What the hell is this prop?!?!

Maybe it isn't my tach lying to me after all. A nice guy that lives in my area tells me that my prop that's giving me too much RPM may be the older "inline" style chopper, which has very thin blades (like mine) among other things. He has had the best advice for me so far. He has the same rig as me, a Vegas XT with a Merc 2.4 200/220 XRi. He ALSO was getting 7200 rpm at 75 mph with a 28" chopper, and says these older EFI's don't have rev-limiters. Is this true? He now runs a newer 30" (V6) chopper at 6200 rpm / 82 mph. He says it's a dog out of the hole, but what do you expect? He is going to check to see what setting his medallion tach is set at, hopefully this will prove helpful in figuring this out. What's the possibility that my stock 200 motor has been damaged running it at 7200 rpm? -Chad



[Edited by pyro on 04-26-2001 at 12:53 PM]

[Instigator]

Pyro, can't help you with the Merc issues but the in-line Choppers are smalleer dia. than the V-6 wheels. I have the V-6 Choppers for my Sonic and they are 14 1/2" dia. and I had an in-line and I think it was only 13 3/4" (??). There are also Chopper I and II's. I can see a difference cosmetically, but think the real difference is only in strength?? 3/4" diameter change would definately show on your tach. Hope this helps, Instigator

[Techno]

With the 28" at 75 mph that gives 26% slip
30" at 82 mph 12%

Now all you have to do is borrow his prop. Then you can check your Tach and check a different prop at the same time. Two stones with one bird.

Honestly, something sounds seriously wrong with those slip figures. I took my rig out for a ride today. When I'm barely over 60 mph, the Medallion tach is already reading 6500. I stopped and changed the selector from "3" to "4" Ah, yes, now the RPM readings are more realistic. I just bought this H'stream, and I haven't got the hang of it completely, so I'm not totally comfortable with it above 70 mph yet. I had it up to 72 today, that was fast enough for me. Around 70 mph, I was turning around 57-5800 r's. At that speed and RPM, the calculated slip figures are more realistic. I'm going to e-mail the other VegasXT owner tomorrow (unless you're on the board tonight, Dan?) and share the findings with him. Is there an e-mail address for Medallion Instrumentation that I can send my question to? I still don't know which tach setting is the correct one for a Merc V6. Thanks for the help, as always! -Chad

[Delta]

Hey Pyro:
I had the same question,regarding the 220 xri and rev limiter.Most qualified responses were:There is no *hard* limiter on that motor.The ECU is designed to begin richening(flooding) the cylinders at around 6200-6400.I guess every motor is a little different,so the RPM's vary.I believe the most reputable person I spoke to with this,was Sean at Rapair.I am sure about the "soft limiter"/flooding function of the ECU.I may be mistaken on the exact RPM's it takes place.Good Luck,Delta

The prop may indeed be fine. I changed the tach setting from 3 to 4, and now it reads 5800 at 72 mph instead of 7200. I started to piss my pants after I hit 70, so I had to back off. I'll try to see what it's spinng at higher speeds this weekend. -Chad

[Dan Dillmann]

Pyro, I have a 0-8000 rpm Medallian tach. I checked it and it is set to 1. A couple years ago I used an inductive pickup tach to check my tach and I thought it was right on. I'll double check it to make sure. I have 3 props, 2 which run close to 10% slip and my 28 pitch inline chopper which runs close to 30% slip. I definitely think there is something wrong with using that prop on a Vegas XT. Does anybody else have any experience with an inline chopper?

Dan Dillmann - '87 Vegas XT/'87 Laser 220 EFI

[Techno]

I personnaly can't see why a smaller diameter prop would turn this kind of rpm. V-6 or inline 6 it's still supposed to propell the boat 27" per revolution. I seem to remember that the smaller diameter was for hole shots to allow the prop to spool up.
Something else for you to check is your speedo. even if the tach is wrong your speedo could be wrong also and that might be why you stop at 70.

I just remembered my merc chopper, it measures 14" dia.
and my digital tach OMC(laying on the floor next to me) is set on 6.
You could always give medallion a call. A google search turned this up
http://www.bwinstruments.com/
http://www.bwinstruments.com/TechSupport.htm

I don't stop at 70. I just happened to check the tach when I was doing 70. I don't quite yet have the balls to take it over 72 mph. The only other fast boat I've owned was a 63 mph Baja. My new rig is capable of 78+ with the current setup, according to prev. owner. I'll be ther soon.

ps bwinstruments is BorgWarner, formerly Medallion. Check my "tach update" post.

Hey, Dan, have you ever tried a newer 28" chopper? I'm curious how your rig would behave with a good 28. -Chad

[Edited by pyro on 04-28-2001 at 03:46 PM]