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  1. #1

    Default V6 to V8 engine swap

    I just bought my boat at the beginning of the season and it has ran fine the few times I've been lucky enough to have it out, until last week. The motor filled with water and started pushing the oil/water mix out of the breather hose up to the carburetor spark arrestor. I'm figuring a blown head gasket, so far.
    Here's where I have to make a decision: 1) Fix what the motor I have. 2) Improve and muscle-up the motor I have... OR 3) Upgrade to a bigger motor.
    Even though the old motor ran fine while it was running, I felt like it was terribly underpowered. It didn't take off quick out of the hole and it didn't go over 35mph at 5500 rpm.
    My first choice is to swap out the 205hp 4.3L Chevy V6 with a 400+hp Chevy V8 stroker.
    I know there is a lot of extra stuff to deal with if I do the swap, like new exhaust manifolds, intake manifold, motor mounts, oil pan, valve covers, etc... not to mention the physical space difference of the two motors.
    Before I make any kind of decision, I'd like to know as much about what I'd be getting into as possible.
    I've done some searches on this forum, looking for anyone else who has done a swap like this and I can't find it. I know there has to be someone else out there who has been in this same predicament. I can't be the only one who has tried to tackle something like this.
    Maybe I've just missed the posts dealing with this, but if not, I'd like as much input on the matter as you can give before I order a new motor.

    ~George~

    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  2. #2
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    Default Re: V6 to V8 engine swap

    My first choice is to swap out the 205hp 4.3L Chevy V6 with a 400+hp Chevy V8 stroker.
    I know there is a lot of extra stuff to deal with if I do the swap, like new exhaust manifolds, intake manifold, motor mounts, oil pan, valve covers, etc... not to mention the physical space difference of the two motors.
    Ayuh,... You'll also need a different Outdrive...
    Or at a minimum regear it...

    The 4.3 was Extremely underpropped if you were spinn' 5500 rpms...
    Any Grease is Better,... Than No grease at All....

  3. #3
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    Default Re: V6 to V8 engine swap

    Your intake manifold on the V6 probably rotted thru under the t-stat.

    If you plan on putting in a 400+ hp engine you will need to step up to a bravo drive and transom assembly. Your Alpha one will not hold up to that kind of hp.

    BTW 5500 rpm's on a 4.3 means your prop is too small.
    Chris
    Dockside Marine Services
    Jersey Shore.
    Mercruiser/Mercury Certified
    Let the insanity begin.

  4. #4

    Default Re: V6 to V8 engine swap

    From the investigating I've been doing, it appears that the Alpha One is rated up to 300 hp. I have the Gen II drive.

    I know boats can become a money pit, but I'm not prepared to shell out the kind of dough to upgrade my outdrive on top of what I'll be spending to replace the motor.

    I've decided to limit my horsepower to under that 300 mark, but the question about the V6 to V8 swap still remains.

    I need more torque to plane out quicker and I will adjust my top speed with a different size/pitch prop.

    A new question I have is can I get 300 hp out of a 4.3L? If so, will it also give me anywhere close to 300 ft-lbs of torque?

    If the 4.3L can be built to this kind of performance, will it be reliable? I'd like this boat to last me for 10 years without breakdowns.

  5. #5
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    Default Re: V6 to V8 engine swap

    Ayuh,... 'bout 250hp for a 4.3l, Reliably anyways...

    They've got a funny kinda crankshaft...
    Any Grease is Better,... Than No grease at All....

  6. #6
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    Default Re: V6 to V8 engine swap

    Put a stock 5.7 and prop it right.
    Chris
    Dockside Marine Services
    Jersey Shore.
    Mercruiser/Mercury Certified
    Let the insanity begin.

  7. #7
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    Default Re: V6 to V8 engine swap

    Yes, go with a properly built 5.7L.
    You may need to change the upper unit gear ratio!

