My thundercat

[1eyedjim]

He never said he was using it for racing and tbh. If he posted this on the thundercat site I'm sure not one person would come up with the idea you did to get more power, plus posting it here I get to see it :-)

I agree that different spark will have a different effect on the engine. On my freestyle Jetski people had updated ignition systems to give a better spark and more power but not one did you alter the gap.

To me. If you wanted to go better on the ignition system it needs to be a total loss system that has no charging etc and the flywheel weighs next to nothing but then this causes issues with torque etc.

I wouldn't be looking to slap an updated set of coils on, open up the gap and hope to make massive differences. It would need looking at from flywheel, stator, cdi all the way through and the only way it would work was if someone made a kit that it all worked together.

Look at the kits for jetskis. They make tons of power over the stock setup but none are just a set of coils.

I think if he does the same to the 70 as he did to the 50 it will be a weapon. Tbh I'd imagine stock it will still fly compared to the 50.

[Neuner]

Ok - hopefully can lighten the mood here.

Wannabe SIB owner.....

[Roflhat]

Originally Posted by Neuner

Okay - so why did you start this thread then in an inflatable boat section of a forum? Why not the devoted engine section? Were you just looking for pats on the back from guys who spend most of their time cruising a bay or river in a SIB fishing with an underpowered engine?

If you're really trying to make improvements it would figure you'd be posting on a thundercat racing forum instead of here.

It was originally just about the boat, but I'd been planning on building up the engine for some years, and thought folk might want to see what I'd done. I know when I was looking for inspiration for building the engine there was nothing out there, because everyone else is building engines for racing, so they don't want to be posting their secrets online. To be honest this thread has become basically an engine build thread, so yeh it probably could be in the engine section.

Also I have the same photos and information and three other forums, one of which is dedicated thundercat forum and the other two are boat racing forums.

[Roflhat]

My plans for the 70 so far are: 90 carbs, carbon reeds and velocity stacks and see how that goes.
It has a lower ratio gear box at 1.71 instead of the 1.86 of the tohatsu, but it's still 13 spline so I can use all the same props. I think 60 knots may be possible with the 70, might have to start doing aerodynamic mods to keep the thing on the water!

It's even possible to build a yamaha 90 short shaft using factory parts, a guy in Australia is just starting to build one

Cheers

[Neuner]

That's fine but if you're serious about the work you're doing, you'll do just a little bit more and get even more power out of it and that means getting it properly tuned and adjusted for the improvements you've made otherwise it's just a kid playing with a toy which you can find anywhere. Had those professionals given you'd advice anyways, I doubt you'd take it since you're not doing it here...

As an example, you don't buy expensive racing tires for a car and then only fill them with 35 psi like everyone else does for their regular car tire. It's actually worse for them and they will greatly deteriorate quicker. No, you put in the appropriate 55psi+ and then see the big improvement.

[Neuner]

Originally Posted by 1eyedjim

I agree that different spark will have a different effect on the engine. On my freestyle Jetski people had updated ignition systems to give a better spark and more power but not one did you alter the gap.



I wouldn't be looking to slap an updated set of coils on, open up the gap and hope to make massive differences. It would need looking at from flywheel, stator, cdi all the way through and the only way it would work was if someone made a kit that it all worked together.

Look at the kits for jetskis. They make tons of power over the stock setup but none are just a set of coils.

Cool on the Freestyle Jetski! I use to ride one a friend of mine had in college when they first came out. Loved them. Looked for one now and they are rare where I'm at. You have to get a license/certification to even buy one. You don't for any other type. Haven't a clue why and it's aggravating.

Good suggestions on the improvements. It's the little things that add up to the total. Trust me, the professionals are squeezing out all they can with even the smallest improvements and some of them don't degrade or blow the engine. Just general improvements for their purpose. Things the OP is rolling his eyes at. Another friend of mine added an additional 170hp to his small V8 Ford 305 Mustang while he was in highschool. Never ported or polished anything so that he could look at himself in the reflection. All done with both big and small improvements. He even changed the pully's and belt to add 5hp. He figured all of the small little things like that added an extra 25-30hp. He didn't shrug off the simple, cheap things that he could do and it paid off. The engine never blew and performed well all through College and on.

