Yamato pipes question

[Little Fork Runner]

Hi i built a C hydro over winter last year. i have a stock yamato 302. i don't race, except for a local drag race near my cabin where i ran the boat all summer. i am looking mainly for top speed. i hit a max speed of 65mph but looking to go faster. i have been doing alot of research on expansion chambers, and megaphones. which one would be better. as of right now i want to try to build my own expansion chamber. i have Jennings Two stroke handbook for a guideline but thats it. does anyone have plans and dimensions, or is that all a secret??? I was just wondering if anyone had any pointers, or techniques that they know work good.

Also i want to get a different prop this upcoming year because i know that has alot to do with speed. last year i was running a Dewalt 7 1/2in leaf shape, not cleaver, with a 12 pitch. any recommendation on what pitch i should try next???

[ZUL8TR]

Hi i built a C hydro over winter last year. i have a stock yamato 302. i don't race, except for a local drag race near my cabin where i ran the boat all summer. i am looking mainly for top speed. i hit a max speed of 65mph but looking to go faster. i have been doing alot of research on expansion chambers, and megaphones. which one would be better. as of right now i want to try to build my own expansion chamber. i have Jennings Two stroke handbook for a guideline but thats it. does anyone have plans and dimensions, or is that all a secret??? I was just wondering if anyone had any pointers, or techniques that they know work good.

Also i want to get a different prop this upcoming year because i know that has alot to do with speed. last year i was running a Dewalt 7 1/2in leaf shape, not cleaver, with a 12 pitch. any recommendation on what pitch i should try next???

Is that a GPS speed? Do you have an accurate tach for rpm? Based on the speed and pitch you note with 14:15 gears in the 302 (gear ratio = 1.0714) the no slip RPM would be about 6190rpm (this calc with 1% (.01) slip the lowest allowed in the link below). Even with 5% slip (typical for high speed hulls) that is about 6450 rpm. Either is to low for the 302. I would suspect that closer to 6800 to 7000 is needed. Example at 7000 rpm, 5% slip (0.05) and 12" pitch the expected speed is 70.5 mph.

Setup is important. What prop shaft end depth below bottom and prop shaft angle relative to bottom are you running? Maybe that can get the revs up if too deep?

Here is a link to calculate theoretical boat speed. Although it is based on the helix pitch advance theory it does provide very good relative results. Slip is a real unknown because it can't be zero but smaller is better to a point. Also prop pitch is the other bugger variable that is dependent on what tool used and how measured on the blade because the surface peircing props used have variable pitch across the blade from lead edge to trail edge at a given radius, thus how was pitch as a single number determined? Average across the blade at what radius, etc? Note props with the same average pitch ar not identical since the change in pitch from lead edge to trail edge at a any radius could be very different in addition to other factors.

http://www.rbbi.com/folders/prop/propcalc.htm

I believe the props that are being used for the C hydros are less than 7.5" diameter. A reduction there and less pitch might do the trick. Playing with props and set up is time consuming and expensive unless you can borrow props to test.

C guys chime in here.

As to pipes? I suppose the mod guys would have lots of input on that so do a search.

[Little Fork Runner]

I have been trying different setups, when i hit 65mph it was on a GPS but i don't have a tach yet so i don't know rpms. i am going to buy a tiny tach first thing next season. my propshaft is directly level with the bottem of my boat, might even be a hair above. it should be pretty level too. i have the motor tilted out as far as it will go, with makes it level with the bottem of the boat. my boat is put away for winter right now so my setup is taken apart, but i thought that it ran the best when i had it jacked up that high. thats why i am going to try a new prop next year. once i get my tach next year i think that will help alot with tuning.
Thanks for all the advice already, it really helpful!!!

[Little Fork Runner]

About the expantion chamber you have for sale, i am going to have to pass. It looks really nice, but my boat is put away for winter. i know that there are many for sale out there but i was thinking about trying to take the challenge and building myself. i am a studing to be an engineer and what to take the challenge.

i don't really know much about them so some of these questions might be really dumb. if i made it out of steel would that be to heavy? i was thinking i could make a test pipe out of steel then try one out of aluminum. the only reason why i ask is because i only have a steel welder as of now.
Also what does a filler block for the lower cyclinder mean??? do you have to block off a port when you add the pipe.
I didn't have time to take that cover off where the exhaust is so i don't know what is under it, that probably why i don't know what some of that stuff is.
Thanks for the info you posted before

[dwhitford]

Expansion-chamber material is normally 20-gage mild steel rolled into the cones and shapes necessary for the design.

[sam]

Most expansion chambers are made of thin gage sheet metal (steel). When rolled into cone shapes and welded, the steel becomes much more rigid than you would guess. In a home workshop, rolling the cones is probably the biggest challenge.

Filler block connects and fills in the space between the exhaust ports and the parts of the pipe you can see. Its the internal pipe section leading from the cylinder to the outside of the motor.