    If you custom build a 5.7L, say no to these..........
    Name:  Dished Piston.jpg
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    ........ and build yourself a Q/E into the combustion chamber of the new one.
    There are much better piston selections for a Marine SBC 5.7L.
    Rick ... aka Ricardo..... AQ series Volvo Penta repair
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

    Please... no PMs! Post your questions on the forum.

  8. #8
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    Default Re: V6 to V8 engine swap

    Quote Originally Posted by RicardoMarine View Post
    Yes, go with a properly built 5.7L.
    You may need to change the upper unit gear ratio!

    If you custom build a 5.7L, say no to these..........
    Name:  Dished Piston.jpg
Views: 20024
Size:  4.0 KB
    ........ and build yourself a Q/E into the combustion chamber of the new one.
    There are much better piston selections for a Marine SBC 5.7L.
    Ayuh,.... Ditto that,....

    D-dished pistons in a vortec headed motor, quench at .043"...
    Any Grease is Better,... Than No grease at All....

  9. #9
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    Default Re: V6 to V8 engine swap

    Quote Originally Posted by bondo View Post
    Ayuh,.... Ditto that,....
    D-dished pistons in a vortec headed motor, quench at .043"...
    Bill, my hat is off to you!
    You're among the few who understand the benefits of a Q/E chamber for any Marine engine using a cylinder head that incorporates a "wedge"..... I.E., the SBC!

    It's often a hard sell to those who do not understand it, or who are not willing to educate themselves on it.

    And why GM and many rebuilders continue using the Full Dished piston......, is beyond me!

    Size the piston dished volume to complement the volume in the cylinder head chamber, and there ya go!
    With the correct piston p/n, this creates no change to C/R and no other mods are necessary!
    For a few beans more, it can be done easily and correctly, and we reduce Detonation potential!


    George, as to what we're talking about, you'd have to do a search re; Quench Effect or Squish Effect, and related this to Marine!
    It's all about what's occuring underneath the wedge, and the potential for Detonation in our Marine gassers.
    The Full Dish piston does a lousy job at this!

    See this image, and imagine the dished portion coming up underneath this wedge area.
    The outer ring landing comes to within correct "deck" or "Quench" dimension, but dished area cannot!
    The dish is OK in the open chamber...... it's coming up under the wedge area that creates the issue.


    (in all fairness, I'd have to say that the full dished piston does not necessarily create an issue, as ignition TA is held back considerably to accommodate it's lack of quench ability and to help against detonation potential............ but it sure as HELL doesn't "HELP" this engine any! )

    BTW, for the Marine build, the quench or squish dimension can be tightened up some..... DM suggests as tight as .038".



    IMO, a good choice for the Vortec chamber may look more like this:




    The D dished piston works well with the standard Non-Vortec wedge:




    Sorry for the Hy-Jack and side-track here, but I get passionate about this... can you tell?????
    Last edited by RicardoMarine; 09-22-2011 at 11:13 AM.
    Rick ... aka Ricardo..... AQ series Volvo Penta repair
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

    Please... no PMs! Post your questions on the forum.

  10. #10
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    Default Re: V6 to V8 engine swap

    I've been using George's thread to link to, so I'm adding a bit of information to it.


    Here's a Hot Rod magazine article (author not listed) on calculating dynamic C/R.
    http://www.hotrod.com/techarticles/e...ression_ratio/

    Note the value used in his method is different from other on-line C/R calculators re; using - or + in front of the entered cc data.
    I'd have to agree that a dish volume is actually adding (+) volume to the cylinder calculation (reducing C/R), whereas a dome is deducting volume (increasing C/R).
    Be sure to use the correct - or + when entering CC data while using certain on-line calculators.


