5.7 Tuning Help!
07-10-2016, 08:34 AM
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5.7 Tuning Help!
Hi guys,
Im not new to boats, but new to this forum. I have a 5.7 Merc in a Wellcraft. It is a built motor and the PO had it set up different than Im used to. It has a 6M-2L ignition and MSD Marine distributor. The 6M-2L ignition system just went out, so I replaced it. While I was there I replaced the distributor as well as the plugs and wires. The PO had locked timing at 36 degrees BTDC. Should I keep it that way or should I use a mechanical advance. If so, what spring setup. He was a full throttle only guy. I do everything in between with cruising to full throttle. I havent been able to drive it with the current settings, as the ignition went out after I purchased it.
Im not new to boats, but new to this forum. I have a 5.7 Merc in a Wellcraft. It is a built motor and the PO had it set up different than Im used to. It has a 6M-2L ignition and MSD Marine distributor. The 6M-2L ignition system just went out, so I replaced it. While I was there I replaced the distributor as well as the plugs and wires. The PO had locked timing at 36 degrees BTDC. Should I keep it that way or should I use a mechanical advance. If so, what spring setup. He was a full throttle only guy. I do everything in between with cruising to full throttle. I havent been able to drive it with the current settings, as the ignition went out after I purchased it.
07-20-2016, 10:16 AM
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Sorry for the delayed reply... Was out of town. Don't know exact compression. Patriot freedom heads, bullet cams, holley 750, and b&m intake. I just ditched my msd marine mechanical advance for vacuum. It seems to run better. I just can't figure out what I should set initial and total advance. Any ideas?
07-20-2016, 11:36 AM
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Maybe pull a valve cover and get the head id's for chamber volume, most sbc are good to maybe 32 degrees all in. Since they are always under load they can detonate much past that. For the likely 5 horses I'd stay 34 all in. At least we get good cooling with outside water to help combat the detonation.
See if you can get a cam card or part #. If you find that it has great quench and high compression maybe push a little on the advance.
If the cam is approaching wild it could need some extra timing at start and idle. A lot of boats that play that card use the Mercruiser V6 electronic module that doesn't advance as far as the V8 ones do.
Since you already have the diz, set it as needed. Boats run under such load that you may as well ditch the vacuum side if possible, since it's a performance cam it probably won't have much vacuum anyway.
See if you can get a cam card or part #. If you find that it has great quench and high compression maybe push a little on the advance.
If the cam is approaching wild it could need some extra timing at start and idle. A lot of boats that play that card use the Mercruiser V6 electronic module that doesn't advance as far as the V8 ones do.
Since you already have the diz, set it as needed. Boats run under such load that you may as well ditch the vacuum side if possible, since it's a performance cam it probably won't have much vacuum anyway.
Last edited by NHGuy; 07-20-2016 at 11:57 AM.
07-20-2016, 11:52 AM
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Don't hook up the vacuum. Leave the port on the distributor un capped. Obviously, cap the vacuum port on the intake or carb it was hooked to.
Set Mechanical for 32 degrees total, Try for 12-16 degrees initial.
Edit in: I won't be shy. That was a mistake getting the vacuum distributor.
Set Mechanical for 32 degrees total, Try for 12-16 degrees initial.
Edit in: I won't be shy. That was a mistake getting the vacuum distributor.
Last edited by SB; 07-20-2016 at 11:54 AM.
07-20-2016, 05:21 PM
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Maybe pull a valve cover and get the head id's for chamber volume, most sbc are good to maybe 32 degrees all in. Since they are always under load they can detonate much past that. For the likely 5 horses I'd stay 34 all in. At least we get good cooling with outside water to help combat the detonation.
See if you can get a cam card or part #. If you find that it has great quench and high compression maybe push a little on the advance.
If the cam is approaching wild it could need some extra timing at start and idle. A lot of boats that play that card use the Mercruiser V6 electronic module that doesn't advance as far as the V8 ones do.
Since you already have the diz, set it as needed. Boats run under such load that you may as well ditch the vacuum side if possible, since it's a performance cam it probably won't have much vacuum anyway.
See if you can get a cam card or part #. If you find that it has great quench and high compression maybe push a little on the advance.
If the cam is approaching wild it could need some extra timing at start and idle. A lot of boats that play that card use the Mercruiser V6 electronic module that doesn't advance as far as the V8 ones do.
Since you already have the diz, set it as needed. Boats run under such load that you may as well ditch the vacuum side if possible, since it's a performance cam it probably won't have much vacuum anyway.
07-20-2016, 05:35 PM
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Can you guys explain why I shouldnt use the vacuum and just cap the carb side and leave vacuum open? Should I return the vacuum and go back to a mech distributor? Suggestions on brands and initial spring settings. I had an old school offshore racing guy (friend of a friend) tell me that vacuum advance would be the best. I have been having a million problems with the MSD pro billet distributor and 6m-2l ignition system, so I figured I should try something different.
