Low power, slow to get in plane. Intermittent backfire

7cstevan · **Joined:** Sun May 12, 2013 7:20 am **Posts:** 34

Sorry to be the bearer of bad news on the valve job. Shoud be about $1K or less with a new head if you do just one. Less money if they can rebuild (put new valves) in your head. Add another $500 if you have both heads done. Your heads are MUCH easier to get to than on my 328 Vista

Rick2752 · **Posted:** Thu Nov 20, 2014 3:30 pm

Sorry haven't checked back in, I haven't wanted to work on it. Now it's cold so can't do anything else. I went ahead and pulled the motor AGAIN! Took the heads off and I have a burnt valve n the head. There is also some marks that I don't like in the cylinders so its looks like its a new motor for me. Any suggestions on where to not buy one from...I have found long blocks for around 2400 delivered to ohio. Thanks everyone for all your help. Now I'm gonna order some new stickers to rename her. I think it's gonna be Shine on! Earned it is the old name and its starting to suck earning it.

LouC · **Posted:** Thu Nov 20, 2014 4:18 pm

Rick sorry to hear of your troubles but good to hear you are working on it again....If you're doing a new engine....think about closed cooling...because if you can do a full closed system....you're less likely to get leaks at the riser/manifold joint which may have been the primary cause of the engine problems. Its common enough here in salt water, where we have replace manifolds every 5-7 years to be on the safe side. I don't think Volvo ever offered full closed cooling on these models, but as long as the raw water pump can supply enough water and you get a large enough heat exchanger, it should be possible....Either that, or see if you can adapt the Merc dry joint manifolds to this engine. I never thought the idea of the life of the engine resting on two thin gaskets, was a good idea.

jayjay4735 · **Posted:** Thu Nov 20, 2014 5:10 pm

Sorry to hear that, I recently ordered a new engine through Michigan Motorz. I ordered the Mercrusier plus series 357 Magnum Bravo 4V. The price was 7000 with shipping to LI, NY. The plus series engines are remanufactured blocks done by Mercruiser with all new parts to make a marine engine. They come with a 1 year Mercruiser warranty, and they are running a special that if you purchase it and have the engine installed and inspected before Dec 31st it will be extended to 3 years. The Bravo 4V is rated at 325 hp at the crankshaft, you can get a Alpha 4V for a little less that is rated at 275 at the crankshaft.

I can say the guys at Michigan Motorz were friendly, professional and courteous, and even went so far as to call my mechanic before they put the order through to make sure he knew what would have to be done to replace a Volvo Penta with a Mercruiser.

Winter Sux · **Posted:** Thu Nov 20, 2014 8:19 pm

If it were me, I'd just match the engine numbers at the boneyard and grab a low miler for about 500 bux in these parts.

Clean it, paint it in factory color. Then, slap the marine parts on the engine. Then slap the engine in the boat. Then, slap the boat on kijiji.

LouC · **Posted:** Fri Nov 21, 2014 7:26 am

The issue with an engine replacement on this boat is that it really needs more power. The 383 small block is pricey but perfect in therms of power and weight. Ideally these should have a big block with 400 ft lbs of torque to move all that weight. If most would want a 5.7 in a sport boat, how is that adequate in a boat they weighs 1500-2000 lbs more?

jayjay4735 · **Posted:** Fri Nov 21, 2014 10:25 am

When I was looking at replacement, the 383 equivalent was another $1100 or so for another 25 hp at the crankshaft. Just didn't seem worth it me as I was already increasing the hp from the 5.7 gsi rated at 280 (not sure if that is at the prop or crank) to 325 at the crank. I have a 258 so I'm sure for a 248 I'm sure the 325hp engine would be good for what most people use a cruising boat for, although the 350hp engine certainly would be better.

Cap'n Morgan · **Posted:** Fri Nov 21, 2014 11:56 am

LouC wrote:

The issue with an engine replacement on this boat is that it really needs more power. The 383 small block is pricey but perfect in therms of power and weight. Ideally these should have a big block with 400 ft lbs of torque to move all that weight. If most would want a 5.7 in a sport boat, how is that adequate in a boat they weighs 1500-2000 lbs more?

