Author Topic: the quest for more speed (Read 11899 times)

mike71Gt-160 · « **on:** July 23, 2010, 02:12:24 AM »

should i move the motor up higher on the transom, this is what it was at when i bought it. im getting 47 mph on the gps would like to be able to get 50+. would like more speed but i dont want it to be a dog on the hole shot. http://lh5.ggpht.com/_vz0WwYlDj5k/TEk0ILm7UOI/AAAAAAAAAB8/ajeUyPKcdmQ/s400/trasnsom%20003.jpg http://lh3.ggpht.com/_vz0WwYlDj5k/TEk0Hg2bMUI/AAAAAAAAACM/i-F7BLh12_c/s400/trasnsom%20002.jpg http://lh5.ggpht.com/_vz0WwYlDj5k/TEk0ILm7UOI/AAAAAAAAAB8/ajeUyPKcdmQ/s400/trasnsom%20003.jpg

Hyperacme · « **Reply #1 on:** July 23, 2010, 06:51:28 AM »

What size prop are you running ?
Whats your RPM's with your prop ?
Do you have plugs to drain hull ?
Why is there a "plate" on your transom ?
Have you run Sea foam, power tune, decarbonizer through motor ?
Remove the wing/whale tail/fin thingy from your cavation plate.

mike71Gt-160 · « **Reply #2 on:** July 23, 2010, 10:24:35 AM »

Im running a 21p stilleto.
5250 to 5500 rpm WOT.
I got a plug in the back of the boat, i tip the bow way up when its parked
the guy i got it from hit something and cracked the fiberglass, so i put the plate on to stop water from getting in and strengthin the transom a bit, the transom internaly is in fair shape. i changed a transom on a 83 rinker (dont know why i put that much time into a rinker) probably goin to split the boat in half this winter and take care of all the dings, new paint hopefully.
I did run some seafoam through it about a month ago didnt see a noticeable change.
and fine ok i will remove the hydofoil. you guys really hate those things.

Hyperacme · « **Reply #3 on:** July 23, 2010, 11:18:24 AM »

Heard good things about Stilleto props, but might not work with your setup.
Have you tried other brands/pitches ?
Have you done a leak down test ?

I use Sea foam Deep Creap, Sea Foam in a spray can, each engine mfg. makes a form of it.
Pull plugs and tilt motor all the way up, spray deep creap/power tune/etc around each cyl. and down by the rings/ring lands.
Let sit for an hour and repeat, put plugs back in and start on muffs or in water.
Might have to do it twice, should get huge clouds of white smoke.
Have you done/had done a link and sink/carb tune/rebuild, fuel pump rebuild ?

Few guys on CGOA forum have GT160's but with older 6 cyl. Merc's.
I think there getting in tthe low to mid 50's.
Are you getting speed from speedo or GPS ?

Laine73GT160 · « **Reply #4 on:** July 23, 2010, 12:24:56 PM »

Wise of you to ask the club for help. They are a great resource, friendly, and helpful. You also have the beauty of a Merc a lot of people have experience with your motor and performance part are available.
I have a 73GT160 it came with a Johnson 85hp and was very useable 43mph by GPS with two adults.
I to have the quest for speed. Now have a 120hp Johnson. Prop SS22Raker.
First test run motor mounted on top hole. Results: Good 0 hole shot time, Hit the throttle and go no plain time, 52mph one adult, tight 360 turns no cavitations, throttle on throttle off boat would stand almost straight up on its tail (an entertaining trick). Bad boat trim only 50% useful 50% dangerous at high plain boat bucked side to side so violently it threw me out of the seat. Also used to much gas 12 gallons on 3 runs on my small test lake.
Second test motor raised now on second hole. Very happy with boat. Good: trim about 95% useable 5% wild. Perfect Hot Rod, fast and usable. On high trim exhaust note changes steering actually locks. I cannot turn it boat, straight ahead fast. Test on Mississippi distance at least 3 times the size of my small lake mostly WOT only used 7 gallons of gas! Bad some time to plain but acceptable and faster than plain time with 85hp. Also some cavitations on tight high speed turns. Again acceptable just have to remember to trim boat down on turns and up on straightaway?s.
Bad dropped GPS in water!
Happy with boat but still have the quest for speed. At some point I realize the speed will reach the limit of the haul design. Then I will need a second Glastron.
Plan: tune engine, check RPM, to see if I can try other props.
Have fun with your set up, it?s part of boating.

