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Thread: 350 to 383?

  1. #1

    Default 350 to 383?

    Anyone convert their 350 to a 383? Did you gain enough hp and torque to make it worth the extra parts and machining?

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    If your going to get the 400 crank and things for the 350, why not just put some .030 pistons in the 400 with a little more compression ratio and have a 406? ( Big bore 383 ) You get the long stroke and the big bore and 56in should be noticable.

  3. #3

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    I have the 350 and don't want to change everything. Just looking to rebuild the long block and wondering if anyone here has gone down the 383 path.

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    Member Sobie2's Avatar
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    I suspect that you are going to find better help on an automotive forum than here for this particular topic. This outdoorsdirectory boat mod page doesn't see much traffic.

    I agree though that you, like myself, are probably competent enough to tackle a rebuild, but that finding a machine shop to bore out the block is cost prohibitive... it also is something you should reserve for when you need to bebuild the engine in the future.

    Don't forget to up your jet drive's impeller to make use of the new found power if you decide to go down that path.

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    Member 1Cor15:19's Avatar
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    Quote Originally Posted by Boud'arc View Post
    I have the 350 and don't want to change everything. Just looking to rebuild the long block and wondering if anyone here has gone down the 383 path.
    I've no experience with inboard jet boats so take this for what it is worth.

    I use to build engines/race cars in my hometown, Concord, NC. I worked and turned wrenches on most things, but Chevys were our passion and small blocks are the most durable, least expensive way to race so we did a lot of SBC. Depending on the application a 383 may be an improvement, but my guess is that you would not pick up the total power you are after by going this route. The 383 is a street/strip motor. It has little application elsewhere. The rotating assembly is too heavy to turn high rpms for long periods of time and its real purpose is to put more c.i. in a bottom breathing car (i.e. 3rd gen camaro) where cooling is a real issue. The 400/406 SB is preferable in every way to the 383, if you have the ability to keep it cool. In fact, our experience showed the that a 350 .030 over will outperform the 383 in a light car at the track and it had much improved life on the street. There is no bad small block with which I am acquainted; the issue is choosing the right profile for your application. I'd research where you want your power curve and build the smallest motor that will provide those specs. You can build more power than you need in the 350 you already have and do it without the cost of a new crank and rods IMO.

  6. #6

    Default 383 isn`t the greatest plan

    About the same horse power but around 30 more lb. feet of torque...good out of the hole but won`t really spin more R`s...1Cor15:19 has it nailed down. Do a bore (0.30) with good cam/intake and you`ll get the power you`re after without as much work and more reliable rpm in the long run.

  7. #7

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    I talked to a fella at the Talkeetna boat ramp last month who another guy called "Mr. Engine". I wish I could remember his name. I think he runs a guide service and a shop. Mr. Engine recommended the 383. I didn't know my motor was coming apart inside then. I was just curios to see if I could get a little more power out of the 350.
    Yesterday I called an engine manufacturer in WA who offers 350s and 383s with a 7 year/500 hours warranty. He claimed the 383 would have 360 hp and a lot more torque than the 350 due to the longer stroke. He didn't say how much more torque but claimed the boat would be able to get up and run with about 800+ more pounds than the 350. He also said if I was happy with the speed of the boat then I should keep the same impeller. According to him the 383 would run at the same or more rpms as the 350 but do it easier and more efficiently. It all sounded too good. That's why I posted this thread.

    1Cor15:19 and AK2AZ,
    I hadn't thought about the 383 rotating essembly being heavier and effecting the longevity. I asked some of my motorhead buddies last week about .30 over and they told me it wouldn't help much. Guess that explains why folks spend thousands to race every weekend. My motor is a Marine Power 310 hp Votec with roller cam. I'm not sure I can improve the cam much unless the CA emmisions standard governing the motor limits the cam. Boring .30 over and changing the cam would be the easiest way to gain some hp but I'm not sure if it would do the trick. I need to stay with the same engine so everthing (fuel injection/electronics/manifolds) will bolt back up. It's not my intent to make a silk purse out of a sows ear but if I have to rebuild it then I'd like to "REBUILD" it. This sure has put a wallop on my cedar strip freighter canoe plans this winter.

