More horses!

[fast fred]

hears one ben workin on a long long time, it's from the mid 70'tys, i had to make a bunch of stuff that ya can't get any more, and chace over the hole planet for all the used parts i could find.

this is 50.7 cubes or about 820cc, makes over a 100hp@8000rpms, race fuel Only. Built for Super Light Tunnel, Class "X" ( SLT= inflatable cat ) what classes are you guys runnin, do you have a class like "X" or similar

[prairie tuber]

Originally Posted by fast fred

hears one ben workin on a long long time, it's from the mid 70'tys, i had to make a bunch of stuff that ya can't get any more, and chace over the hole planet for all the used parts i could find.

this is 50.7 cubes or about 820cc, makes over a 100hp@8000rpms, race fuel Only. Built for Super Light Tunnel, Class "X" ( SLT= inflatable cat ) what classes are you guys runnin, do you have a class like "X" or similar

How much will that outboard weigh when all is finished?

[fast fred]

on this mid, about 175lbs give or take 5lbs or about 80kilos

about 30lbs more than a Yamaha 50hp

[lenok]

We’ve been hunting for the engine guru all over the world and you seam to be very appropriate person to ask for engine tuning tips. We are starting Thundercat movement in Russia, riding Gemini ZII and other local tunnel hulls. As everyone who has been there before we are struggling to understand Yamaha and Tohatsu pros and cons. Our team chose 50Tohatsu and now my pilot is driving me nuts trying to uncover secretes of R/R engines. All we got is a list of legal modifications from Auzie websites and British pilots’ whispers during Zapcat final in Cornwell. I’d appreciate any info that could help, please drop me a line on lenok@lycos.co.uk

[fast fred]

i'd need to see the specs that thay gave you. Tack the crank, snip the revlimiter, she wakes up. can do for yas, thare is more you can do, that powerhead shot is for my SLT ( Super Light Tunnel) same as yours, yamaha 50hp wakes up too.
this is a Hot-Sue crank, make yours look the same, Mains and throughs

[fast fred]

To- hot- su guys you got to weld the crank, then snip the revlimiter,( gray or white wire comes out of the black box, makes a loop and goes back in to the black box, Cut it, tape it off. you want the 50hp tuner pipe, if you got a 40hp
you want to find 50hp carbs.through the muffler box out, change the gear oil in the foot to some lighter weight. cut the head till she bumps up to 140lbs psi
on the compression gauge, run high test gas hit a 20deg max advance.

thinkin 130- 135 on the main jet, ya thats what i'm thinkin.

[Rooster21]

Hi Fred, Most of what you mention reagrds the Tohatsu 50 mods has been done. I ve done. It make a bit of difference but not much. Not enough put it that way.

My own thoughts are on the exhaust side, as to where the main restrictions are. Not sure how to over come them.
I wish I had the time and knowledge to maufacture a tuned pipe.

Ever tried "dry stacking" if possible, one these motors.????

I mean 50hp from an 800cc 2 stoke is just pedestrian.

Even with the mods the zapcat just dosent fullfill its potential. 40 knots just aint fast enough. Unless its in the surf.

50knots + and I think that would make them special. Flat water raceable that is.

Sounds like you have that across the pond. Any vids around ???

[fast fred]

unless your guna buy Fuel, 110+oct, comes by the drum,it will never make the power your lookin for. you can dry stack, good for about 4hp total.
makin tuners is no big deal, hears the formula, what ever the size goin in x 2 1/2
goin out, make it look like a cow bell, 6"- 7" long.
you need a bigger moda. Yamaha 70hp CES, this is a good place to start, on fuel
she'll make over a 100hp and pull to 8000rpms, sendin the hull up over 70mph.
i'll look around for some vids

[Rooster21]

Ive tried Avgas, which I think was 100LL, and didnt notice any difference.

I Thought I had slight improvement with Nitromethane in varying percentages. But it was not that noticeable in race condtions.

Using a 70 is not really an opption as all the Zapcats here run 50 Tohatsu,s.
So would need to get more from the Tohatsu.

Any pics of an expansion chamber ??? Insitue

Do I understand you correctly in that you are fiitng the chamber inside the leg ?

Sorry for being abit dumb.

Thanks for the replies v.interesting

[fast fred]

"the thing with AVgas" the trick with avgas is you got to COMPRESS IT!
otherwise the hull will slowdown, a min' of 26cc's head chamber size.
on the compression gauge about 150lbs psi crankin on the starter, the higher the Octain the less it wants to lite, you got to squish it to excite it, then it will lite, and Then it MAKES POWER.

once on AV, you can't go back, unless you change the head.

[Rooster21]

Thanks Fred. Thought as much.
A few more if I may.
Am getting 140lb as standard on a pull start.
Ive got a spare head that I can mod.
Do you have a min value for chamber volumes ???
And is an original gasket ok to use?

Also what think of a Wiseco pistons. Worth the expense ?

Thanks Again Fred

[lenok]

Guys,
Thanks a bunch for the info, was engulfed in snowmobile madness – winter has come to Russia only in February. Will С what we can do but should wait until spring to give it a go.

[fast fred]

the thing with clipin the head is, the squish band area has to stay positive,
so not to interfere with the flaim front.

the squish band is on the edge of the head chamber, cuzz you got a slight dome
on that piston it becomes imporant (flat top pistons are way easier ) .

when the pistons is at TDC the distance between the piston crown from the out side edge , to the top of the head needs to be .025min should grow to .035 as it moves to the chamber.

the hole idea is to make the chamber smaller but keep the squish band the same
OR it WILL BURN DOWN.

24-22cc's light that LL100 , head gasket be just fine, do not over torque, just like the book says, a dab of thin oil on the threds and torque to spec.

let me know if your followin any of this.

[fast fred]

settin the squish clearances in this head, a cut has been made over the deck surface of the head, .150", then the squish clearances are put back.

on this Race Moda, the piston crown pulls out of the block, past the head gasket and in to the head

[Rooster21]

Wow. I never would have believed you could deck the head that much, and get away with it.

Thanks for the pic.
I probably wont be that brave to start with.

Any Idea of the copmression ratio you end up with ???

Thanks again Fred

[fast fred]

needs 110oct. min. about 190lbs.psi- 200lbs.psi , stock is about 120 -125 lbs. psi.

[fast fred]

this is my copy of the OMC CC FT 19s, F3 race Moda ( not a motor).
makes about 104hp a 6700rpms pulls to 8000rpms @ just under 100hp

thinkin i should paint it white, buffin gets old fast.
all that could be New is,

[fast fred]

ya can, yes you can hit it with NOS, you can fog it in the air box, a high amount of fog can and has froze the reeds open, and the cyl shuts down, you can plum it behind the reeds to keep that from happenin , NOS is Oxygen, with out an enrichment fuel , soon as you hit the button it Blowsup, Nos and enrichment hit at the same time. Nos wakes it up

[fast fred]

hears an udder one, got 12 venturies on it,

check the fly wheel

[fast fred]

some more

and another one