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  1. #1
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    Default can you convert a carburated motor to EFI?

    I have a 1978 26 foot Uniflite sedan with a small block 350 chevy and a velvet drive transmission. Last year, I rebuilt the motor and I've put about 50 hours on it. The motor runs great and it performs well I'd say for an eight thousand pound boat. It will do about 28-30 wot and I cruise about 18-22. You may ask "what's the problem?" The problem is that I am a red-blooded American and I want more. It's not that I want to impress anyone, I would really like to be able to cruise at about 25-28 somewhat efficiently.
    I've thought about converting to a big block or even possibly diesel. I think, however, an EFI small block probably would be best because I am so close to my goal already and it wouldn't mean adding any more weight to speak of. That's where my question lies. I have a good motor, but don't know the details of what putting an EFI would be. I am sure it is probably possible, but is it probable? Should I just look for an EFI 350? I would say that I am handy, being the owner of an excavation company, but I am by no means a certified mechanic. I would really appreciate any advice on what should I be looking for etc. If it matters at all I do have an 87' 350 out of a Trophy that I am rebuilding.

    Thanks in advance,
    Jaxon

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    Commander 45Auto's Avatar
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    Default Re: can you convert a carburated motor to EFI?

    No big deal to convert a carbed 350 to EFI. Block is the same, its all just bolt on pieces. Won't be cheap.

    What do you think you'll gain with the EFI over a properly running carbed motor? You won't see any gains in power because of the EFI.

    8000 pounds is a heavy boat for a small block. Only way you'll make a 25% to 30% gain in cruise speed is with significantly more power.
    Any opinions expressed above are worth exactly what you paid for them!

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    Moderator Bob_VT's Avatar
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    Default Re: can you convert a carburated motor to EFI?

    Well more power is the only way to go........ you could stay on the 350 platform and install a 383 Stroker........

    The other scenario is maybe re-prop the boat. If the 350 is hitting proper rpms you might be able to go up in pitch a hair.
    This is a great link to boat specifications http://boatspecs.iboats.com/
    Please, shop iboats first!!


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    Default Re: can you convert a carburated motor to EFI?

    Quote Originally Posted by 45Auto View Post
    No big deal to convert a carbed 350 to EFI. Block is the same, its all just bolt on pieces. Won't be cheap.

    What do you think you'll gain with the EFI over a properly running carbed motor? You won't see any gains in power because of the EFI.

    8000 pounds is a heavy boat for a small block. Only way you'll make a 25% to 30% gain in cruise speed is with significantly more power.
    I guess I was under the impression that in a marine application a stock EFI 350 are generally about 50 horse more than the carburated ones and run more efficeiently. I don't know exactly why that is, whether they have more compression, higher performance heads, intakes, etc. or just a combination of these things? It's true that the crusader motor that's in my boat does post about 270 horse stock which is higher than a run of the mill marine 350 and since it was rebuilt and bored over I'm sure it's in the neighborhood of 300 horse but nothing real crazy. Am I all wet on this idea?

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    Default Re: can you convert a carburated motor to EFI?

    Quote Originally Posted by Bob_VT View Post
    Well more power is the only way to go........ you could stay on the 350 platform and install a 383 Stroker........

    The other scenario is maybe re-prop the boat. If the 350 is hitting proper rpms you might be able to go up in pitch a hair.
    I did re-prop the boat and run two different props. I use one up here in Idaho on the lakes, and another down on the coast on the salt. It will run about 4000-4200 wot, which I think is about right. As far as stroking the motor goes, It's something that I've always wanted to do, but never have. I'm sure there is alot more involved in doing so, and I don't think you would want to stroke a used motor, would you? If I was going to stroke the motor, is there a basic formula that you would use in doing so, meaning heads compression, etc. I know there are all kinds of different configurations, where would you start and what kind of gains can I expect? What about efficiency and reliability, is that compromised.

  6. #6

    Default Re: can you convert a carburated motor to EFI?

