those holes can supply much more volume than the tube can handle. I have done MANY of these with no problem on mercs and OMC'. On my 2.0L lower with a Low water pick up it only has 5- 5/16" holes in it. Carl's still has more holes than mine and mine is a performance cone. Just my thoughts....

Carl Guffey · Jul 28, 2009

Wrechin,

The bit worked well. I have about three more coats of primer to do and then I am going to start the finish coats. I looked at this thread: http://bbcboards.zeroforum.com/zerothread/357425-torque-master-lowe... and although it is time efficent, it just looked a little sloppy. When I am done the finished product show look like it came straight out of the factory. The other side is that there will be far less turbulance and hopefully better performance from glassing the inlets. Even at 1/16 of a mile an hour, 80 and 1/16 mph is faster than 80 mph and it shows on the water.

sdfd504 · Jul 28, 2009

I hope it works out for you. Sure it may look a little "sloppier" from the way that is shown on the BBC, but atleast if you don't have enough water pressure you can take the screws out. Also I don't think you have a warranty on your motor from what I remember, but if you do I believe they only recommend plugging up the top 4 holes and if there are any problems they are likely to deny the claim if there are more then 4 plugged up.

wrechin2 · Jul 28, 2009

Apples to Apples. That article is on a 3.0L torquemaster with dual intakes. This is on a 2.5L with side intakes in a fleet case with a small water pump and 1/2" tube. This is the same lower as found on the 2.0L, 2.4, and 2.5L engines. Mercury actually builds 2 FACTORY cases for these engines that has 2 total holes and 4 total holes. Theses are the 2 and 4 hole CLEs.These are factory high performance cases. If mercury builds a 2 and 4 hole total lowers, don't you think 6 is enough?? Every one of these I have done have increased in pressure. But it is simple math really. The inlet side is larger (6-5/16" holes) than the outlet size (1/2" inner diameter of the tube). Here is the math...........................

Take the 5/16" intake holes= .3125 / 2 = .15625 rounded to .156 which is radius. Now squared= .156X.156= .024336 X 3.14 = .076415 rounded to .076. .076 is the AREA of each 5/16 hole. Now times that X 6 = .456. This is the TOTAL AREA of the 6 holes combined.

1/2" outlet tube= .500 / 2 = .250 which is the radius. Now squared .250 X .250= .0625 X 3.14 = .19625 rounded to .196. This is the AREA of the tube.

Now take the area of the inlets (.456) and divide by the area of the tube (.196) and you will see that 6 of the 5/16" holes has 2.3 more intake area than output area. This is how that filling all but 6 holes will allow the water pressure to rise with no issues. That is a 2:1 ratio on the area.

I can give you plenty of peoples names and number that I have done this on. I am building the engine for Carl and giving the warranty. If I didn't feel confident in this, I would have NOT told him to do it. If you know ditchdoc ask him what this did for his. His water pressure increased to 18-19 PSI from 14 at WOT and his only has the 3 on each side. I build alot of engines and do this automaticly on most to protect the engine and keep it from having a warranty issue from a overheat. Example is with the modifications to docs boat it started lifting much higher from the result from faster speeds. We did his after the first couple of passes and seeing the lower water pressure. Mercury wants at least 12PSI at WOT but I like the high numbers. Even though it was in specs why chance it????? Just my opinion....but what do I know?

Carl Guffey · Jul 29, 2009

Factory warranty is not an issue as the motor is a 97 version. As far as reworking , all I would need to do is simply drill another hole, spaced evenly above the other three, and port. I have looked at several different scenarios and one problem I kept looking at was that as the pressure decreased on the upper holes, in the stock (factory) configuration the lower holes would actually blow out the upper as the lower unit climbed toward the surface with speed, causing the engine to overheat due to lack of pressure. With the new set up, the chamber above the lower three holes actually acts like a bellows, building and holding pressure until it can be released into the waterpump. The upside is that I can now raise my motor a minimum of three inches over stock height and thatequals speed.

NRG · Jul 29, 2009

I just wish I had the HP to worry about it lol.. my lil v4 90 at best I'll prob see is 45, I have relieved my 17.5 Hydra-Sport of some its un-needed weight, removed the Big heavy plywood lids.
I replaced them with Aluminum lids, the rear lid and the rod locker lid are now Aluminum, that shaved off about 100 or so lbs from the boat. Every lil bit helps when you but is as big as mine lol
Now if I can just find a reasonable cost 4 or 6" Jack Plate!

