CMI Sport Tube Header Test Results

[Carl C]

I DID IT!!! I went 102 mph!..........Oh, wait a minute.....no I didn't. :eek!: I got out for a quick run today. Limited time since I must go to work at 2:00. 78 degrees F, high humidity, low gas, light load. Todays best:73.6 (gps) @ 4,800 rpm (dash tach). I don't rely on saving max speed. This was me watching the gps while holding it between my legs. I need to test more before drawing any conclusions. Also had to drag a little port tab today. Not a drop of fluid from the oil cooler. This speed is about what I'd have expected before the headers but todays test was short and conditions not ideal.

[smoothie]

What was your speed before the headers? and how did they sound:cool:

[Carl C]

It's hard to say how it affected the sound. It seems a little louder and a slightly different tone. Todays test was not a conclusive one, it was more to check for any leaks or problems. I'll post more #s as I get them. Yeah, I should have posted "before numbers":

Really hot weather or heavy load: about 72

Average conditions: low 73s

Best to date w/excellent conditions: 75.6

[Carl C]

I've had the boat out 2 more times now. Hit 74.1 mph yesterday. There is definately more midrange power and the sound is a little louder and has a raspier tone. I like it. I'm still not finding much more top end or rpms but need more seat time in different conditions.

[Pismo]

More trim.

[Carl C]

More trim. I'm running a lot of positive trim now. To the point where the boat's getting squirrelly and the u-joints vibrating a little. Maybe I need a prop with more bow lift? (25 M+ now) I might try this old 24 turbo tomorrow just for kicks even though it's sure to put me on the limiter. It was on a 200 outboard.

[undertaker]

I would think you should be on the limiter with your factory prop...I had to go up to a 26P TXP Turbo after my exhaust install because I was all over the limiter....something does not seem right to me...do some more running and check back in..:):):)


Undertaker:pimp:

[BaldEagle]

Carl, Ive hit 75 with 25 Turbo with 3/4 gas and extra passenger with 1-2 footers on L. MI. The tattletale is helpful. If you are just eye balling a GPS between your legs, you may have missed a higher speed, or a bikini on the beach.

[Carl C]

I would think you should be on the limiter with your factory prop...I had to go up to a 26P TXP Turbo after my exhaust install because I was all over the limiter....something does not seem right to me...do some more running and check back in..:):):)
Undertaker:pimp: Were you running a 25p M+?

Carl, Ive hit 75 with 25 Turbo with 3/4 gas and extra passenger with 1-2 footers on L. MI. The tattletale is helpful. If you are just eye balling a GPS between your legs, you may have missed a higher speed, or a bikini on the beach. I've never used the max speed funtion so I got the instructions out and when I found the "mxspd" it read 78.2!! The max I've ever observed was 75.6. I bought it new and it has only been turned on while in the boat, never while towing. I reset it and will use it for today's testing. I'll also try to hook up my Snap-On service tach. It will be hot and humid today and I may be on a small lake unless I get ambitious and tow her to Lake St. Clair. I'll try the 24p Turbo another day. Is it OK to clip the test tach to the back of the dash tach and run them both together?

[Pismo]

Get the max speed function working then just throw it on the back seat and read it later, but then you need to repeat several times to get a true best. I got 77.1 GPS once but I got 75.5 GPS many times so that is what I believe. I got 74.5 with a 25 M+ with trim almost to the limit and no tabs. It gets very squirrely. Do you have muffer tips? if so, remove them. Steering is next, then it will be solid.

[Carl C]

No mufflers, open tips from George Carter's old Minx. I am aware that the max speed function can give false readings and that's why I'm not a big fan of it but I will do as you suggested today and record the results. I think I will go to Lake St. Clair today.

[undertaker]

Were you running a 25p M+?
I've never used the max speed funtion so I got the instructions out and when I found the "mxspd" it read 78.2!! The max I've ever observed was 75.6. I bought it new and it has only been turned on while in the boat, never while towing. I reset it and will use it for today's testing. I'll also try to hook up my Snap-On service tach. It will be hot and humid today and I may be on a small lake unless I get ambitious and tow her to Lake St. Clair. I'll try the 24p Turbo another day. Is it OK to clip the test tach to the back of the dash tach and run them both together?