    Is it a 2 or 4 barrel carb.
    I've got a full roller 350 out of a zz4 camaro that put down 335 horsepower with a 2 barrel put a 4 barrel just for dyno purposes and went up to 360. went back to the 2 barrel for economy but if I
    needed the power it is nice to know what I would get with a 4 barrel. with the 2 barrel I am pushing my 7200# 32 mph at 5000rpms. I cruise most of the time at around 26mph at 3000rpms.
    Fuel injection will make more power and economy will be better. Why is EFI better then a finely
    tuned carb. Fuel atomization is better, With higher fuel pressures and injectors causing fine
    atomizing of the fuel instead of carbs producing droplets the power is increased as well as the
    economy. Another benefit to EFI is quicker cold starts and no need for chokes.

  7. #7
    Rear Admiral Scott Danforth's Avatar
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    Default Re: can you convert a carburated motor to EFI?

    Holley makes a Marine Pro-jection unit that bolts on to the manifold where the carb was. it is a TBI setup, however you would be a step above the carb with fuel management
    1988 Cruisers Rogue 2420 - VP AQ271C / 290DP "Rock'n Along"
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  8. #8
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    Default Re: can you convert a carburated motor to EFI?

    Quote Originally Posted by snake77 View Post
    Is it a 2 or 4 barrel carb.
    I've got a full roller 350 out of a zz4 camaro that put down 335 horsepower with a 2 barrel put a 4 barrel just for dyno purposes and went up to 360. went back to the 2 barrel for economy but if I
    needed the power it is nice to know what I would get with a 4 barrel. with the 2 barrel I am pushing my 7200# 32 mph at 5000rpms. I cruise most of the time at around 26mph at 3000rpms.
    Fuel injection will make more power and economy will be better. Why is EFI better then a finely
    tuned carb. Fuel atomization is better, With higher fuel pressures and injectors causing fine
    atomizing of the fuel instead of carbs producing droplets the power is increased as well as the
    economy. Another benefit to EFI is quicker cold starts and no need for chokes.

    I wonder how much performance would be increased by making a non-roller a roller motor and what the cost would be. If I found an EFI motor out of a car what changes would have to be made to make it a marine motor. I know that a marine application puts the motor under load the whole time. Can you just swap out a car motor and then hang your marine alternator, etc. or is it more involved?

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    Commander 45Auto's Avatar
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    Default Re: can you convert a carburated motor to EFI?

    Why is EFI better then a finely tuned carb. Fuel atomization is better, With higher fuel pressures and injectors causing fine atomizing of the fuel instead of carbs producing droplets the power is increased as well as the economy. Another benefit to EFI is quicker cold starts and no need for chokes.
    What you say is true. Instead of 260 HP with his carb, he'll have 261 HP with the fuel injection. Instead of 2 MPG with the carb, he'll get 2.01 MPG with the fuel injection. Neither is going to make a significant enough difference for him to notice.

    It is definitely much easier to start a fuel injected motor. Just turn the key. If he's incapable of figuring out how to pump the throttle a few times before the first cold start of the day as required with a carb, fuel injection may be a huge benefit.
    Any opinions expressed above are worth exactly what you paid for them!

  10. #10
    Lieutenant Commander 25thmustang's Avatar
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    Default Re: can you convert a carburated motor to EFI?

    As stated by others, I see fuel injection as a way to get easier starting, and better economy, not so much more performance. Boats can be touchy, where adding a good amount of power, only nets a knot or two. Sure it's better, but the expense may not be worth the slight gains. I have thought about taking my carbed Crusaders and going FI, but for the time being the carbs are working perfectly fine.

    I will say, your performance numbers look pretty good for a 28' 8000 lb boat with a single small block. Mine is just slightly faster, but has twin 270 Crusaders.
    Boat: 1987 29' Cruisers Inc 297 Elegante. T/270 Crusaders. (SOLD)
    Boat #2: 1984 34' Silverton 34C. T/270 Crusaders. Westerbeke Gen.
    Updating Thread: http://forums.iboats.com/boat-restor...vy-534493.html
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  11. #11
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    Default Re: can you convert a carburated motor to EFI?

