Repower time for the 370

Interesting stuff Henry.......thanks. I guess I will just see exactly what these monitors can do. Ummm, as far as the budget, it is depleted after this little upgrade......LOL

John
 
Final cost was 30.5k, however they didn't charge me for winter storage or shrinkwrap (boat was inside all winter), so I saved a few bucks there. Plus I was able to sell the old motors on my own. I've winter stored at this marina forever and have a great relationship with them, they treated me very good IMO.

John
 
Couple words of advice as I went through this as well but since I had new carbs I purchased new long blocks, FWC, etc. The newer engines have roller cams, and if you remain with the current log-style exhaust of the previous 7.4s you run the risk of sucking water up due to the static line being too low (I went with the 6 inch extensions). Also, I don't know what the power rating is on those engines, but you should have 1.25" shafts. Maybe someone else knows what they are rated for. You also might need to visit your prop selection to prevent the engines from either over/under working. I am not claiming to be the ultimate authority, but these were gotchas that I was warned about in considering my repower options.
 
Just another point to consider....my 380DA originally came with 7.4 Horizons, and those were replaced with 8.1s by the PO. Water injestion with the old exhaust system.... The 8.1 has more torque, and Sea Ray equipped the 8.1 boats with a 21x23, 4 blade props. The early boats had 21x22 props. The result for me is a boat that leaps when the throttle is applied, but doesn't run quite as fast on top end. You might want to verify your current prop specs. There might not be a need to adjust, but to better understand if your performance is a bit different.

Keep us informed,

Don
 
ATC said:
Couple words of advice as I went through this as well but since I had new carbs I purchased new long blocks, FWC, etc. The newer engines have roller cams, and if you remain with the current log-style exhaust of the previous 7.4s you run the risk of sucking water up due to the static line being too low (I went with the 6 inch extensions). Also, I don't know what the power rating is on those engines, but you should have 1.25" shafts. Maybe someone else knows what they are rated for. You also might need to visit your prop selection to prevent the engines from either over/under working. I am not claiming to be the ultimate authority, but these were gotchas that I was warned about in considering my repower options.
Click to expand...

1.25" shafts with 8.1s is probably not a good idea. 1.5" would be more like it.
 
The marina will be sea trailing the boat this week to determine any changes needed with the props. They had discussed this with me way back in the fall before the project started and just again this past weekend. They are not new to these type of repower jobs and I trust their judgement.

ATC.........you mentioned "static line"........what does that mean. There is a significant downward angle of the exhaust between the elbows and the "log", much more then the 7.4s had.
 
Last edited:
I have to concur with the previous posts about the exhaust. I would want the new style can mufflers installed not the older log style mufflers. There have been many boats with water ingestion due to the log style. I would certain as the marina about it as the original engines in my boat suffered the water ingestion fate.
 
Copied from another site. Spelling not my responsibility: "The static line is a measurement of the true water line on the engine to the top of the riser.(example half way up the exhaust manifold.)The way you find the static line is to take a one inch clear hose that's about 15 feet long. You take one end and put in in the water the other end you fill with water and bring it in to the boat. You make a loop in it and hold it up against the engine with the top of the hose above the engine with the loop below the engine with water still in the hose. What you end up with is the level in the hose is the true water line. You then make a mark on the engine usally on the exhaust manifold and you measure to the top of the riser. This is the static line. The water line to the top of the riser. Since the roller cam being used in the marine engine it has made the static line be increased because of the duration of the cam being used.The positive pull on the exhaust on the compression stroke. All engine manufactures are fighting this problem. (Water reversation) The manufactures have redesigned there exhaust requirements when installing the roller cam engine. There have been extentions made that go in between the manifold and risers. New style exhaust flappers. Mercruiser has made a resignator and Volvo has done some redesign on there risers they have tried pulse tubes. Now they have new guide lines for there exhaust requirements. Now they require so much drop with 90 degree turns on each turn."
 
would look for a set of water lift mufflers. Another Sea Ray owner at my marina bought them after he drowned his first set of new heads. No problems after that.
 
Last edited:
My 370 was retrofitted with water lift mufflers from the original design of the log style before I got it. This was Sea Ray's attempt to fix the issue of valve timing with the back pressure of the water in the exhaust. I've had my boat since '06 and no problems.

Gene
 
I'm not certain that the "suck back" caused by the Gen VI 7.4s is going to be a problem with the 8.1s. I would also note that John's '95 370DA had Gen V 7.4s which did not suffer as many problems as the late 90s gen VIs. However, it is also important to note that in subsequent boats equipped with 8.1s (2002 and up), SR moved completely away from "log" mufflers to water lifts.

BTW, this "suck back" issue was not confined to just SRs. I have a friend with a 2002 Carver 346 and another with a 2001 Formula 34PC (yes, a rare one with inboards) that suffered complete 7.4L Merc Gen VI engine failure. I think the 2000 and 2001 SR 340DA was also plagued.
 
Southpaw II said:
My 380DA does have 1.5" shafts.Don
Click to expand...

Mine does too. Even the 30 foot Tiara Opens with 8.1s come with 1 1/2" shafts. Not sure smaller shafts will be robust enough for 8.1s. I'd at least go over the issue with the yard doing the work and press the point a bit.
 
While I have no intention of trying to get into all the ins-and-outs of cam timing, overlap, camshaft design, etc., I will say this: Water lift, log style, sterndrive bullhorn, straight through transom pipes - non of that is the issue. Each engine has requirements for exhaust tube down angle, tube length, and static line - that's where the criticality lies. Any exhaust will work if it meets those requirements (among others). Sea Ray used water lift mufflers to improve the static line dimension along with the down angle - not because the water lift mufflers are magically more resistant to water reversion issues. In effect, the water lift mufflers create a new water line in the boat - one that is lower than the water line outside the boat - and thus a greater static line dimension. They also provide an advantage in a following sea or while backing down, by providing a buffer between the vessels exhaust outlet and the engine.

Now, Mercury marine has very clear specifications concerning the installation of their engines, and the 8.1 is no exception. From the 8.1 installation manual, their specifications are:

1 - Minimum 10 degree downward slope, for not less than 18 inches, with an allowable reduction to 3 degrees for the portion of the exhaust that is greater than 18 inches from the elbow.

2 - Static line Not Less Than 15 inches.

3 - No sharp bends, and the exhaust must continuously slope downwards, such that a low spot is not created.

Now, if the OP’s log style exhaust meets these requirements, as well as the other requirements stated in the 8.1 engine installation manual (and there are many), then I would expect him to enjoy a long and happy engine life.

On the other hand, neglecting any one of these requirements is an expensive gamble, and should be avoided. It is the responsibility of both the vessel’s owner, and the yard, to verify that all applicable specifications have been met. If they are not met, then I would recommend remedial action, and that action may include the transition to a water lift muffler.

Dale
 
Subscribed

Did you have to change your shafts or are the 1.25" shafts solid enough? Did the 8.1's connect directly to your existing transmissions? Which transmissions do you have?

Interested because I have one engine (both are still the original engines with about 550hrs) that's starting to run warmer and have lower oil psi than the other engine.

What did you end up doing as far as displaying engine data?
 
Last edited:
You must log in or register to reply here.

Forum statistics

Threads
113,219
Messages
1,428,826
Members
61,115
Latest member
Gardnersf
Back
Top