DarkHorseRacing
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How do those exhaust tips work?
Daves been busy with gelcoat murals already View attachment 1387178
How do those exhaust tips work?
So you need 30’s or 32’s?View attachment 1387187 View attachment 1387188 So our first round of prop tests
Signature 5 blades / boat gets on plane in 1/3 the time it did before and no tabs required.
4000 rpm - 64 mph
Wide open slightly over trimmed 5,000 rpm 78 mph.
The drives are stamped “A” which I believe means is has a 1.5 ratio in them. B means 1.34
I’m wondering if the scx lowers are really scrubbing that much speed off this thing.
For reference Chad Bixby’s boat runs 92-93 mph with 625 Ilmors / SC lowers..
So you need 30’s or 32’s?
What’s Chad running for props? Are his turning out like yours? Lots of variables, including the weather.
12% slip not bad but you might be able to get it down to 10-11 at best on big veeView attachment 1387187 View attachment 1387188 So our first round of prop tests
Signature 5 blades / boat gets on plane in 1/3 the time it did before and no tabs required.
4000 rpm - 64 mph
Wide open slightly over trimmed 5,000 rpm 78 mph.
The drives are stamped “A” which I believe means is has a 1.5 ratio in them. B means 1.34
I’m wondering if the scx lowers are really scrubbing that much speed off this thing.
For reference Chad Bixby’s boat runs 92-93 mph with 625 Ilmors / SC lowers..
that's better. and its warming up so you still loosing some rpmDo with the prop slip calculator we are currently running a 12% slip.
Oh we are gonna try quite a few different props.. lolSo "have you tried a different prop?" actually applies to this thread.
I had a set of bravo 32" that were hacked n wacked so who knows what they actually were. Ours cavitated pretty good coming on plane with those but, I was able to get up on a single ski with them so... I have tried a set of 30" Maximus props but could only spin them to 5000 rpm or so at around 81. They had very little cavitation coming on plane. I have a set of bravo 30" on there now. Again, very little cavitation coming on to plane. I haven't run them wot yet though. Mine are turning out as well. Our boat is a much different set up though. It has Imco SCT uppers with SC lowers, stand-off boxes and transmissions. I have personally seen a tick over 90mph up here. We are at 1800" of elevation too. The gps has seen 94 and I believe it.So you need 30’s or 32’s?
What’s Chad running for props? Are his turning out like yours? Lots of variables, including the weather.
I’ve run my boat with 32 pitch Maximus props and 1.5 gears to 103MPH at 5,500RPM. FYI.So in theory if I put on 26’s and run it to the rev limiter of 6200 (actual is 6300) the boat should run 90.
I’d be fine with that and keep the larger scx lowers.. if it doesn’t do that we will likely switch to sc lowers to pick up the extra 10mph.
RD
Dave, congratulations to you and family! Very nice looking boat. You need to name this boat “Make Boating Great Again” That is my favorite RDP T shirt.
Also, check if there is adequate airflow to these engines. Your pictures don‘t show a lot vents. Maybe this is one of several issues contributing to performance that you refer too.
That shows the power the SCX drives scrub compared to XR's. Boat ran that with the motors in stock form at 5200.I’ve run my boat with 32 pitch Maximus props and 1.5 gears to 103MPH at 5,500RPM. FYI.
So when we looked at this boat for sale in 2016 it had 24 Bravo 1's. Had a pair of 26's in the boat. Owner used the boat at Powell mainly. Makes sense now. I forgot the rev limiter was that high.So in theory if I put on 26’s and run it to the rev limiter of 6200 (actual is 6300) the boat should run 90.
I’d be fine with that and keep the larger scx lowers.. if it doesn’t do that we will likely switch to sc lowers to pick up the extra 10mph.
RD
On Lake Tahoe 2 years ago, with 5 people in the boat and a half tank, and these props, best I got was 93. Don’t remember the RPM.That shows the power the SCX drives scrub compared to XR's. Boat ran that with the motors in stock form at 5200.