    Repeat after me class - there's no replacement, for displacement!

    Others have said it, strictly a swap to EFI won't do it. You need to add other hop-ups to get the power out of the motor. Need to weigh the cost of those vs the cost of going to a big block.
    Jon Hunter
    Marion, NY

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    Master Chief Petty Officer tswiczko's Avatar
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    Default Re: can you convert a carburated motor to EFI?

    Quote Originally Posted by Captain Jaxon View Post
    I did re-prop the boat and run two different props. I use one up here in Idaho on the lakes, and another down on the coast on the salt. It will run about 4000-4200 wot, which I think is about right. As far as stroking the motor goes, It's something that I've always wanted to do, but never have. I'm sure there is alot more involved in doing so, and I don't think you would want to stroke a used motor, would you? If I was going to stroke the motor, is there a basic formula that you would use in doing so, meaning heads compression, etc. I know there are all kinds of different configurations, where would you start and what kind of gains can I expect? What about efficiency and reliability, is that compromised.
    You might be over propped you're WOT on a 5.7L should be about 4500 rpm
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    Default Re: can you convert a carburated motor to EFI?

    Supercharge it? A little boost goes a long way.
    1987 Skeeter 175 Starfire with a Yamaha 150 ProV

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    Petty Officer 1st Class saxrulez's Avatar
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    Default Re: can you convert a carburated motor to EFI?

    Quote Originally Posted by Angrywasp View Post
    Supercharge it? A little boost goes a long way.
    Towards pre-detonation and other quick ways to have to rebuild an engine if not done properly.

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    Default Re: can you convert a carburated motor to EFI?

    Quote Originally Posted by Captain Jaxon View Post
    I wonder how much performance would be increased by making a non-roller a roller motor and what the cost would be. If I found an EFI motor out of a car what changes would have to be made to make it a marine motor. I know that a marine application puts the motor under load the whole time. Can you just swap out a car motor and then hang your marine alternator, etc. or is it more involved?
    Depends on the water you're running in. I'm no expert, but as I understand it, you need special marine head gaskets if you're going to run in salt water, a different cam for a marine application, and all of the marinized components attached to the engine, such as alternator, starter, distributor.
    I would suggest turbo charging, but like super charging, the bottom end of your engine needs to be built to handle the higher cylinder pressures, and with a turbo I imagine you have to have a special marine turbo that has a water jacket around the exhaust housing.
    You may find it cheaper to repower with a big block.

    Chris
    1996 Rinker Flotilla, 4.3, 1998 Seadoo GSX Limited, 1995 Hydra 24' Pontoon, 70hp Force, 1995 16' Alumacraft Jon boat, 25hp 'Rude, 1968 Fibra with Volvo stern drive, and various other boats used for parts.

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    Default Re: can you convert a carburated motor to EFI?

    Quote Originally Posted by saxrulez View Post
    Towards pre-detonation and other quick ways to have to rebuild an engine if not done properly.
    Only if you push too much boost. Most motors will take 6-8lbs of boost without any problem and last quite a while (GM 3800 Series motor owners are a good example. I know because I'm one of them). I'm not sure if it crosses over to the marine side of motors but it's still a SBC that was recently rebuilt. Biggest concern with it would be getting enough fuel into the motor and running premium.
    1987 Skeeter 175 Starfire with a Yamaha 150 ProV

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    Petty Officer 2nd Class zagger's Avatar
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    Default Re: can you convert a carburated motor to EFI?

    To op, you will NOT see any HP increase by just adding TBI system. Fuel injection was developed for the purpose of economy and cleaner pollution not HP gains. FI when properly done it will cost more than a used big block. You have to not only have to change over the carb but the whole fuel delivery and return system, electronic engine control module and proper tuning etc,etc. MPI (multi port injection is even more involved as it will require swapping manifolds, timing components etc, etc. Turbocharging will most likely melt your boat from within but a supercharger will double the horsepower output for every 14.7 pounds of boost, on a used motor that is a big gamble since there will be no asphalt for the pistons to bounce off of when she lets go. Beside adding boost will definitely increase your fuel consumption. As others said changing the motor is best way to gain performance. A merc 5.0MPI will put out 260 HP and same VP will do 270 prop horsepower, no solution will be cheep. For the special occasions where you need to impress someone just get NOS installed, that will be like getting extra 150 HP at a push of a button - this last one was a joke and please don't add explosive gas to your boat.

