I have a strong running '57 javelin 35HP on a small thompson ski boat. I would like to increase the performance of the motor. I would like to get more torque to pull heavier skiers up, and more top end. I would be willing to sacrifice some torque for more top end.
I know that this is asking for a lot. I am NOT interested in replacing the motor for something larger. this is a resto, and changing out the motor for something that was not available at the time isnt feasable.
the way I look at it, i have several options that will accomplish this.
1. I am running the stock factory brass prop from 1957. I think I can replace this with a stainless prop. what should I look for to improve performance? The factory prop is clean with no dings or chunks missing, and the lake that I am running this in has no hidden debris, so durability is not a factor. I don't know the pitch of the existing prop, so I am starting from scratch here.
2. I can mess with the exhaust. the motor is a simple 2 stroke. expanding the i.d./ raising the height of the exhaust port should increase performance. I have parts(exhaust covers(manifolds)) available to mill until they are correct, so if my mods aren't beneficial, the cost of the cover is pretty minimal. I can also attempt to fabricate some sort of expansion chamber exhaust that will significantly increase the HP output of the motor(this is how the very small motocross motors can generate so much power).
I dont think building an expansion chamber is a real option, as fitting any additional exhaust under the cowling will be an engineering nightmare. I do know that johnson had a small bullet exhaust that exited out of the side of the cowling. I could fabricate that pretty easily, but I am not certain what the performance benefits would be.
The high performance motorcycle folks tell me I should just deck the cylinders to increase the "squish: This is intriguing, as the cost is minimal (<$100) and is a pretty common procedure in the 2stroke motorcycle world.
3. other stuff. spark plugs/racing gas/etc. this is wide open.
4. I could turn this into a dual motor boat (2 javelins), as that was an option for this boat, however the amount of transom and steering/controls work would be significant.
I'll take any advice/recommendations.
I know that this is asking for a lot. I am NOT interested in replacing the motor for something larger. this is a resto, and changing out the motor for something that was not available at the time isnt feasable.
the way I look at it, i have several options that will accomplish this.
1. I am running the stock factory brass prop from 1957. I think I can replace this with a stainless prop. what should I look for to improve performance? The factory prop is clean with no dings or chunks missing, and the lake that I am running this in has no hidden debris, so durability is not a factor. I don't know the pitch of the existing prop, so I am starting from scratch here.
2. I can mess with the exhaust. the motor is a simple 2 stroke. expanding the i.d./ raising the height of the exhaust port should increase performance. I have parts(exhaust covers(manifolds)) available to mill until they are correct, so if my mods aren't beneficial, the cost of the cover is pretty minimal. I can also attempt to fabricate some sort of expansion chamber exhaust that will significantly increase the HP output of the motor(this is how the very small motocross motors can generate so much power).
I dont think building an expansion chamber is a real option, as fitting any additional exhaust under the cowling will be an engineering nightmare. I do know that johnson had a small bullet exhaust that exited out of the side of the cowling. I could fabricate that pretty easily, but I am not certain what the performance benefits would be.
The high performance motorcycle folks tell me I should just deck the cylinders to increase the "squish: This is intriguing, as the cost is minimal (<$100) and is a pretty common procedure in the 2stroke motorcycle world.
3. other stuff. spark plugs/racing gas/etc. this is wide open.
4. I could turn this into a dual motor boat (2 javelins), as that was an option for this boat, however the amount of transom and steering/controls work would be significant.
I'll take any advice/recommendations.