3.7l engine w/ 3.0l drive

ProudFather1215 · #1 04-10-2009, 02:21 AM

the 470 package i was recently given came with a 3.0l outdrive for the 3.7l engine. no idea how, but dident realize until the motor was in and the housing on. they both came right from the same boat, and had only 80 or so hours on the engine. the owner of the glaxy swore they came like that together, and he had no problems on his 19' with it.

now, i took the v20 out for the first cruise today, and rpm's top out right around 5k where they should be, yet she dont seem to be planing off for me, even at WOT and cruising around 40-45mph. aside from no planing, she ran amazingly *knock on wood* and was purring like a kitten even at WOT

the drive has one of the fins on there, no clue what make, but the boat has no trim tabs. would adding tabs, or maybe removing the fin change anything?? or is it the fact that i have the smaller drive bolted up to the motor?

THEFERMANATOR · #2 04-10-2009, 11:04 AM

What pitch prop were you running? You say it hit WOT turning 5K RPM's, how fast were you going? There's a good chance that the 3.0L outdrive has a 2:1 ratio and isn't allowing the engine to get loaded properly, I believe the 3.7L uses a 1.81:1 ratio. Spare would know better on this matter as he deals with more I/O's.

ProudFather1215 · #3 04-10-2009, 11:30 AM

i dident bring any electronics on board, but im guessing i was around 40-45mph while at WOT which topped at just over 5k.

as far as the prop, i have no clue, as it came with the drive. i honestly dident bother to check, hoping that since it came together, the prop would have been matched up correctly.

rb437 · #4 04-10-2009, 04:55 PM

I have the 3.7l w alpha 1 out drive. I believe WOT for that engine should be about 4400 rpm. As for the fin, I found that the boat gets up on plane easier with the fin. I changed out drives last year and the new one did not have the fin. This year I'm putting the fin back on.

THEFERMANATOR · #5 04-10-2009, 07:44 PM

The V-20 hull planes out around 13 MPH I believe, so it sounds like you were planing out. The WOT does sound high, to my knowledge only the newer VORTEC engines turn more than 4600.

ProudFather1215 · #6 04-13-2009, 12:51 AM

a mechanic i asked where i keep my boat said it was normal for the 3.7 to turn 5k at WOT, but i dont like taking one persons opinion for something

so should i be worried my engine is maxing at 5k?

rb437 · #7 04-14-2009, 11:02 AM

I'll check the repair manual I have at home tonight, but I'm almost certain that the spec I read was 4400 rpm.

spareparts · #8 04-14-2009, 06:21 PM

the 3.7 is best to turn in teh 4500-4600 wot rpm range, they will turn higher, but it tends to get tough on valve train. there was a guy in Atlanta running one of those engines in a dragster, I think he was turning it over 10, but he had roller rockers and changed from a chain drive cam to a gear driven($$$$$$$). 5000 isn't going to break you bottom end, but I doubt you are making good power at that rpm, you're above the curve with the stock cam/carb/ intake/exhaust package. The 3.0L drive came with a 1.98 ratio adn the 3.7 with a 1.82 ratio. The 1.98 was the alternative ratio for the 3.7 in high altitude set ups. First thing you need to do is check your tack against a shop tach, usually only about one in ten is even close to being accurate, next borrow a gps(hand held will work fine), check your existing set up. I doubt your are crusiing at 40 mph, that would probably be closer to the top end speed. What prop are you spinning? I'd try a 19 or 21 Mirage

rb437 · #9 04-14-2009, 08:17 PM

The manual I have lists WOT at 4200 - 4600 for the 165, 170, and 3.7l and 4400 - 4800 for the 180, 180, and 3.7lx