  18. #18
    Rear Admiral Scott Danforth's Avatar
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    Default Re: can you convert a carburated motor to EFI?

    while an EFI motor does have a higher output than carbed version of the same engine (Example - Mercruiser 5.0 liter 220hp carbed, 260hp MPI). the output is based on the ability to properly manage fuel and spark while balancing on the edge of detonation vs. relying on a glorified toilet float (carburetor) and a simple distributor.

    Can you change to EFI - yes. can you to it cheaply - depends. is it worth it - dont know (you have to answer)

    depending on the rebuild that you did (stock refresh, new lower, etc?), here is what I would suggest:
    switching to Vortec heads. if you have closed cooling, then switch to a set of aluminum AFR heads.

    Change cam - suggest looking to go with a comp cam - either the CL12-236-3 or the CL12-232-3 there are more radical cams, however I wouldnt suggest them without knowing more about your drive, which company did the marinization, etc.

    The head change will require a manifold change (go aluminum if you have a closed cooling system). Also look at the carb - is it big enough?

    Careful shopping gets you everything in the $1500 range (unless you buy the AFR heads) and about 300-320 hp (depending on cam, tune, elevation, fuel, etc.)

    if that is not enough and you want to stay with a small block, then build a 383 and get 350-420hp, or build a blower motor out of a 350 or 383 for 400-550hp. Then again if you intend to go that route for the same money, I would simply spring for the LSA marine engine at 425hp. you get aluminum engine, supercharger, EFI all in one package.

    speed costs money. I would also look at how much you want to spend to take your cruiser faster vs how many margaritas I could buy while pulling a pair of jet skis with me
    1988 Cruisers Rogue 2420 - VP AQ271C / 290DP "Rock'n Along"
    http://forums.iboats.com/showthread.php?t=500145
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  19. #19
    Moderator QC's Avatar
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    Default Re: can you convert a carburated motor to EFI?

    Moved this to non-Repair Inboard as we try to keep the Boat section free of engine topics.

    A couple of comments. Blowing one of these seems a little over the top. A more modern design stroker with or without EFI seems doable. Odd that we have had some cam discussion here, and some auto vs. marine discussion without any mention of reversion . . . Mr. Danforth sort of alludes to it, but definitely needs to be addressed here somewhere

  20. #20
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    Default Re: can you convert a carburated motor to EFI?

    To answer your question, "can you convert a carburated motor to EFI?", yes you can, I've done it.
    Will it do what you want it to do? In your case, I doubt it. It sounds to me like you have a healthy engine and it's doing very well to move your boat at those speeds. Other than making sure that is in a very fine state of tune, and after that, if you still want more speed, I'd side with the camp that suggests re-powering with a big block for a reliable power increase.
    Electronic engine management in general, and programmable electronic engine management in particular, just does the same thing as a conventional carburetor and ignition system except that it allows you a much finer degree of control. A well tuned carb and ignition system does a good job of delivering the right fuel mix and ignition timing, particularly in the upper speed and load ranges. EFI can improve on this a bit, but not much. Where EFI can make the most gains is in the lower load, lower RPM ranges. There are significant economy gains to be made here, but if I understand your post correctly, this is not the area you are looking to improve.
    Hope this helps.
    Robert
    1993 Bayliner 3288 "Hocus Pocus"
    351 Fords
    Converted to tuned port programmable EFI

  21. #21
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    Default Re: can you convert a carburated motor to EFI?

