Hi mate, Yeah me too, that tinny is still relatively heavy. My friend has a bathtub race boat we may try it on in the future which should be faster but nothing like a hydro could achieve. Cheers 🍻 Aussie Boat Guy 😎
Hey mate, my 8ft punt (very light) with a 9.8hp 2 stroke Tohstsu does 41km/h stock in still water. I haven’t looked at motor height but it does have a factory prop & 150psi on both pots. So you 5hp is moving!! Looking forward to the 9.8hp next 🤙
Thanks mate 👌 Yeah that’s the numbers I’ve had with the 9.8hp as well in the past on light boats. The 9.8hp has a whole heap more torque though compared to my mod 5hp. Yeah, I’m very curious to see if I can get the same ratio of increase out of the 9.8hp as I did with the 5hp. All the best Aussie Boat Guy 😎
I like so much your mods on the little one. I run surface props on my r.c fast boats and find many common theories. Your lower hand made unit is a master. Greetings from Greece.
Hi mate, Thanks so much for your comments 😊 Yeah, I’m sure that the RC surface props act the same. The RC race boats are very fast, love that stuff. All the best Aussie Boat Guy 😎
Crazy speed from a 5 hp! I have a light fiberglass boat, about 4m long with a 20 autolube Yamaha. Goes a bit above 50 kph without too much optimizations. I use it to go fishing with the kids etc, so I´m not going crazy with it. But I think for next summer I´ll try to dig a bit more speed from it. Currently it´s close to -30 C, so I´ll have to wait for a while for spring to arrive. But nice videos to watch in the meantime!
Hi Mate, Thanks for your comments, really appreciate it 👌 Is your motor the twin carb model? they are pretty good 👍 they race them in the dinghy derby here in Aus. keep me posted champ, I’m very interested. cheers 🍻 Aussie Boat Guy 😎
@@25hpboatracerman Yep, the twin carb from around 1990 ish. I relaminated the transom with fresh plywoods and reinforced it a bit from original since the motor is a bit oversized, also sanded and repainted the bottom last spring. Fitted trim tabs, since it was a bit sketchy at higher speeds. Probably fitted those a bit too low, since it lost a couple of kph, but at least it is stable and goes on a plane really nice now. Currently it has a composite Pro Pulse 4 blade prop. I fitted that to get an idea of a good pitch, since the original alu prop was way too small. IIRC it´s a 10,4" and running at 14" pitch now. 15" or 13" give pretty much the same top speed. I think I´ll try a 13" alu prop, modify it a bit and get a bit more revs/power from the motor. Didn´t have a tacho last summer, but now I have one waiting to be installed. I´ve been playing with two strokes since I was a kid, so I´ll do some simple tricks with the motor, but nothing major.
I’d like to hear your insight. I found a 10,5x13” “sport” steel prop. Could that be worth the money? About 300 e. I’m running the engine as high as I could with the alu prop. High enough to have some issues. The 4 blade propulse bites better and has some cupping. The boat has pretty poor lift in the bow but a pretty low V in the transom. It likes all the weight in the back - never gallops, no matter how much you try to trim it. I’d be quite happy with about 55 kph and good bite. When I rebuilt the transom, I set the base height with the ventilation plate a tad above the bottom. If I could jack it up about an inch or so with the steel prop, it would for sure go pretty well. There is also an 11x15 cleaver, but I think that is too much for me.
When you checked your before and after speed was it on the same water conditions? Glass smooth water slows my boat down. A wee bit of chop is faster. Your velocity stack made a much bigger difference than I would have guest. Coolest boat videos ever. Thanks for sharing your hobby.
Hi Mate, Thanks for your comments. Yeah, it did make a bigger difference than I expected and on further investigation - I believe that the fact it allowed the motor to draw cool air instead of the warm air inside the cowl also added to the increase in speed. The inlet in the original cowl was just a super tiny slot and probably restricting flow. Cheers 🍻 Aussie Boat Guy 😎
I’d actually experiment with a plenum after the stack, I’d spent quite a lot of time tuning two strokes with a variety of modded intakes and have found that an intake expansion chamber can give torque but also chop the sound right out! My 29cc whipper snipper outboard uses a flash lube valve saver bottle fitted to the walbro trumpet with quality used radiator hose and zip tie engineering! and without it deafening but completely refined when installed!
Hi Mate, Thanks for your input 👍 I have heard that can make a big difference, I will have to try a few different length extensions to check it out. cheers 🍻 Aussie Boat Guy 😎
@@25hpboatracerman the bottle pretty much is a plenum chamber the trick to noise canceling is to have the intake redirected another method is use a convoluted hose the ribbing cancels a lot of sound too
Hi mate, Thanks 😊 It’s central coast (Brisbane Waters) Ps: don’t really know why it’s called Brisbane Waters 🤷♂️, probs should find out 😂 All the best, Aussie Boat Guy 😎
Hi Mate, No I don’t need to tilt it up. The normal pickup is under the cav plate, all I have done is bend the water inlet tube to outside of the lower unit but it still falls so when I disconnect the external water tube it drains well. Cheers 🍻 Aussie Boat Guy 😎
Beautiful. Well done mate. I think you could be eligible for a record holder in the Guinness Book of Records. I tried to search it for you, but could not see any such listing. Maybe I was wrong?
