Motor RPMs

Finally got some bugs worked out on the boat I recently purchased. The carbs needed cleaned and needle valves replaced. I couldn't wait to get on the lake. I opened her up all the way on Lewisville and trimmed it up a quarter of the way according to my gauge. I shut it down at 65-67 and around 6200 RPM's. The motor sounded great and I think it had more to give. It was loaded up with gear and nearly a full tank with me.

I noticed the other day after being on the water and cleaning her up the motor tag said max RPM's 5,500. A buddy said he heard never run a motor above 5k. Anyways, I'd like to know more about this. It's a 2003 Bass Cat Sabre with a 150 Merc XR6 V6 2.5 liter 2 stroke. From I've read these are killer motors that love to be ran wide open and can even be modified. Not that I want to but just sayin. It has a tempest plus 23 pitch prop.

People are for the most part....clueless.

XR6 is indeed a fine motor, as bullet proof as they come, but you need to understand it's happy place, and you and your motor will love each other a long time.

XR6 cannot by modified to much of any degree to get more out of it, Fact. Why? it all has to do with the port design, it's got little finger ports that won't enable you to get any more compression, or flow to it. Bummer, but it is what it is. You can install composite reeds and pick up a little acceleration, but that's about all it's capable of doing.

Now, rpms...the ignition module has a passive rev limiter, after 5,800 rpms it'll start retarding timing, you might be spinning faster, but you're making less power. So, you want to stay at 5,800 WFO. Whatever prop takes you there will give you the best results.

And...I don't like your oil pump to spin any faster than 6,000 rpms, that plastic gear isn't happy at that speed, and unless you want to disable it and pre-mix, you won't want to either.

You need to go up to a 24 or 25 pitch prop.

mostly what Pat n Gary says... its got a 'lectronic control module (usta call 'em ecm's but folks kept gettin' it confused with ecu..).. that's what usually keeps tha r's down.. just like all production stuff every once in a while something "odd" slips thru.. if your turnin' a 23 tempest ona stock gear case buried 62 and still pullin' think ya might of got one a tha "odd" ones.. that motor is plenty happy at 65 hunred plus on a surfaced, lite weight hot rod buttttttt. like Pat n Gary says, ya might wanna prop it a little bigger and stay 'round 6 ta 62 max wfo.. ya oiler is good ta 'bout 6800 since its identical ta 2.5 ProMax which usually have a max at 6750 unless its one of tha "odd" ones also........

One of tha best Merc built 'cept i'm partial to tha pre 'lectronic, O-ring head motors.. those two things squash any ideas of makin' any more horse power...

jmo

Couldn't he just have a bad tach??

might be but "normally" a bad tach will have symptoms other than justa high readin'.. at least tha very few I've seen did.

Isn't that motor pretty commonly propped at a 23 pitch?? Seems like it couldn't turn it 6200 unless the motor is hot

donno? maybe tha gear case/gears changed at one time.. possibly 2 ta 1's.. this is not tha first of one of these "box stock" motors that I've seen and/or heard of that seems exceptional...

Just talked to a customer that I rebuilt his 2004 XR6 on a Nitro and he is running a 24 pitch Tempest turning 5900rpm. That's at this altitude 2250ft.

tha problem here is its an 0-ring, electronic motor and "unless ya do some MAJOR work including changin' "ALL THA ELECTRICS(which requires some parts fab)" its gonna be what ever its gonna be......set up/prop will be tha only variables available to tha normal consumer....

I've heard some of those first XR's were 180+ HP.....it's my favorite Mercury motor though XRi's are close

there's VERY little difference in tha XR's compared to tha so called normal motors other than "marketing"...when ya check parts list ya see that 99% parts are identical (2.0, 2.4 and 2.5's).. Tha XRI is just tha first EFI designation... it was used from '87 till '94/'95 I think then letters changed ta EFI...

other than tha XR2 tha rest of tha XR's (XR4 and XR6) were bigger displacement than "other carbureted 150's)....that's tha performance difference..

Lots of great information guys... Thanks. Would a 24 or 25 prop reduce speed or just lower my RPM's? Went out yesterday and wanted to open it up again but the wife was with. She wants nothing to do with that lol. Got it up to 50 at most hitting 5k roughly for a few seconds before getting screamed at.

i'd talk ta Steve on here... he should be able ta help maximize your set up and prop thing.. have ya got a water pressure gauge on that thing? how much offset? motor height etc?

Careful with the all the same talk.
Yes a lot of parts are interchangeable but the ports are different, especially on the XR6 and it changes everything in the way they work.

How do I get a hold of Steve? At idle my water pressure it 8-10... WFO it's around 22-24 I believe. I need to read and understand offset and motor height. I'll pick up my boat tomorrow later in the day and should be able to post those numbers Saturday at the latest.

http://www.stevescustomprops.com/props.html
go ta his site.. some of what ya lookin' for is on it...

your right 'bout port timin'..but that's a given with what ever block ya got. that's tha basic differences in all tha horse power. ya gotta have that ta benefit with most other "bolt on's".. if ya can't get in and can't get it out ya just pissin' in tha wind... tha rest of tha internal parts are pretty much generic..

btw.. those aren't "finger ports".. those went away with tha chrome bore....they're exhaust relief "slot/notch".. easier start and smoother idle so they say.. they have little effect on comp off idle...

^^^ Thanks... Very informative site. Can't wait to get those measurements and see how it's setup. Thanks again guys

Guys I really apologize for the huge delay. I've been busier than a one legged man in an azz kickin contest. I was finally able to take some measurements. These may be a tad bit off but I'm confident they're very close. I used Steve's Custom Props website as a guide for the following. From pad to ground is 26 1/2". From center prop shaft to ground is 13 1/4" giving me a 13 1/4" gap. That's 10 1/4" off according to them.

My water pressure gauge registers about 8-10 at or near idle speed. When I'm around 50 it's at 20. When I'm
Pushing upper 50's and into 60's it's 22-24.

Thanks again guys and sorry for not responding sooner.

if all those figures are right ya need some "MAJOR" adjustments...

No freaking way....... 65-67 and let out of it???? And the prop shaft is 13+" below pad???? Get someone else to check it.....

if tha "pad" is 26 1/2 inches off tha ground that's gotta be one "butt ugly" deep water trailer!

Hell if it goes 67 mph don't let anyone touch it!

I'm such an idiot lol. I knew something just wasn't right with this number. I measured the edge of the pad not center of it....

Going back to the drawing board. Will get the numbers tomorrow.