Max RPM for a 150 XR2

[Zenrider]

I have a mid 80's 150 XR2 on a 20' Tunnel V Sleek Craft with a 30 pitch chopper. I'm wondering what is the max RPM for this motor. It's spinning up to 7500 right now and I think that is to high.

Any info would be great

Zenrider

[Water_Dog]

For a stock engine with the oil injection still on, yes, that's too high IMO. If it's a well built engine, with all the proper goodies and premix, you could spin it up to 7500.

[Zenrider]

For a stock engine with the oil injection still on, yes, that's too high IMO. If it's a well built engine, with all the proper goodies and premix, you could spin it up to 7500.

The oil injection is off and I just picked this up last year, so I don't think any mods have been done to it. I just raised it up to the last hole to try and get it to stop the chine and top speed. It helped, but I picked up 300 more RPMs and that's why I'm thinking of going to the 32.

Thanks

[ZonkaRacing]

20' tunnel, 30p chopper, 7500rpm's..

Either a lot of trim or a really powerful XR2 you got there :eek:

[Zenrider]

20' tunnel, 30p chopper, 7500rpm's..

Either a lot of trim or a really powerful XR2 you got there :eek:

I just signed up and need to get some pictures and set up info, but we just redid the floor and put a new beam in and now the boat is rock solid. After I raised the motor to the top notch I can't trim it very much at all and its spinning right up to the 7500.

I will get the info and pics up and ask for reccomendations.

Thanks

[pyro]

Check your tach setting. Even with 2:1 gears, there's no way it's turning that much RPM with a 30p unless you're somehow breaking 90 mph doing it.

[Water_Dog]

20' tunnel, 30p chopper, 7500rpm's..

Either a lot of trim or a really powerful XR2 you got there :eek:

:iagree: I missed that on first read, one heck of a 2L.

[Zenrider]

I will have to check into that, we are only in the low 80's last time we checked. I just don't want to blow the thing up

[wrechin2]

Maybe it is one of the over the pond XR2's that made it over here.

[HStream1]

Check your tach setting. Even with 2:1 gears, there's no way it's turning that much RPM with a 30p unless you're somehow breaking 90 mph doing it.

:iagree: Maybe even high 90's>. Or, thats a highly modified 2L :eek:.

[Zenrider]

I bought it on EBay and it was from the south. It's in rough shape but it does get up and rock some what and we only have 5K invested right now/Users/agulczynski/Desktop/IMG_0025.JPG

[Zenrider]

Thanks guys for the responses. Let me get the pics and set up info and get back to you.
I really appreciate any help I can get


Andy

[pyro]

Find out what gearcase ratio you have first.
Stock XR2 cases were 2:1, but it may have a 1.87 now.
Punch in some numbers: http://www.rbbi.com/folders/prop/propcalc.htm

Picking up RPM is only a good thing if slip doesn't go up.

I still think the tach is on the wrong setting, and your actual RPM is closer to 6600-7000.
I've been wrong before...

[Zenrider]

Thanks, let me dig into it. It doesn't have air box which would make me think someone new what they were doing before we bought it. Once we redid the beam and floor and raised the motor our trim is way down.

Thanks again for the help

Andy

[83PREDICTOR]

For the 2L to ge that boat on plane with that prop really amazzzzzzesssssss me.

[Zenrider]

A couple of questions:
how do you find out your gear ratio and how do you figure out how much slipage you have.


Thanks

[wrechin2]

Ratio is pretty easy. Put in foward gear and rotate the engine 1 full round to top dead center, 0* on your flywheel. This takes out the slack. Put a piece of tape on the prop at 12 oclock position. Rotate the engine 2 full turns back to TDC. If the tape is at 12 o'clock then it is a 2:1, it is is around the 1-2 o'clock position it is a 1:87. The 1:78 would be a small gear case and would be around the 3 o'clock position. Hope this helps

[wrechin2]

To find out prop slip, go here http://www.rbbi.com/folders/prop/propcalc.htm and put in the know parameters. It will figure it out based on what info you fill in.

[Zenrider]

Thanks for the info

[wideglide55]

I think 6500rpm would be more reasonable for it to live very long.Sounds like you have alot of slip.My first prop for my Eliminator was a stock Merc 28 Chopper. It ran 85 at 6400 on the limiter,changed to a 29 MazcoRE-3 that was labbed and my boat ran [email protected] 11 mph with just a prop change.

[Zenrider]

Once we fixed the floor, the boat chined a lot. We thought we needed to raise the motor (our thinking was that the motor was to low and was raising the back of the boat, causing the chine), so we raised the motor to the top hole (1" up), the center of the hub is about 2" below the bottom of the center sponson. The boat has less chine, but the RPMs are up. I would think a 30 pitch prop would not be able to spin that fast and it sounds like so does everyone else.