That is great on Tahoe.On Lake Tahoe 2 years ago, with 5 people in the boat and a half tank, and these props, best I got was 93. Don’t remember the RPM.
I think you have 1.35 ratio drives. The numbers don’t make sense with 1.50. Max RPM I think is 6400 on the Ilmors.View attachment 1387187 View attachment 1387188 So our first round of prop tests
Signature 5 blades / boat gets on plane in 1/3 the time it did before and no tabs required.
4000 rpm - 64 mph
Wide open slightly over trimmed 5,000 rpm 78 mph.
The drives are stamped “A” which I believe means is has a 1.5 ratio in them. B means 1.34
I’m wondering if the scx lowers are really scrubbing that much speed off this thing.
For reference Chad Bixby’s boat runs 92-93 mph with 625 Ilmors / SC lowers..
Is turning the props to the outside the ideal setup in your case?So yesterday we took it out for a brief run.. 26’s now we ran 5400 rpm and again 78 mph.. if I sat there and leaned on it, probably would have got to 80..
That said I noticed something the last time I had it out and again this time.. At wide open the boat would have a slight lean to starboard.. so I’d drop a little tab to get it balanced..
I started thinking about it and said to myself I’ll be the port motor is making more power than starboard for some reason?
So backed off to 35 mph and ran the port motor up real quick and then inversely the starboard.. port pulled way harder than starboard, but what I noticed as well is it sounded different..
I believe I may have figured out what is going on here.. I think the spring loaded mufflers on the starboard side are getting stuck and either not opening or opening all the way.
Motors have been gone through so there is no issues there to my knowledge.
So the mufflers are coming off and exhaust tips are going on.. boat has already been dropped off at Absolute Speed and Marine this morning.
If that’s it, we are gonna gain a shit load of speed and hp, because the port motor has for lack of a better term been “carrying” the starboard motor at upper speeds and rpm..
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Hopefully that is the case Dave! I would think you would have seen that on the tachs though. Glad you are ditching those crappy mufflers. I love CMI but those mufflers are the worst. We have the IMCO gatlins on ours and I really like how they sound. Not too loud but loud enough!So yesterday we took it out for a brief run.. 26’s now we ran 5400 rpm and again 78 mph.. if I sat there and leaned on it, probably would have got to 80..
That said I noticed something the last time I had it out and again this time.. At wide open the boat would have a slight lean to starboard.. so I’d drop a little tab to get it balanced..
I started thinking about it and said to myself I’ll be the port motor is making more power than starboard for some reason?
So backed off to 35 mph and ran the port motor up real quick and then inversely the starboard.. port pulled way harder than starboard, but what I noticed as well is it sounded different..
I believe I may have figured out what is going on here.. I think the spring loaded mufflers on the starboard side are getting stuck and either not opening or opening all the way.
Motors have been gone through so there is no issues there to my knowledge.
So the mufflers are coming off and exhaust tips are going on.. boat has already been dropped off at Absolute Speed and Marine this morning.
If that’s it, we are gonna gain a shit load of speed and hp, because the port motor has for lack of a better term been “carrying” the starboard motor at upper speeds and rpm..
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If they’re both turning the same RPM, I’m not sure how that makes sense???
Have you tried giving it more Stbd throttle to see if the boat straightens up?
This is an excellent pointYou can have an engines turning an RPM and have different loads on it. One engine could be producing the power and the other "coasting" and creating drag.
You can have an engines turning an RPM and have different loads on it. One engine could be producing the power and the other "coasting" and creating drag.
The coasting prop is going to be be turning slower... there's no way around that. Prop slip says its impossible for the coasting prop to be turning the same RPM as the one producing the power.. it might be close...
Still, If more power (even more RPM) is added to the stbd engine, will the boat straighten up?
IDK.. Lol... I've never owned a twin engine Boat.