Carl I ran the factory 25P mirage for a short time (did not like it) but could turn it to 4850 RPM, they I switched to a 25P Turbo (not TXP) ran that until the exhaust change, turned the 25P Turbo 4850 at 74mph (GPS speedo), upgraded exhaust tried my 25P Turbo was all over the limiter, tried a 26P Turbo TXP ran 6-7 passes of 76MPH GPS at 4950, no passengers, lighter in fuel, have run 74MPH with a boat load and full fuel. I also tried a 27P TXP could only turn it 4700 at 72MPH... Do some more testing you should need to up the pitch on your prop, but what do I know I am still learning...:yes::yes::yes::yes:

By the way a GPS Speedo IMO is the only way to go, you can keep your eyes on the water at those speeds and when ya slow down you hit the tattle tale and then read the top speed...much safer..:):):)


Undertaker

[Carl C]

I'm hitched up and ready to head to Lake St. Clair where I can really let her rip. :boat: Will post results later and then head to the Woodward dream cruise in the '82 Mustang GT.:yippie::convertib:

[Carl C]

Well I guess Lake St. Clair isn't the best place for top speed runs in a 22 footer! Most of the lake was behaving but 4 foot rollers appear from nowhere! I made the obligatory run to the Detroit waterfront. The river was a real mess:eek!:yikes:eek!:! I headed back north and decided to explore the channels which I haven't done since Oleredalert Bill showed me around them last year. Found some good water for a couple of top speed runs. I managed 74.0 and 74.3 in less than perfect conditions. My top rpm was 4,850 on the dash tach. I may have had a little tab down and could have used more trim but it is dangerous in these waters. There is a bit more speed to be found and of course it will run faster on a cool, dry day (today is very humid). 74.3 is my best post-header speed and I will do more testing before discussing props more.:propeller:

[Rootsy]

last time I was on the st. clair river my GPS said there was a 3 - 4 mph southbound current...

[Carl C]

last time I was on the st. clair river my GPS said there was a 3 - 4 mph southbound current... I was running north in the South Channel. It isn't safe to raise the tabs and really air it out there because even in the channels you come upon rogue ship or yacht wakes with little warning:eek!:. If you've boated there you know what I'm talking about. Even Lake Huron is more predictable. My top speed testing will be on Lake Oakland from now on.:yes:

[gcarter]

last time I was on the st. clair river my GPS said there was a 3 - 4 mph southbound current...
Jamie, do you mean that if Carl had run South he'd have hit 80?????
Man!!! I'm glad he didn't.
We'd have NEVER heard the end of it!!:boggled::boggled:

[Ranman]

Anchor Bay, Muscamoot Bay or the Middle Channel would have been the ticket. Of course, with average depths in the 3 to 5 foot range, you would need to know where you were going. The Middle Channel at 30+ feet deep would have worked well, but there is still some current in there.

Unfortunatly, the real world results don't sound like there's 40hp in the headers. :bonk:

[Carl C]

Anchor Bay, Muscamoot Bay or the Middle Channel would have been the ticket. Of course, with average depths in the 3 to 5 foot range, you would need to know where you were going. The Middle Channel at 30+ feet deep would have worked well, but there is still some current in there.
Unfortunatly, the real world results don't sound like there's 40hp in the headers. :bonk: I have charts but I'm still leery of those areas. The last time I tried to find the middle channel I missed the buoys and ended up in a foot and a half of water. There is definately not 40 hp or 4-5 mph in headers alone as some claim and if I hadn't discussed that here first I'd have been awfully dissapointed. There is more midrange, a little more top end, better sound, good looks and they will be needed when I do more engine mods in a year or two. Here is a cool chart of Lake St. Clair. You can click on different areas for close-ups. http://www.lakestclair.net/charts/lsc_full_chart.htm

[roadtrip se]

Jamie, do you mean that if Carl had run South he'd have hit 80?????
Man!!! I'm glad he didn't.
We'd have NEVER heard the end of it!!:boggled::boggled:

I ran 87 on the St Clair River once. Can't quite understand why I haven't been able to do it since....:cool::cool::cool:

[Ranman]

I have charts but I'm still leery of those areas. The last time I tried to find the middle channel I missed the buoys and ended up in a foot and a half of water. There is definately not 40 hp or 4-5 mph in headers alone as some claim and if I hadn't discussed that here first I'd have been awfully dissapointed. There is more midrange, a little more top end, better sound, good looks and they will be needed when I do more engine mods in a year or two. Here is a cool chart of Lake St. Clair. You can click on different areas for close-ups. http://www.lakestclair.net/charts/lsc_full_chart.htm

Paper charts are good to give you a general sense, but on LSC, GPS navigation is NECESSARY. If you run a Garmin unit, use Mapsource and the BlueCharts on your PC to create a set of routes for the places you like to go. I have over 30 routes plotted for the lake. Clinton to Muscamoot, Clinton to Middle Channel, Clinton to North Channel, etc. Once you get out there, load the route and follow the steering guidance. The BlueCharts will work on your PC without an unlock code. You need the unlock to load the actual charts to the unit, but once you have the routes loaded the charts are unnecessary. I can send you my Garmin file with all my routes for LSC so you can load them to the unit again assuming you're running a Garmin.