Not sure if going in the right direction ? Need help

Andy

[pyro]

Just to clarify:
A "Chine" (n) is the edge of the bottom where it meets either side of the hull.
Chine-walking (v) is the handling quirk of whick you speak. ;)

Sloppy steering and rubber (vs hard) motor mounts are the biggest things that make it worse. Rasing the motor helps because it reduces the radius between the hull's centerline of balance and the propshaft, thus making the hull act like a shorter playground teeter tooter, and thus easier to control. ;)

[T-REX]

I've had sum aquaintn'sis wit sum purdy mopdified 2liters dat wouldn't turn a 30 pitch cleaver 7500rpm????.....If U git 7200 out ov a stock 2liter wit a 2:1 geer and a 24 yamaha drag wheel, U doin better tha tha 3 SS 2liters I built, and dat iz wit a bote raceready, wit driver 1075#s!!......I did have a XR2 once on a skiff turn'd 7600, wit a 24" LaserII prop...But thank it had sum tach issues...sho wish I had dat mota back if it wuzn't tach problemz..:D

[Zenrider]

I will definitely check the tack.

[Zenrider]

I finally checked the gear ratio and it's 2 to 1 ratio. I haven't had any luck getting the calculator to work on the site to figure out the slippage.










Ratio is pretty easy. Put in foward gear and rotate the engine 1 full round to top dead center, 0* on your flywheel. This takes out the slack. Put a piece of tape on the prop at 12 oclock position. Rotate the engine 2 full turns back to TDC. If the tape is at 12 o'clock then it is a 2:1, it is is around the 1-2 o'clock position it is a 1:87. The 1:78 would be a small gear case and would be around the 3 o'clock position. Hope this helps

[pyro]

I already tried to explain this, and others backed me up...
YOUR MOTOR IS NOT TURNING 7500 RPM, TRUST ME.
CHECK THE LITTLE DIAL ON THE BACK OF THE TACH.

The calculator works, but your numbers don't add up. Enter "2" for the gear ratio for 2:1. Slip will likely be between 10% and 15%. (enter .1 or .15 for slip)
If you leave one field blank and fill in the others, it will calculate the blank field. (sometimes it's glitchy, but it works)

[Zenrider]

Thanks, got it to work. I went in at 7,000 RPM , 2 for ratio and 79 MPH and this is what I received for slipage - 0.20548571428571427.

I'm not doughting you on the tack, I agree it doesn't add up, but I still think I can get more speed out of it.



I already tried to explain this, and others backed me up...
YOUR MOTOR IS NOT TURNING 7500 RPM, TRUST ME.
CHECK THE LITTLE DIAL ON THE BACK OF THE TACH.

The calculator works, but your numbers don't add up. Enter "2" for the gear ratio for 2:1. Slip will likely be between 10% and 15%. (enter .1 or .15 for slip)
If you leave one field blank and fill in the others, it will calculate the blank field. (sometimes it's glitchy, but it works)

[pyro]

OK, we're getting somewhere now. We have a top speed number.

When I first got my boat 9 years ago, the previous owner told me the 2.4L 200 was turning 7500 rpm, because that's what the tach was reading. The dial was on the wrong setting. Same deal.

[Zenrider]

Now what do you think is the next step?
I was thinking of getting a bigger jack plate - 6" or 8" set back
Also maybe changing the prop or re-cupping???

Let me know waht you think.

Thanks

[transomstand]

You still need to work out the tach issue and get a gps. You must establish an accurate baseline so you can effectively observe the changes your making.

[Capt.Insane-o]

I'm going to hedge 58-64 mph at about 5500 ;)

[TEXAS20225]

what makes you think its a Xr2 the cowling say so??? i bought a trailer load of old motors a few years ago for Tommy warren when we got them back to the shop there were several to look at one of them had no cowl which turned out to be a 1981 225 and a screamer what is the serial number on the welch plug

[JP Love]

You have tach problem take the digital to see..... Dont overrev this engine more than 6500 and anayway a limiter..... Last longer on torque....

[AnthonySS]

Lets see a pic of that XR2...I ran one for years and it ranks as one of my favorite motors...a 2.0L merc with a 200 Exhaust chest and tuner...I would be concerned with that motor turning 7500 rpm with the single steel reeds...I would run mine to about 6400 rpm...the Hp starts to drop off after about 6200 rpm...so at 7500 rpm it may not be making all the hp it is making at a lower RPM.

Maybe you have a XR2 (power head) - by Merc Racing?

[Zenrider]

I finally took the tack out and it has four settings on the back (1, 2, 3 & 4). It's on number one right now. Does anyone know which setting it should be on?


Thanks

[Vinnie]

I had a 150 Mariner Mag (same as a 2.0 Merc) on a 1986 Stratos bass boat. Though it ran very good (high 60s), there is NO way that motor can turn 7500 even with a 22" prop.. Either it is modded big time or like the others have said, the tach is way off.

I am curious about the holeshot with a 30" prop? The boat has to weigh 500 lbs..

JMHO:cheers:

[Zenrider]

I'm not sure if the tack is on the right setting. We GPS'd a couple times before we redid the floor and we were in the high 70's with spike to 82. As far as a holeshot, yeah it has a hard time getting up to plane, likes to cavitate and then you have to back off to get the prop to grab.