[machinedcomp]

Yamato Expansion Chamber

I have a proven design, if you provide a mailing address or fax number I'll send you a copy of the print. The first pipes I built from 24 guage sheet metal. Then Brazed together.

[Little Fork Runner]

I have a proven design, if you provide a mailing address or fax number I'll send you a copy of the print. The first pipes I built from 24 guage sheet metal. Then Brazed together.

I sent a private message to you regarding my information. Thank you sooo much!!!

[Little Fork Runner]

Here's what I wound up with for NBRA 25MOD....Used the side cover and filler and built my own version from a AAEN snowmobile chamber and Bayer meg.....demensions almost identical to the Seay/Schultz pipe...........

Wow that looks really cool. so is the chamber the exact dimensions that it needs to be, or if it is off is that ok. like if its within a certain amount is that still ok for motor and performance. like when i build mine if it isn't exactly perfect but within like a 1/16 of each dimensions will it still be ok for the motor, and still give me good performance.

Also I saw that picture of your racing foot/ bottem of the lower unit, and it looks really cool. where does the water get sucked up for the cooling system. i take it that it is in front so that when you drive it just gets draged in the water and gets forced up to the block. The black hose on the left side of the foot is where the water goes correct, it doesn't go throught the lower unit anymore.
Also since there is more of a point on the racing foot do you ever experience the back end pulling in one direction because the point is kindof steering the back of the boat. my friend got a point welded on his but it started to pull just a little not much, but he had to get it rounded off. it wasn't an actual racing foot, that also could have been the problem.
I have see some racing foots for sale, but what do they go for brand new, and what would be a general price for a used one?
Thanks

[STEVE FRENCH]

Another thread of interest with some/errrr...... a ton of............. cool pics/discussions!!!!!

http://www.hydroracer.net/forums/showthread.php?t=18594

HAPPY BUILD"N!!!!!!

100N/Steve

[fcliff]

Sure Steve. Here is a picture of the Mod kit I make for APBA installed on a straight stock 302. It is a 15 minute job to bolt on and be ready to run. The pipe is a slider pipe and works efficiently. The system can be purchased directly from APBA. Anyone with questions can get me at fcliff@yahoo.com
Cliff Johnson
Cliff's Edge Racing

[fcliff]

Ooops. Missed the picture

[Little Fork Runner]

Sure Steve. Here is a picture of the Mod kit I make for APBA installed on a straight stock 302. It is a 15 minute job to bolt on and be ready to run. The pipe is a slider pipe and works efficiently. The system can be purchased directly from APBA. Anyone with questions can get me at fcliff@yahoo.com
Cliff Johnson
Cliff's Edge Racing

How much does a kit for a 302 cost?

[fcliff]

The mod kit includes filler block, side plate, elbow manifold, pipe slider cone, expansion chamber, pipe support system, pipe ring mounted on vibration isolators and all hardware. The kit sells for approximately $700 plus shipping. There is also a similar kit for the 80.
The 102 has a different port arrangement requiring a different elbow. I am working on that system.

[Little Fork Runner]

Thanksss... Pics of my boat

Hey Thank you everyone who has posted here and helped me out. Here are some pictures of my C Stock hydro as of right now, this is how i ran it all summer.
My Goals for next year are...
1) Stickers/pinstripe/paintjob.
2) Finish the boat with a clear coat too protect it and give the bottem a smoother finish.
3) Get a Tiny Tach
4) Polish the exhuast ports/ build expansion chamber.
5) Get a better prop
6)??? Get a nose for the Foot for lower water pickup.??? (maybe the year after next)
I know it sounds weird that i just use this boat for laking running, but i live on a chain of 13 lakes and i can open her up on all of them. I love the sport and glad i got into it. This is my first boat build, i did it all myself besides the fact i bought it as a kit, but love riding it.

[Little Fork Runner]

yea this is a Darrel Sorenson kit. i was very happy with how it turned out. i thought that the tiny tach was supposed to work with the 302. doesn't it just wrap around the spark plug??? i have no idea what kind of tach to get otherwise. I don't have a height/ angle checker, but i use a straight edge to check the height. at the end of the season i was running about level with the bottem (I knew that was not STOCK regulations but i just lake running so it didn't matter). That is a good idea with letting the water drip down the boat to see how well it is cooling. i usually just watch it carefully. I have never had steam so i think its doing alright, but i really like that idea of the nose cone that picks up the water. i am going to have to look into that.
My friend is getting his yamato 202 exhuast polished, and thats why i thought i would. we both lake run and i was faster then him this year so he is getting his motor rebuilt, and exhaust ported. i guess i will wait and see if it improves perforance enough before i do that to my motor, and ruin the motor for racing regulations.
Is there a place i can go and find a different head for my motor cause right now i have these giant spark plugs, and i heard you can get a smaller head so i could run standard snowmobile plugs??? i don't rememeber what i have but they are like NGK-R racing plugs and i cant find them anywhere.
Thanks