Yamaha 6m6 61x 62t and 64x question

[keefer]

I did a few high speed water checks when I had the true 760 engine in my old SN. It is amazing how many times the human body will actually skip across the water at 53mph. Feels like semi hardened concrete for the first couple of skips.. :lmao:

 

[Freakrider]

if you read and search, and ask around, you will probably hear that the 760 power band is all "top end"

and of course you know, thats terrible for a stand up, and will probably result in you being thrown from the watercraft in a spectacular fashion.

ok gottcha....I think that's why Yamaha put in the 155mm pump and dual 44's on the Dbl blaster to compensate and help with the low end and get that nose heavy boat up and going...yep 760's need help

 

[EightySeven550]

What if I got my 6m6(or 61x) cylinders bored out to 760 and used my 760 pistons?

Would that eliminate my problem of "all top end" power? and would that have more than a 62t/61x combo?

 

[WaveDemon]

yes, thats what a big bore is.

 

[Matt_E]

Eh....I would call that a cheap-bastard big bore, because there is hardly any room for overbores left.
A true BB uses BB sleeves.
IMHO...but I'm a hack.

 

[keefer]

The 61x port timing really starts to make good power once you get it up to 84mm and above. My "cheap-bastard" ported BB with 210psi makes great power.

 

[WaveDemon]

Eh....I would call that a cheap-bastard big bore.

yes, but you must consider the source. me :icon16:

 

[EightySeven550]

Can I bor emy 6m6 to a 760? or sdhould I stick with the 61x being bored and then bore my 6m6 to a 701?

 

[Mouthfulloflake]

I dont think you can bore a 6m6 to 84mm.

group K lists 81.25 as the max safe bore on a 6m6, they are known to be conservative though.

info gleaned from here.

http://www.groupk.com/y633-781sj-all.htm

 

[Kennay]

Why the hell would you want 6m6 port timing? I though the port size and timing were terrible?

 

[SUPERTUNE]

They are! Way to small to support any bore over 81mm

 

[EightySeven550]

Why the hell would you want 6m6 port timing? I though the port size and timing were terrible?

Because i didnt know that there was too much of a difference than the 61x cylinders. I posted the question to get ideas. Gotchya, :bad3: dont do it.

Appreciate everyone's advice so far.
Heres the steps so far.

SN-1
61x Cylinders on 62t.

SN-2
6m6 into SN-2 (eventually get a 61x cylinder and pistons)

Put the 62t cylinder on the 701 crank for a back up (i NEED to ride) engine.

Now for sale.(Using funds to purchase B-pipe and tubbies maybe.)
64x (will sell carbs seperately)
Dual Carbs from stock yamaha 760
62t cylinder and pistons
61x Crank and carb

 

[Matt_E]

yes, but you must consider the source. me :icon16:

Hey, I've made two of those myself.
The last one was super-cheap - I removed the bored out X sleeves out of a busted casting, and put them into another casting.

Now THAT's cheap.

 

[Kennay]

So do the X cases with the 62t cylinder make more power than the T cases with the 62t cylinder???

 

[Matt_E]

Consult a dyno.

:haha:

 

[Kennay]

Ok, to better phrase my question....


Through crunching numbers, or going on known theory, is there any reason 61x cases should work better than t cases for a t cylinder?

 

[Matt_E]

Not that I know of.

The reason people go that route is money.

 

[keefer]

I guess you could call it a "cheaper-bastard" engine if you don't like calling it a Frankenstein.:silly: No boring involved unless you have to. They run pretty good, but not as good as the old T case X cyl setup.

 

[Crab]

So whats a good T701 cylinder and pistons worth?

 

[Matt_E]

Five dollah