Q4 prop/top end

hi all,

I'm new to this forum and new to boating. I just bought a 07 tahoe q4 w/ the 4.3 fuel injected motor. After having it out on the lake this past weekend I was very disappointed in the top speed. The boat only went about 43 mph (speedo)

I had read quite a bit about the q4 and thought that the 220hp motor was suppose to top out around 50-55mph. The boat is equipped with a sting ray hydrafoil and a 21p merc vegeance prop (13 3/4")

I'm sure this prop is great for pulling skiers and wakeboarders, but I am also looking for something to get better top end. What kind of prop would help with doing so? Would adjusting the trim level raise my top speed? Any advice would be a great help. Thanks in advance

Re: Q4 prop/top end

Yep, your top speed sounds a little low - I would expect 50+. I have the 07 Q6 with the carburetor 190 hp and I get 47 with a 21P 4 blade AL prop at 4600 rpm. My boat's heavier longer and I have less hp!

What is your wide open throttle rpms? Find a long, straight, smooth stretch of water with no traffic - push the throttle to the limit and trim up slowly. Watch the rpms and speed. As you trim up both speed and rpms will increase - until the prop starts blowing out (the rpms increase without any increase in speed). Trim down slightly... this is the optimum trim for speed (may porpoise a bit so be prepared to trim on down til it stabilizes). Look at the rpms. should be between 4400 - 4800 rpm? If lower than that you have too much pitch, over 4800 too little pitch.

Re: Q4 prop/top end

Oh, that hydrofoil may be holding you back as well. These boats tend to be a little sensitive to trim levels - porpoising when trimmed up for speed. The hydrofoil may be the last owners solution to the instability... I have smart tabs like alot of other Tahoe owners and am very happy with the performance of the boat with them... prior to the tabs I struggled with trim level for speed without porpoising.

Re: Q4 prop/top end

I agree with getting rid of the "whale tail" and installing the smart tabs.

Re: Q4 prop/top end

Hey thanks for the advice. ill be taking it out tomorrow and try adjusting the trim level. I thought something wasnt right. (I'm a newbie:redface
ill check into smart tabs. can you run smart tabs and the hydrafoil together?

Re: Q4 prop/top end

Well good for you for getting the MPI. For comparison sake my tank of an 18 footer (not a Tahoe) with the tiny 190hp Mercruiser (versus the 270hp optional power) will get 51.8mph on gps in the best possible conditions meaning two aboard, 6+- gallons of gas, very light chop original 21pitch, aluminum black max prop. Your Tahoe should absolutly fly past that. I just upgraded to a Hustler 21pitch, aluminum prop with some cupping and vent holes and lost 600 rpm's and more than 8mph. I was expecting better hole shot and wishing for higher wot speeds. Of course like an idiot I tried it out on a new, much shallower, lower clarity than usual lake on an unusually windy day and dinged it up almost right away so the results are kind of iffy. The key for all prop discussions is knowing your wot RPM's and of course not dinging up your prop. As for smart tabs and the hydrofoil together, you wouldn't want or need to do that because tabs are generally very effective. The foils are kind of shunned around here but tabs are vaunted. As for trim adjustments and to speed, it depends on the prop. With my Mercury brand Black Max prop, by triming I could get about 7mph more so it responded well to trim but with the Hustler prop with the cupping, trim at most adds 1mph. Because the ding's to the new hustler aren't much worse than the original prop (sand dings not boulders), I believe it is simply too agressive for such low HP. Take a look around and you will find some shops and websites have a prop exchange program where you can try until you find the correct one and keep returning them until you do. Also, it is mandatory to show off your new boat with pictures here.

Re: Q4 prop/top end



I will be looking into purchasing some smart tabs and sell the hydrafoil.
As for the wot RPMS, im not sure where they were at. I will check this weekend and watch it closely. the lake ill be at is pretty high in elevation so i don't expect to see a huge increase in speed when triming up. but i hope that it helps with the top speed.

Re: Q4 prop/top end

titancj1 said:

I will be looking into purchasing some smart tabs and sell the hydrafoil.
As for the wot RPMS, im not sure where they were at. I will check this weekend and watch it closely. the lake ill be at is pretty high in elevation so i don't expect to see a huge increase in speed when triming up. but i hope that it helps with the top speed.

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Yep, the rpm's will guide you. If I heard you were say getting 50mph at 4200 rpm's as an example, the exta rpm's up to your max WOT rpm rating for your engine would tell me you have a lot left. I see now why you have the mpi engine if you are at high elevation. I say that because here in flat Minnesota, we are still in the dark ages with an overwhelming majority of Carb engines. Elevation is performance drainer as I bet you are fully aware. What is the elevation were you boat? Even though I have boated since I was 3 months old, until I joined this site, I didn't realize the science and calculations behind propeller performance. Take a look at the prop slip calculator on http://go-fast.com/Prop_Slip_Calculator.htm. You can figure out the hypothetical top speed of your boat based on several metrics. In other words, the fastest possible speed when you sit there and wonder how fast it is capable of. Then with your wot rpm's and true speed based on your next ride you can figure out where you stand. You will need to know your out drive ratio and for an mpi v6 merc it should be 1.60:1.

By the way that is a great looking boat. Is that a stainless steel rub rail and LED docking lights?

If you trailer a lot, I'd figure out a way to protect that wide area of yellow gelcoat on the part of the beam that is wider than your truck.

Re: Q4 prop/top end

Thank you. I am extremely happy with the boat, other than the top end (but i think i have that figured out now)

The lake i have had it on was about 1000'. the lake im going to this weekend (to do some smallmouth fishing) is about 5500'. im usually going to be on the lower evelation lake, this is just a vacation cabin weekend.

ill check out the outdrive ratio and watch my wot rpms this weekend. thanks for the help

Re: Q4 prop/top end

It's hard to tell, but did someone upgrade the trolling motor to the wireless Motorguide? I did the same upgrade to my 2006 Q6 S/F

Re: Q4 prop/top end

There are some try before you buy prop dealers out there. You might check the internet to find a location near you

Re: Q4 prop/top end

mccownk said:

It's hard to tell, but did someone upgrade the trolling motor to the wireless Motorguide? I did the same upgrade to my 2006 Q6 S/F

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no, i would love to have the wireless but its a minnkota powerdrive v2 55lbs w/ foot control. im going to be upgrading to the i-pilot very soon

Re: Q4 prop/top end

As for the top speed... i hit 50 mph in some chop on a lake at 5500'
just trimmed up a little bit and found a good balance with little to no porpoising. my rpms were at 4200 so i know i have some room to go faster. as for now, i think i may stay with the prop i have and test it out on a smoother lake near sea level. i like the pull it has to get out of the hole for wakeboarding. thanks everyone. been a big help

Re: Q4 prop/top end

I still say dump the whale tail for smart tabs. You won't be sorry. Best $100 you'll ever spend on the boat.

Re: Q4 prop/top end

mccownk said:

I still say dump the whale tail for smart tabs. You won't be sorry. Best $100 you'll ever spend on the boat.

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thanks. i think im going to get some. im a little tight on money after the purchase and everything. plus im moving into a new house this weekend. but i will soon pick some up and take the "whale tail" off

Re: Q4 prop/top end

mccownk said:

I still say dump the whale tail for smart tabs. You won't be sorry. Best $100 you'll ever spend on the boat.

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Do they still sell the blems on the site...looked, but I didn't see em'?

Re: Q4 prop/top end

I sent an email to IBoats asking if they still have the blems. The reply said they no longer have any of the blemishes in stock. So the regular priced Nauticus SX tabs are $119.95. Still the best $120 bucks you'll spend on your boat!