    Back to SBC cylinder heads and pistons for a minute:
    Some of us do not understand the importance of cylinder head and piston combination.
    We cannot randomly or arbitrarily pick a cylinder head without knowing which pistons we want to use, and visa-versa.
    The two must go together and compliment one another, especially if building a Marine version 377/383.
    As mentioned...., No full dished pistons with the SBC .... that is a bad choice for a Marine build!
    That piston has no place in a SBC Marine Engine... Period!

    Do not confuse Deep Dish with Full Dish. You DO NOT want a Full Dished piston underneath the wedge.
    You want a piston that has a flat deck surface that mirrors the wedge and with a dish volume that controls C/R.
    This can be a flat top with the correct stroke and cylinder head chamber volume.... typically in a 5.7L with 76cc chambers.

    In other applications, we choose either a D dished (non-Vortec heads 64cc or 383 build w/ 76cc), or a L/C Quench for the Vortec heads (64cc) that mirrors the widow peek of the wedge.
    Either piston must be of the correct dish volume, or your C/R numbers won't be right.
    The right wedge, deck height, and head gasket thickness is needed to create the squish or quench area of .038".
    The quench or squish dimension will be higher for street engines since these turn a higher RPM.... but we're not building a street engine!
    So don't fear the tighter Quench for the Marine build.

    Read up on the squish or quench that can built into these for marine use.
    Both the Chevy and Chrysler wedge head guys have known about this for years.
    A good piston supplier can give you just about any combination you need and in any type of material and grade from forged aluminum, to cast aluminum to a decent Hypereutectic material.

    This is so easy to do that there is actually no reason NOT TO.

    ******************

    Here is a link to forum called Grumpys Garage that you may someday stumble onto. I found it while reading a thread on building a 383 marine engine.
    http://forum.grumpysperformance.com/...hp?f=52&t=4081

    NOTE: I'm fully aware that his write-up was not intended for Marine...... just say'n be careful when reading automotive forums when/if building your own SBC Marine Engine!

    If you should find this, note that member "grumpvette" (who seems to be the primary in this thread) primarily deals with the automotive version, and no mention of Marine.
    I can't speak to the accuracy of this guy, but did note that he misses several points in his write up re; the main chamber being "smaller" than the quench area, PCP @ 12-14* ATDC, and perhaps several other points.
    Later in the write-up as he quotes John Erb (Chief Engineer KB Performance Pistons), and the PCP error is corrected as John refers to it as 12* ATDC.... of which is more in line.
    Some suggest 12-14* ATDC.
    (I'm loosing faith in this poster as I read)

    You'll also read that he defines Quench and Squish differently.
    Many piston manufacturers will refer to either with what appears to be a similar principle. Are we splitting hairs here????
    (use your own judgement on this)
    He has yet to define that the Quench/Squish principle is effective for a Wedge Type cylinder head chamber ONLY.
    (I'm loosing more faith as I read)

    He goes on to quote another gentleman who I believe is referring to a non-wedge chamber engine.
    (you decide on that one)

    The ignition TA specs that he suggests are clearly for High Performance automotive.. not Marine.
    Again, I'd suggest that we use caution with some of this information when applying it to marine loads.
    In fact, I'd suggest that we not use any of this without some good qualified clarification since these two engine usages are not nearly the same.

    No offense to this man....... I just don't want any of us Marine guys to take this as gospel if we should stumble onto this thread and attempt to use the information for a Marine build.
    (you decide)



    .
    Last edited by RicardoMarine; 01-31-2012 at 01:00 PM.
    Rick ... aka Ricardo..... AQ series Volvo Penta repair
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

    Please... no PMs! Post your questions on the forum.

  11. #11
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    Default Re: V6 to V8 engine swap

    Dang, I was timed out for an edit... here's a closing comment.

    We will be much better off if we listen to those who have true Marine Cruiser Engine experience. This can include machine shop owners and technicians who currently or have previously owned a cruiser and who have true Marine SBC experience.
    If these guys are street performance only...... you'd best educate yourself.

    .
    Rick ... aka Ricardo..... AQ series Volvo Penta repair
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

    Please... no PMs! Post your questions on the forum.