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    Member theultrarider's Avatar
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    Since yours is a modern fuel injected motor, that makes modding it even tougher in some ways. If you do much in the way of cam, compression and stroker, it will change your fuel requirements for your motor. It is easy to rejet a carb. It is more difficult for the average guy to reprogram your injection system. Until I read that you were injected, I would have said go with the 383. We raced them in both dirt track ovals here in Ak, and in our race mud trucks. The 383 does have a much noticable increase in the botttom end in the mud trucks where torque makes a big difference. In the stocks cars, they are lighter and less hook up so it is more about hp than torque. In either case, we were running 8000+ rmp in those motors and had no issues with them holding together. Like was said above, boat application and cars are very different uses. I think it is going to hard to get a good knowedgeable source of info on what you are trying to do. There are alot of 383's running around in hotrods and trucks. Boats, I have know clue. Big thing is getting the right cam in it, and the right fuel set up. Good luck.

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    Quote Originally Posted by Boud'arc View Post
    Yesterday I called an engine manufacturer in WA who offers 350s and 383s with a 7 year/500 hours warranty. He claimed the 383 would have 360 hp and a lot more torque than the 350 due to the longer stroke. He didn't say how much more torque but claimed the boat would be able to get up and run with about 800+ more pounds than the 350. He also said if I was happy with the speed of the boat then I should keep the same impeller. According to him the 383 would run at the same or more rpms as the 350 but do it easier and more efficiently. It all sounded too good. That's why I posted this thread.
    Again, I state I have no experience with inboard jets. The hp numbers on the 383 sound reasonable, but he is going to change more than the crank to get them. It will use more fuel, but it may be more efficient, I can't say. I will add this, as far as when the boat is on step, without changing something in the impeller system it will take the same rpms to run the same speed regardless what size your motor is. The 383 will use more fuel to produce similar power and if it puts out in the neighborhood of 18-20% more power than your 350 I would suspect even an efficient 383 to use 15% more fuel at a minimum.

    Quote Originally Posted by Boud'arc View Post
    1Cor15:19 and AK2AZ,
    I hadn't thought about the 383 rotating essembly being heavier and effecting the longevity. I asked some of my motorhead buddies last week about .30 over and they told me it wouldn't help much. Guess that explains why folks spend thousands to race every weekend.
    When I mentioned going .030 over I meant to also change some other components. There is not a lot of difference in a 355 and a 350, I should not have said it that way. Most build projects begin with a 350 block and to clean up the cylinders a .030 bore is pretty common. If you have a fresh block I would not bore it for the extra c.i. The advantage in the build would come from reworking the heads, new cam, etc.

    Quote Originally Posted by Boud'arc View Post
    My motor is a Marine Power 310 hp Votec with roller cam. I'm not sure I can improve the cam much unless the CA emmisions standard governing the motor limits the cam. Boring .30 over and changing the cam would be the easiest way to gain some hp but I'm not sure if it would do the trick. I need to stay with the same engine so everthing (fuel injection/electronics/manifolds) will bolt back up. It's not my intent to make a silk purse out of a sows ear but if I have to rebuild it then I'd like to "REBUILD" it. This sure has put a wallop on my cedar strip freighter canoe plans this winter.
    310 Vortec is a good engine. You are correct in that you can't pick up a lot of hp in the cam and while you can polish the heads, changing the porting will affect your power curve and probably not in a positive way.

    You have a couple of options. You can rebuild your existing motor to stock specs and have some electronics mods to deal with timing and fuel delivery. I suspect that these are already fairly aggressive in your application so the gains may not be huge.

    You can purchase an aftermarket head setup (matching cam/lifters/rockers) in addition to the electronics tune and this will give you noticeably more hp with a mild decrease in fuel economy. You can also change the intake manifold within the parameters of your existing injectors and you may find some hp and torque gains there as well. As you approach this build you should remember to keep things in balance. Change a system not a part. For example, a "bigger" cam without larger valves and stronger springs will not make a significant difference in hp output; it can even decrease the performance of your motor.

