GT-40 power vs. 351W carb??

[boysrus]

Lorin, I should have checked the posts yesterday as I went out last night.... I'll probably be out again this weekend, so I'll get some numbers and post or PM them. I was really hoping to hear that the 470 was awesome!

Jeff

[east tx skier]

I havent been in one personally, but from what Ive heard the newer MC's (190/197) are not very quick out of the hole. I remember when Waterski published acceleration numbers a few years ago that the MC was quite a bit slower to 36 than the 196 or RLXi.

If it performs similarly, your Sport/Air might be performing at its full potential and simply isnt as quick as your old Ski Nautique.

Either way, I would expect you to see an increase in performance by going to the Acme 470. It outperforms the 422 in every way, and with 1/2" less pitch it will help you pull some more RPM's.

While altitude is probably the biggest factor, a lot of it has to do with the fact that the newer boats seem to have more wetted surface and a good deal more drag than the older boats do (well, maybe not so much the Malibus). The new MC's especially have a good deal more due to the hook on the 2002 TT boats and production Pro Stars from 2003 forward. This tends to be pretty evident in lower top ends.

As for the WSM boat buyers guides, keep an eye on what the setup is with the MC. More recently, they have been sending WSM the boats with the 1:1, which tend to run mid to high 6 second range to 36 mph. Strange they would send those as the 1:1s aren't even submitted for AWSA testing anymore.

The boat buyers guide I have at the office is from 2003. In that edition, the were running a 350 hp with a 1.52:1 powerslot, which did 0--36 in 5.0 seconds, just a hair faster than the TSC2 196, which I believe ran a 5.3 second time. I assume there's not much difference between the times of the TSC2 versus the TSC3. The 2007 SN I skied behind last week practically set the water on fire when going to 36 while I was riding shotgun (and that was starting off in a turn).

I have no idea what their newer MCs with the 1.26:1 run, but presumably slower than that 5 second flat time they got in 2003 with the old slot). For me, it's too many combinations not to keep straigh (for a while, the big blocks still came with the 1.52:1, no idea if that's still the case).

Either way, hats off to SN for gear reduction and 330 hp as standard equipment.

Also, by way of comparison, my 93 PS 205 (carb'd GT-40 upgraded to neighborhood of 300 hp and spinning an Acme 13x12) took 7.6 seconds to get to 36 mph when I timed it for a prop test. But similar to the comments above, from the end of the line, I still think it tugs harder on my arms than the newer boats. Strange like that.

[coloradonautique]

Jeff,
No worries. I'll be running this weekend to get some more numbers as well. I also need to do some due diligence and check the fuel filter, spark plugs and intake just to make sure the engine is getting the fuel and spark it needs at WOT.
Whenever you have some numbers to share, that would be great. No rush. The boat is usable just not at the performance I am looking for long term. 8^)


Thanks,

Lorin

[boysrus]

Lorin,

I sent you a PM with my speed/RPM measurements.

Jeff

[coloradonautique]

Folks,
I am happy (and embarrassed) to report, I have solved my power/prop problem. Yellow_Flash_Colorz:

Just for giggles, I took some numbers yesterday. I was pulling 39mph @ 4400 for WOT and 36mph @ 3500. I clocked 0-35mph at about 11 seconds without a skier behind the boat.
I started pulling parts off and checking the throttle, plugs, intake etc. By the time I got to the first spark plug on the port side I noticed it was loose and not connected anymore. HA HA HA HA HA!!! Running on 7 cylinders will definitely effect your performance. Yellow_Flash_Colorz:
After re-attaching the plug wire and running again on all 8 cylinders, the boat ROCKED! No problems ripping us out of the water and it felt rock solid in the slalom course (it felt like I was pulling against a brick wall!).

Unfortunately I cannot compare my old prop (OJ 13x16) with the new 470 since I swapped props with someone out east. But I can tell you the GT-40 with the ACME 470 feels great now that we are kicking full HP out of the engine. I am now getting ~43mph @ 4900 rpm for WOT (not like I will normally run at this speed). 0-35mph time dropped to 8 seconds (3 second improvement).
Thanks to all who offered their input. I am an idiot for not finding the problem sooner. The really impressive thing is that the engine still ran smooth even though the cylinder was not firing. Crazy! I would have expect a rough idle or at least a rough under load acceleration.

Thanks again to all,

Lorin