    Quote Originally Posted by zagger View Post
    To op, you will NOT see any HP increase by just adding TBI system. Fuel injection was developed for the purpose of economy and cleaner pollution not HP gains. FI when properly done it will cost more than a used big block. You have to not only have to change over the carb but the whole fuel delivery and return system, electronic engine control module and proper tuning etc,etc. MPI (multi port injection is even more involved as it will require swapping manifolds, timing components etc, etc. Turbocharging will most likely melt your boat from within but a supercharger will double the horsepower output for every 14.7 pounds of boost, on a used motor that is a big gamble since there will be no asphalt for the pistons to bounce off of when she lets go. Beside adding boost will definitely increase your fuel consumption. As others said changing the motor is best way to gain performance. A merc 5.0MPI will put out 260 HP and same VP will do 270 prop horsepower, no solution will be cheep. For the special occasions where you need to impress someone just get NOS installed, that will be like getting extra 150 HP at a push of a button - this last one was a joke and please don't add explosive gas to your boat.

    Yeah I don't want to get silly about this. Reliabilty is a huge part of my decision making process. If I wanted to build a real high output motor I don't think this is the boat for it. Great advice, thank you.

  22. #22
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    Default Re: can you convert a carburated motor to EFI?

    Quote Originally Posted by Scott Danforth View Post
    while an EFI motor does have a higher output than carbed version of the same engine (Example - Mercruiser 5.0 liter 220hp carbed, 260hp MPI). the output is based on the ability to properly manage fuel and spark while balancing on the edge of detonation vs. relying on a glorified toilet float (carburetor) and a simple distributor.

    Can you change to EFI - yes. can you to it cheaply - depends. is it worth it - dont know (you have to answer)

    depending on the rebuild that you did (stock refresh, new lower, etc?), here is what I would suggest:
    switching to Vortec heads. if you have closed cooling, then switch to a set of aluminum AFR heads.

    Change cam - suggest looking to go with a comp cam - either the CL12-236-3 or the CL12-232-3 there are more radical cams, however I wouldnt suggest them without knowing more about your drive, which company did the marinization, etc.

    The head change will require a manifold change (go aluminum if you have a closed cooling system). Also look at the carb - is it big enough?

    Careful shopping gets you everything in the $1500 range (unless you buy the AFR heads) and about 300-320 hp (depending on cam, tune, elevation, fuel, etc.)

    if that is not enough and you want to stay with a small block, then build a 383 and get 350-420hp, or build a blower motor out of a 350 or 383 for 400-550hp. Then again if you intend to go that route for the same money, I would simply spring for the LSA marine engine at 425hp. you get aluminum engine, supercharger, EFI all in one package.

    speed costs money. I would also look at how much you want to spend to take your cruiser faster vs how many margaritas I could buy while pulling a pair of jet skis with me

    This is some really useful information, thank you. I've got some thinking to do. One big reason for wanting to get the boats cruise speed up, is that the bow really sits down about 25 mph, and rides really nice and flat. As it is now the bow rides pretty high and vision isn't the best. I've played around with moving some weight up front and it definitely helps. I don't use the boat much for cruising, we really enjoy our trips to Canada ocean fishing. The guys I go with have smaller boats and it seems like I spend a lot of time steaming while they're fishing. Of course there are lots of trade offs and when the weather is nasty I do have an advantage, that's why I bought the boat. I guess the real question is, if 50 or so horse power would gain my speed issue. I still haven't gotten a clear idea on what differences auto motors and marine motors have? I thank you all for the responses, this is a useful resource. Can anyone give me help on trying to identify the kind of heads I have on my 270 crusader. I can't help but think she is running a little better than stock?

  23. #23
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    Default Re: can you convert a carburated motor to EFI?