    I have done this for years and there is no such thing as a free lunch concerning hp. Regardless what the salesman said you cannot have more c.i., more power and better economy. It just doesn't work that way. You are going to spend more money and have more maintenance and shorter service intervals with a more powerful engine, at least you do on the street. Build smart and you'll be happy in the end product.

  10. #10

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    theultrarider, The local shop in Anchorage said the same thing. I called "US Engines" in WA yesterday. Saw them on the web. I asked about the fuel injection and computer issues when discussing options. To my suprise, he said he has built and installed hundreds of 383's with no need to reflash anything. He said it bolts right back on and works as designed. He explained to me that everything pretty much stays the same except the piston travels farther creating more torque. He claims that he argues with manufacturers all the time but he knows it works from experience. He joked that he should start charging people to reflash their computer, spray them with pledge to make them shiny and send them back intead of arguing. For $600 more than the long block price I can ship my complete motor to him and he will rebuild it to a 383/360 hp then send it back complete and ready to install with my fuel system in tack. The 7 year/500hour waranty caught my attention. That's better than the worthless Marine Power 2 yr warranty that went out a few months ago with less than 50 hours. His long block price is $600 less than a new Marine Power 350 long block. The complete motor with shipping is about half the price that a local Anchorage shop quoted me to replace the motor.

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    He sounds like a used car salesman and is telling you what you want to hear. How good is his warrenty as you are floating backwards down a set of rapids dead in the water Or when your boat does not perform as you expect it to? I would do ALOT more research before spending a dime with him. His work per'se may be fine, but as 1st pointed out, all the componants must match and compliment each other or you will end up with an under performing motor that burns alot of fuel and has less hp than you started with. Or is running lean and goes pop! Call around to some big name boat shops and get some advise from those in the know.

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    1Cor15:19,
    Thanks for being so helpful. I've rebuilt a couple engines before but never anything that required this much brain power. I can follow instructions and turn wrenches but I'll be at the mercy of the machine shop and someone smarter than me to gather the right pieces to the puzzle. The good news is the motor isn't burning oil, smoking, and the oil pressure is still good. I caught it early. Returning it back to specs is definitely my fall back plan.

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    Member broncoformudv's Avatar
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    Marine Power and KEM both offer 383 engines with fuel injection and there are plenty of them in boats out there. I have never heard of anyone that dropped a 383 in place of a 350 wishing they had never made the swap.

    The torque curve is at a lower rpm and is flatter than the 350's are which is great for our jetboats.

    The one bad thing is the vast majority of 383's require mid grade or premium fuel not a big deal unless you are making long distance trips in remote Alaska areas were that is hard to find.
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    I just did a 350/383 swap this past month. However I have a airboat rather then a jet at this time. got a longblock from S&J in Spokane, and changed over all the intake, etc. The old 350 was pretty strong with a lot of pull. when i bought it this summer the owner told me it was 375hp, but that was just part of his sales pitch i thought. however it did have some performance work done on it we saw when disassembled, screw in studs, etc so it had been improved on, heads were trash, not able to regrind, etc so had to go long block route. The one i bought was fairly mild, stock, with 9:1 comp ratio, marine, with rv cam. Runs and sounds good, but I am not happy. Does not have near the pulling power as the old 350. I am still tweeking it, but am running it every week hunting now, hopefully I will figure out a way to get more power out if it to where it is as strong as the old 350 was. i really thought that with the additional torque of the 383 that it should run circles around the old 350, but not the case. Bud

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    Here are a few last thoughts of mine.

    The 383 has more torque than a 350 all else being equal, but a good rule of thumb is about 1 ft lb per c.i. so maybe you pick up 30-35 ft lbs in the bigger motor or about 10%. It will not be a flat curve out of the hole, but it will be a general improvement over the entire power curve. Things like cam profiles, timing, intake and exhaust manifolds, etc. determine where the curve is and since these are not being upgraded you can expect more power if the fuel delivery is there, but it will be in the same places.