07-20-2016, 05:50 PM
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So I found this on a MOPAR website. Kind of summarizes the benefits of vacuum advance that the offshore race guy I talked to mentioned to me. The last paragraph states what NHguy was referring to re: cam and vacuum. Im not partial to vacuum or mech or locked timing. Im curious as to what you guys think I should do (looks like 2 votes for no vacuum)...I just would like some clarification on the subject. Regardless, read this and let me know what you all think.
TIMING AND VACUUM ADVANCE 101
The most important concept to understand is that lean mixtures, such as at idle and steady highway cruise, take longer to burn than rich mixtures; idle in particular, as idle mixture is affected by exhaust gas dilution. This requires that lean mixtures have "the fire lit" earlier in the compression cycle (spark timing advanced), allowing more burn time so that peak cylinder pressure is reached just after TDC for peak efficiency and reduced exhaust gas temperature (wasted combustion energy). Rich mixtures, on the other hand, burn faster than lean mixtures, so they need to have "the fire lit" later in the compression cycle (spark timing retarded slightly) so maximum cylinder pressure is still achieved at the same point after TDC as with the lean mixture, for maximum efficiency.
The centrifugal advance system in a distributor advances spark timing purely as a function of engine rpm (irrespective of engine load or operating conditions), with the amount of advance and the rate at which it comes in determined by the weights and springs on top of the autocam mechanism. The amount of advance added by the distributor, combined with initial static timing, is "total timing" (i.e., the 34-36 degrees at high rpm that most SBC's like). Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the "total timing" equation.
At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected). The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at 50mph).
When you accelerate, the mixture is instantly enriched (by the accelerator pump, power valve, etc.), burns faster, doesn't need the additional spark advance, and when the throttle plates open, manifold vacuum drops, and the vacuum advance can returns to zero, retarding the spark timing back to what is provided by the initial static timing plus the centrifugal advance provided by the distributor at that engine rpm; the vacuum advance doesn't come back into play until you back off the gas and manifold vacuum increases again as you return to steady-state cruise, when the mixture again becomes lean.
The key difference is that centrifugal advance (in the distributor autocam via weights and springs) is purely rpm-sensitive; nothing changes it except changes in rpm. Vacuum advance, on the other hand, responds to engine load and rapidly-changing operating conditions, providing the correct degree of spark advance at any point in time based on engine load, to deal with both lean and rich mixture conditions. By today's terms, this was a relatively crude mechanical system, but it did a good job of optimizing engine efficiency, throttle response, fuel economy, and idle cooling, with absolutely ZERO effect on wide-open throttle performance, as vacuum advance is inoperative under wide-open throttle conditions. In modern cars with computerized engine controllers, all those sensors and the controller change both mixture and spark timing 50 to 100 times per second, and we don't even HAVE a distributor any more - it's all electronic.
Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it.
If you look at the centrifugal advance calibrations for these "ported spark, late-timed" engines, you'll see that instead of having 20 degrees of advance, they had up to 34 degrees of advance in the distributor, in order to get back to the 34-36 degrees "total timing" at high rpm wide-open throttle to get some of the performance back. The vacuum advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle, which caused all manner of problems - "ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more.
What about the Harry high-school non-vacuum advance polished billet "whizbang" distributors you see in the Summit and Jeg's catalogs? They're JUNK on a street-driven car, but some people keep buying them because they're "race car" parts, so they must be "good for my car" - they're NOT. "Race cars" run at wide-open throttle, rich mixture, full load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation. Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they don't understand what vacuum advance is, how it works, and what it's for - there are lots of long-time experienced "mechanics" who don't understand the principles and operation of vacuum advance either, so they're not alone.
Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren’t fully-deployed until they see about 15” Hg. Manifold vacuum, so those cans don’t work very well on a modified engine; with less than 15” Hg. at a rough idle, the stock can will “dither” in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15” Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8” of vacuum, so there is no variation in idle timing even with a stout cam.
For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively. Don't ask Summit or Jeg's about it – they don’t understand it, they're on commission, and they want to sell "race car" parts.
TIMING AND VACUUM ADVANCE 101
The most important concept to understand is that lean mixtures, such as at idle and steady highway cruise, take longer to burn than rich mixtures; idle in particular, as idle mixture is affected by exhaust gas dilution. This requires that lean mixtures have "the fire lit" earlier in the compression cycle (spark timing advanced), allowing more burn time so that peak cylinder pressure is reached just after TDC for peak efficiency and reduced exhaust gas temperature (wasted combustion energy). Rich mixtures, on the other hand, burn faster than lean mixtures, so they need to have "the fire lit" later in the compression cycle (spark timing retarded slightly) so maximum cylinder pressure is still achieved at the same point after TDC as with the lean mixture, for maximum efficiency.