  12. #12
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    Default Re: V6 to V8 engine swap

    Here are a few more images that should have been added to post #10.

    In this image, Jeff Smith shows how the quench deck of a correct piston mirrors the wedge area of the cylinder head.
    (article found here)
    When this style piston deck surface is brought into close proximity with the wedge surface, it creates the quench area...........




    ......... as Jeff demonstates here in these two images.
    (forget the dome in the second image, we won't be using a dome piston for a Marine cruiser engine)


    ...................


    What we eliminate is a full dished area from coming up underneath the wedge as does the quench deck area of the above style piston (see first piston image).
    The full dished area cannot create a quench!


    Here is an engine block fitted with pistons that provide a quench.
    (example only.... as this is a street performer engine.... but the idea is the same)



    In addition to the piston deck style, the dish volume (of which controls C/R for a given chamber volume), wrist pin location and skirt length, etc...... we use a head gasket (that when compressed), offers the correct quench dimension of .038" for Marine.
    (larger dimension for High Performance Automotive due to increased operating RPM).

    All we need to do is to provide our build specs and selected components to a good piston supplier.
    They can then provide the correct piston for us.
    Often this is only a phone call away.

    ***********************
    Again, and just to be clear, the premise and primary reason for the Marine quench build is to lesson the likihood and potential for Marine Load Detonation.
    As a result, C/R can be increased slighly and Ingition TA can be increased slighly without further risk of Detonation.
    In general, this equates to better and more performance as a result of a more clean and correctly placed PCP (peek cylinder pressure) at/near 12* to 14* ATDC.

    If you read Jeff's write up, note his closing comments in the last paragraph.

    .
    Last edited by RicardoMarine; 02-17-2012 at 11:52 AM.
    Rick ... aka Ricardo..... AQ series Volvo Penta repair
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

    Please... no PMs! Post your questions on the forum.

  13. #13
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    Default Reason for quench effect updated photo

    I just made this image for another person. Thought I'd share it here on ME.com.
    Rick ... aka Ricardo..... AQ series Volvo Penta repair
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

    Please... no PMs! Post your questions on the forum.

  14. #14
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    Default Re: V6 to V8 engine swap

    Had trouble uploading. Here it is.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Rick ... aka Ricardo..... AQ series Volvo Penta repair
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

    Please... no PMs! Post your questions on the forum.

  15. #15
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    Default Re: V6 to V8 engine swap

    Here's an updated version of my last drawing.
    I made a mistake earlier w/ regard to the cylinder head's quench surface by calling it the wedge area.
    (the wedge actually refers to the combustion chamber shape).
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Rick ... aka Ricardo..... AQ series Volvo Penta repair
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

    Please... no PMs! Post your questions on the forum.

  16. #16

    Default Re: V6 to V8 engine swap

    How did this project ever go?
    Did you do it or work it out?

    I did this exact thing that you are proposing

    You have an Alpha gen 2 drive - and should have no issues if you don't stiff arm the throttles EVER!

    Anyway, let me know if I can help - I had a Vortec 4.3L 1998 engine that did the same thing from winterization failure and swapped with a 1979 260/350ci Mercruiser

    Converted all ignition components, etc.

    let me know if I can help

  17. #17

    Default Re: V6 to V8 engine swap

    Well I can not get the pics to work, try try again

  18. #18
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    Default Re: V6 to V8 engine swap

    Look at Dennis Moore's SBC Marine Performance book also.
    Dennis' book is hard to find, and expensive when you do, but apparently your local library can bring one in for you.

    Rick ... aka Ricardo..... AQ series Volvo Penta repair
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

    Please... no PMs! Post your questions on the forum.

  19. #19

    Default Re: V6 to V8 engine swap

    Yes, that's a nice thing the book there you see

  20. #20
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    Default Re: V6 to V8 engine swap

    Update to this thread pertaining to the Quench Effect -vs- No Quench:

    A few things that I should have included earlier.