[Carl C]

I only have a basic "Garmin 12". I don't think it is capable of chart plotting. Maybe I will upgrade next summer since I'm spending more and more time on the big lakes.

[Ranman]

I only have a basic "Garmin 12". I don't think it is capable of chart plotting. Maybe I will upgrade next summer since I'm spending more and more time on the big lakes.


Chart plotting and using the route feature are two different things. The Garmin 12 while non-mapping, can handle 20 routes with up to 30 waypoints each. You would need the PC interface cable to download if you don't already have one though. They can usually be found on ebay for cheap.

Once you learn the world of plotting routes and using them, you'll never look back. Having a GPS and using it for only speed numbers and trackback is like buying a computer and only using it to play solitare.

I study the charts and plot routes for every boat trip I take. St. Clair, Cumberland, White Lake, you name it. It takes a lot of the worry out of boating knowing that you're taking the best course to a destination. I figure since I like St. Clair so much, if the GPS saves me 1 $500 prop, it was worth the money. Plus I got tired of pushing my boat off of sandbars out there.

[Carl C]

Chart plotting and using the route feature are two different things. The Garmin 12 while non-mapping, can handle 20 routes with up to 30 waypoints each. You would need the PC interface cable to download if you don't already have one though. They can usually be found on ebay for cheap.
Once you learn the world of plotting routes and using them, you'll never look back. Having a GPS and using it for only speed numbers and trackback is like buying a computer and only using it to play solitare.
I study the charts and plot routes for every boat trip I take. St. Clair, Cumberland, White Lake, you name it. It takes a lot of the worry out of boating knowing that you're taking the best course to a destination. I figure since I like St. Clair so much, if the GPS saves me 1 $500 prop, it was worth the money. Plus I got tired of pushing my boat off of sandbars out there. I looked at the instruction book and you are right. This thing's capable of a lot more than I thought. There is just so much to learn about gps navigation. I hear they even have classes for it. And it does take a weird 4 prong cable. There is a lot to like about St. Clair for sure. And the rivers; I was amazed how beautiful the lower Detroit River is. I will try to learn more about this but it might be best to get a nice up to date color chartplotter for $600 or so.

[Ranman]

I looked at the instruction book and you are right. This thing's capable of a lot more than I thought. There is just so much to learn about gps navigation. I hear they even have classes for it. And it does take a weird 4 prong cable. There is a lot to like about St. Clair for sure. And the rivers; I was amazed how beautiful the lower Detroit River is. I will try to learn more about this but it might be best to get a nice up to date color chartplotter for $600 or so.

Basic navigation is easy. Plot a route and load it to the unit. Call up the route when you're ready to go and follw the steering guidance. An updated GPS would be nice. I like the GPSMAP 276C. It works well on the water and also can do the auto turn-by-turn navigation. I know Garmin released the 278, 378, etc. Some of those models have additional features or come preloaded with maps. Find one that suits you and learn how to use it. If it's a garmin I can help with the routes part. Like I said, it makes boating (especially on St. Clair) much more enjoyable. We never get lost, we now go out at night (or at least stay out later) and we avoid all of the hazards on the water.

[Pismo]

Sooo how's the top speed tests?

[Carl C]

Sooo how's the top speed tests? I still haven't been able to get a really good run in but my best so far with the CMIs is 74.3. That is about 1 mph faster than I'd have expected with the stock exhaust in those conditions. I probably won't get out again until late next week but should get some good runs in then on Lake Oakland. The only way I can get the port tab completely up is with lots of positive trim. This combo makes the boat pretty squirrelly and dangerous in much more than one foot chop but it is where the max speed is. When the air gets a little cooler and drier and I get out on the smaller lake where I won't kill myself on a yacht wake I will know what I've gained in top end. So far every test run has been a little faster and I think I will find the extra 2 mph I was hoping for. Do Turbo props help stop the listing to port? Do they add more bow lift? I also have an odor like when you put a new exhaust on a car. It seems odd that I can smell that when going 70+. The headers are not overheating. I'll post new numbers when I get them. The oil cooler and chartplotter will wait until the off season.

[undertaker]

Exhaust odor is normal I had the same issue with my new exhaust it will go away shortly.....:):):)


Undertaker:cool:

[Carl C]

Exhaust odor is normal I had the same issue with my new exhaust it will go away shortly.....:):):)
Undertaker:cool: Exhaust odor seems to have gone away. I got out alone for some testing on Lake Oakland today. Running fairly light, tabs all the way up lots of trim: today's best, 73.5 mph. It was hot and VERY humid though. So far I'm not finding much, if any, increase in top end or rpms. It accelerates like a rocket though. Really pins you to the seat! I still need to test on a cool dry day to see for sure if I picked up any top end. So far I see no need for a prop change and am having second thoughts on going to a labbed prop due to the lower durability of the thinner blades.