Hi mate, Thanks, I’m having so much fun with the 5hp 😁 I know there are faster modified 5hp out there unfortunately. I did build it so it would still be reliable too, it’s done over 7hrs now at full throttle 😂😂 Cheers 🍻 Aussie Boat Guy 😎
Hey aussie Boat guy! This is a older vid so you will prob not see this but, at the start of the vid you were showene How to run the Engine high with that water tube and i was wondering if you Are able to do the exact same thing with a Yamaha 9.9 hp? Thanks! Ps, ik i just asked this question but i did not quiet understand What u said sry
Hi mate, yep, I can’t see why not. Check out what I did to my 9.8hp for low pickups, lots more work but so happy with it and works on all motors. Cheers 🍻 Aussie Boat Guy 🍻
Hi Mate, sorry for the late reply 🤦♂️ yeah would be super cool to do an expansion chamber tuned pipe, we will see if I get to it, will be so loud 😁 cheers 🍻 Aussie Boat Guy 😎
I don’t claim to be any sort of expert, but I understand that the best of inlet stacks should have a full return inlet bell, and the ability to quiet the air from turbulence. In addition, the ability to tune the stack length for optimization. Man of your enthusiasm and capabilities would be able to test this… ?
Hi mate, You are correct 👌 Unfortunately I am now turning my attention to another build, may get into a tunable stack for the next one. Cheers 🍻 Aussie Boat Guy 😎
Hi Mate, I make them all myself, I couldn’t buy anything off the shelf to modify the 5hp. I put up a detailed video on the channel of what I did to it if your interested. Cheers 🍻 Aussie Boat Guy 🍻
I wonder what hp you’re actually getting now… hard to know for sure without a dyno, but I’m thinking something like 8 or so? Maybe a touch more? What speed does the 9.8 get? Although for a fair comparison you’d need a water pickup and surface prop…
Hi mate, Yeah, I reckon between 7 and 8hp but the speed comes because it’s ported to run at a higher rpm. Very true about the 9.8hp comparison, you would need to surface the prop etc for a fair comparison. Also the 6, 8 and 9.8hp have a slightly better gear ratio for speed than the 5hp which would need to be taken into account too. Stock 9.8hp on a really light tinny with stock 8.5p alloy prop setup really well gets just over 40kph from tests I’ve done in the past. I have not yet decided on a speed I’m hoping for yet with the modified 9.8hp, what would you reckon?? Cheers 🍻 Aussie Boat Guy 😎
Holy Grail for me would be the same performance out of the 9.8 as an 18hp Tohatsu/Merc, without needing a modified pickup. I don’t think it’s achievable, but that would be amazing. Light enough for easy travel, but enough power to be useful! Im looking forward to seeing what you can achieve!
@@michaelnelson912 Yeah, that would be awesome. Don’t think it could ever match the torque unfortunately. I reckon you could get 12 to 13hp. Unfortunately the 9.8 is already a modified block in a way. Ports are still pretty small though but not much room to port the transfer ports. The crank and rods are pretty small too. Will have to see if what I’ve done works with the 9.8hp block.
Hi mate, unfortunately I am just not drawn to the four strokes yet. Once I’m done with the two strokes, turbo four strokes interest for sure. cheers 🍻 Aussie Boat Guy 😎
Hi mate, Absolutely, so pumped. Already modded the parts, hope what I’ve done all works 🤷♂️ could be a trial and error thing. Gone pretty wild with the reed plate, maybe too far. Time will tell. Cheers 🍻 Aussie Boat Guy 😎
@@25hpboatracerman Nice, the reason why that 6hp 4-stroke series might go viral since theres really no videos getting more power out of them and yet theres like billion guys wanting it😆
Hi mate, Yep I manufactured it out of 316 stainless steel. Not sure how much room in the 8 Yamaha but I’m sure you could make something. Also getting cool air under the cowl makes a difference too if you cannot fit a velocity stack. Cheers 🍻 Aussie Boat Guy 😎
@@25hpboatracerman I'm thinking about removing the airbox in front of the carburetor, I've got a spare cover so I guess I could actually cut a hole in it. I'd like to see some close-up pictures of that when you made.
@@rrrttt1112 Hi mate, I tried taking it out without the air box on with the cover off the motor, it was faster just like that. Even removing your air box and getting some cool air in should give you a gain. Cheers 🍻
We set a record with a 7 1/2 hp, a little over 72 mph. That's good rpm for a mercury. We ran champions, twisted 9200 for the record. The champion had rotary valve. Makes a world of difference
@@independentthinker8930 That’s awesome 👌👌 I bet it was not on a tinny (aluminium monohull) Was that on a hydroplane, with a very light driver? I would love to hear more about that, sounds amazing 🤩 All the best, Aussie Boat Guy 😎
i have a 8hp tohatsu 1996 and im trying to get as much speed out of it as possible, im getting 36kmh with the stock 8.5 pitch prop and was wondering if a velocity stack and new prop would help much, thanks
Hi champion, sorry for the late reply. a propeller may help and you can try just taking to cover off the motor, that will sort of show how much a stack will help. cheers 🍻 Aussie Boat Guy 😎
Coming from the motor cycle drag racing world, I know for a fact that stacks do not make power, they move power in the rpm range. So unless you are turing more rpms you are not ganing anything, Stacks on this motor are a waste of time.....
Hi mate, Thanks, that would have been fun, dangerous though. It was turning about another 400rpm. With your added information, maybe 🤔 it was more that the factory air box is very restrictive and I know for a fact the cover on that motor seals very well with only a tiny slit for air inlet so that the air under the cover becomes heated. Thanks for your comments, will have to try without the stack but leave the original air box off and cover off and compare. Cheers 🍻 Aussie Boat Guy 😎