    Any piston type reciprocating engine must see a LPCP (location of peak cylinder pressure) at/near 12* to 14* ATDC, according to many engineers.
    This is "After Top Dead Center" while the crankshaft throw is being forced downwards producing power and torque.
    Combustion gasses have achieved their greatest expansion value at/near this crankshaft angle.

    In order to achieve this, combustion must begin at the correct crankshaft angle.... typically BTDC... since combustion of gasoline is not instantaneous.
    All components play a role in this, and in particular Ignition Timing.

    In comes Marine Load Detonation potential.

    Detonation is a result of additional fuel flashes, causing a hammering or a knock affect within the cylinder.
    Detonation can be very destructive to an engine under heavy load.
    GM and many engine re-builders continue using the dreaded "full dished" piston in the SBC engines.



    With the above piston, ignition advance (i.e., TA) is held back as to help prevent Detonation, but as a result this gives us a lazy LPCP, often falling behind by several degrees.

    Ultimately, we want a combustion chamber that is most efficient at combating detonation by not giving any portion of the flame front a place to hide, as will the full dished piston.
    To achieve this, and with a wedge style combustion chamber (I.E., the SBC cylinder heads) we want to make certain that we incorporate a "quench area" or a "squish area" (like the choices previously shown).
    With a good Quench Effect or Squish Zone, we can allow more ignition advance (i.e, TA), and with no additional risk of Detonation.


    The image below should help explain the differences between what a full dished piston Cannot do, and what a Quench style piston Can do.

    FYI:
    Any quench style piston's dish volume can be changed to accommodate the different SBC cylinder head combustion chamber volumes as to achieve the desired C/R.

    The only piston that limits us, would be the Flat Top piston used in a 5.7L with the 76cc chamber cylinder heads.
    This is usually a good combination for a SBC Marine engine when the correct quench dimension is maintained..... but not a good choice with the 64cc, 65cc or 72cc chamber cylinder heads.
    Also, if given a choice between double valve relief pistons, and single valve relief pistons, go for the single valve reliefs.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by RicardoMarine; 10-24-2013 at 08:32 AM.
    Rick ... aka Ricardo..... AQ series Volvo Penta repair
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

    Please... no PMs! Post your questions on the forum.

  21. #21
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    Default Re: V6 to V8 engine swap

    Update to my image to add a bit of clarity.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	Quench and Squish area explained.jpg 
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    Rick ... aka Ricardo..... AQ series Volvo Penta repair
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

    Please... no PMs! Post your questions on the forum.

  22. #22
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    Default Re: V6 to V8 engine swap

    This is an update for one of the members at another boating forum.

    Walt, I am not a member of your forum, but I do occasionally read the threads there.
    Bill and I are cyber friends.

    I am not an ultimate authority regarding the small block Chevy Marine Engine, however, I do have approximately 48 years experience with this engine.
    I am no stranger to the proper and correct SBC Marine build.

    I don't want to burden Bill by asking him to post this, so I'm going to ask him to simply provide a link to this updated MarineEngines.com thread.

    ****************

    Walt, I have no dog in any fight here. My posts on this subject are intended to simply provide additional information for anyone who may perhaps desire a better engine build for Marine cruiser use.

    Marine Engine load detonation is a real concern for us with the SBCs fitted with full dished pistons. Merc, Volvo Penta and the others combat detonation (regarding the typical GM build with these silly full dished pistons) by holding back ignition advance! When ignition advance is held back, so is a good LPCP, of which is critical for good torque.
    LPCP is best when at/near 12*-14* ATDC, according to most engineers!
    At a typical 26* TA @ 3.2k rpm, it just doesn't cut it, and makes for a lazy LPCP.