Lou, have you ever driven a 248 Vista with a 5.7 ??? If so, you could not possibly say it "needs" more power. It does not at all.
That is a perfect engine for that boat. Your question is not valid, this is not a sport boat, and know one in their right
mind would expect it to perform like one. They are not designed nor intended to do that.

Sure, more HP is always nice to have, but totally unnecessary for his boat.

ric · **Posted:** Fri Nov 21, 2014 12:36 pm

The 248 Vista is a 23"10' boat. 320hp is more than enough.

LouC · **Posted:** Fri Nov 21, 2014 5:15 pm

Firstly a garden variety 5.7 does not have 320 hp, more like 260. Secondly, that boat weighs in at close to 6,000 lbs. It is not about the HP it is the torque. While it may seem to have enough power, they labor getting up on plane and the extended time it takes them to plane is what overheats combustion chambers and tulips valves. I've been on many boats of this size with the same engine and they all seem to labor getting up on plane compared to a smaller boat with the same engine. The big block has close to 100 more ft lbs of torque. Torque is what it takes to move weight, not hp. Think not of that it feels 'fast enough' but rather how fast does it plane? I can recall of a few different boats of this size same engine, same failure, tuliped/overheated valves. My opinion its the boat companies being cheap. I would not put a garden variety 350 in a 6,000 lb truck and expect it to be a good tow vehicle either.
If these engines are not propped right they really do not last.

RotaryRacer · **Posted:** Fri Nov 21, 2014 6:51 pm

LouC wrote:

I would not put a garden variety 350 in a 6,000 lb truck and expect it to be a good tow vehicle either.

My 98 3/4 ton would argue that it makes a perfectly good tow vehicle. It has comfortably handled at its full GCWR of 13,500. It has a garden variety 350 making 255 hp.

Also have an 89 1 ton. It has moved boats as heavy as 30,000 lbs. It has a TBI 350. If not for the frame rusting out it would still be moving big boats.

LouC · **Posted:** Fri Nov 21, 2014 8:17 pm

You have gears and a final drive ratio for towing. Tractor trailers also pull 80,000 lbs with 400 hp and 800 ft lbs of torque the same way.
These boats have a single speed transmission.
Regardless of what decisions Merc or Volvo made, I bet that GM did not design these engines to move 6,000 lbs through a single speed transmission. This is the main reason why big boats have diesels. Very high torque at very low revs moves the weight without strain.
A DP drive helps for sure, but there ain't no replacement for displacement. Since GM discontinued the 7.4 (454) the modern big block was very expensive and that's why you don't see many boats with them.

ric · **Posted:** Sat Nov 22, 2014 12:31 am

Fuel prices are going down. 502's for everyone!!

rpengr · **Posted:** Sat Nov 22, 2014 9:02 am

LouC wrote:

Torque is what it takes to move weight, not hp.

The engineer in me cringes whenever I hear this tired old argument, but HP is what it takes to move weight (or more specifically--accelerate weight and overcome drag forces). HP is Torque x RPM (actually HP = ft-lbs X RPM / 5252). Here are some examples:

1. A 10HP lawnmower engine with 18 ft-lb of torque could be connected to a 20:1 gear reduction and output 360 ft-lbs of torque at a low rpm. Would that get a Vista up on plane? (No)

2. An engine producing 400 ft-lbs of torque at 2250 rpm would have the same HP as an engine producing 200 ft-lbs at 4500 rpm. If geared & propped correctly, they would both push the boat at the same speed.
(I know we could talk about torque/power curves of diesel vs gas, but those curves represent torque and horsepower)

3. The brakes on your car are capable of producing 5000 ft-lbs of torque at 0 rpm, but they are not capable of pushing your car at all... No HP: (5000 x 0 = 0)

Pushing a boat (or truck) requires "work" or "energy". "Work" and "energy" are measured in Horsepower, not Torque.

alex8q4 · **Posted:** Sat Nov 22, 2014 10:21 am

I was just about to post that exact same thing... I sware!

lol.

That was very well said, I can say I learned something today.

www.iFourWinns.com

Low power, slow to get in plane. Intermittent backfire

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