640LX

[byron cooley]

I am looking for anyone else that is running the massive Optimax on a 640LX. I purchased a 2004 640LX with 75hp Optimax. The boat tag says that it is rated for up to 90hp but nitro.com and the dealer will only upgrade to 75hp. So I went for the 75 Optimax. Being in southern California the 75hp carb model is not an option due to emissions. The boat has great cruise and top end is not to bad, 44gps / 48 speedo @ 5200rpm. Dry comfortable,ride. Only maybe 2ft of boat in the water when trimmed out. My only complaints I believe are motor relatted. The hole shot is terrible with a lot of bow lift even with the moter trimmed in all the way. The other problem is all the water that comes over the transom when you stop ( I have to hit forward as the wake catches up or take on water). Even though the manufacturer offers the 75 Opti as an option, I don't really think that the 640 was designed for a 370lb motor. Right now I am running the factory 21 pitch prop. It uses a 2.33-1 lower unit. Can sombody recomend a good choice for a stainless prop that might help the hole shot and gain the missing 550 rpm. Running at 5200rpm@wot looking for 5750rpm@wot.

 

[Staci Matheis]

Byron -



There are some VERY knowledgable people on this board who will be happy to help you!



While you're waiting for them, you may want to go to the Mercury Marine website and check it out with their Prop Selector! Link Below.



Good luck!

me!
http://www.mercurymarine.com/prop_selector

 

[Michael Snow]

Ask your dealer to swap you for a 19p. The rule of thumb is 200 rpms per inch of pitch. So, this would increase your RPMs by 400 roughly. I don't think I'd go with an 18 because that would put you just over redline.



Your holeshot will be much better, but your top end speed really won't change much.

 

[TrepMan]

Bryan - Can't help you on performance, but your dealer is not informed or correct (Patt Goff and Dan J. correct me if i'm wrong) but the 640 IS rated to 90HP AND any intelligent and knowledgable dealer WILL sell you one no questions. The Tracker/Nitro site (i've spoken with the webmaster) does NOT always show EVERY available motor option on every boat, just the MOST selected/purchased. So if your dealer told you you could NOT get a 90hp, he was wrong - period.



Now, someone may chime in and say that a 4 stroke 90hp might be too much weight on the transon but that would have to be verified by Tracker, i'd think from a liability perspective if it WOULD NOT hold a 90 fourStroke they would either A) decrease the coastguard Max HP to say 75 or B) put a disclaimer on the boat/site/brochure saying 90hp up to XX lbs.



Just my opinion.



Great looking boat, hope the other guys get you going in the right direction on props!

 

[Pat Goff]

There are motors we're not supposed to rig, examples:

90-115 fourstrokes on a PT 185

115 Optimax on a PT 185

115 Fourstrokes on NX 640/700



There are limits to a hull design, and we have to abide by the manufacturers wishes on what we can put on what, I'll check on the 640/90 Optimax situation.



Previous statements are true, figure 200 rpm for each inch of pitch change.



Now, not meaning to bite the hand that pays my taxes, but Mercury props are second rate on mid hp engines..the selection they have is both very expensive and second rate on performance. Since the smaller hp engines don't come factory rigged with a stainless prop, I have free reign on what we can rig, and it usually isn't a merc prop.

 

[byron cooley]

I think that by the way my 640 sits in the water and the unstoppable bow lift on take off, the Opti's are too heavy for a 16ft boat. I would love the little rig if I could just get the nose down but I think it's the 370lb motor. The 75, 90, 115 Optimax's all way 370lbs dry, all 1.5 liter 3 cyls---Different chip and exhaust. What do you think of Laser2 prop, maybe a 19 or 20?? Think this might be a good choice??

 

[Steve Hutson]

Byron, I used to have a 1997 640LX with the old Force 75. My old boat got up on plane with no problems. I did have the same problem with water coming over the back of the boat when stopping. All I did was start slowing down before I got tho the area that I was going to stop at. Next, I would "burp" the throttle as the wave caught up to me. It seemed to work for me. I hope this helps, although it sounds like you were pretty much doing it already.

 

[Greg Duggan]

Byron,

trim all the way in before slowing down, this will dump the bow back into the water and work like brakes.

this limit the amount of water that comes rushing in over the transom. work with it a little and you will find the right amount throttle vs trim in to keep the water to a minimum.



GregD

 

[Jim Storck Sr]

Same problem with my past 700 LX and my now 882 NX .You have trim motor down before coming to a stop and backwash wont happen.As for getting on plane,I had the same problem with mt 03 882 NX with 175 optimax,you have to try diff props or even add a hydro foil,after I added a foil and raised motor up,problem gone.Get help at your dealer.they may let you try diff props until you find the one that gives the best performance

 

[Michael Snow]

Pat, give the man some suggestions. Michigan Wheel, Powertech, what?

 

[Brian Bell2]

Stilleto makes a real nice prop, and I think it comes in 19"

 

[Richard Ehlers (SevenPin)]

Pat - Any updates on your dial in? I've got the PT185 with the 90 Tracker / Mercury and anything that you find out may help me. It's not the Opti but maybe I can learn something about my boat in general (weight distribution, engine height, etc...)

Thanks.

 

[Wes Newton]

i got a 700lx with a 75 merc and run a 19"...works great on mine..i forgot what brand..as my wife saw that i was looking at one..it may be powertech...i had same problem on bow lift..this prop said stern lifter or somthing but it run great on mine much easier to trim out for good ride( maybe i just learned whta the heck i was doing)...