    When we take advantage of the quench or squish area (spelled NO full dish underneath this surface), and give the flame front no place to hide, we drastically change the dynamics of the combustion chamber and the potential for Ignition induced detonation.

    A good quench build does not necessarily cause the need for other component changes..... although these changes can complement the quench effect.
    Futhermore, a quench style combustion chamber alone is well worth the efforts regrading better detonation prevention.


    Also, this is not a high performance build technique..... this is a proper build technique for any gasoline marine engine that incorporates a quench surface....., such as the SBC, Chrysler Wedge Head engines, the Ford 335 series Windsor engines (5.0 and 5.8), and the Chrysler 318/360.

    Building a good quench and good quench dimension into a SBC is very simple. Most any engine builder can do this for the asking, and it should not affect the warranty whatsoever!
    It will however cause the need for multiple piston part numbers and extra alertness during the assembly.

    A phone call to their piston supplier is all that's required.
    The piston supplier's expert can provide the correct piston part numbers for the shop. All he needs are the desired specs!

    If the builder cannot provide this build, you'd best find another builder!


    Walt, your dismissing of, and your down-playing of this style SBC Marine build is somewhat puzzling to me.
    Your comment regarding the dish and quench being "meaningless", and the "choking down" also puzzles me, and in particular since you appear to have very good engine building knowledge!

    No offense, Walt...... This is just simply conversation and my observation!




    .
    Last edited by RicardoMarine; 01-10-2014 at 10:50 AM.
    Rick ... aka Ricardo..... AQ series Volvo Penta repair
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

    Please... no PMs! Post your questions on the forum.

  23. #23
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    Default Re: V6 to V8 engine swap

    A good friend of mine ran some numbers a while back, and here's what he came up with:
    (this is using base figures for a Q/E built SBC engine with an approximate XX more HP from that over the OEM equivalent! these numbers may be even better with a lessor HP gain engine. this is an approximation only!)


    *********


    The potential difference between a quench built SBC Marine engine and a full dish piston built SBC Marine engine may equate to approximately 4 gallons of fuel burn difference per hour.
    Much will depend on the size and weight of the boat!

    If this is anywhere near accurate or close, think about a 10 hour long day cruise @ a fuel burn rate savings of 4 gallons/hr !!!
    ...... of which could equal 40 gallon fuel consumption difference @$4 a gallon.
    ....... of which may equate to a savings of $160 in one day!

    Now use an average of 100 hours a year on this same boat.
    That's 400 extra gallons of fuel savings per year...... or roughly a $1,600 fuel expense savings!


    As a customer who is wanting and asking for information regarding a new replacement SBC Marine engine, wouldn't you want to know of these potentials and possibilities?
    Not to even mention the grandiose benefit of lessor Detonation concerns!

    I certainly would!





    .
    Last edited by RicardoMarine; 01-10-2014 at 01:59 PM.
    Rick ... aka Ricardo..... AQ series Volvo Penta repair
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

    Please... no PMs! Post your questions on the forum.

  24. #24
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    Default Re: V6 to V8 engine swap

    Connecting rod length for a Marine SBC 6.2L or 6.3L build (377/383):

    We will see both strong and weak points with regard to using longer connecting rods. The explanation could get quite involved, and would possibly show us the trade-offs with either scenario.


    The longer rods are great for a 6.2L or 6.3L street performance build.
    However, longer rods cause the need for a higher wrist pin location, of which shortens the effective piston skirt length.
    We want the skirt length for the 6.2L or 6.3L Marine build!

    The Hot Rods guys may perhaps not quite understand this....., but the engine builders with true Marine SBC Cruiser Engine experience, will understand!

    Side note.
    The automotive SBC engine builders know their stuff, and these guys are very capable of building a great SBC auto engine.
    But the subtle differences that make for a good Marine SBC, are often misunderstood or are simply not known to them.
    Dennis Moore's Small Block Marine Performance book would be a good read for any of us, and in particular with regard to a good "quench" dimension.


