701 Conversion- How To.

[Mouthfulloflake]

I personally think 83mm would be suffocated by the 6m6 cases, and needs to be on 62T's.

Stock bore 61x cylinders on 6m6 cases, with porting and a shaved head, running at 185 psi has ample power at a fraction of the cost.

The move from 6m6 to 61x's just does not make sense to me, when you can pretty much spend the same money and have a 62T with more options.

:dunno:

I disagree here, I have bought a few sets of 61x cases from $40-$60 each.

I havent seen a 62t for less than $150.

so basically 61x and 6m6 are NEARLY the same $$$.

Ill have to do some math, and work up the V.E. and CFM flow of a 701 vs 735 at 7000 RPM and see what the actual difference is.

 

[Rickster]

Ill have to do some math, and work up the V.E. and CFM flow of a 701 vs 735 at 7000 RPM and see what the actual difference is.

That would be interesting...

 

[Mouthfulloflake]

alright, CFM requirments for an engine that is 100% vomumetrically effencient ( none are)

RPM x Discplacemnet divided by 3456

701 engine at 7000 rpm

7000 * 42.7 ( 701cc in cubic inches)
divided by 3456
= 85 CFM required.

7000 * 44 ( 735cc in cubic centimeters - 83mm bore)
divided by 3456
=89 CFM required.

hmmm.

Not alot of difference, but that assumes 100 VE, probably closer to 70 on a stock engine, and 80 on a Lamey type set up ( pure guesses)

so they would actually need 30 or 40% more flow than that

 

[Rickster]

with a 650 engine needing about 79cfm at VE...

only about 7% difference between the 701 and a 650...

Not much!:cheer:

 

[Mouthfulloflake]

true.

650 needs 79 cfm
701 needs 86 cfm
735 needs 89 cfm

there is a bigger jump though between 650 and 701 than between 701 and 735.

so if 650 cases are starving a 83 mm bore, they are likely not well feeding a 81mm bore either.

 

[Rickster]

so if 650 cases are starving a 83 mm bore, they are likely not well feeding a 81mm bore either.

and since they do feed a 81mm bore fine, a 83mm bore should be fine.:scratchchin: :dunno:

 

[Mouthfulloflake]

and since they do feed a 81mm bore fine, a 83mm bore should be fine.:scratchchin: :dunno:

hehe

Ive got extra 61x cases, so I will likely use them, but I was just curious about the old 650 stuff too, I hate to have them collecting dust.

cool info though.

Now I guess we need velocity and carb throat flowability.

ad the 20-30% more CFM the engines need to the above numbers for the V.E. losses, and see what size carb, and how much velocity is required to feed it.

 

[Matt_E]

flowability.

:biggthumpup:

 

[Rickster]

At the Cylinder bores we are talking about, I don't think the carb and or intake would be an issue. I've seen big bores on single 48's hit like Tyson on his honeymoon.:biggrin:

I think it would come down to case volume and transfer ports, and whether the cases could keep up with the flow required in the larger bores...

It sure would be nice to have a machine shop with a set of each cases, and a bunch of cylinders lying around to experiment with...:biggrin:

 

[Mouthfulloflake]

:biggthumpup:

hehe, when im in a hurry, I just make up words.

it works too, you knew what I meant, and so did Rickter!

buzz off, bendix boy.

:biggrin:

 

[Idok]

I remember reading on this board that the 650 carb has different internal circuitry.

+1

per HK

 

[Mouthfulloflake]

+1

per HK

I thought I read on the GroupK website, that they modify the carbs?

hmm

I think im running a 650 carb on my 701.

how do you tell what its original application was? ( ive got both carbs, I swapped them when the needle/seat went south)

 

[DaUpJetSkier]

with all this talk about putting a 61x on a 6m6 bottom I am thinking im going to for sure do it this winter. So besides a 61x cylinder, pistons, and head is there anything else I will need other than the usual cir slips pins etc. Should I remove my rev limiter or get an msd enhancer while im at it. Can any machine shop simply clearance the 650 bottom end if they have the piston in hand?? thanks

 

[Rickster]

with all this talk about putting a 61x on a 6m6 bottom I am thinking im going to for sure do it this winter. So besides a 61x cylinder, pistons, and head is there anything else I will need other than the usual cir slips pins etc. Should I remove my rev limiter or get an msd enhancer while im at it. Can any machine shop simply clearance the 650 bottom end if they have the piston in hand?? thanks

You just need the cylider, head and pistons, and any machine shop should be able to do it for you.

I beleive the 650 and 701 wrist pins are the same, but double check...

 

[cookerq62]

I am running a 61x cylinder that has the sleeve cut. Paul saw them and said it was possibly to fit in 6m6 cases. Don't the 62t cylinders have a thicker sleeve that is cut to fit 62t cases that accept the 61x cylinder? I have only seen pics but it looks like the part of the slevees that are in the case are thinner.

Also douglee25 has 6m6 jugs that have been resleaved (81mm) and ported. I haven't had much time on the ski but its got plenty of power even at 140psi. I think the 6m6 cylinder is limited to how big you can make the exhaust ports. Does anyone know if you can fit 760 sleeves in a 6m6 jug???

 

[Matt_E]

The exhaust ports would be extremely limited if you did that.
I recently ported a 6M6 cylinder and let me tell you....there isn't much meat on the casting to widen the exhaust ports much.

So I don't know why anyone would want to stick 760 sleeves in there. The exhaust port would be too small.

 

[romack991]

I remember reading on this board that the 650 carb has different internal circuitry.

Damn, I stand corrected. Good to know since I am getting 2 650's and planned on have one carb converted to a 48.

 

[Matt_E]

FWIW, Phill is using a 650 carb on his ported/piped 760.

 

[DaUpJetSkier]

another ?, is it worth it to get a 61x mildly ported if I were to put it on a 6m6 bottom.

 

[Matt_E]

IMHO, yes.