Biggest struggle I have since switching to outboards I miss that big block sound.Loud pipes save lives.
The way it should be
Outboards sound decent but nothing beats the sound of a healthy big blockBiggest struggle I have since switching to outboards I miss that big block sound.
Would like to know if the tech is just a ground issue? Mine has done the same since I bought it and I’ve never had the mind to start poking aroundI’d rather use my phone gps.. right now I went out by myself and it’s hard to hold the phone take the screen shot / take the picture etc..
I’m battling a couple problems on the gauges as well. The left tach has a ground problem so it’s all over the place.. and the gps keeps dropping to zero, then 30, then back to reading right..
Absolute speed and marine is going to be on that and a water pump problem next week.
RD
I bet if you swapped out those lowers for DDS lowers you’d pick up 10mph.So yesterday we took it out for a brief run.. 26’s now we ran 5400 rpm and again 78 mph.. if I sat there and leaned on it, probably would have got to 80..
That said I noticed something the last time I had it out and again this time.. At wide open the boat would have a slight lean to starboard.. so I’d drop a little tab to get it balanced..
I started thinking about it and said to myself I’ll be the port motor is making more power than starboard for some reason?
So backed off to 35 mph and ran the port motor up real quick and then inversely the starboard.. port pulled way harder than starboard, but what I noticed as well is it sounded different..
I believe I may have figured out what is going on here.. I think the spring loaded mufflers on the starboard side are getting stuck and either not opening or opening all the way.
Motors have been gone through so there is no issues there to my knowledge.
So the mufflers are coming off and exhaust tips are going on.. boat has already been dropped off at Absolute Speed and Marine this morning.
If that’s it, we are gonna gain a shit load of speed and hp, because the port motor has for lack of a better term been “carrying” the starboard motor at upper speeds and rpm..
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This. Dave is probably going to go tips, then clamp on's if he doesn't like the sound.Boats going to be loud AF now too....lol. Great troubleshooting
Just the tipsSo yesterday we took it out for a brief run.. 26’s now we ran 5400 rpm and again 78 mph.. if I sat there and leaned on it, probably would have got to 80..
That said I noticed something the last time I had it out and again this time.. At wide open the boat would have a slight lean to starboard.. so I’d drop a little tab to get it balanced..
I started thinking about it and said to myself I’ll be the port motor is making more power than starboard for some reason?
So backed off to 35 mph and ran the port motor up real quick and then inversely the starboard.. port pulled way harder than starboard, but what I noticed as well is it sounded different..
I believe I may have figured out what is going on here.. I think the spring loaded mufflers on the starboard side are getting stuck and either not opening or opening all the way.
Motors have been gone through so there is no issues there to my knowledge.
So the mufflers are coming off and exhaust tips are going on.. boat has already been dropped off at Absolute Speed and Marine this morning.
If that’s it, we are gonna gain a shit load of speed and hp, because the port motor has for lack of a better term been “carrying” the starboard motor at upper speeds and rpm..
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If you dropped it off how are you gonna be at the run Saturday? jk
Ok how about I say it like this. Let's say one engine for what ever reason isn't running 100%. Doesn't gain power after 4000 rpm like it should. The other engine runs normally. When you get to 5800 rpm engine number 1 is turning that rpm but only producing 650 HP. The 2nd engine at the same rpm is producing 700 hp. This would cause the boat to pull to one side. It will turn to what ever side has less HP.
To answer your 2nd question. If you were to add power or rpm to the stbd engine to match the other side it would drive straight.
If RD could mount go-pro's filming the exhaust as he goes high rpm you could probably see which exhaust isn't opening fully and confirm his theory.
The coasting prop is going to be be turning slower... there's no way around that. Prop slip says its impossible for the coasting prop to be turning the same RPM as the one producing the power.. it might be close...
Still, If more power (even more RPM) is added to the stbd engine, will the boat straighten up?
IDK.. Lol... I've never owned a twin engine Boat.