    .
    Last edited by RicardoMarine; 01-13-2014 at 08:30 AM.
    Rick ... aka Ricardo..... AQ series Volvo Penta repair
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

    Please... no PMs! Post your questions on the forum.

  25. #25
    Join Date
    Mar 2009
    Location
    Portland, Oregon,
    Posts
    9,189

    Default Re: V6 to V8 engine swap

    As some of you know, I'm 2850Bounty on the BOC forum.
    Here are several mote threads regarding the SBC quench build.

    http://www.baylinerownersclub.org/in...or-trophy-2860

    http://www.baylinerownersclub.org/in...ngine-question

    I put this thread together to show us some Engine cut-a-way views.

    http://www.baylinerownersclub.org/in...-be-interested


    .
    Last edited by RicardoMarine; 01-31-2014 at 10:40 PM.
    Rick ... aka Ricardo..... AQ series Volvo Penta repair
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

    Please... no PMs! Post your questions on the forum.

  26. #26
    Join Date
    Mar 2009
    Location
    Portland, Oregon,
    Posts
    9,189

    Default Re: V6 to V8 engine swap

    Here's a neat little GIF file showing the 4 engine cycles.
    This GIF was actually created to show the difference between a "wedge" shaped combustion chamber (SBC on our left side) and a "hemispherical" shaped combustion chamber (Chrysler Hemi on our right side).

    So basically this GIF is showing two combustion chamber designs, either of which benefits from a correct LPCP.





    NOTE: this GIF shows a domed piston on the left side wedge chamber. Imagine the GM Full Dished piston in it's place.

    Also note:
    the fuel/air does not explode. It actually burns, and there is a duration for this burn, and is why Ignition Spark Advance is so critical, and especially for the Marine Engine.



    There is a draw-back with the wedge style combustion chamber when the GM Full Dished piston is used as it creates a place for a portion of the flame front to hide (demonstrated here by the dotted lines).

    With this style chamber, ignition advance must be held back to avoid Marine Load Detonation potential.
    The Q/E forces the gasses out into the flame front, reducing detonation potential and also allows for more ignition spark advance.
    With a greater spark lead, we can now have a much better LPCP.





    Look at the left side cylinder during the ignition and burn cycle.






    As the fuel/air burn reaches it's maximum expansion, this is our Peak Cylinder Pressure location in degrees of crankshaft angle.
    We want this LPCP to be near 12* to 14* ATDC.


    Here's my rather crude attempt of showing LPCP as per crankshaft angle.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	LPCP explained.jpg 
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ID:	10291  
    Last edited by RicardoMarine; 11-18-2014 at 08:16 AM.
    Rick ... aka Ricardo..... AQ series Volvo Penta repair
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

    Please... no PMs! Post your questions on the forum.

  27. #27

    Default Re: V6 to V8 engine swap

    hello i have a 1987 forrester cuddy 190 E with a 4 banger 3.0l in it and the whole lower unit is bad, i was looking at swapping the motor/upper and lower unit for a 302 OMC cobra engine with a computer upper and lower unit assembly will this work on my boat, im sure im gunna have modifications to do but dont know how much? thank you!!

  28. #28

    Default Re: V6 to V8 engine swap

    If I can jump in, I have Sea Ray with a Mercruse V6 and want to upgrade to a 350 Chev. The mounts do not lineup of course. Is there an aftermarket mount that will for this application or will I have to make one.

  29. #29
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    6,824

    Default Re: V6 to V8 engine swap

    The mounting system should be the same....the rear should line up on the transom plate....the forward ones will have to be moved forward to account for the longer block....just make sure you have enough clearance in the front before you start...you'll also be better served regearing the upper drive and repitching the prop....

  30. #30

    Default Re: V6 to V8 engine swap

    I am trying to replace a 4.3L with a 360 ci V8. Is there an after market mount that will make up the additional length using existing mounting holes?

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