[Roflhat]

I'm happy to listen to advice, and it was advice from people who'd done it before that got me to where I am now. Some from former world champion thundercat racers, some from professional engine builders. But I can't be listening to everyone because not everybody is right...
For example some folk said to advance the timing, some said to retard. I'm not even sure what advice your offering to be honest, I can't open the spark plug gap because thats detremental to high RPM performance, I've already upgraded the coils and spark plugs and adjusted the timing. Show me an engine you've built, or a speed record you've set, then I know that you know what you're talking about. Also there is a lot of difference between a two and four stroke engine, as I'm sure you know, so what applies to one may not apply to another.

I've spoken to the fastest guys in the world, guys that know this engine inside out, and not a single person has mentioned redesigning the entire ignition system. One guy in germany is running programmable CDI ignition, but he builds engines for a living and has a dyno at his disposal.

I know what you mean about the car engines too, I've got a 1967 VW Beetle which I've put a 2.0 type 4 engine into. Course everyone has advice on them, "porsche engine bolts straight in you know..." or "my uncle had one with a porsche engine".

[Neuner]

Originally Posted by Roflhat

Looks like i didn't gain any RPM with the exhaust mod. Sounds better and acceleration is considerably better but the top speed remained the same.
I had a fiddle with the timing while I was out today but advancing or retarding it from standard both seemed to make it slower. What I can say is that putting the ignition closer to 24* made the acceleration even better, and that the other way made it worse. Makes me wonder why it didn't help the top end though..

This is something you should study and look into. You will need to tune it as you make any improvement.

Originally Posted by Neuner

Majority of the time I see the profs running a simple copper plug without internal resistors. You can have a larger gap and get a larger, hotter spark but if you don't have a coil that can handle it, it will fry.

In a different application, I ran a better coil, copper plugs and a greatly increased gap. Made enough of an improvement to note. Also improved my efficiency.

Just trying to help if you hadn't already gone down that route yet.

Originally Posted by Roflhat

i've not looked into it much, sounds interesting though

Originally Posted by Roflhat

Sorry I misunderstood!
yeh I'll look into it for sure. I've got uprated - nakuru - coils (from a motorbike) and iridium plugs on it on the moment. So dyou reckon an increased plug gap would increase power?

Edit: looked into it, and apparently increased spark plug gap gives greater power except usually at WOT, when you may even want less gap to prevent misfire?

Originally Posted by Roflhat

That's the conclusion I'd come to to be honest! haha

I offered a suggestion, you looked into and that's good. You don't have to do it, can blow it off for all I care but a lesson in etiquette, don't be a jackass about it.

Originally Posted by Neuner

If you really are trying to get the most out of the engine like you say, then that would mean you'd look at every aspect to gain more power. Polishing the ports and all of the other work you did is a hell of a lot more than anything I suggested.

My come back to your jackass remark. You were showing you have a lot of studying to do.



Just to refresh your memory since you seem to easily forget. You've now contradicted yourself. So there is no information out there which is why you posted here but yet now you say your improvements are because you are talking to a professional who is the best in the world. Funny, thought you just said they're not giving out their 'secrets'.

Guess no one needs to offer you any more help since you obviously know it all or won't listen to anyone unless they have broken some type of speed record...

Do yourself a favor, study hard and when you grow up go get a Mechanical Engineering degree from one of the top colleges as myself and then you might start to understand what these improvements do and how they affect all of the other systems and operations all the way down to the power at the prop. Get a job in Engineering and you'll also understand why the engines were built and designed to be the way they were when you purchased them. It's more than cost and 'manufacturing defects' as you refer to them.

Until then, guess you can go on now proving to the SIB guys of this forum that you are the expert and have shown them the light in small engine 2-stroke improvements. Congratulations.

By the way, hard to tell in your videos, but didn't look like you were wearing any protective gear in your 'water speed record test'.

[Roflhat]

Let's not make this personal hey, we're both adults...

The information isn't out there, all the information I've got is through email. I don't claim to be an expert, and I'm certainly not trying to put anybody down. This is my hobby and I do it because I enjoy it. Let's keep the thread relevent if possible, feel free to PM me.

[Roflhat]

Put the 50 carbs back on today, complete with the new stacks. Unfortunately these are so big that the vent in the cowl had to go. Still no break in the weather so testing will have to wait...