Im working on my boat again.. sanding it now .. preping for epoxy, then base coat/clear paint, and carpet.. Hope to have it on the water within 2 weeks .. Im so excited to be getting close to done

wrechin2 · Jul 29, 2009

Carl,
It looks really good man!!! Can't wait to see it in person when we put the engine back on.

One of the biggest issue is the aerated water, the white water filled with AIR bubbles at the surface. Just getting below these will raise the pressure. That is where filling them really helps. When you get them completely out of the water, that is when they overheat due to low or no pressure.

NGR.....You know there is ALOT of potential with that engine you have. They can be made into a sleeper especially on that hull you have. Kinda wish I had never got rid of it. But oh well, I still have the potato chip hydrasport.

Hagen · Jul 29, 2009

Why do they put so many holes in it if you only need three? What about if your just idling around? How is the water pressure at low speeds?

wrechin2 · Jul 29, 2009

REMEMBER Water pressure is a direct result of rpms. You will have 1-3 PSI at a IDLE and around 10 PSI at 3-4,500K RPM's and need at least 12 PSI at WOT. This mod will ususally cause around 16-19 PSI at WOT. They put so many on them so if something does get sucked on the side there will be enough area that it will still get water in. Having all 8 on each side is ok if you do not have a performance need to raise it. Even with 8 holes mercury specs for 2.0L, 2.4L, and 2.5L is 1-3 PSI and at wot needs to be 12PSI. I have seen in some V-6 manuals 2-5 at idle. Mercury has a factory "fleet" case for the XR-4 and it has 4 holes per side.

This modification works well for most performance applications. If you add a Low Water Pick up such as a Bob's nose cone it will actually slow a boat down by around 4 MPH due to the added drag from the added lenth if you don't need a LWP. It will increase in speed if you have a surface piercing prop such as a chopper and raise it up very high then it will gain speed. You also need a LWP if your boat has speeds of 84MPH with a stock case as the shape will cause a void in front of the prop and cause the prop to "blow out" and you may go swimming.

So for a application such as his, this works very well. I have done alot of these and NEVER had any issues with water pressure. They always have great water pressure. This just allows for the case to run higher and result in more speed if the prop can handle being raised up. Ususually the biggest benefit is to get the water pump to pull solid water underneath the aerated water at the surface. This alone is the result for increase Water pressure.

Not saying everyone needs to fill up all their holes....But if you have a need to raise the lower, this is the best and cheapest and neatest way here. Carl's engine is here being rebuilt due to a overheat and melted 2 pistons very badly. It has hit his wallet hard. On most rebuilds I reuse pistons after being bead blasted and measured. If they pass, they ger reused. On a 2.5 with a overheat they ALL GET REPLACED. The reason is the locator pins. If the piston has ever gotten hot. It is not a question of IF but WHEN will they come out and eat his engine. So he knows all too well what will happen if you don't have enough water pressure.

After his is going again hopefully he will post how much more water pressure his had than before and be another sucess story...................

Later!

Hagen · Jul 30, 2009

Sounds interesting thanks for the answere. Wrench2 is DA MAN!

wrechin2 · Jul 30, 2009

No problem and thanks!

Hook1 · Jul 30, 2009

Wow, thats a pretty neat job. You may think of repairing damaged boats on the side if your paintings any good!

Carl Guffey · Jul 30, 2009

Hook1 - 7/30/2009 10:53 AM Wow, thats a pretty neat job. You may think of repairing damaged boats on the side if your paintings any good!

No thanks, there are a lot of very good people out there that are quite capable. I prefer working with wood and getting to fish a little. The way some boaters steer would make me work all of the time....

Carl Guffey · Oct 4, 2009

Just got my boat back in the water with some slight modifications. I finished painting the foot and made some test runs to check guage pressure, here are the results

idle: 6 psi

2500: 12 psi

3500: 15 psi

4500: 18 psi

sudden burst run: 20-22 psi

wrechin2 · Oct 4, 2009

Will get a thread wrote up on the engine build tomorrow. Maybe then you will know more about the engine as it will be close to broke in. Later!

Improved Mercury Water Intake

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