    Forget about this being as durable as a 350, they most emphatically are not. There are numerous geometry issues why this is so, but you will not get the same amount of high rpm life out of a 383. Dirt tracks and street cars may touch 8000 during a lap or a pass at the track, but they do not stay there for more than an instant and then they are back down, the boat application is different with the throttle locked in place for maybe an hour at a time. The 383 is a good motor, but it is limited in applications. Street rodders use them because they are different, hot rodders use them because they must (over heating) racers may use them, but I've no idea why other than rule restrictions for c.i. The 400/406 is a BETTER motor for that application.

    The price of a rebuilt motor should be cheaper than a new crate motor. He's not doing you much of a favor in that regard. However, $600 is not peanuts and if you can save that much money with a rebuild and have a warranty that is more than a piece of paper, it sounds pretty good to me. One of the questions I would ask is about the cam. Roller cams are very durable and a lot of rebuilds will not include a new cam or lifters. It's not the end of the world to reuse the old cam, but there is the biggest part of your savings over crate motor.

    I am still uncertain about the electronics. It seems a little to good to be true, but maybe it works. The MAF can read the increase in airflow and this can adjust the fuel delivery, but I would suspect changing to a larger MAF would give improved throttle response and more power in general. Also I would check your exhaust manifolds, The 350 exhaust is not designed to flow an increase of 10% efficiently. This is not going to be a straight bolt in swap regardless what "they" say. More power and efficiency requires different components in a couple of places, but then you have an extra $600 to spend on exhaust and injectors if you need too.

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    Quote Originally Posted by broncoformudv View Post
    The one bad thing is the vast majority of 383's require mid grade or premium fuel not a big deal unless you are making long distance trips in remote Alaska areas were that is hard to find.
    It's compression & ignition timing not c.i. that dictate fuel octane requirments. So long as these are similar to the 350 you are now using it will not be an issue.

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    Quote Originally Posted by Boud'arc View Post
    The good news is the motor isn't burning oil, smoking, and the oil pressure is still good. I caught it early.
    What is wrong with your motor?

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    Quote Originally Posted by 1Cor15:19 View Post
    It's compression & ignition timing not c.i. that dictate fuel octane requirments. So long as these are similar to the 350 you are now using it will not be an issue.
    I never said it was due to the increase in cubic inches. Yes it is due to the increase in compression ratio that causes the need for higher octane fuel. The majority of 383 engines for sale run a higher compression ratio to help build even more power, you will find very few out there that are built to run on 87 or 88 octane unleaded. Yes if one was building their own engine or having an engine built to their specs they could request it be built to run on 87 or 88 octane fuel.
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    my new 383 long block with 9:1 comp runs fine on 87 octane, however, maybe I should have gotten a higher compression motor and run on 89. bud

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    Quote Originally Posted by broncoformudv View Post
    I never said it was due to the increase in cubic inches. Yes it is due to the increase in compression ratio that causes the need for higher octane fuel. The majority of 383 engines for sale run a higher compression ratio to help build even more power, you will find very few out there that are built to run on 87 or 88 octane unleaded. Yes if one was building their own engine or having an engine built to their specs they could request it be built to run on 87 or 88 octane fuel.
    I apologize if I came across the wrong way. That was not my intention. I was simply replying to your post.

    You can use 9:1 or even 10:1 on 87 octane, but at 10:1 you can't be too aggressive with the timing. The Vortec heads in question probably have a 64cc chamber so you'll need to consider what type of piston you need to arrive at the correct compression. Of course you can check the MP 310 Vortec and perhaps a bump in compression is called for, but I would guess at that hp it's probably about 9.5-10:1 with your present motor.

    The discrepancy in compression may explain some of the performance gain in the 383s. You can't compare 11:1 383s with 8.5:1 350s. It's apple to oranges.

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