Replaced Volvo Penta 4.3GL with Mercury reman engine - lost 3 to 5 mph off top end.

In spring 2011, I had a Mercury remanufactured 4.3L V6 engine installed in my 20' Chaparral. It was a complete engine (minus intake and carb) that was fitted up with all the accessories from the original engine. A new intake and original carb were placed on the new engine. With the new engine, I have lost 3 to 5 mph off the top end. The mechanic says that everything is adjusted properly and that it "is what it is". It seems odd to me that a remanufactured motor would produce 10% less top end than an engine that needed to be replaced (due to a bent crank that I didn't know about when I bought the boat - argh!). Although I can't quote specific numbers on rpm, the wot is well within the range for the engine and the engine runs fine. No changes were made to the prop or outdrive (except new bellows and gimbal bearing).

I am wondering if I should accept the "it is what it is" diagnosis or if there is something more I can check. I don't know much about boats but I have turned a few wrenches on car/truck engines. So, I can check most anything that doesn't require special tools, etc. Should I be looking at timing or a carb adjustment (carbs can be tricky). It goes without saying but I will say it anyway - thanks in advance for any suggestions.

Here are the Volvo Penta numbers:

Engine - 4.3GL PEFS (4012004849), Outdrive - SX-M 1 79 (4112094763), Transom - SX-MLT (4111633176)

Re: Replaced Volvo Penta 4.3GL with Mercury reman engine - lost 3 to 5 mph off top en

Kinda repeating Bubba's question:

So what was the WOT RPM of the old engine and WOT RPM of the new engine?

Re: Replaced Volvo Penta 4.3GL with Mercury reman engine - lost 3 to 5 mph off top en

For some reason my reply didn't post - user error I'm sure. Anyway, I can't say specifically what the WOT of the old engine was. As I recall, it was in the range of 4800 rpm, can't be specific. Likewise, I don't have the actual WOT of the new engine yet. But, without verification, I would say it is in the same range. I admit that I have been focused on speed and not rpm. I will get the specifics on the WOT rpm of the new motor.

Hypothetically, let's say I had the WOT for the old engine and the WOT for the new engine and the old engine was 100 rpm greater. Would there be anything I could do to increase the WOT of the new engine (within the specified range), or would I then just know that the old engine made more rpm at full throttle and that is why it was faster?

Re: Replaced Volvo Penta 4.3GL with Mercury reman engine - lost 3 to 5 mph off top en

Hypothetically, if the rpm is the same and nothing changed, yes you should have the same speed.

Just curious, you aren't one of those guys that trims the drive by looking at a gauge are you? If you are and your gauge is wrong, you could be in trouble. Try trimming the drive up and down for best speed and rpm at the same time.
High rpm and low speed, trim it down. Low rpm and speed, trim it up.

Re: Replaced Volvo Penta 4.3GL with Mercury reman engine - lost 3 to 5 mph off top en

{{{{A new intake and original carb were placed on the new engine.}}}}

Was there a problem with the old intake as in it did not mate up correctly?????

Re: Replaced Volvo Penta 4.3GL with Mercury reman engine - lost 3 to 5 mph off top en

Hey Don, thanks for reading my post. I have read many of your comments on other threads and "you are the man". As for trim, I usually adjust based on the feel of the boat and the speed on the GPS. I try to trim to achieve the maximum speed at a given throttle setting without causing the boat to handle poorly. My trim gauge porivdes only a gross indicator of position. Maybe they are all like that but mine couldn't really be used to adjust anything in a reproducible manner. I am eager to get back on the water and nail down the WOT and associated speed. That will most likely be Easter weekend.

As for the manifold, it was cracked due to freeze damage (on the old engine). Nevermind that I paid to have the boat winterized including running antifreeze through it. So, I read with interest the whole debate on the winterization thread. This will be the first year I do it myself and I fall into the "drain it" camp. It's hard to see how air would freeze under normal conditions. As far as I know (which isn't far), the old mani would have bolted up to the new engine if it hadn't been cracked. Although the remanufactured engine is from Mercury, I think it is the same exact engine as from Volvo. I was told Volvo didn't provide remanufactured engines. They only sell new ones and the cost difference is rather large.

Re: Replaced Volvo Penta 4.3GL with Mercury reman engine - lost 3 to 5 mph off top en

Take it easy on a new engine, you shouldn't be doing top speed runs until you've put a few hours on it. 3-5mph isn't a lot depending on the conditions you were boating in. How the boat is loaded, how much fuel and gear is aboard, there are a lot of factors involved. I know that in cold water, my boat runs a bit slower so that could also be a factor in play.

Re: Replaced Volvo Penta 4.3GL with Mercury reman engine - lost 3 to 5 mph off top en

bnicov said:

I know that in cold water, my boat runs a bit slower so that could also be a factor in play.

Click to expand...

I really doubt cold water is a factor unless there is ice in it.

Re: Replaced Volvo Penta 4.3GL with Mercury reman engine - lost 3 to 5 mph off top en

As posted earlier, deffinately go easy on the new engine until she's properly broke in, you might just get that mph back once it's broke in.
Personally, as far as WOT throttle goes I would ONLY go by an accurate tachometer. When you achieve max WOT on your tack with your boat properly loaded your top speed will be your top speed.

Your engine doesn't care how fast the boat goes. Your eingine on the other hand very much does care how fast it is spinning. Run er over 4800 (likely your WOT) too much and you'll be looking for another reman engine. Just sayin.. . .

Re: Replaced Volvo Penta 4.3GL with Mercury reman engine - lost 3 to 5 mph off top en

The engine was broken in per Mercury specs and now has about 35 total hours on it. So, I think she is well broken in. Most of my cruising is in the 2600 to 3000 rpm range. It's only occassionally at or near WOT. And even then, it's not there long because like you said, I don't want to be looking for another motor! I just want to optimize this one.

Thanks for all the replies and suggestions!