Hyperacme · « **Reply #5 on:** July 23, 2010, 02:06:14 PM »

Hi Laine and welcome to CGOAMN !
Took ya long enough ...LOL
J/E V4's arn't known for there good mileage, 52 mph is pretty good though ...

dorelse · « **Reply #6 on:** July 23, 2010, 02:32:41 PM »

Quote from: Laine73GT160 on July 23, 2010, 12:24:56 PM

I have a 73GT160 it came with a Johnson 85hp and was very useable 43mph by GPS with two adults.
I to have the quest for speed. Now have a 120hp Johnson. Prop SS22Raker.

This makes me think that my 235HP Johnson really ought to push my CVZ-19 faster than 57...I might need to do some prop testing as well.

GIL_CV21 · « **Reply #7 on:** July 23, 2010, 04:19:46 PM »

Laine , nice GT ya got there , got one my self . looks like ya need some decals on it . i can get them made for a good price . here are a few pics of my pocket rocket , and yes they will throw you right out of the seat if your not careful lol ( been there ) lol . i too have the need for speed, i just jumped up a few feet and HP with a project CV21 . Gil

terry · « **Reply #8 on:** July 23, 2010, 06:05:53 PM »

HAVE YOU MEASURED THE DISTANCE FROM THE BOTTOM OF THE BOAT TO THE CENTER OF THE PROP SHAFT?WHAT ARE YOUR NUMBERS WITH OUT THE FOIL?

Mike2500 · « **Reply #9 on:** July 24, 2010, 01:38:15 PM »

In this quest for speed has anybody ever used a jack plate? I herd it set's back the motor and you can raise or lower motor, they say when tou set the motor back away from transom you will get better speeds and burn less fule. Is that true?

Hyperacme · « **Reply #10 on:** July 24, 2010, 01:50:56 PM »

I think ....
Jack plate's give you a quick way to adjust motor on transom.
A six inch set back might make a differance in boat handling but don't think you would burn less fuel.
I think ...

V153 · « **Reply #11 on:** July 24, 2010, 02:15:10 PM »

Yes you should see an increase in top end speed. And it might be a little more efficient @ cruising speed.

The theory with a set back/jack plate is the motor is running in 'cleaner', less aerated water further away from the transom. Thus giving the prop better 'bite'. This in turn allows you to raise the motor height.

I think ...

mike71Gt-160 · « **Reply #12 on:** July 24, 2010, 11:30:13 PM »

From the bottom of the boat to the center of the prop shaft is about 7"... all the plugs in the hull are removed, so im not holding a bunch of extra water weight. I ran it without the foil today and i did gain 1 to 2 mph. rpms are about the same. without the foil the boat doesnt feel as stable in the rough water. but thats something i can deal with, it will just take some getting use to. I would love to have a jackplate i have even looked into some manual ones, so i can keep the cost down, if you do put a jackplate on a gt your going to have to change your steering linkage if anyone finds a good way to do it please post it. Thinkin about goin up one more hole on the transom as is it plains out in no time ( and free ) dont have the funds for a new prop yet. What kind of deal do u get from a prop shop if u trade in your old one and its in good shape ?