The centrifugal advance system in a distributor advances spark timing purely as a function of engine rpm (irrespective of engine load or operating conditions), with the amount of advance and the rate at which it comes in determined by the weights and springs on top of the autocam mechanism. The amount of advance added by the distributor, combined with initial static timing, is "total timing" (i.e., the 34-36 degrees at high rpm that most SBC's like). Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the "total timing" equation.
At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected). The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at 50mph).
When you accelerate, the mixture is instantly enriched (by the accelerator pump, power valve, etc.), burns faster, doesn't need the additional spark advance, and when the throttle plates open, manifold vacuum drops, and the vacuum advance can returns to zero, retarding the spark timing back to what is provided by the initial static timing plus the centrifugal advance provided by the distributor at that engine rpm; the vacuum advance doesn't come back into play until you back off the gas and manifold vacuum increases again as you return to steady-state cruise, when the mixture again becomes lean.
The key difference is that centrifugal advance (in the distributor autocam via weights and springs) is purely rpm-sensitive; nothing changes it except changes in rpm. Vacuum advance, on the other hand, responds to engine load and rapidly-changing operating conditions, providing the correct degree of spark advance at any point in time based on engine load, to deal with both lean and rich mixture conditions. By today's terms, this was a relatively crude mechanical system, but it did a good job of optimizing engine efficiency, throttle response, fuel economy, and idle cooling, with absolutely ZERO effect on wide-open throttle performance, as vacuum advance is inoperative under wide-open throttle conditions. In modern cars with computerized engine controllers, all those sensors and the controller change both mixture and spark timing 50 to 100 times per second, and we don't even HAVE a distributor any more - it's all electronic.
Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it.
If you look at the centrifugal advance calibrations for these "ported spark, late-timed" engines, you'll see that instead of having 20 degrees of advance, they had up to 34 degrees of advance in the distributor, in order to get back to the 34-36 degrees "total timing" at high rpm wide-open throttle to get some of the performance back. The vacuum advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle, which caused all manner of problems - "ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more.
What about the Harry high-school non-vacuum advance polished billet "whizbang" distributors you see in the Summit and Jeg's catalogs? They're JUNK on a street-driven car, but some people keep buying them because they're "race car" parts, so they must be "good for my car" - they're NOT. "Race cars" run at wide-open throttle, rich mixture, full load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation. Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they don't understand what vacuum advance is, how it works, and what it's for - there are lots of long-time experienced "mechanics" who don't understand the principles and operation of vacuum advance either, so they're not alone.
Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren’t fully-deployed until they see about 15” Hg. Manifold vacuum, so those cans don’t work very well on a modified engine; with less than 15” Hg. at a rough idle, the stock can will “dither” in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15” Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8” of vacuum, so there is no variation in idle timing even with a stout cam.
For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively. Don't ask Summit or Jeg's about it – they don’t understand it, they're on commission, and they want to sell "race car" parts.
07-20-2016, 06:46 PM
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Vacuum advance in road applications works as there are so many times the engine is under a very light load. Light load= not much air charge in the cylinders=can start the ignition way early. Boats are always under what would be say 60%-100% load so this is never the case except while idling.
07-20-2016, 06:55 PM
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#1 There is no marine legal vac distributor.
#2 Since an I/O boat is always under load, the only time the vac portion can helpyou is at idle. Well,with bushings and etc you can give your dist a lot more initial if you want,
Article you brought up is mostly car related. 99.9% graduated from performance cars before getting into boats. As far as cooling, sure, works good for performance street, but your car doesn't have a 130 billion gallon radiator.
#3 MSD, even the marine versions, rust out super fast, and even if trailered and on fresh water. You should rust proof any of them. Was a recent thread on what to use. CRC makes it.
#4 MSD marine boxes are quite unreliable. Have a spare box and mag pickup if you continue to keep using one.
You will here more negative comments on their systems, many of us don't bash to just bash, it's because alot of us here are old and have been doing this for a long time.
You ask advice, we give it. Please give it some major consideration.
I'll get this over with.
My Spark Died
My Spark Schit
Multiple Sparks Died
May Soon Die
May Soon Schit
There will be more.
#2 Since an I/O boat is always under load, the only time the vac portion can helpyou is at idle. Well,with bushings and etc you can give your dist a lot more initial if you want,
Article you brought up is mostly car related. 99.9% graduated from performance cars before getting into boats. As far as cooling, sure, works good for performance street, but your car doesn't have a 130 billion gallon radiator.
#3 MSD, even the marine versions, rust out super fast, and even if trailered and on fresh water. You should rust proof any of them. Was a recent thread on what to use. CRC makes it.
#4 MSD marine boxes are quite unreliable. Have a spare box and mag pickup if you continue to keep using one.
You will here more negative comments on their systems, many of us don't bash to just bash, it's because alot of us here are old and have been doing this for a long time.
You ask advice, we give it. Please give it some major consideration.
I'll get this over with.
My Spark Died
My Spark Schit
Multiple Sparks Died
May Soon Die
May Soon Schit
There will be more.
Last edited by SB; 07-20-2016 at 06:57 PM.
