Poor performance from GT-40?

Do you realize that you have posted this topic three times? I would suggest going back and deleting the extas

I realize your new... welcome!

Sorry I have no input on your problem

nuttyskier2002 wrote: Is your 01 a Pro Boss engine?

He's got the GT40 MPEFI motor. I doubt that a lower octane gas would cause such a noticeable decrease in performance, but its something to consider.

Wasabi, I assume by Air Nautique youre referring to the direct drive model based on the Sport- not the V-drive Super Air based on the Super Sport. If so, I wouldnt expect there to be a significant decrease in performance, as the extra hp should make up for the extra weight. If you could fill us in on some RPM numbers that would be helpful. WOT numbers and the RPM you get instantly when coming out of the hole. Also let us know what prop youre running- brand, size, etc.

Pete, the AN does not have a hull made for wakeboarding. It is the TSC hull. The boat is about 1.5ft longer, and about 320 lbs heavier. Also, the 330 horse is the Chevy engine. Even at 330 HP, the Chevy is known to have a weaker hole shot than the 310HP Ford GT40.

Lorin, my buddy has an 02 AN with the GT 40. Should be the same boat as yours. With the stock prop, at sea level, we get 43-44 mph at 4600 RPMs. BKH

I'll try to answer all questions:

Sorry for the triple post.. Webpage hung several times and I had to restart. Pretty sure I deleted the other posts.

Don't know what prop is on there now. I will know tonight after I swing by the boat on my way home.

Yes, Boat is a Air Nautique, which in 2001 is identical to the Sport Nautique (TSC1 hull stretched 1.5 feet). Supposed to be a crossover boat and the wake at 32mph was great (better than my '91 SN). It does have a tower and ballast but we were running with the ballast empty. GT-40 engine has about 400hrs.

We are mainly slalom skiers and just starting to do some light wakeboarding/wakesurfing. I am concerned about the hole shot for slalom skiing since if it struggles to get me up (140lb guy), it will be struggling even worse with the bigger guys.

I also thought about the knock sensor but did not think that was it. I am running 89 octane which at altitude should be plenty.

I will get the current prop info tonight and the RPM numbers next weekend. ACME suggested a 12.5 x 15 three blade or 12.5 x 15.5 four blade given the power loss at altitude. They said it would run 300 more RPMs and 1-2 MPH faster top end. What's the downside of more RPMs?? Is it just burning more gas at ski speed?

Thanks all,

Lorin

It's all good my friend. A little surprised that the 206 didn't get it done for you, but the "live testing" you did, doesn't lie. BKH

I'd compare the Torque versus HP since it's Torque that yanks you out of the water. Just guessing that the torque values between the two engines is not that dissimilar in the lower rpm ranges. Probably not much different at the upper end either...but I'm sure someone on the forum will have these torque curves in their shirtpocket.

If the torque values are similar from idle to 2500 rpm's I'd say the heavier V-Drive boat with accessories will definitely be the weaker of the two boats when pulling a slalom skier.

Our 2005 SN with the Excalibur grunts and groans on the big boy's....especially if their form is off. Very noticeable when the slalom skier is over 200lbs and has both feet in a narrow ski like the "Truth" or "Monza" and has layed off for several months. But if their form is correct, we can hardly tell the difference between them and the lighter skiers.

Like you, I expected the new boat to run circles around the old boat (289 with slight mods). They're both SN's and run almost identical to 40 MPH, but the new boat does pull harder on deepwater starts.

Mark, It's great that you have joined in to this site with a great group of people. I've really enjoyed it and it is one thing I'll miss when I go up north on vacation. I'll have to go in to the library daily to use the computor to get on line and visit!

Great to here about the slow no wake but I think the fishing group are still planing on "studying" the problem.

Mark, You and Patty need separate checking accounts like Didi and I do!! Of coarse that doesn't make much difference since mine is always empty anyway! Put it on your home equity!

So, you are trying to get the MC to go faster! What you need is a Nautique to foot behind!

Didi, Colin and I are going to the Green Lake reunion this summer. Tim will be there. You should plan on at least stopping for a day.

Mark, I talked to Chuck this morning and he thought you got the better top end with the new CNC machined prop. We both think you foot to fast!!!

I took a look at the prop this weekend. It is a 4-blade OJ Legend 13 x 16. Would a 12.5 x 15.5 really make that much of a difference? Does the CNC machined prop really make that much of a difference? I won't be able to get on the water (and check RPM values) for the next couple of weeks. I will post numbers then.

Thanks.

Lorin

wasabiskier wrote: I took a look at the prop this weekend. It is a 4-blade OJ Legend 13 x 16. Would a 12.5 x 15.5 really make that much of a difference? Does the CNC machined prop really make that much of a difference? I won't be able to get on the water (and check RPM values) for the next couple of weeks. I will post numbers then. Thanks. Lorin

If youre asking if going from an OJ Legend to an Acme 422 would be a noticeable improvement, the answer is yes. However, the 470 (12.5x15 3-blade) would be an even bigger improvement.

I run closer to sea level with a lighter, unweighted boat, and the 470 outperforms the 422.

I would expect to see 200 RPM more from the 470, and 1-2 MPH coming from the OJ. I made the same switch a year ago.

The best price Ive found on Acmes is through Delta Propellor. Both CCFan and PN have a discount code good for 5% off there, and they ship for free. I think their prices went up slightly, but its still the best you'll find.

Acme wont sell direct for anything less than retail price. This is how they protect their dealers.

Some interesting comments on the GT-40 vs the Excalibur, we have had both motors in direct drives and felt they preformed very similar, although the GT-40 was in a bit larger boat, 99' Air @ 21' vs 05' 206 Air @ 20.5' both with stock props. The top end on the 206 is much better and neither boat ever had/has any issue with a hole shot, I am 225 and only need 3/4 throttle to get up quickly on a high end slalom w/1 or 2 feet in. Last summer with the 206 we pulled 4 barefooters at the same time and also pulled 3 footers deep water no problem.

Regarding the "Air" logo, it does not necessarily indicate "Wake Board Boat", on the 206 I could have ordered "Air" or "Ski" insignia's, in reality the 206 is a Ski Nautique Open Bow (SNOB).

It's hard for me to say which motor pulls better because we had them in different boats however the 206 provides the best pull of any Nautique I have owned. If I was buying a Nautique for show skiing it would be a 196 with the ZR6.