terry · « **Reply #13 on:** July 25, 2010, 08:03:23 AM »

yes you will have to change your steering.i have a 6"plate im putting on mine in the fall.here are some photos of a guys how he did it and ran his steering.you have to watch with the plate that you dont get the motor to high and starve the motor for water.its always good that you have a nose cone.i know mercury makes these plates that go on the side of your water pickups they are about 50-70 bucks,that some guys use. im sure you can ask at yor local mercury shop.if you have proplems i can get you the part number from mercury.i would try also going up a hole.the cost is a tube of silicone(lol)

Laine73GT160 · « **Reply #14 on:** July 25, 2010, 11:32:00 AM »

I am a newbie; do not have a lot of experience. Listen to the experienced members. But start with the easy and cheap thing first. Correct motor height bolt hole?s, tune-up, prop. Come to events some members have extra props or will trade props for test runs.
Get your boat at its best with a little help from your friends.
On you GT 160 even a lite aluminum jack plate will add weight. BAD
Your transom is already brook from that big heavy motor. Even if you repair the transom your boat hates weight on the back. A jack plate with any setback and the weight on the transom is multiplied many times BAD, the center of balance of that haul design will be messed up BAD you will be adding weight in the front of the boat.
Don?t get me wrong I love jack plates. In the 70?s I had a friend with a 14 inch setback jack plate running a 115 merc. Racing the and consistently winning in the 150hp class. They do put the prop in smooth water behind the boat.
Get your GT160 running at its best and love it for what it is. I am at in the low 50mph and it is fun, I enjoy the challenge of set-up and will maybe get in to the higher 50?s next year.
Your boat looks cool and fast sitting still. Its 40 years old and cooler than those ugly $40.000 dollar bass boats with 300 to 600 HP. They may run 70mph but I will keep my Glastron.
My second Glastron may be a pieced together, cheap one seated fast boat that will only run on calm strait smooth water.

V153 · « **Reply #15 on:** July 26, 2010, 04:13:53 PM »

I would definitely experiment with raising the motor a hole, or two. My motor height is approx 22". Prop shaft approx 5 1/2" under hull.

Here's a chart that might help: Plugging my data into it my speed comes out right about where it should be.

V153 · « **Reply #16 on:** July 26, 2010, 04:26:19 PM »

You might also want to verify that the motor is indeed centered on the transom. Might look like it? But mine was off 11/16"!

Edit: Evidently they used the drain hole to "center" the motor. Don't!

terry · « **Reply #17 on:** July 30, 2010, 03:31:48 PM »

tom brown was the guy to talk to on the speed department on the 16s.what ever happen to his site anybody know?i think they had that link of the guys cvx16 called the black pearl that had the yamaha 200 or 225?wish i could find the video-tryed to find it on youtube.that boat was bad.

V153 · « **Reply #18 on:** July 30, 2010, 06:18:10 PM »

Sadly it appears CarlsonSpeed is down for the count. Ya believe there was a 225 on Tom's boat for awhile. Think he experimented with 'pads' too. Bummer the site is down.

Laine73GT160 · « **Reply #19 on:** July 30, 2010, 07:18:40 PM »

National Glastron club has a forum also. I asked a simple question and got a lot of replies. Caution though a lot of the replies were just talk, some were very useful; you have to sort them out. I trust the local club. Also 71-75 GT160 were all the same haul design. 77 haul was redesigned and advertised for a larger out board. It is hard to find good information and honest speeds on old GT160. I did at one time find some videos of old GT160?s but I cannot find them now. And the person would not share his speed. Newer 16 foot Glastrons, cvx?s are more stabile and faster. Post the speed question for 71-75 GT160s on the national forum. Glastrons were sold all over the world. I would love to read the responses. Speed cost a lot of money, 50mph do able, 55mph strong motor and prop and good setup hundreds of dollars (and I bet the ride will be fast enough), Hotrod that merc, prop, and setup, add more 0?s to the word hundreds. Good luck, glad you have the quest for speed. I am a newbie also hope we can find more old GT160 owner?s and help each other.