    Quote Originally Posted by E4ODnut View Post
    To answer your question, "can you convert a carburated motor to EFI?", yes you can, I've done it.
    Will it do what you want it to do? In your case, I doubt it. It sounds to me like you have a healthy engine and it's doing very well to move your boat at those speeds. Other than making sure that is in a very fine state of tune, and after that, if you still want more speed, I'd side with the camp that suggests re-powering with a big block for a reliable power increase.
    Electronic engine management in general, and programmable electronic engine management in particular, just does the same thing as a conventional carburetor and ignition system except that it allows you a much finer degree of control. A well tuned carb and ignition system does a good job of delivering the right fuel mix and ignition timing, particularly in the upper speed and load ranges. EFI can improve on this a bit, but not much. Where EFI can make the most gains is in the lower load, lower RPM ranges. There are significant economy gains to be made here, but if I understand your post correctly, this is not the area you are looking to improve.
    Hope this helps.
    If I did go to a big block would weight difference cancel out potential gains? Which motor would you go with? Thanks
    Jaxon

  24. #24
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    Default Re: can you convert a carburated motor to EFI?

    I'm not familiar with your boat, but you say it has a velvet drive transmission, so I assume that it is shaft drive. If the boat's attitude is an issue, would trim tabs be of some help?

    As for choice of engines is concerned, there really are no bad ones, so a major consideration would be cost and availability of the marine specific parts. The 454 GM engines have been around in marine form for some time. Parts are relatively cheap and readily available. Others may be able to advise you better than I can in this regard.
    Robert
    1993 Bayliner 3288 "Hocus Pocus"
    351 Fords
    Converted to tuned port programmable EFI

  25. #25
    Rear Admiral Scott Danforth's Avatar
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    Default Re: can you convert a carburated motor to EFI?

    Quote Originally Posted by Captain Jaxon View Post
    This is some really useful information, thank you. I've got some thinking to do. One big reason for wanting to get the boats cruise speed up, is that the bow really sits down about 25 mph, and rides really nice and flat. As it is now the bow rides pretty high and vision isn't the best. I've played around with moving some weight up front and it definitely helps. I don't use the boat much for cruising, we really enjoy our trips to Canada ocean fishing. The guys I go with have smaller boats and it seems like I spend a lot of time steaming while they're fishing. Of course there are lots of trade offs and when the weather is nasty I do have an advantage, that's why I bought the boat. I guess the real question is, if 50 or so horse power would gain my speed issue. I still haven't gotten a clear idea on what differences auto motors and marine motors have? I thank you all for the responses, this is a useful resource. Can anyone give me help on trying to identify the kind of heads I have on my 270 crusader. I can't help but think she is running a little better than stock?
    both Automotive and Marine motors come from the same parts bin. Now the difference - Marine motors have brass freeze plugs vs plated steel, and different head gaskets and head spacers to handle salt water. the cam for marine is to provide a nice flat torque curve vs automotive which is more peaky. Marine electrics are non-sparking and must be to prevent explosions in the bilge. Fuel systems are slightly different for the marine environment, and the spark management is slightly different.

    you have a 270 crusader which is a basic small block marinized by crusader (now pleasurecraft) and based on a 1978 industrial engine which is a truck engine with a different cam, so switching to vortec heads (new pair about $600) would help over your basic late 70's castings. if you did nothing but refresh it and not jump into the meat of the engine, cam, or fuel system, you have about 270hp the engine came with.

    do you have a closed cooling system? if so, then you can run aluminum engine parts such as heads, and intake and lighten up the engine by 80#

    you will have to verify with the v-drive the maximum power you can put thru it regardless of big block vs small block. over the years there have been 4 itterations of small blocks and 4 itterations of big blocks in the non-performance marine world. add to the mix the new LS based engines, diesels, etc. and the mix gets heady quickly.

    would an extra 50 help - probably

    the fact that your front end is pointing skyward indicates that you have an issue there as well. your boat should plane out flat. trim tabs will help here.
    1988 Cruisers Rogue 2420 - VP AQ271C / 290DP "Rock'n Along"
    http://forums.iboats.com/showthread.php?t=500145
    1970 Wooster Hellion 7' of cool mini boat with a Merc 9.8
    Recent Boats
    2002 SeaRay 190BR - MC 5.0 / Alpha I series II "Cheasheads in Paradise"
    1984 Avanti 170DLI - OMC 3.0 / OMC Stringer 400 "Ship Happens"

    The problems we face today can not be addressed at the same level of intelligence we were at when we created them - Albert Einstein Or with the same level of $ - Me

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