88' V6 200hp merc isn't going as fast as it should

[KCLOST]

Re: 88' V6 200hp merc isn't going as fast as it should

andy,<br /><br />It's more of an assurance thing. The trigger is what sends the "trigger" to the switchboxes to release the spark to the coils at the proper time. Assuming everything went back together exactly as they were before, and assuming that the new trigger acts exactly as the old one (when it was working properly), you wouldn't need to do lync and sync. And, assuming there is a slight difference in the assembly, trigger performance, etc. the lync and sync adjustments will most likely be rather minor. All the stator does is charge the switchboxes and sends voltage to the rectifier. So it doesn't mater what position it is in.<br /><br />If you feel the motor is running properly, and you are reaching the proper idle/WOT rpms, you may be ok. But it is nice to do it if you can. RPM's is the key, not necessarily speed. Are they similar to your old engine?

 

[andy6374]

Re: 88' V6 200hp merc isn't going as fast as it should

I couldn't put an exact number on the difference in RPM's on the two engines, but would definitely say they are within 1-2% of each other. Like I said the new engine (new to me, 88') runs at ~5300 RPMs, which according to the factory specs is right in the thick of the operating range at WOT (5000-5500 RPMs). <br /><br />So if I am well withing the operating range, I guess I don't have to worry about damaging the enigne,right?<br /><br />The only thing i can say is...the first time I go to full throttle, if I do it slowly, the engine doesn't sound right at the those RPM's (~2000-2500 RPM's). But if I quickly thrown down the throttle, it's fine. And once the engine has run at WOT, it has no problem (at 2000-2500 RPMs) if I go from idle to WOT slowly. Probably the way old mercs are, they like to be run hard. The engine is happiest when she is running like the raped ape she is. However, the spark advance stop screw hits the powerhead before I'm at WOT. It starts to advance the spark at those mid RPM's<br /><br />Thanks KCLOST, I couldn't put a price on the input you provide. Hopefully one day I can help you out.<br /><br />All in all, my engine is a superior engine since I started using this forum. Thanks to everyone.<br /><br />-andy

 

[KCLOST]

Re: 88' V6 200hp merc isn't going as fast as it should

Andy,<br /><br />This has me a little confused.... You have basically the same WOT rpms, the same lower unit, the same prop, but you have lost 6kts in speed...<br /><br />Something doesn't make sense...

 

[andy6374]

Re: 88' V6 200hp merc isn't going as fast as it should

"You have basically the same WOT rpms, the same lower unit, the same prop, but you have lost 6kts in speed..."<br /><br />You think I am not confused? I don't get it either. Everything is the same except the max speed. Boat bottom is clean. Same GPS. <br /><br />Could two different engines of the same horsepower perform differently?<br /><br />Like I said before the engine I bought originally had a 25'' shaft, so the mech who was installing it called me and said...houston we have a problem, your transom is only 20''. (Note at this point the only thing i knew about my engine was how to change the spark plugs). He said he would combine my old engine with the one I was buying and naturally I just thought he put the new powerhead in the old (89') engine. Could he have done something different? Perhaps the engine is to low in the water and that is where the extra speed is going.<br /><br />-andy

 

[timmathis]

Re: 88' V6 200hp merc isn't going as fast as it should

Also Andy you could have some prop slip!!!

 

[andy6374]

Re: 88' V6 200hp merc isn't going as fast as it should

Good point...My second prop is in the shop right now, actually it should be almost ready. I will try the prop straight out of the shop and report the results.<br /><br />-thanks<br />andy

 

[KCLOST]

Re: 88' V6 200hp merc isn't going as fast as it should

He could very well have... A longer shaft will drop speed, as well as a lower motor height, as well as a different gear ratio in the lower unit possibly...

 

[andy6374]

Re: 88' V6 200hp merc isn't going as fast as it should

If the engine is fully trimmed down, how far should the bottom of the steg be under the lowest point of the boat. I would hate to think the mech just installed the whole engine with the 25'' shaft, giving that my transom is 20''. <br /><br />-andy

 

[KCLOST]

Re: 88' V6 200hp merc isn't going as fast as it should

I would start with the anti-cavitation plate which is the plate on the lower unit just above the prop. That plate should be level or maybe an inch above the very bottom of the hull. If you have a stepped transom/hull it could even go higher... Check this with the plate level with the hull.

 

[KCLOST]

Re: 88' V6 200hp merc isn't going as fast as it should

Do you have a picture of the lower unit that is now on the motor?

 

[KCLOST]

Re: 88' V6 200hp merc isn't going as fast as it should

Here is a v6 motor with a 20" shaft<br />

<br /><br />Here are a few 25" V6 motors<br />

 

[redspiv]

Re: 88' V6 200hp merc isn't going as fast as it should

You said that the motor you installed is a rebuild, nothing else has changed and the boat's bottom is clean. Typically, a waxed bottom will run slower than a slightly dirty bottom. Kind of like sharks, if they had smooth skin they would be slower than they are with the coarse denticles they possess. As for the rebuild, a 25% loss in power is fairly common to the industry. You might enquire as to what was specifically done during the rebuild. Were all cylinders reworked or just one, etc.?

 

[andy6374]

Re: 88' V6 200hp merc isn't going as fast as it should

First off, shaft length is fine.. Second, it gained some extra speed on this last outing (long run) can go about 30.5 kts (maybe that cylinder is getting broken in). Thirdly, my operating range is 5300-5800 RPM;s (not 5000-5500). So there is still some ground to make up. Will do a compression check. Rectifier is bad, don't know if this has been messing up the ignition system. Will report back.<br /><br />Total powerhead rebuild. All rebored. The head and the cranshaft are the only reused items (as well as lower unit, and ignition components.)<br /><br />-andy

 

[andy6374]

Re: 88' V6 200hp merc isn't going as fast as it should

People hear and others I talked to, thought that since cylinder 6 was getting fuel and oil that it shouldn't be damaged from getting no spark.(Previous above posts).<br /><br />I got thinking about it. It is known that it is bad for the engine not to run at its recommended max RPM at WOT. Well, if I was only turning 4500 RPMS and spark advance was set to a maximum (i.e. 21 BTDC at WOT) couldn't this damage the whole engine?<br /><br />-andy